CN100392513C - All-solid-state continuous broadband mid-infrared coherent light source - Google Patents

Abstract

The invention relates to a laser light source, in particular to an all-solid-state continuous broadband laser light source, and belongs to the technical field of nonlinear optical frequency conversion. The present invention utilizes the continuous 1064nm laser pumping periodically polarized _LiNbO3 crystal (PPLN) optical parametric oscillator produced by continuous pumping of the Nd: _YVO4 crystal on the end face of the semiconductor laser, and adopts the inner cavity OPO scheme of placing the PPLN crystal in the laser resonator, By adjusting temperature and other related parameters, a mid-infrared tunable light source with high efficiency, large tunable wavelength range, long life, compact structure and small volume can be obtained, which can meet the applications in many fields such as optical communication, infrared countermeasures, environmental monitoring and spectroscopy research. need.

Description

All-solid-state continuous broadband mid-infrared coherent light source

technical field

The invention relates to a laser light source, in particular to an all-solid-state continuous broadband laser light source, and belongs to the technical field of nonlinear optical frequency conversion.

Background technique

Infrared light has three main transmission windows in the atmosphere: 1-3 μm, 3-5 μm, and 8-12 μm, among which the 3-5 μm band is the infrared window with the least attenuation. Lasers in this band have strong penetrating power to fog, smoke, etc., and are less absorbed by gas molecules and scattered by suspended matter when transmitted at sea level. The response range of the infrared guided missile detector is in the 3-5 μm band, so the photoelectric countermeasures against the infrared seeker urgently need a laser light source in this band. In the 3-5μm region, most important hydrocarbon gases and other toxic gas molecules have strong absorption characteristics, so mid-infrared coherent light sources have a wide range of civil value in the field of trace gas detection: such as oil field exploitation, natural gas pipeline leakage detection, atmospheric Greenhouse gas detection, drug inspection, methane gas detection in coal mines, etc. Since the 3-5μm band laser has important application value and prospects in many fields such as spectroscopy, remote sensing, medical treatment, environmental protection and military affairs, the research on the 3-5μm band laser has become a very popular topic in the world.

For nearly 40 years, optical parametric oscillators (OPOs) have been considered as ideal sources for obtaining coherent light in spectral ranges beyond the reach of conventional lasers. One OPO can obtain continuously tunable output in a very wide spectral range, and OPO also has the advantages of all-solid-state design, high efficiency and considerable output power, and from the time domain, OPO can output continuously or output such as Ultrashort pulses such as femtoseconds.

The performance parameters of OPO depend almost entirely on the spectral properties and beam quality of the pump laser, as well as the properties of the nonlinear crystal. Judging from the current development of lasers, the coherent light source in the mid-infrared spectrum still depends on OPO (using PPLN crystals). From the perspective of the working spectrum and time domain, the OPO market for pulse (ns) and mode-locked (ps/fs) There are already many formed products, but the lack of continuous OPO in the mid-infrared band (3-5 μm) has been plagued by researchers.

The all-solid-state laser with laser diode-pumped solid-state laser as the pump source has become the most excellent laser so far due to its high power, high beam quality, high efficiency, small size, and light weight. In recent years, with the maturity of quasi-phase matching technology (QPM), the nonlinear optical frequency conversion technology using periodically poled crystals has attracted widespread attention. The biggest advantage of quasi-phase matching technology is that the nonlinear conversion efficiency is high, and it can make those Under normal conditions, crystals and light-passing bands that cannot achieve phase matching can achieve frequency conversion, broaden the application range, increase tuning methods, and make it possible to output high-efficiency and wide-band lasers that have troubled people for a long time. At present, the common use Periodically polarized crystals for quasi-phase matching include PPLN, PPKTP, and PPLT, among which PPLN has a large effective nonlinear coefficient (16pm/V), and the polarization technology is mature, making it the most widely used periodically polarized crystal, PPLN-OPO It is an important means and effective way to realize nonlinear optical frequency conversion, and it is also another research hotspot in tunable light sources. Therefore, using all-solid-state tunable lasers to pump quasi-phase-matched optical parametric oscillators, by adjusting related parameters, such as pump The wavelength, temperature and cycle of the polarized crystal can be used to obtain a continuously operating infrared tunable light source with high output power, high efficiency, large tuning range, long life, and compact structure.

Contents of the invention

The purpose of the invention of this patent is to use the all-solid-state end-pumped continuous Nd:YVO ₄ laser as the pump source to pump the inner cavity PPLN-OPO to generate a 3-5μm broadband infrared light source, which can meet the needs of spectroscopy, remote sensing, medical treatment, and environmental protection. and military and many other fields.

The technical scheme of the present invention is as follows: an all-solid-state continuous broadband mid-infrared coherent light source, including a pump source, a PPLN parametric oscillator crystal, an optical parametric resonator, and a laser resonator, wherein the pump source is an all-solid-state laser, using The Nd:YVO4 crystal is continuously pumped on the end face of the semiconductor laser diode, and the continuous 1064nm laser is generated by means of close-fitting or self-focusing coupling. The end close to the output end is coated with 808nm and 1064nm high-transparency films; the optical parametric resonant cavity is a cavity composed of an OPO total reflection mirror and an OPO output mirror. , the other side is coated with a 1064nm high-transparency film and a 1400-1500nm high-reflection film. Coated with 3000-5000nm high-transparency film, the cavity length of the optical parametric resonant cavity is 110mm, the radius of curvature of the OPO output mirror is 150mm; the polarization period of the PPLN parametric oscillator crystal is 28.5μm, and both ends are coated with 1064nm high-transparency film , 1400-1500nm high-permeability film, 3700-4000nm high-permeability film, located in the above-mentioned resonant cavity, and fixed in a temperature-controlled furnace whose furnace temperature can be continuously changed from 300K to 473K; the laser resonant cavity is made of Nd:YVO4 One end of the crystal close to the end face of the semiconductor laser diode and the concave surface of the OPO output mirror are formed, and the cavity length is 140nm.

For the above-mentioned all-solid-state continuous broadband mid-infrared coherent light source, the size of the crystal Nd:YVO4 may be 3×3×5 mm, and the doping concentration may be 1.0 at%.

The present invention has following beneficial effect:

①All solid-state lasers are compact, durable, and cheap, and occupy a very important position in laser applications.

② The beam quality of the end-pumped laser is good, and it can be better matched with the cavity mode of the solid-state laser in space. Moreover, the coupling efficiency of the end-pump method is extremely high, which shows obvious advantages in the application of low-to-medium power lasers, especially in continuous laser applications.

③The use of periodically polarized crystals to realize quasi-phase-matched optical parametric oscillators is a new type of important means and effective way to realize tunable infrared light sources. Using the specific wavelength output by high-power all-solid-state lasers to pump periodically polarized crystals, By adjusting relevant parameters such as temperature and cycle, an infrared tunable light source with high output power, high efficiency, wide tunable wavelength range, long life, compact structure and small volume can be obtained, which is an ideal tuning method.

④ The all-solid-state continuous wave PPLN optical parametric oscillator not only has the advantages of high power level, compact structure, and low price of all-solid-state lasers, but also has the advantages of broadband tunability and small size of quasi-phase-matched optical parametric oscillators. Trace gas analysis, photoacoustic spectroscopy, exhaust gas detection, airborne large-scale land and ocean pollution detection, air pollution analysis, military applications and other fields have broad scientific research value and broad application prospects and fill the field of technology blank.

Description of drawings

Fig. 1 is a schematic structural view of the all-solid-state continuous broadband mid-infrared coherent light source of the present invention, in the figure,

1. Laser diode; 2. Nd:YVO ₄ crystal; 3. OPO mirror; 4. PPLN crystal; 5. OPO output

Detailed ways

The present invention all adopts all-solid-state devices, utilizes the continuous _1064nm laser pumping periodic poled LiNbO crystal (PPLN) optical parametric oscillator produced by semiconductor laser end face continuous pumping of Nd:YVO ₄ crystal, adopts PPLN crystal placed in the laser resonant cavity The internal cavity OPO solution, by adjusting the temperature and other related parameters, obtains a mid-infrared tunable light source with high efficiency, large tunable wavelength range, long life, compact structure and small volume, which meets the needs of optical communication, infrared countermeasures, environmental monitoring and spectroscopy. Research and many other fields of application requirements.

Laser diode end-pumped solid-state lasers have high pump conversion efficiency. By adjusting the pump spot and optimizing the design of the resonant cavity, high beam quality laser output near the diffraction limit can be obtained. It is the first choice for small and medium power continuous lasers. The laser components are all solid-state and compact in structure. At present, the domestic laser diode production process is mature, and the single-tube power has reached 5W. Therefore, the laser diode end-pumping method is used in this scheme.

Nd:YVO ₄ crystal has a large stimulated emission cross-section, the output light has polarization characteristics, and the growth technology is mature. The light-to-light conversion efficiency of 1064nm laser obtained by pumping Nd:YVO ₄ crystal with laser diode can be greater than 50%, M ² < 2, so this scheme chooses laser diode end-pumped Nd:YVO4 laser as the pump source of OPO, and makes full use of its high beam quality and polarization characteristics to achieve high-efficiency nonlinear optical frequency conversion.

Optical parametric oscillators are considered to be the most important nonlinear optical frequency conversion technology that extends a single wavelength to a long wavelength, and has the advantages of miniaturization, high efficiency, and wavelength tunability. Combining optical parametric oscillators with all-solid-state lasers is the main way to obtain high-power long-wavelength tunable light sources. This program uses PPLN optical parametric oscillator to expand the 1064nm laser to long wavelength to obtain 3-5μm laser output. The intracavity OPO scheme is selected, the nonlinear crystal is placed in the laser resonator, the OPO resonator is combined with the laser resonator through coating, and the high power density in the laser resonator is fully utilized. Since the quasi-phase matching technology has extremely high nonlinear conversion efficiency, this patent uses a periodically polarized crystal to realize a quasi-phase matching optical parametric oscillator solution. PPLN has a large nonlinear coefficient d ₃₃ (16pm/V), mature polarization technology, stable physical and chemical properties and is not easy to deliquescence. Therefore, PPLN is selected as the nonlinear crystal of OPO.

Below in conjunction with accompanying drawing, the present invention is described in further detail:

Referring to Fig. 1, the laser light source of the present invention has following structure: 1. system all adopts all-solid-state device; 2. utilizes semiconductor laser diode end face to continuously pump Nd: YVO Crystal, adopts close to or self-focusing coupling mode, produces continuous 1064nm laser; ③④The material of OPO mirror is K9 or BK7 glass. Flat mirror, φ=20mm, one side is coated with 1064nm high-transparency film (HT), the other side is coated with 1064nmHT, 1400-1500nm high-reflection film (HR); 28.5 μm. Both ends are coated with 1064nmHT, 1400~1500nmHT, 3700~4000nmHT films. ⑥The OPO output mirror is a plano-concave mirror with φ=20mm and radius of curvature R=150mm, using CaF ₂ material. 1064nmHR, 1400~1500nmHR, 3000~5000nmHT films are plated on the concave surface, 3000~5000nmHT films are plated on the plane; ⑦1064nm resonant cavity length is 140mm, and OPO resonant cavity length is 110mm. By controlling the cavity length and the size of the radius of curvature, 1064nm can be achieved Matching with the mode of 1500nm light, the radius of the fundamental mode spot at the working substance is 120μm; ⑧The working temperature of the laser diode and laser crystal is 18℃, semiconductor refrigeration; the PPLN crystal is fixed in the temperature-controlled furnace, and the temperature of the temperature-controlled furnace is 300K to 473K Can be changed continuously; ⑨Output 3~5um continuously adjustable mid-infrared broadband light source in continuous operation.

Claims (2)

1. infrared coherent source in the solid continuous wide band comprises pumping source, PPLN parametric oscillation crystal, and the optical parameter resonator cavity, laserresonator is characterized in that:

Described pumping source is an all solid state laser, utilize the continuous pumping Nd:YVO4 of semiconductor laser diode end face crystal, employing is close to or the self-focusing coupling scheme, produce continuous 1064nm laser, described Nd:YVO4 crystal is near end plating 808nm high transmittance film, the 1064nm high-reflecting film of semiconductor laser diode end face, near the end plating 808nm and the 1064nm high transmittance film of output terminal; The cavity of described optical parameter resonator cavity for constituting by OPO total reflective mirror and OPO outgoing mirror, described OPO total reflective mirror is flat mirror, it simultaneously plates the 1064nm high transmittance film, another side plating 1064nm high transmittance film and 1400～1500nm high-reflecting film, described OPO outgoing mirror is the plano-concave mirror, its concave surface plating 1064nm high-reflecting film, 1400～1500nm high transmittance film and 3000～5000nm high transmittance film, its plane plating 3000～5000nm high transmittance film, the chamber of optical parameter resonator cavity is long to be 110mm, and the radius-of-curvature of described OPO outgoing mirror is 150mm; The polarization cycle of described PPLN parametric oscillation crystal is 28.5 μ m, both-end plating 1064nm high transmittance film, 1400～1500nm high transmittance film, 3700～4000nm high transmittance film, be positioned at above-mentioned resonator cavity, and be fixed on furnace temperature in 300K can the continually varying temperature controlling stove to 473K;

Described laserresonator is for being made of an end and the OPO outgoing mirror concave surface of Nd:YVO4 crystal near the semiconductor laser diode end face, and its chamber is long to be 140nm.

2. infrared coherent source in the solid continuous wide band according to claim 1 is characterized in that, described crystal Nd:YVO4 is of a size of 3 * 3 * 5mm, doping content 1.0at%.

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