CN105552698B - Side pump bar waveguide DPAL laser - Google Patents

Abstract

A kind of side pump bar waveguide DPAL laser, including LD pump module L, LD pump module R, photoconductive tube L, photoconductive tube R and one-dimensional wave guide resonant cavity, wherein LD pump module L and LD pump module R, photoconductive tube L and photoconductive tube R are symmetrically placed both with respect to the one-dimensional wave guide resonant cavity；And each semiconductor laser stacks or linear array of LD pump module L and LD pump module R are placed on the spherical surface centered on the pumping window of the one-dimensional wave guide cavity in respective direction, the pumping window is directed toward in direction.Laser of the invention uses bilateral profile pump mode, substantially reduces high power density pump light and alkanes palm a possibility that carbon granules that gas reaction generates pollutes laser output window piece off as；Beam shaping process is simplified, pump light distribution unevenness problem is avoided；Using modularization idea, it is suitable for a variety of optically pumped gas laser devices.

Description

Side Pumped Slab Waveguide DPAL Laser

technical field

The present invention relates to gas laser technology, and more particularly to a side-pumped slab waveguide DPAL (semiconductor-pumped alkali vapor laser) laser.

Background technique

DPAL laser is a new type of optically pumped gas laser whose gain medium is alkali metal in vapor state, and the temperature of gain medium is usually 100-200℃. The gain medium of DPAL is mainly potassium, rubidium or cesium in the vapor state, and its energy level structure is shown in Figure 1. In the figure, n is the number of electron layers where the outermost electrons are located, and the corresponding n of K, Rb, and Cs are 4, 5, and 6, respectively. nS _1/2 is the ground state energy level, and nP _1/2 and nP _3/2 are the excited state energy levels generated by the splitting of the outermost electron spin-orbit interaction. The transitions from the ground state to the two upper energy levels correspond to the D2 and D1 lines, respectively.

The DPAL laser was first developed in 2003 when Krupke et al. of the Lawrence Livermore National Laboratory realized the D1 line laser output of an alkali metal laser. The alkali metal laser of this mechanism is pumped by a pump source corresponding to the wavelength of the D2 line, and has a quantum efficiency of more than 95%, and the gain medium is gas, and the thermal lens effect is not obvious. Therefore, the DPAL laser is considered as a new type of laser that is expected to achieve single-aperture MW-level laser output. Its potential in high-power output has also attracted the attention of many high-power R&D institutions at home and abroad.

In 2011, Zweiback et al. of General Atomics used an alternative light source to study a side-pumped alkali metal laser, and obtained a slope efficiency of 75%, which experimentally verified the development potential of side-pumping in DPAL power amplification. A schematic diagram of the scheme is shown in Figure 2. In this scheme, stainless steel is used as the material of the laser head, and a laser window with a size of 7cm×1cm and a pump window with a size of 13cm×1cm are left on the side of the laser head respectively. The alkali metal vapor chamber is heated by electric heating. The alexandrite laser was used as the pump light source, and the astigmatic telescope composed of cylindrical lenses with focal lengths of 100mm and 750mm placed orthogonally on both sides was used to shape the beam of the alexandrite laser, and then focused into the vapor chamber through the 1250mm focal length lens, and the laser output The window adopts a Brewster window design to avoid reflection loss. The resonant cavity consists of a back cavity mirror with a curvature radius of 1m and a coupling-out mirror with a reflectivity of 20%.

However, the above solution still has the following technical defects:

(1) In the scheme shown in Figure 2, the gain area is only formed at the focal position in the vapor chamber, the activation volume is small, and the alkali metal atoms in the vapor chamber cannot be effectively utilized;

(2) The placement between the steam chamber and the heating device is relatively loose, and effective thermal management cannot be performed;

(3) The shaping optical path is long, the components are many, and the system is complex, which is not conducive to miniaturization;

(4) The stable cavity design is adopted, and the mode matching is poor, which is not conducive to high beam quality output.

SUMMARY OF THE INVENTION

In view of this, an object of the present invention is to provide a side-pumped slab waveguide DPAL laser.

In order to achieve the above object, the side-pumped slab waveguide DPAL laser of the present invention includes an LD pump module L, an LD pump module R, a light guide L, a light guide R and a one-dimensional waveguide resonator, wherein:

The one-dimensional waveguide resonator is provided with a pump window L and a pump window R;

The LD pumping module L and the LD pumping module R have the same structure, and are both composed of semiconductor laser stacks or semiconductor laser arrays;

The light guide L and the light guide R have the same structure, and the light guide L is located between the LD pump module L and the pump window L of the one-dimensional waveguide resonator, and the light guide R is located at the between the LD pump module R and the pump window R of the one-dimensional waveguide resonator; the pump light is emitted by the LD pump module L and the LD pump module R, and passes through the light guide L and the light guide respectively After R convergence and homogenization, it enters the one-dimensional waveguide resonator;

wherein, the LD pumping module L and the LD pumping module R, the light guide L and the light guide R are symmetrically placed with respect to the one-dimensional waveguide resonator; and

The semiconductor laser stacks or linear arrays of the LD pump module L and the LD pump module R are placed on a spherical surface centered on the pump window of the one-dimensional waveguide cavity in their respective directions, and the directions point to the the pump window.

Wherein, the light guide L and the light guide R adopt a solid or hollow light guide structure, and the reflectivity of the pump light on the side wall thereof is at least greater than 90%.

Wherein, the one-dimensional waveguide resonator includes upper and lower waveguide wall plates, an all-inversion front cavity mirror, an all-inversion rear cavity mirror, an output coupling mirror and a pump window, wherein the distance between the upper and lower waveguide wall plates is 0.5-2.5mm.

Wherein, the upper and lower waveguide wall plates close to the one-dimensional waveguide resonant cavity are further provided with a temperature control device, and the temperature control device is integrated with the one-dimensional waveguide resonant cavity.

Wherein, the vapor chamber of the one-dimensional waveguide resonant cavity is filled with neon gas, argon gas or helium gas for collision broadening and alkane gas for accelerating the mixing rate of fine structure.

Based on the above technical solutions, the laser of the present invention has the following advantages and beneficial effects:

a. The bilateral side pumping mode is adopted. Since the pump light does not directly illuminate the laser output window, the possibility of contamination of the laser output window by carbon particles generated by the reaction between the high power density pump light and the alkane mixed gas is greatly reduced;

b. Use the light guide to realize the pump light coupling. The light guide integrates the triple functions of pump light convergence, pump light coupling and pump light homogenization, which not only simplifies the beam shaping process, but also avoids the problem of semiconductor lasers to a certain extent. The problem of uneven distribution of pump light caused by the stacking method;

c. The use of one-dimensional waveguide structure avoids the shortcomings of poor beam quality and inconsistency of the fast and slow axes of semiconductor lasers and poor beam distribution uniformity, thereby greatly simplifying the requirements for beam shaping of semiconductor lasers. It also provides high-power pumping for multi-array semiconductor lasers. Pu provides an effective solution;

d. Using an unstable cavity design in the lateral direction can make full use of the lateral width of the gain region, and can also obtain a collimated laser output close to the diffraction limit; this way will rely on increasing the cavity length to increase the "line increase" of the laser power. The conversion of the "ratio" method into the "area increase ratio" technology can not only increase the utilization rate of the gain interval, but also provide a feasible technical route for the high power output of DPAL, and can also simplify the steps of beam shaping of the semiconductor laser array;

e. The temperature control device is closely attached to the waveguide structure, which can make the heating process more effective and uniform on the one hand, and make the whole device more compact on the other hand;

f. The whole device adopts the idea of modularization, and the number of pump modules can be increased beyond the affordability of the light guide coupling scheme;

g. The present invention is suitable for a variety of optically pumped gas lasers. For example, the buffer gas in the vapor chamber is replaced with inert gases such as neon and helium, which will form a broadband pumped alkali metal excimer laser (XPAL) with the alkali metal vapor. system.

Description of drawings

1 is a schematic diagram of the energy level structure of an alkali metal vapor laser in the prior art;

Fig. 2 is a typical side-pumped DPAL laser in the prior art;

3 is a top view of the device of the side-pumped slab waveguide DPAL laser of the present invention;

4 is a side view of the device of the side-pumped slab waveguide DPAL laser of the present invention;

5 is a schematic diagram of a one-dimensional waveguide resonator of the side-pumped slab waveguide DPAL laser of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

The invention discloses a side-pumped slab waveguide DPAL laser, comprising an LD pumping module L, an LD pumping module R, a light guide L, a light guide R and a one-dimensional waveguide resonant cavity, wherein:

The one-dimensional waveguide resonator is provided with a pump window L and a pump window R;

The LD pumping module L and the LD pumping module R have the same structure, and both consist of semiconductor laser stacks or semiconductor laser arrays;

The light guide L and the light guide R have the same structure, and the light guide L is located between the LD pump module L and the pump window L of the one-dimensional waveguide resonator, and the light guide R is located between the LD pump module R and the one-dimensional waveguide resonator. between the pump windows R; the pump light is emitted by the LD pump module L and the LD pump module R, and enters the one-dimensional waveguide resonator after being converged and homogenized by the light guide L and the light guide R respectively;

wherein, the LD pump module L and the LD pump module R, the light guide L and the light guide R are symmetrically placed with respect to the one-dimensional waveguide resonator; and

The semiconductor laser arrays or linear arrays of the LD pump module L and the LD pump module R are placed on a spherical surface centered on the pump window of the one-dimensional waveguide cavity in their respective directions, and the directions point to the pump window.

Preferably, the one-dimensional waveguide resonator adopts an unstable-waveguide hybrid cavity structure.

Preferably, the wavelength of the pump light output by the DPAL laser is the same as the wavelength corresponding to the nP _1/2 →nS _1/2 transition of the alkali metal atoms in the one-dimensional waveguide resonator, and the linewidth of the pump light is resonant with the one-dimensional waveguide. The linewidths of the nS _1/2 →nP _3/2 transition spectra of the alkali metal atoms in the alkali metal vapor chamber of the cavity are matched.

Preferably, the light guide L and the light guide R are solid or hollow light guide structures, and the reflectivity of the pump light on its sidewall should be as close to 100% as possible, at least greater than 90%.

Preferably, the one-dimensional waveguide resonator includes upper and lower waveguide walls, an all-inversion front cavity mirror, an all-inversion rear cavity mirror, an output coupling mirror and a pump window, wherein the spacing between the upper and lower waveguide walls is 0.5-2.5mm .

Preferably, the reflectivity of the upper and lower waveguide walls of the one-dimensional waveguide cavity is as close to 100% as possible, at least greater than 95%, and the materials used have the properties of chemical stability to alkali metals and good thermal conductivity.

Preferably, the reflectivity of the all-reflection rear cavity mirror is 99%-100%; the reflectivity of the all-reflection front cavity mirror is 99%-100%.

Preferably, the output coupling ratio of the output coupling mirror is 15%-90%.

Preferably, the transmittance of the pump light window of the one-dimensional waveguide resonator should be as close to 100% as possible, and at least greater than 95%.

Preferably, a temperature control device is further provided on the upper and lower waveguide wall plates close to the one-dimensional waveguide resonant cavity, and the temperature control device is integrated with the one-dimensional waveguide resonant cavity.

Preferably, the vapor chamber of the one-dimensional waveguide resonant cavity is filled with argon gas or helium gas for collisional broadening and alkane gas for accelerating the mixing rate of fine structures.

As a preferred embodiment of the present invention, the structure of the side-pumped slab waveguide laser of the present invention is shown in FIGS. 3 and 4 . The structure of the device of the present invention is described below by taking a rubidium vapor laser as an example.

The laser device of the present invention is composed of a semiconductor laser array, a light guide tube, a one-dimensional waveguide resonant cavity, and a temperature control system, wherein the one-dimensional waveguide resonant cavity adopts a one-dimensional waveguide structure, and it is required to select the one with good thermal conductivity and stable chemical properties of alkali metals. Material. There are long and narrow pump windows on both sides of the one-dimensional waveguide resonator for side pumping. The front and rear cavity mirrors and the output coupling mirror are installed in the laser output direction. A temperature control system is attached on both sides of the one-dimensional waveguide cavity to control the temperature in the resonant cavity.

The pump source is composed of a plurality of semiconductor laser stacks, each of which can be collimated by a fast and slow axis collimating microlens, and then an external cavity semiconductor laser can be formed under the external cavity feedback of a volume Bragg grating (VBG). The output laser linewidth is about 0.1nm, the slow axis divergence angle can be controlled below 50mrad, and the fast axis divergence angle can be controlled within 1°. The present invention takes the DILAS semiconductor laser stack as an example, and the size of the outgoing light spot after collimation is 11.5×9 mm ² (slow axis and fast axis direction). The present invention intends to use 12 pump modules on both sides as a demonstration example, and each side uses 6 VBG external cavity semiconductor laser stacked pump modules with the same narrow linewidth output, arranged in two rows in the direction of the fast axis, and in the direction of the slow axis. Place three in each row so that the light spot of each LD pump module points to the pump light window. In a preferred embodiment, the length of the pump window of the one-dimensional waveguide resonator used in the present invention is 10mm, the width is 1mm, the length of the pump light propagation direction is 5mm, and the waveguide structure is composed of a medium that can be polished on both sides and is resistant to alkali metal penetration. (such as stainless steel, alumina ceramics, quartz glass, etc.), the reflectivity is 99%-100%. The spacing is 1mm. To ensure the coupling rate of the light guide, the window is embedded in the waveguide cavity. The pump light passes through the light guide and is coupled into the waveguide cavity. In a preferred embodiment, the length of the light pipe light entrance along the slow axis direction is 30mm, the length along the fast axis direction is 18mm, the length of the light outlet along the slow axis direction is 10mm, the length along the fast axis direction is 1mm, and is close to a Dimensional waveguide cavity pumping window. 100% coupling of the above-mentioned pump light can be achieved when the length of the light guide is greater than 150 mm. An unstable-waveguide hybrid cavity and an output coupling mirror are installed in the light-emitting direction of the waveguide cavity, wherein the unstable-waveguide hybrid cavity is composed of a front cavity mirror and a rear cavity mirror. The front cavity mirror and the rear cavity mirror can be either spherical mirrors or cylindrical mirrors, which correspond to different waveguide losses. In a preferred embodiment, the size of the vapor chamber of the one-dimensional waveguide is 10mm×5mm×1mm, and the curvature radii of the front and rear cavity mirrors are -600mm and 700mm respectively (positive values indicate concave mirrors, and negative values indicate convex mirrors). The cavity is filled with alkali metal and a mixed gas composed of helium and alkane, which is used to widen the D2 absorption line of the alkali metal atom and increase the mixing rate of the fine structure. The temperature in the cavity can be controlled by TEC temperature control sheets attached to both sides of the waveguide. When working, the temperature in the cavity is stably controlled by the TEC temperature control sheet within its optimal working temperature range.

In another preferred embodiment of the present invention, the grating line width is used instead of the VBG line width; in another preferred embodiment of the present invention, a solution in which a solid glass light guide and a glass vapor chamber are integrated can also be used.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned specific embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principle of the present invention, any modifications, equivalent replacements, improvements, etc. made should be included within the protection scope of the present invention.

Claims (10)

1. A side-pumped slab waveguide DPAL laser, comprising an LD pump module L, an LD pump module R, a light guide L, a light guide R and a one-dimensional waveguide resonator, wherein: The one-dimensional waveguide resonator is provided with a pump window L and a pump window R; The LD pumping module L and the LD pumping module R have the same structure, and are both composed of semiconductor laser stacks or semiconductor laser arrays; The light guide L and the light guide R have the same structure, and the light guide L is located between the LD pump module L and the pump window L of the one-dimensional waveguide resonator, and the light guide R is located at the between the LD pump module R and the pump window R of the one-dimensional waveguide resonator; the pump light is emitted by the LD pump module L and the LD pump module R, and passes through the light guide L and the light guide respectively After R convergence and homogenization, it enters the one-dimensional waveguide resonator; It is characterized in that, the LD pumping module L and the LD pumping module R, the light guide L and the light guide R are symmetrically placed with respect to the one-dimensional waveguide resonator; and The semiconductor laser stacks or linear arrays of the LD pump module L and the LD pump module R are placed on a spherical surface centered on the pump window of the one-dimensional waveguide resonator in their respective directions, and the directions point to the pump window. 2 . The side-pumped slab waveguide DPAL laser according to claim 1 , wherein the one-dimensional waveguide resonator adopts an unstable-waveguide hybrid cavity structure. 3 . 3 . The side-pumped slab waveguide DPAL laser according to claim 1 , wherein the wavelength of the light output by the DPAL laser is equal to nP _1/2 → nS of the alkali metal atoms in the one-dimensional waveguide resonator. 4 . The wavelength corresponding to the _1/2 transition is the same, and the linewidth of the pump light is the same as the nS _1/2 → nP _3/2 transition of the alkali metal atom after the buffer gas in the alkali metal vapor chamber of the one-dimensional waveguide resonator is widened The spectral line widths are matched. 4. The side-pumped slab waveguide DPAL laser according to claim 1, wherein the light guide L and the light guide R adopt a solid or hollow light guide structure, and the reflection of the pump light on its sidewall rate is at least greater than 90%. 5 . The side-pumped slab waveguide DPAL laser according to claim 1 , wherein the one-dimensional waveguide resonator comprises upper and lower waveguide wall plates, an all-inverting front cavity mirror, an all-inverting rear cavity mirror, and an output coupling mirror. 6 . and a pumping window, wherein the distance between the upper and lower waveguide wall plates is 0.5-2.5mm. 6 . The side-pumped slab waveguide DPAL laser according to claim 5 , wherein the reflectivity of the upper and lower waveguide walls of the one-dimensional waveguide resonator is at least greater than 95%, and the materials used have chemical resistance to alkali metals. 7 . Stable properties and good thermal conductivity; The reflectivity of the all-reflection rear cavity mirror is 99%-100%; the reflectivity of the all-reflection front cavity mirror is 99%-100%. 7 . The side-pumped slab waveguide DPAL laser according to claim 5 , wherein the output coupling ratio of the output coupling mirror is 15% to 90%. 8 . 8 . The side-pumped slab waveguide DPAL laser according to claim 1 , wherein the transmittances of the pump window L and the pump window R of the one-dimensional waveguide resonator are at least greater than 95%. 9 . 9 . The side-pumped slab waveguide DPAL laser according to claim 1 , wherein the upper and lower waveguide wall plates that are close to the one-dimensional waveguide resonator are further provided with a temperature control device, and the temperature control device is connected to the DPAL laser. 10 . The one-dimensional waveguide resonator is integrated. 10. The side-pumped slab waveguide DPAL laser according to claim 1, wherein the vapor chamber of the one-dimensional waveguide resonator is filled with neon, argon or helium for collisional broadening, and Paraffinic gases used to increase the rate of fine structure mixing.