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CN119065173B - Nonlinear optical crystal continuous wave frequency conversion device, working method and preparation method thereof - Google Patents

Nonlinear optical crystal continuous wave frequency conversion device, working method and preparation method thereof

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Publication number
CN119065173B
CN119065173B CN202410272410.5A CN202410272410A CN119065173B CN 119065173 B CN119065173 B CN 119065173B CN 202410272410 A CN202410272410 A CN 202410272410A CN 119065173 B CN119065173 B CN 119065173B
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light
crystal
optical crystal
nonlinear optical
parallel surfaces
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CN119065173A (en
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王晓洋
刘丽娟
王丽荣
邹宏新
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Technical Institute of Physics and Chemistry of CAS
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Technical Institute of Physics and Chemistry of CAS
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
    • G02F1/3544—Particular phase matching techniques
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/355—Non-linear optics characterised by the materials used
    • G02F1/3551—Crystals

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

本发明涉及三方晶系非线性光学晶体变频器件，所述变频器件具有第一组平行表面和第二组平行表面，所述第一组平行表面与光学晶体c轴平行且与a轴呈第一夹角β，第二组平行表面与第一组平行表面垂直且第二组平行表面的法线与所述光学晶体c轴呈第二夹角α，第二夹角α和第一夹角β具有式1和式2所示关系 θPM为所述非线性光学晶体满足入射基频光和出射变频光的相位匹配角，θB＝arctann，为布儒斯特角，n为所述非线性光学晶体入射基频光相应的折射率，所述第二组平行表面为所述变频器件的通光输入面和通光输出面。本发明基于薄片状原晶提供了一种具有尽可能大的通光方向长度且适于连续波应用的非线性光学晶体变频器件的制备方法。

The present invention relates to a trigonal nonlinear optical crystal frequency conversion device, wherein the frequency conversion device comprises a first group of parallel surfaces and a second group of parallel surfaces, wherein the first group of parallel surfaces is parallel to the c-axis of the optical crystal and forms a first angle β with the a-axis, and the second group of parallel surfaces is perpendicular to the first group of parallel surfaces and the normal of the second group of parallel surfaces forms a second angle α with the c-axis of the optical crystal, and the second angle α and the first angle β have the relationship shown in formula 1 and formula 2 θ PM is the phase-matching angle of the nonlinear optical crystal required to satisfy the phase matching between the incident fundamental frequency light and the outgoing frequency-converted light. θ B = arctann, which is the Brewster angle. n is the refractive index of the nonlinear optical crystal corresponding to the incident fundamental frequency light. The second set of parallel surfaces constitute the light-passing input and light-passing output surfaces of the frequency conversion device. The present invention provides a method for fabricating a nonlinear optical crystal frequency conversion device suitable for continuous-wave applications, based on a thin sheet-like primary crystal, having a maximum possible length in the light-passing direction.

Description

Nonlinear optical crystal continuous wave frequency conversion device, working method and preparation method thereof
Technical Field
The present disclosure relates to the field of intraocular lens optics, and in particular to techniques for fabricating brewster's frequency doubling devices using lamellar nonlinear optically uniaxial crystals.
Background
Deep ultraviolet (wavelength less than 200 nm) laser has extremely important application in the fields of information, scientific research, national defense and the like. The multistage frequency conversion technology of the nonlinear optical crystal is an effective way for realizing deep ultraviolet laser at present, wherein the frequency doubling crystal of the last stage is called deep ultraviolet nonlinear optical crystal. Only potassium fluoborate (KBE 2BO3F2, KBBF for short) and rubidium fluoborate (RbBe 2BO3F2, RBBF for short) meet the condition of deep ultraviolet nonlinear optical crystal at present, namely, laser with the wavelength smaller than 200nm can be directly output through frequency doubling, and particularly, six-time frequency (177.3 nm) output of Nd-YAG laser and four-time bandwidth tuning output of titanium-sapphire laser can be realized. The comprehensive performance of KBBF crystal is obviously better than RBBF crystal.
The KBBF crystal has serious lamellar growth habit, and the grown complete primary crystal is approximately a lamellar hexagon. The normal direction of the large hexagonal surface is a crystallographic c-axis (also called as a crystal c-axis or a crystal c-axis), the hexagonal surface is a plane formed by the a-b directions of the crystal, the a-axis and the b-axis are two crystallographic axes which are equivalent, an included angle of 120 degrees is formed (the physical included 3 equivalent a-axes), and the a-axis and the b-axis are perpendicular to the c-axis. The crystals may be as long as a few centimeters in the a-axis and b-axis directions, while the thickness d in the c-axis direction does not exceed 10mm, typically 5mm. For convenience in describing the physical properties of the crystal, a set of physical rectangular coordinate systems is established herein according to the following rule, the c-axis direction of the crystal is conventionally defined as the Z-axis, the a-axis direction is defined as the X-axis, and the directions perpendicular to the a-axis direction and the c-axis direction are defined as the Y-axis, see fig. 1. To achieve laser frequency doubling output, the fundamental light must travel in the crystal along a specific phase matching direction WO, which is represented in a rectangular coordinate system by azimuth angles θ PM and Φ, where θ PM is the angle between the phase matching direction and the Z axis, and Φ is the angle between the projection of the phase matching direction on the X-Y plane and the X axis. The KBBF crystal belongs to a trigonal system, the c-axis is the optical axis of the crystal, and the structural symmetry determines that the expression of the effective nonlinear coefficient d eff is d eff＝d11cos(θPM)cos3φ,d11 which is a nonlinear optical coefficient and is approximately equal to 0.49pm/V. It can be seen that the maximum effective nonlinear coefficient d eff, i.e. the maximum doubled optical power, can be obtained at phi=0°.
Fig. 2 schematically illustrates a schematic of a prior art first example of the preparation of a frequency doubling optical device from a lamellar primary crystal. In the hexagonal KBBF flake-like primary crystal 10, for example, a rectangular parallelepiped ABCD-EFGH is cut in accordance with the phase matching direction WO, and its 4 edges AE, BF, CG and DH are all parallel to the phase matching direction WO. The two parallel end faces ABCD and EFGH are optically polished to serve as a light-transmitting input surface and a light-transmitting output surface, respectively, to form a frequency multiplier 11 for pulse laser frequency multiplication output. The fundamental frequency laser travels along the phase matching direction WO, enters the crystal from the end face ABCD, is continuously converted into frequency-doubled light in the crystal, and finally both the frequency-doubled light and the remaining fundamental frequency light exit the crystal from the end face EFGH. Fig. 3 is a projection of the primary crystal 10 of fig. 2 and the frequency doubler 11 cut therein in the XZ plane, where L is the light-passing direction length of the frequency doubler 11 in this example, h represents the distance between the parallel surfaces ADHE and BCGF (also referred to as the light-passing surface first side length), k represents the distance between the parallel surfaces ABFE and DCGH (also referred to as the light-passing surface second side length), for example ab=h, ad=k, the side length represented by k being parallel to the X-Y plane. As can be seen from fig. 3, the light-transmitting direction length L is limited firstly by the thickness d of the crystal in the Z direction and secondly by the first side length h. The KBBF crystal has no help to increase the light transmission direction length L, although it has a larger size in the a-direction and the b-direction. The maximum value L max of the light-transmitting direction length is d/cos θ PM, where h=0. The first side length h of the light-transmitting surface of the frequency multiplier 11 is not too large, because the light-transmitting direction length L is determined by the formula l= (d/cos θ PM–h×tanθPM), and as the first side length h increases, the light-transmitting direction length L decreases, and therefore the side length h is generally selected to be 1mm. In order to ensure the stability and service life of the frequency multiplier, a method of changing the incidence of the point is often adopted, namely, when the laser works at a certain point on the light-transmitting surface for a certain time limit, another point is changed to continue working, and the like, the whole area of the light-transmitting surface is changed once and then a new frequency multiplier is changed. The requirement of point changing incidence in the laser frequency doubling process can be met by reasonably selecting the size of the second side length k of the light-passing surface and changing the point along the direction of the second side length k.
For continuous wave laser frequency doubling, the higher the transmission of the frequency multiplier for fundamental frequency laser, the better, and preferably, the closer to 100%. There is thus a need for an improvement of the frequency multiplier 11 shown in fig. 2. There may be two technical solutions, the first is to plate an antireflection film on two light-passing surfaces ABCD and EFGH, so that the fundamental frequency light can pass through the two light-passing surfaces without loss. But the anti-laser damage threshold of the anti-reflection film is lower, one to two orders of magnitude lower than the anti-laser damage threshold of the crystal, and is easily damaged by laser. If the antireflection film is applied to the continuous wave frequency multiplier of the KBBF crystal, the excellent characteristic of the high laser damage resistance threshold value of the KBBF crystal is not used, so that the antireflection film continuous wave frequency multiplier can only be used for low-power continuous wave laser frequency multiplication.
The second technical scheme is that 2 light-passing surfaces are cut according to a brewster angle theta B, theta B = arctann, wherein n is a refractive index corresponding to the wavelength of incident fundamental frequency light of the nonlinear optical crystal. When the polarization direction of the fundamental frequency light is located in the incident plane (the plane formed by the incident laser light and the normal line of the light passing surface is the incident plane), the fundamental frequency light can pass through the light passing input surface and the light passing output surface almost without damage. Fig. 4-6 schematically illustrate a second example of the prior art for preparing a frequency multiplier 12 with a brewster angle θ B from a flake-like primary crystal, where the two light-passing surfaces ABCD and EFGH of the frequency multiplier ABCD-EFGH illustrated in fig. 2 are further cut according to the brewster angle θ B, i.e., the rectangular parallelepiped ABCD-EFGH is cut to form a rectangular parallelepiped AD 'HE' -BC 'GF' after 2 right triangular prisms are cut, to obtain the frequency multiplier 12. The light-passing surfaces of the frequency multiplier 12 are ABC 'D' and E 'F' GH. As shown in the projection of fig. 6, the dashed line indicates the travel of light in a crystal having brewster angle θ B, and the light-passing direction length thus becomes L'. The scheme inevitably reduces the length of the light passing direction while improving the transmittance of incident laser. As shown in fig. 5 and 6, the light-transmitting direction length L '=l-k×ctgθ B, where the distance k between the surfaces ABF' E 'and D' C 'GH is larger in the case of determining the original light-transmitting direction length L, the shorter the light-transmitting direction length L', that is, the light-transmitting direction length is limited by the second side length k in addition to the crystal Z-direction thickness D and the first side length h in the brewster angle cut device. As previously mentioned, to guarantee the need for a frequency doubler change point, it is necessary to increase the value of the distance k between the parallel surfaces ABF 'E' and D 'C' GH, since the distance h between the parallel surfaces AD 'HE' and BC 'GF' is limited. However, the wider the distance k, the shorter the light-transmitting direction length, i.e., the light-transmitting direction length and the device width are not compatible. The frequency multiplication efficiency is in direct proportion to the square of the length of the light transmission direction, and the frequency multiplication conversion efficiency is directly influenced by the fact that the length of the light transmission direction is too short.
In summary, since the KBBF crystal is too thin, the frequency doubling device with a sufficiently long light-transmitting direction length is limited to be cut directly from the primary crystal, which makes the device impractical.
Currently, the practical application of KBBF crystals depends on devices with sandwich structure prepared by a so-called prism coupling technique, see in detail chinese patent application CN1381930a. The prism coupling device has the defect that the integral photodamage resistance threshold of the device is greatly reduced due to the fact that the interfaces of the KBBF crystal and the prism are more than 2, and the integral photodamage resistance threshold is one to more than two orders of magnitude lower than that of the KBBF crystal. Therefore, prism coupling devices can only be used for low power laser outputs, for example 177.3nm lasers currently used in advanced scientific instruments are typically only on the order of milliwatts. In addition, the overall transmittance of the prism coupling device is also greatly reduced compared with that of a pure crystal device, because 2 optical cement interfaces are heterogeneous interfaces, perfect lack is impossible, and scattering and absorption and unavoidable Fresnel reflection caused by the difference of refractive indexes of crystal and prism materials exist. The prism coupling device is limited to be used for continuous wave laser output, especially short wavelength continuous wave laser output due to low overall transmittance.
Accordingly, there is a need to provide a method of manufacturing a frequency conversion device having high transmittance and high continuous wave laser output power using a lamellar nonlinear optical crystal.
Disclosure of Invention
To solve the above problems, one aspect of the present invention provides a trigonal nonlinear optical crystal frequency conversion device, wherein
The frequency conversion device is provided with a first group of parallel surfaces and a second group of parallel surfaces, the first group of parallel surfaces are parallel to the c axis of the optical crystal and form a first included angle beta with the a axis, the second group of parallel surfaces are perpendicular to the first group of parallel surfaces, the normal line of the second group of parallel surfaces forms a second included angle alpha with the c axis of the optical crystal, and the second included angle alpha and the first included angle beta have the relation shown in the formulas 1 and 2
Θ PM is that the nonlinear optical crystal satisfies the phase matching angle of the incident fundamental frequency light and the output variable frequency light,
Θ B = arctann, the brewster angle, n is the refractive index corresponding to the fundamental frequency light incident by the nonlinear optical crystal,
The second group of parallel surfaces are a light-transmitting input surface and a light-transmitting output surface of the frequency conversion device.
The continuous wave frequency converter prepared by using the lamellar primary crystal with smaller c-axis direction of the trigonal nonlinear optical crystal can increase the width of the light-transmitting surface and keep the length of the light-transmitting direction as long as possible, namely has the characteristics of both the length direction of the light-transmitting and the width of the light-transmitting surface, thereby realizing high frequency conversion efficiency.
Preferably, the nonlinear optical crystal has parallel surfaces of the lamellar primary crystal perpendicular to the c-axis (i.e., 2 parallel large faces of the lamellar primary crystal) as its third set of parallel surfaces. Therefore, in the process of preparing the frequency conversion device, the thickness of the trigonal lamellar nonlinear optical crystal primary crystal is utilized to the greatest extent.
Preferably, the frequency conversion device is a continuous wave frequency conversion device. The method for preparing the frequency conversion device by cutting the lamellar trigonal system is particularly suitable for preparing a deep ultraviolet band continuous wave frequency conversion device by utilizing a nonlinear optical crystal of the lamellar trigonal system such as KBBF, and the light transmission direction length of the obtained frequency conversion device is far longer than that of a traditional prism-free frequency conversion device. Compared with the prism coupling device which is obtained and applied at present, the problem of lowering the integral photodamage resistance threshold and the integral transmittance of the device caused by more than 2 additional optical cement interfaces is solved, and the continuous wave frequency conversion device with high transmittance and high power continuous wave laser output is provided.
The frequency conversion device is a frequency multiplication device, the optical crystal is a negative uniaxial crystal, and the refractive index n is the o-light refractive index;
Or alternatively
The frequency conversion device is a sum frequency device, the optical crystal is a negative uniaxial crystal, and the refractive index n is the o-ray refractive index of first incident fundamental frequency light, wherein the wavelength of the first incident fundamental frequency light is larger than that of the second incident fundamental frequency light.
Preferably, the nonlinear optical crystal is a KBBF crystal, RBBF crystal, gamma-BBF crystal or other trigonal nonlinear optical crystal.
Preferably, the second set of parallel surfaces have a face spacing not greater than d/cos a, d being the thickness of the platelet.
In a second aspect of the present invention, a method for operating a nonlinear optical crystal frequency conversion device is provided, where the frequency conversion device is a frequency multiplier device, the method comprising
The continuous wave fundamental frequency light is incident into the nonlinear optical crystal from one of the second group of parallel surfaces of the nonlinear optical crystal along the Brewster angle, the incident surface formed by the fundamental frequency light and the normal line of the second group of parallel surfaces is vertical to the first group of parallel surfaces, the polarization direction of the fundamental frequency light is vertical to the c axis of the optical crystal, so that the projection of the light after being incident into the crystal on the plane vertical to the c axis is parallel to the a axis, the light in the crystal actually travels along the phase matching direction,
The frequency doubled light exits the nonlinear optical crystal from the other of the second set of parallel surfaces.
In a third aspect of the present invention, a method for operating a nonlinear optical crystal frequency conversion device is provided, where the frequency conversion device is a sum frequency device, the method includes
The nonlinear optical crystal is made to be incident with first incident fundamental frequency light and second incident fundamental frequency light from one of the second parallel surfaces, the incident surface is perpendicular to the first parallel surface, the first incident fundamental frequency light is made to enter the crystal along the brewster angle, the second fundamental frequency light is made to be collinear with the first fundamental frequency light after entering the crystal, and the projection of the two light rays in the crystal on the plane perpendicular to the c-axis is parallel to the a-axis, wherein the wavelength of the first incident fundamental frequency light is larger than the wavelength of the second incident fundamental frequency light, and the brewster angle is determined by the first incident fundamental frequency light,
And frequency light exits the nonlinear optical crystal from the other of the second set of parallel surfaces.
In a fourth aspect of the present invention, there is provided a method for manufacturing a continuous wave nonlinear optical crystal frequency conversion device, the method comprising:
taking flaky primary crystals of a trigonal nonlinear optical crystal;
Determining the brewster angle theta B = arctann, wherein n is the refractive index corresponding to the incident fundamental frequency light of the nonlinear optical crystal;
Determining a phase matching angle theta PM based on the wavelength of the incident fundamental frequency light and the emergent variable frequency light of the nonlinear optical crystal;
determining a first included angle beta and a second included angle alpha according to formulas 1 and 2 by using the Brewster angle theta B and the phase matching angle theta PM;
The nonlinear optical crystal is in a trigonal system, a first group of parallel surfaces are cut parallel to the c-axis of the optical crystal, and a first included angle beta is formed between the first group of parallel surfaces and the a-axis of the optical crystal;
And cutting a second group of parallel surfaces perpendicular to the first group of parallel surfaces, so that a second included angle alpha is formed between the normal line of the second group of parallel surfaces and the c-axis direction of the optical crystal, and the frequency conversion device is obtained.
Preferably, the second set of parallel surfaces have a plane spacing not greater than d/cos α, d being the thickness of the sheet-like primary crystal, i.e., the thickness in the c-axis direction.
Advantageous effects
The invention calculates and determines the cutting position of the lamellar nonlinear optical crystal by utilizing the phase matching angle and the Brewster angle determined by the properties of the nonlinear optical crystal, provides a nonlinear optical crystal frequency conversion device which has the maximum light transmission direction length and the device width and is suitable for continuous wave laser application for the lamellar trigonal nonlinear optical crystal, and provides a method for conveniently and rapidly preparing the nonlinear optical crystal frequency conversion device.
According to the nonlinear optical crystal cutting method, the Brewster angle is not required to be specially cut when the sheet-shaped nonlinear optical crystal is cut, so that the length of the light passing direction is not sacrificed for cutting the Brewster angle unlike the conventional technology. According to the nonlinear optical crystal cutting method, the length of the optical device in the light transmission direction can be kept unchanged under the condition of increasing the width of the optical device obtained by cutting, so that a variable frequency device with high conversion efficiency continuous wave laser output can be obtained by using the lamellar optical crystal. Compared with the prism coupling device which is obtained and applied at present, the problem of lowering the integral photodamage resistance threshold and the integral transmittance of the device caused by more than 2 additional optical cement interfaces is solved, and the continuous wave frequency conversion device with high transmittance and high power continuous wave laser output is provided.
The light-transmitting input surface and the light-transmitting output surface of the nonlinear optical crystal frequency conversion device obtained by the invention have the characteristics of the phase matching angle and the Brewster angle of the nonlinear optical crystal, and the length of the light-transmitting direction can be twice as long as the number of frequency converters prepared by the traditional processing method.
Drawings
The following describes in further detail the specific embodiments of the present disclosure with reference to the drawings.
Fig. 1 shows a schematic diagram of the physical rectangular coordinate system of KBBF crystals.
Fig. 2-3 are schematic diagrams showing a first example of a prior art frequency conversion device using a plate-like nonlinear optical crystal.
Fig. 4-6 are schematic diagrams showing a second example of a prior art continuous wave transducer device using a plate-like nonlinear optical crystal.
Fig. 7-8 show schematic diagrams of the present invention for producing a continuous wave transducer device using a plate-like nonlinear optical crystal.
Fig. 9-11 show the operation of a continuous wave transducer device according to the invention.
Detailed Description
The technical scheme of the present invention will be described in detail with reference to the accompanying drawings in combination with preferred embodiments of the present invention. The various elements of the drawing are not drawn to scale. It should be understood that the preferred embodiments of the present invention are illustrative and not restrictive, and that the scope of the invention is to be defined by the claims.
The invention provides a method for preparing a nonlinear optical crystal frequency conversion device by novel cutting crystals. For the lamellar trigonal nonlinear optical crystal, the length of the light passing direction of the frequency conversion device can be kept unchanged under the condition of increasing the width of the frequency conversion device obtained by cutting, so that the preparation of the frequency conversion optical device with high conversion efficiency continuous wave laser output by using the lamellar optical crystal is realized.
In a first embodiment of the present invention, there is provided a method for producing a variable frequency optical device using a lamellar primary crystal of a nonlinear optical crystal, comprising
The crystal axis is determined by taking a plate-like primary crystal of a trigonal nonlinear optical crystal, for example, the thickness direction of the plate-like primary crystal is generally the c-axis of the optical crystal.
Determining the brewster angle θ B = arctann, wherein n is the refractive index corresponding to the incident fundamental frequency light of the nonlinear optical crystal, and as a specific example, the nonlinear optical crystal is a negative uniaxial crystal, and the refractive index n is the refractive index of o light;
Determining a phase matching angle theta PM based on the wavelength of the incident fundamental frequency light and the emergent variable frequency light of the nonlinear optical crystal;
determining a first included angle beta and a second included angle alpha according to formulas 1 and 2 by using the Brewster angle theta B and the phase matching angle theta PM;
the first set of parallel surfaces S1, S2 is cut from the flake-like primary crystal parallel to the c-axis of the crystal to obtain a strip, wherein 4 edges of the parallel surfaces form a first included angle β with respect to any one of the three equivalent a-axes, the height of the strip is the height of the flake-like primary crystal at the c-axis, and the width of the strip can be cut to be wider, for example, 4-12mm, as shown in fig. 7. It will be appreciated that, due to the relationship of the three-degree rotational symmetry of the trigonal system, although the first set of parallel surfaces S1, S2 are at a first angle β with respect to the a-axis in fig. 7, the first set of parallel surfaces S1, S2 may also be at an angle- β with respect to the a-axis, or (60 ° - β). The technical scheme of the invention can be realized by a person skilled in the art by selecting the use method of the optical crystal frequency converter after cutting according to the specific position relation between the cutting plane and the a axis when cutting the crystal. For the sake of brevity, no further description is provided herein.
A second set of parallel surfaces A1B1F1E1 and D1C1G1H1, also called parallel slopes or inclined planes, are cut perpendicular to the first set of parallel surfaces S1, S2, naturally the projection of the normal to said parallel slopes onto the XY plane forms a first angle β with the a-axis, and the normal direction of the parallel slopes forms a second angle α with the C-axis of the crystal, thus cutting a straight parallelepiped B1C1G1F1-A1D1H1E1, see fig. 8. In order to ensure that the laser light is only incident and emitted on the parallel inclined surfaces, the plane spacing l of the parallel inclined surfaces cannot be larger than d/cos alpha, and d is the thickness of the sheet-like optical crystal along the c-axis direction.
The cut second group of parallel inclined planes A1B1F1E1 and D1C1G1H1 are the light-transmitting input surface and the light-transmitting output surface of the obtained frequency conversion device respectively. The group of parallel surfaces are polished to meet the optical level requirement of the optical device, namely the manufacture of the whole frequency conversion device is completed, and the preparation steps are very simple.
As a specific example, the nonlinear optical crystal has parallel surfaces perpendicular to the c-axis of the flake-like primary crystal as its third set of parallel surfaces. The processing method of the frequency conversion device provided by the invention can obtain the nonlinear optical crystal frequency conversion device which has the maximum light transmission direction length and is suitable for continuous wave laser application for the flaky trigonal nonlinear optical crystal with the thickness d of not more than 10mm in the c-axis direction. In other words, compared with the prior art, under the condition that the thickness of the primary crystal material is limited, the frequency conversion device is cut out to have the maximum possible length in the light transmission direction and the enough wide change point width, so that the problem that the prior art cannot prepare the frequency conversion device with the length in the light transmission direction and the device width by using the lamellar optical crystal is solved.
As a specific example, the nonlinear optical crystal is a KBBF crystal, RBBF crystal, γ -BBF crystal, or other trigonal nonlinear optical crystal.
According to the method, after the angles of the first included angle beta and the second included angle alpha are determined, in the processing process, the flaky primary crystal is continuously cut in a mode of cutting the first group of parallel surfaces, so that a plurality of strip-shaped crystals can be obtained, and then the strip-shaped crystals are continuously cut in a mode of cutting the second group of parallel surfaces, so that a plurality of nonlinear optical crystal frequency conversion devices can be quickly and simply obtained.
The method of preparing the variable frequency optical device of the present invention will now be described by way of example with respect to 193nm continuous wave transducers of KBBF crystal.
The c-axis and a-axis of the crystal axis were determined by taking the KBBF flaky primary crystal 10. The thickness direction of the KBBF crystal is the c-axis of the optical crystal.
The brewster angle is first determined. The KBBF crystal is a negative uniaxial crystal, 386nm fundamental frequency light is o light in the crystal, and the Brewster angle θ B = arctann, wherein n is the o light refractive index corresponding to the wavelength of the fundamental frequency light of the KBBF crystal. Bringing n o @386 nm= 1.4934 into the above gives θ B =arctan 1.4934 =56.19°.
And then determining a second included angle alpha. The value of the second included angle α is determined by equation 1 above, and for doubling the 386nm incident light to 193nm, the phase matching angle θ PM =55.4 °. The angle α=46.9° is calculated according to the formula 1.
Finally, a second angle β is determined, and calculated according to equation 2, to obtain β=42.5°.
After the above parameters are determined, the specific cutting method is described in detail as follows:
two knives were cut parallel to the c-axis (vertical) in a direction offset from the β -axis of the a-axis to obtain a set of parallel surfaces S1, S2, and a strip was cut with 4 edges each at 42.5 ° to the a-axis, see fig. 7. The height of the strip is the thickness of the KBBF crystal in the c-axis direction, and the width can be cut to be wider, for example, 6mm, and then the strip is used as the second side length (width) of the light-transmitting surface of the frequency conversion device.
Then a set of parallel inclined planes A1B1F1E1 and D1C1G1H1 are cut perpendicular to a set of parallel surfaces S1 and S2 and at an angle α to the normal and the C-axis, and a straight parallelepiped B1C1G1F1-A1D1H1E1 is cut for producing the nonlinear optical crystal frequency conversion device 31, see fig. 8. The included angle between the normal line of the inclined planes A1B1F1E1 and D1C1G1H1 and the C-axis of the KBBF crystal is alpha, namely, the included angle between the parallel inclined plane and the X-Y plane is alpha, and meanwhile, the projection of the normal line of the parallel inclined plane on the X-Y plane meets the requirement that the a-axis included angle is the first included angle beta. The plane spacing l of the parallel inclined planes is smaller than d/cos alpha, wherein d is the thickness of the flaky KBBF primary crystal along the direction c, so that the laser is ensured to enter and exit only at the parallel inclined planes.
And polishing inclined planes A1B1F1E1 and D1C1G1H1 serving as light-passing surfaces to meet the optical level requirement of an optical device, namely completing the manufacture of the 193nm continuous wave frequency converter of the KBBF crystal.
The nonlinear optical crystal frequency converter of the present invention can be used as a frequency multiplier. In use, see fig. 9-11, fundamental light is incident into the frequency multiplier from one of the optional light-passing surfaces, e.g., D1C1G1H1, along the brewster angle and exits the frequency multiplier from the other light-passing surface A1B1F1E 1. The incident fundamental frequency light and the normal line of the light passing surface D1C1G1H1 form an incident surface, the incident surface is vertical to the first group of parallel surfaces, the first parallel surfaces, the second parallel surfaces and the incident surface are planes which are mutually vertical to each other, the included angle between the normal line of the incident surface and the C axis of the optical crystal is the complementary angle of the second included angle alpha, and the polarization direction of the fundamental frequency light is vertical to the C axis of the optical crystal, so that the projection of the light after entering the crystal on the plane vertical to the C axis is parallel to the a axis. Thus, the fundamental light enters the nonlinear optical crystal, is all o-light, and advances along the phase matching direction. Since the phase matching condition is satisfied, the incident fundamental frequency light is gradually converted into frequency-doubled light. Fig. 9 is a projection view of this device in the c-axis direction, with arrows indicating the directions of the incident light and the outgoing light, and with broken lines indicating the paths of the light traveling in the crystal. It can be seen that the projection of the ray represented by the dashed line in the crystal on the X-Y plane is parallel to the a-axis, satisfying phi=0 for the KBBF crystal phase matching direction. Fig. 10 is a projection of the first set of parallel surfaces B1C1G1F1 (side surfaces), and it can be seen that the three light rays, i.e., the incident light ray, the light ray in the crystal and the outgoing light ray, are in the same plane, and the plane is the incident plane and the outgoing plane that are coincident, and the incident plane and the outgoing plane are coincident because the two light-passing planes are parallel. This plane is perpendicular to the light-transmitting input surface D1C1G1H1 and the light-transmitting output surface A1B1F1E 1. The angle between the normal line of the incident surface and the c-axis is the complementary angle (90-alpha) of the second angle alpha. It should be noted that, the frequency multiplier is a parallelepiped, and only a part of the area, namely a cuboid labeled as C1D1JK-MNE1F1 in fig. 10, is actually used, the actual light-transmitting surfaces (also referred to as light-transmitting windows) are C1D1JK and MNE1F1, and the length of the first side length C1K of the light-transmitting window is h. For convenience, the cuboid C1D1JK-MNE1F1 is not specially cut.
The invention relates to a method for preparing a frequency conversion device by using a lamellar nonlinear optical crystal, which utilizes 2 large surfaces (two parallel surfaces perpendicular to a c axis) of a lamellar primary crystal of the nonlinear optical crystal, cuts a first group of parallel surfaces S1 and S2 in parallel to the c axis according to the calculation result of a first included angle beta to obtain a bar-shaped crystal blank, cuts a second group of parallel inclined surfaces perpendicular to the first group of parallel surfaces on the bar-shaped crystal blank according to a second included angle alpha, and makes the normal direction of the second group of parallel inclined surfaces and the c axis direction of the crystal form a second included angle alpha to obtain a parallelepiped, wherein the projection of the normal on a plane perpendicular to the c axis direction of the crystal forms a first included angle beta with the a axis direction of the crystal. And polishing the parallel inclined planes to obtain the nonlinear optical crystal continuous wave transducer. After two included angles are determined, the invention can cut out a plurality of strip-shaped crystal blanks, and then each crystal blank is cut into a plurality of parallel inclined planes, so that primary crystals are utilized to the maximum extent, and a plurality of continuous wave frequency conversion devices with good consistency are directly obtained, and the manufacturing method is simple.
The frequency conversion device obtained by the method is characterized in that for the point-conversion type continuous wave frequency conversion device, the length of the light transmission direction is not influenced by the width of the light transmission surface, and the length of the light transmission direction is far greater than that of a continuous wave frequency doubling device obtained by cutting in a traditional mode. The comparison of the length in the light transmission direction is described below by taking a 193nm continuous wave frequency multiplier of KBBF crystal as an example. θ PM＝55.4°,θB =56.19° of 193nm frequency doubler of KBBF crystal. For the continuous wave frequency multiplier manufactured by cutting in the conventional technology, taking the thickness d=4mm of the original crystal of the sheet-like KBBF as an example, the length h=1mm of one side AB of the light-passing surface in fig. 3, the length k=6mm of the other side AD, and the length l= (d/cos θ PM-h×tanθPM) = 5.595mm of the light-passing direction if the requirement of changing the point is met. Still further, according to fig. 6, after two parallel slopes are cut at brewster's angle, the light-transmitting direction length becomes shorter, and L' =l-k×ctgθ B = 5.595-6×ctg56.19 ° =1.578 mm. If k continues to become larger, the light passing direction length continues to become smaller.
If the technology of the invention is adopted, the first included angle alpha=46.9 degrees and the second included angle beta=42.5 degrees are obtained. According to fig. 10, the projection of the length of the light transmission direction on the side of the frequency multiplier is the plane spacing l between the light transmission input plane D1C1G1H1 and the light transmission output plane A1B1F1E 1. Calculated as in fig. 3, l=d/cos α -h×tan α= 4.786mm. According to fig. 11, the actual light-passing direction length l1=l/sin θ B = 5.759mm. The length is far longer than the length of a common continuous wave frequency multiplier in the light transmission direction by 1.578mm, and the length is 3.6 times of the length of the common continuous wave frequency multiplier in the light transmission direction. The reason for this is that the length in the light passing direction of the device of the present invention is not affected by the increase in the width k of the light passing surface. According to the frequency conversion device, the width of the light-passing surface can be selected according to the size of an original crystal or according to the working requirement of the frequency converter, for example, the width is 4mm-12mm. Therefore, the nonlinear optical crystal frequency conversion device obtained by the preparation method can realize high frequency conversion efficiency, meet the power requirement of actual use and the use requirement of a continuous wave frequency converter, and enlarge the applicability and application range of the deep ultraviolet laser frequency conversion device.
As a specific embodiment, the continuous wave frequency conversion device is required to be placed in a resonant cavity with an incidence cavity mirror and an emergent cavity mirror, incident fundamental frequency light is only reflected by the emergent cavity mirror after being emitted from the incidence cavity mirror to the nonlinear optical crystal frequency converter, and is re-emitted to the nonlinear optical crystal frequency converter, so that the intra-cavity circulation is realized, the repetition is continuously realized, the resonance enhancement is realized through locking the cavity length, and the converted frequency light is only emitted from the emergent cavity mirror to the resonant cavity once.
As a specific example, the nonlinear optical crystal frequency converter of the present invention can be used as a frequency mixer. When the nonlinear optical crystal is used, first incident fundamental frequency light and second incident fundamental frequency light are emitted into the nonlinear optical crystal from one of parallel inclined planes C1D1H1G1, the wavelength of the first incident fundamental frequency light is larger than that of the second incident fundamental frequency light, an incident plane is formed by the incident fundamental frequency light and the normal line of the inclined plane C1D1H1G1, so that the incident plane is vertical to the side surface, the included angle between the normal line of the incident plane and the C axis of the optical crystal is necessarily the complementary angle of a second included angle alpha, the first fundamental frequency light enters the nonlinear optical crystal along the Brewster angle, the Brewster angle is determined by the first incident fundamental frequency light, the second fundamental frequency light is in collinearly with the first fundamental frequency light after being emitted into the crystal, the projection of the two light rays in the crystal is parallel to the a axis vertical to the C axis plane, and the frequency light is emitted out of the nonlinear optical crystal from the other inclined plane B1A1E1F 1.
The technical scheme of the invention is described in detail below by way of examples.
Example 1
A frequency doubling optical wavelength 193nm continuous wave frequency doubling device was fabricated with a KBBF master crystal having a thickness d=4 mm.
First, the brewster angle is determined.
The refractive index of o-ray of the KBBF crystal at the wavelength 386nm of fundamental frequency is n o @386 nm= 1.4934, and the Brewster angle θ B＝arctanno =arctan 1.4934 =56.19°.
Then, a second included angle alpha is determined using equation 1,
The KBBF crystal multiplies the fundamental frequency light 386nm to the phase matching angle θ PM =55.4° of the frequency-multiplied light 193 nm. Solving for α=46.9° according to 1.
Then, a first included angle beta is determined using equation 2,
Calculated, β=42.5 °.
After determining the second included angle α and the first included angle β, the flaky KBBF crystal was cut out of the first set of parallel surfaces parallel to the c-axis along a direction offset from the a-axis by 42.5 ° (β -angle), to obtain a cuboid having a height of d=4mm and a width of 6mm of the pitch of the first set of parallel surfaces.
Then cutting parallel inclined planes perpendicular to the first group of parallel surfaces at 46.9 degrees (alpha angle) according to the normal line and the C axis to obtain a straight parallelepiped, wherein the surface spacing of the parallel inclined planes is 4.7mm, so that the first side length h of the light passing surface can be ensured to reach 1mm (C1K in figure 10), and meanwhile, the projection of the normal line of the parallel inclined planes on the X-Y plane inevitably meets the requirement that the alpha-axis included angle is 42.5 degrees.
The set of parallel inclined planes is polished to meet the optical level requirement of the frequency doubling device, thereby completing the manufacture of the nonlinear optical crystal for the frequency doubling device by a very simple process. In the obtained frequency multiplier device, a part of the area of the parallel inclined plane is a light passing surface of the frequency multiplier (as shown in fig. 10). The actual light transmission direction length was 5.759mm as calculated above.
When the device is used, the device is placed in a resonant cavity, a beam of continuous wave laser with the wavelength of 386nm and the power of 4W is transmitted through an incidence cavity mirror and is incident into a KBBF crystal frequency multiplier from one of inclined planes along the Brewster angle, the incident light and the normal line of the inclined planes form an incidence plane, and meanwhile, the incidence plane is required to be vertical to the first group of parallel surfaces, so that the included angle between the normal line of the incidence plane and the c axis is necessarily 43.1 degrees (namely, the residual angle of the alpha angle), and the polarization direction of 386nm laser is vertical to the c axis. The 386nm laser enters the crystal and then advances along the phase matching direction, and gradually converts into continuous wave 193nm frequency doubling light, and the continuous wave 193nm frequency doubling light is emitted out of the crystal. The rest 386nm laser is reflected by the cavity mirror, continuously oscillates in the cavity, passes through the KBBF crystal for multiple times, repeatedly and realizes resonance enhancement by locking the cavity length. The newly generated 193nm laser is output once through the emergent cavity mirror, the long-term stable power of the finally output 193nm laser reaches 20mW, and the output power is about 10 times of that of the existing prism coupling device frequency multiplier.
Example 2
A177.5 nm continuous wave frequency doubling device was fabricated using a KBBF (K-BBF) precursor with a thickness of 4 mm.
The brewster angle is first determined.
The index of refraction of o light at 355nm of the KBBF crystal is n o @355 nm= 1.4974, and the brewster angle θ B＝arctanno =arctan 1.4974 = 56.26 °.
Then, a second included angle alpha is determined using equation 1,
The KBBF crystal multiplies the frequency of the fundamental frequency light 355nm to a phase matching angle θ PM =64.3° of 177.5 nm. The solution according to 1 is α= 58.57 °.
Then, a first included angle beta is determined using equation 2,
Calculated β=38.05 °.
After the second included angle α and the first included angle β are determined, the sheet-like KBBF crystal is cut into a first group of parallel surfaces parallel to the c-axis along the direction 38.05 ° (β -angle) away from the a-axis, so as to obtain a cuboid, wherein the height of the cuboid is d=4mm, and the width of the cuboid is 6mm of the spacing between the first group of parallel surfaces.
Then a set of parallel inclined planes are cut perpendicular to the first set of parallel surfaces at 58.57 DEG (alpha angle) to the normal line and the C-axis to obtain a right parallelepiped, the plane spacing of the parallel inclined planes is 6mm, so that the first side length h of the light passing surface can be ensured to reach 1mm (C1K in figure 10), and meanwhile, the projection of the normal line of the parallel inclined planes on the X-Y plane meets the condition that the alpha-axis included angle is 38.05 deg.
The parallel inclined planes are polished to meet the optical level requirement of the frequency doubling device, so that the whole device is manufactured very simply. A part of the 2 parallel slopes is the light-passing surface of the frequency multiplier (as shown in fig. 10).
According to fig. 10, the projection of the length of the light transmission direction on the side of the frequency multiplier is the plane spacing L between the light transmission input plane and the light transmission output plane, calculated by imitating fig. 3, l=d/cos α -h×tan α, and values such as d=4mm and h=1mm are substituted to obtain l=4/cos 58.57 ° -1×tan58.57 ° =6.034 mm, and according to fig. 11, the actual length of the light transmission direction l1=l/sin θ B =6.034/sin 56.26 ° = 7.256mm.
When the device is used, the device is placed in a resonant cavity, a beam of continuous wave laser with 355nm power of 4W is transmitted through an incidence cavity mirror, is incident into a KBBF crystal from one of inclined planes along the Brewster angle, the incident light and the normal line of the inclined planes form an incident plane, and the incident plane is vertical to a first group of parallel surfaces, so that the normal line of the incident plane automatically forms an included angle of 31.43 degrees with the Z axis (namely, the residual angle of an alpha angle), the polarization direction of 355nm laser is vertical to the Z axis, 355nm laser enters the crystal and then advances along a phase matching direction, is gradually converted into power continuous wave 177.5nm frequency doubling light, and is emitted out of the crystal. The newly generated 177.5nm laser is output through the emergent cavity mirror, the rest 355nm laser is reflected by the cavity mirror, continuously oscillates in the cavity, repeatedly passes through the KBBF crystal for multiple times, and realizes resonance enhancement by locking the cavity length. The 177.5nm laser is output through the emergent cavity mirror for a single time, and the finally output continuous wave 177.5nm laser power reaches about 10mW.
Example 3
A153.43 nm continuous wave sum frequency device was fabricated using a KBBF primary crystal of 4mm thickness.
Yb laser with the wavelength of 1074nm is used as first fundamental frequency light, six times frequency 179nm laser of the first fundamental frequency light is used as second fundamental frequency light, and the sum frequency process of the Yb laser with the wavelength of 1074nm and 179nm laser sum frequency is 153.43nm laser.
The brewster angle is first determined. Because the sum frequency process is that two beams of fundamental frequency light with different wavelengths are incident, the refractive indexes are different, and thus the Brewster angles are also different. Clearly, the brewster angle can not be cut out to meet both wavelengths. Based on 1074nm with longer wavelength, the refractive index of o-light of KBBF crystal at 1074nm is n o @1074nm= 1.4713, and the Brewster angle θ B＝arctanno =arctan 1.4713 =55.80°.
The angle alpha is then determined. The value of angle alpha is determined by the equationIt was determined that the KBBF crystal phase matching angle θ PM =52.1° for the sum frequency of 1074nm laser and 179nm sum frequency 153.43nm laser. Alpha=42.3° is calculated.
Finally, the angle beta is determined,Calculated β=45.3 °.
After the above parameters were determined, the flaky KBBF crystal was cut out along the direction 45.3 DEG (beta angle) from the a-axis to obtain a rectangular parallelepiped with a height of 4mm and a width of 6mm.
Then a group of parallel inclined planes are cut at an angle of 42.3 degrees from the normal line and the C-axis perpendicular to the first group of parallel surfaces, the plane spacing is 4.4mm, so that the first side length h of the light passing surface can reach 1.1mm (C1K in FIG. 10), and the projection of the normal line of the parallel inclined planes on the X-Y plane necessarily meets the requirement that the angle between the normal line and the a-axis is 45.3 degrees.
The 2 parallel inclined planes are polished to meet the optical level requirement of the frequency doubling device, so that the whole device is manufactured. A part of the parallel inclined planes is the light-passing surface of the frequency multiplier (as shown in fig. 10).
According to fig. 10, the projection of the length of the light transmission direction on the side of the sum frequency device is the plane distance L between the light transmission input plane and the light transmission output plane, calculated by imitating fig. 3, i=d/cos alpha-h×tan alpha, and values such as d=4mm, h=1.1 mm are substituted to obtain values such as l=4/cos 42.3 ° -1.1×tan42.3 ° = 4.407mm, and according to fig. 11, the actual length of the light transmission direction l1=l/sin θ B = 4.407/sin55.80 ° = 5.328mm.
When the device is used, the device is placed in a resonant cavity, fundamental frequency light is continuous wave laser with the wavelengths of 1074nm and 179nm, wherein the power of first fundamental frequency light with the wavelength of 1074nm is 8W, and second fundamental frequency light with the wavelength of 179nm is six times of that of 1074nm, namely frequency multiplication and frequency summation are carried out, and the power is only 1mW. The method comprises the steps of enabling 1074nm first fundamental frequency light to enter a KBBF crystal from one of inclined planes along the Brewster angle through an incidence cavity mirror, enabling the incident light and the normal line of the inclined planes to form an incidence plane, enabling the incidence plane to be perpendicular to a first parallel surface, enabling the included angle between the normal line of the incidence plane and the c axis to be 47.7 degrees (namely the residual angle of an alpha angle), enabling the polarization direction of laser light to be perpendicular to the c axis, enabling the polarization direction of the laser light to be perpendicular, enabling the laser light to circularly resonate in the cavity repeatedly to be enhanced, enabling 179nm laser light to enter the inclined planes of the KBBF crystal at the Brewster angle and be collinear with 1074nm laser light in the crystal. The 1074nm and 179nm laser enters the crystal and then advances along the phase matching direction, and gradually and frequently converts into 153.43nm sum frequency light, and the crystal is emitted. The newly generated 153.43nm laser is output through the emergent cavity mirror, the rest 1074nm laser is reflected by the cavity mirror, continuously oscillates in the cavity, passes through the KBBF crystal for multiple times, and continuously generates 153.43nm sum frequency light. The laser power of the finally output continuous wave 153.43nm reaches more than 0.1 mW.
It should be apparent that the foregoing examples of the present disclosure are merely illustrative of the present disclosure and not limiting of the embodiments of the present disclosure, and that various other changes and modifications may be made by one of ordinary skill in the art based on the foregoing description, and it is not intended to be exhaustive of all embodiments, and all obvious changes and modifications that come within the scope of the present disclosure are intended to be embraced by the technical solution of the present disclosure.

Claims (10)

1.一种三方晶系非线性光学晶体变频器件，其特征在于，1. A trigonal nonlinear optical crystal frequency conversion device, characterized in that: 所述变频器件具有第一组平行表面和第二组平行表面，所述第一组平行表面与光学晶体c轴平行且与a轴呈第一夹角β，第二组平行表面与第一组平行表面垂直且第二组平行表面的法线与所述光学晶体c轴呈第二夹角α，所述第二夹角α和第一夹角β具有式1和式2所示关系The frequency conversion device has a first group of parallel surfaces and a second group of parallel surfaces, the first group of parallel surfaces is parallel to the c-axis of the optical crystal and forms a first angle β with the a-axis, the second group of parallel surfaces is perpendicular to the first group of parallel surfaces and the normal of the second group of parallel surfaces forms a second angle α with the c-axis of the optical crystal, and the second angle α and the first angle β have the relationship shown in Formula 1 and Formula 2 θPM为所述非线性光学晶体满足入射基频光和输出变频光的相位匹配角，θ PM is the phase matching angle between the incident fundamental frequency light and the output frequency-converted light of the nonlinear optical crystal, θB＝arctann，为布儒斯特角，n为所述非线性光学晶体入射基频光相应的折射率，θ B =arctann, which is the Brewster angle, and n is the refractive index of the incident fundamental frequency light of the nonlinear optical crystal. 所述第二组平行表面为所述变频器件的通光输入面和通光输出面。The second group of parallel surfaces is the light input surface and the light output surface of the frequency conversion device. 2.根据权利要求1所述的非线性光学晶体变频器件，其特征在于，2. The nonlinear optical crystal frequency conversion device according to claim 1, characterized in that: 所述非线性光学晶体以片状晶体的垂直于光学晶体c轴的平行表面作为其第三组平行表面。The nonlinear optical crystal uses the parallel surfaces of the plate-shaped crystal that are perpendicular to the c-axis of the optical crystal as its third group of parallel surfaces. 3.根据权利要求1所述的非线性光学晶体变频器件，其特征在于，所述变频器件为连续波变频器件。3 . The nonlinear optical crystal frequency conversion device according to claim 1 , wherein the frequency conversion device is a continuous wave frequency conversion device. 4.根据权利要求1所述的非线性光学晶体变频器件，其特征在于，4. The nonlinear optical crystal frequency conversion device according to claim 1, characterized in that: 所述变频器件为倍频器件，所述光学晶体为负单轴晶体，折射率n为o光折射率；The frequency conversion device is a frequency doubling device, the optical crystal is a negative uniaxial crystal, and the refractive index n is the refractive index of o light; 或者，or, 所述变频器件为和频器件，所述光学晶体为负单轴晶体，所述折射率n为第一入射基频光的o光折射率，其中第一入射基频光的波长大于第二入射基频光的波长。The frequency conversion device is a sum frequency device, the optical crystal is a negative uniaxial crystal, the refractive index n is the refractive index of the o light of the first incident fundamental frequency light, wherein the wavelength of the first incident fundamental frequency light is greater than the wavelength of the second incident fundamental frequency light. 5.根据权利要求1所述的非线性光学晶体变频器件，其特征在于，所述非线性光学晶体为KBBF晶体、RBBF晶体、γ-BBF晶体或其它三方晶系非线性光学晶体。5 . The nonlinear optical crystal frequency conversion device according to claim 1 , wherein the nonlinear optical crystal is a KBBF crystal, a RBBF crystal, a γ-BBF crystal or other trigonal nonlinear optical crystals. 6.根据权利要求2所述的非线性光学晶体变频器件，其特征在于，所述第二组平行表面的面间距不大于d/cosα，d为所述片状晶体的厚度。6 . The nonlinear optical crystal frequency conversion device according to claim 2 , wherein the interplanar spacing of the second set of parallel surfaces is no greater than d/cos α, where d is the thickness of the plate-like crystal. 7.一种根据权利要求4所述的非线性光学晶体变频器件的工作方法，其特征在于，所述变频器件为倍频器件，该方法包括7. A method for operating a nonlinear optical crystal frequency conversion device according to claim 4, wherein the frequency conversion device is a frequency doubling device, and the method comprises: 将连续波基频光从非线性光学晶体第二组平行表面之一沿布儒斯特角入射所述非线性光学晶体，所述基频光和所述第二组平行表面的法线所确定的平面构成的入射面与第一组平行表面垂直且所述基频光的偏振方向与光学晶体c轴垂直，使射入晶体后光线在垂直于c轴平面的投影平行所述a轴，A continuous wave fundamental frequency light is incident on the nonlinear optical crystal from one of the second set of parallel surfaces of the nonlinear optical crystal along the Brewster angle, the incident plane formed by the plane defined by the fundamental frequency light and the normal of the second set of parallel surfaces is perpendicular to the first set of parallel surfaces, and the polarization direction of the fundamental frequency light is perpendicular to the c-axis of the optical crystal, so that the projection of the light on the plane perpendicular to the c-axis after entering the crystal is parallel to the a-axis, 倍频光从所述第二组平行表面中的另一个射出所述非线性光学晶体。The frequency-doubled light exits the nonlinear optical crystal from another one of the second set of parallel surfaces. 8.一种根据权利要求4所述的非线性光学晶体变频器件的工作方法，其特征在于，所述变频器件为和频器件，该方法包括：8. A method for operating a nonlinear optical crystal frequency conversion device according to claim 4, wherein the frequency conversion device is a sum frequency device, and the method comprises: 将第一入射基频光和第二入射基频光从所述第二组平行表面之一入射所述非线性光学晶体，且入射面和第一平行表面垂直，第一入射基频光沿布儒斯特角入射晶体，所述第二入射基频光射入晶体后和第一入射基频光共线，两光线在垂直于c轴平面的投影平行a轴，其中第一入射基频光的波长大于第二入射基频光的波长且所述布儒斯特角由第一入射基频光确定，A first incident fundamental frequency light and a second incident fundamental frequency light are incident on the nonlinear optical crystal from one of the second group of parallel surfaces, with the incident surface being perpendicular to the first parallel surface. The first incident fundamental frequency light is incident on the crystal along the Brewster angle. After the second incident fundamental frequency light enters the crystal, it is collinear with the first incident fundamental frequency light. The projections of the two light rays on a plane perpendicular to the c-axis are parallel to the a-axis. The wavelength of the first incident fundamental frequency light is greater than the wavelength of the second incident fundamental frequency light, and the Brewster angle is determined by the first incident fundamental frequency light. 和频光从所述第二组平行表面中的另一个射出所述非线性光学晶体。The sum frequency light exits the nonlinear optical crystal from another one of the second set of parallel surfaces. 9.一种连续波非线性光学晶体变频器件的制备方法，其特征在于，该方法包括：9. A method for preparing a continuous-wave nonlinear optical crystal frequency conversion device, characterized in that the method comprises: 确定布儒斯特角θB＝arctann，n为所述非线性光学晶体入射基频光相应的折射率；Determine the Brewster angle θ B =arctann, where n is the refractive index corresponding to the incident fundamental frequency light of the nonlinear optical crystal; 基于非线性光学晶体入射基频光和出射变频光的波长确定相位匹配角θPM；Determine the phase matching angle θ PM based on the wavelengths of the incident fundamental frequency light and the outgoing frequency-converted light of the nonlinear optical crystal; 由所述布儒斯特角θB和相位匹配角θPM，根据式1和式2确定第一夹角β和第二夹角α；The first angle β and the second angle α are determined according to the Brewster angle θ B and the phase matching angle θ PM according to equations 1 and 2; 所述非线性光学晶体为三方晶系，平行于光学晶体c轴切取第一组平行表面，所述第一组平行表面与所述光学晶体a轴呈第一夹角β；The nonlinear optical crystal is a trigonal crystal system, and a first group of parallel surfaces are cut parallel to the c-axis of the optical crystal, and the first group of parallel surfaces forms a first angle β with the a-axis of the optical crystal; 垂直于所述第一组平行表面切取第二组平行表面，使该第二组平行表面的法线与光学晶体c轴方向呈第二夹角α，得到所述变频器件。A second set of parallel surfaces is cut perpendicularly to the first set of parallel surfaces so that the normals of the second set of parallel surfaces form a second angle α with the c-axis direction of the optical crystal, thereby obtaining the frequency conversion device. 10.根据权利要求9所述的制备方法，其特征在于，所述非线性光学晶体为片状晶体，所述第二组平行表面的面间距不大于d/cosα，d为所述片状晶体的厚度。10 . The preparation method according to claim 9 , wherein the nonlinear optical crystal is a plate-shaped crystal, and the interplanar spacing of the second set of parallel surfaces is no greater than d/cosα, where d is the thickness of the plate-shaped crystal.
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