CN103236639A - Self-injection structure for realizing isotropic medium output linearly polarized single-frequency laser - Google Patents

Abstract

The invention relates to a self-injection structure for outputting linearly polarized single-frequency laser from an isotropic medium, and relates to a self-injection structure of a laser, in particular to an end-pumped self-injection single-frequency Tm ³⁺ :YAG laser. The 785nm light enters the crystal from the end face, pumps the end face, and uses the combination of FP etalon and volume grating to select the single longitudinal mode, and the volume grating is used as the output cavity mirror, and after passing through the beam splitter mirror, the generated laser light passes through The 1/2 wave plate and the Glan prism form linearly polarized light, and a small part of the light is reflected by the total reflection mirror through a part of the mirror, and the linearly polarized light is re-injected into the crystal and continues to oscillate, thus forming a Structure of a self-injected linearly polarized single-frequency laser. The design of the whole machine realizes the linearly polarized output in the isotropic crystal by the method of self-injection, and obtains a high-power, linearly polarized, and stable single-frequency laser. This method is comprehensive and accurate, and is suitable for including Tm ³⁺ :YAG in Injection frequency-locking technology research in single-doped thulium isotropic medium, the application fields include photoelectric countermeasures, laser radar and laser medical treatment and other fields.

Description

A self-injection structure for outputting linearly polarized single-frequency laser from isotropic media

Technical Fields

The present invention relates to a self-injection structure for obtaining a linearly polarized single-frequency laser output, in particular to a self-injection single-frequency Tm ³⁺ : YAG laser structure, which is suitable for the research of injection frequency locking technology, and its application fields include photoelectric countermeasures, Laser radar, laser medical treatment, etc.

Background technique

The 2μm band laser produced by thulium-doped lasers is widely used in the fields of photoelectric countermeasures, lidar, and laser medical treatment due to its particular wavelength. First of all, the 2μm band laser can be used as a pumping source to generate 3-5μm and 8-12μm infrared lasers, which can be used for laser infrared directional jamming, which is an optoelectronic countermeasure technology for combating infrared missiles guided by the next generation of infrared staring focal plane detectors . Directional jamming is to concentrate the infrared jamming energy into a narrow beam. When the infrared missile approaches, the beam is fired at the infrared seeker of the incoming missile. Various jamming programs and "confusing" modulations are used to make the incoming missile seeker work in confusion. Unable to lock on to the target and misses the target. Secondly, due to the small transmission loss of the 2μm wavelength in the atmosphere, the green vegetation and moist soil have a large absorption of it, the reflection is small, and it is safe for human eyes, so it is very beneficial to distinguish the ground target from the background in laser detection, so 2μm band laser is an excellent light source for lidar, such as 2μm coherent Doppler wind radar and 2μm differential absorption lidar are the current focus of lidar research. Doppler wind measurement lidar can provide accurate wind field data for global numerical weather forecasting, prevent and resist disastrous weather, carry out sports events smoothly, and provide accurate wind field detection over the airport; 2μm differential absorption lidar can realize local Real-time monitoring of CO ₂ gas concentration, aerosol, water vapor, ozone, and temperature in the environment. Finally, 2μm lasers are also widely used in laser medicine. The new continuous wave thulium-doped (Tm ³⁺ ) laser can output continuously, and when it is used as a scalpel, it only produces small mechanical damage, and the area of biological tissue damage caused by the incision is also very small. The Tm ³⁺ laser only affects the front end less than 2mm Tissues within the distance will act; tissues or organs beyond this distance will be protected by the shielding of the aqueous medium, which will provide great technical support for minimally invasive surgery, in which pumping Tm ³⁺ :YAG with 785nmLD is a very effective method.

Injection frequency locking technology can obtain narrow pulse width, high power, high energy fundamental transverse mode and single longitudinal mode laser output, which is also an important technology when researching coherent Doppler wind radar. There are two ways to inject frequency locking, one is external injection of seed light, and the other is self-injection of seed light. The external injection method is composed of two lasers, a seed laser and a power amplifier, but this method has high requirements on the stability and time synchronization of the two lasers. The self-injection method uses a laser to form a seed cavity Therefore, it is superior to the external injection method in terms of stability and synchronization. This is an important innovation and advantage of the present invention. Scholars at home and abroad have mainly focused on the external injection method for the research on seed injection technology, but the use of self-injection There are still many gaps in the research of lasers for seed laser injection, so mastering self-injection technology is more conducive to the research of injection frequency-locking technology, and will occupy a dominant position in this research field.

For isotropic media, the laser generated after pumping is circularly polarized light, and the increase in pumping power will cause depolarization, which seriously affects the output power of the laser. The circularly polarized light is converted into linearly polarized light and re-injected into the In the resonant cavity, this depolarization phenomenon is avoided, which is an important innovation point of the present invention.

For frequency selection technology, both F-P etalon technology and transmission volume Bragg grating technology (T-VBG) are quite mature. The F-P etalon has different transmittance characteristics for light of different frequencies, so that the F-P etalon determines The free spectral region is equivalent to the gain linewidth of the laser medium, and achieves single longitudinal mode laser output, and by using T-VBG to reduce the output of other wavelengths, the power of the seed injected in the direction of the output mirror becomes larger, which is beneficial to the frequency locking of the system, so Higher power single-frequency laser output can be achieved by using double F-P combined gratings. the

Contents of the invention

The purpose of the present invention is to design a self-injection structure that produces a 2μm linearly polarized single-frequency laser output. While the laser is oscillating in the resonator, the 2μm laser generated by itself is used as a seed laser by using the self-injection technology, and is transformed by a polarization element. The linearly polarized light is re-injected into the resonant cavity, and the competition between the seed mode and the natural mode is used to obtain high-power, linearly polarized, single-frequency laser output with better monochromaticity and higher spectral purity.

A self-injection structure for isotropic media to output linearly polarized single-frequency lasers, using a continuous laser diode laser as a pumping source to pump a Tm:YAG crystal, using two F-P etalons and a transmissive volume Bragg grating (T -VBG) as the frequency selection element, and T-VBG as the output cavity mirror at the same time to obtain single-frequency laser output; at the same time, the self-injection system is used to re-inject the output 2μm laser into the resonator from the output cavity mirror, and the self-injection system is controlled by It consists of beam splitter, 1/2 wave plate, Glan prism, total reflection mirror and partial reflection mirror.

The self-injection structure for outputting linearly polarized single-frequency laser from an isotropic medium is characterized in that a 785nm continuous laser diode is used as a pumping source. the

3×7mm³，掺杂浓度为3.5%。 The self-injection structure for realizing the output linearly polarized single-frequency laser of the isotropic medium is characterized in that it adopts Tm:YAG crystal, and the crystal size is

3×7mm ³ , the doping concentration is 3.5%.

The described self-injection structure for realizing isotropic medium output linearly polarized single-frequency laser is characterized in that two P-F etalons are used as frequency-selective elements, wherein the thickness of one F-P etalon is 0.1mm, and red quartz material is used; Another F-P etalon has a thickness of 1 mm and is made of YAG material.

The self-injection structure for outputting linearly polarized single-frequency laser from an isotropic medium is characterized in that a transmissive volume Bragg grating (T-VBG) is used as an output cavity mirror. The grating has a linewidth of less than 1 nm and a diffraction efficiency greater than 99.5%, the transmission center wavelength is 2010nm.

The self-injection structure of the described realization of isotropic medium output linearly polarized single-frequency laser is characterized in that it adopts a 45 ° beam splitter, which is coated with a 2010nm anti-reflection film with a transmittance of 60%; a 785nm total reflection film ( R>99.5%).

The self-injection structure for outputting linearly polarized single-frequency laser from an isotropic medium is characterized by a self-injection system, which consists of a 1/2 wave plate, a Glan prism, a total reflection mirror and a partial reflection mirror.

The self-injection structure for realizing the output of linearly polarized single-frequency laser from an isotropic medium is characterized in that a 1/2 wave plate is used.

The self-injection structure for outputting linearly polarized single-frequency laser from an isotropic medium is characterized by using a Glan prism with a size of 9×9×10mm ³ and a prism wedge angle of 40°.

The self-injection structure for outputting linearly polarized single-frequency laser from an isotropic medium is characterized in that it adopts a total reflection mirror and is coated with a 2010nm high reflection film.

The self-injection structure for outputting linearly polarized single-frequency laser from an isotropic medium is characterized in that it adopts a 45° partial reflector, is coated with a 2010nm anti-reflection film, and has a transmittance of 80%.

In the design process of the self-injection structure, the present invention firstly adopts FP etalon technology combined with transmission volume Bragg grating (T-VBG) frequency selection technology, compared with ordinary frequency selection technology, since the output cavity is replaced by T-VBG mirror, which can make the wavelength of laser oscillation avoid the absorption peaks of water molecules and CO ₂ gas, reduce the loss in the cavity, and do not introduce new components to the resonator, so it is very beneficial to improve the single-frequency output power; at the same time, the self- Injection technology, using 1/2 wave plate and Glan prism to make the output light through the partial reflection mirror and part of the laser light returning to the resonator through the total reflection mirror are linearly polarized light, and the part returning to the resonator will induce the resonator The output laser becomes linearly polarized light, which avoids the depolarization phenomenon, and has better monochromaticity and higher spectral purity than that without self-injection.

The outstanding effects of the present invention will be further described in the specific implementation manner.

Description of drawings

FIG. 1 is a schematic diagram of a self-injection structure device for realizing the output of linearly polarized single-frequency laser in an isotropic medium according to the present invention.

Detailed ways

Below in conjunction with accompanying drawing and specific example the present invention is described in more detail:

The laser device of the present invention comprises: central wavelength is 785nm laser diode pumping source 1; The optical fiber 2 of coupling output 785nm laser; Coupling lens group 3; Tm:YAG crystal 4; F-P etalon group 5; Transmissive volume Bragg grating (T -VBG) 6; 45° beam splitter 7; 1/2 wave plate 8; Glan prism 9; 45° partial reflection mirror 10; total reflection mirror 11.

The working process of a high-power single-doped thulium self-injection single-frequency solid-state laser device of the present invention is as follows: the LD pumping source adopts a laser diode with a center wavelength of 785nm, and is coupled through an optical fiber 2. The core diameter of the optical fiber is 400 μm, and the numerical aperture is 0.22. The laser coupling lens group 3 is used for collimation, the two focusing lenses are plano-concave mirrors, the focal length of the two lenses is 25mm, the surface element is Ф20mm, the thickness is 3mm, the coupling ratio is 1:1, and the incident Tm ; The left end face of YAG crystal 4 is coated with a film system with high transparency to 785nm and high reflection to 2010nm, the spot center of the 785nm pumping light is 2mm away from the left end face, and Tm; the left end face of YAG crystal 4 is used as a cavity of the resonant cavity The laser passes through the first F-P etalon with a thickness of 0.1nm. In order to obtain a 2010nm single longitudinal mode output, the 0.1mm F-P is placed at 6.25° through calculation, and the first F-P etalon from the left is fixed. Then go through the second F-P etalon with a thickness of 1mm, and adjust the second F-P etalon from the left to 1°, which is the best angle for obtaining 2010nm single longitudinal mode laser output, and then pass through the transmission volume grating (T-VBG ) 6, and the transmission volume grating (T-VBG) 6 is used as the output cavity mirror, so that the resonant cavity is formed between the left end face of the crystal and the grating, and the laser oscillation is performed. Through the setting of the transmittance, more 2010nm single-frequency laser Output, where double F-P etalon and transmission volume grating (T-VBG) can be used in combination to obtain higher power laser output. The output 2010nm laser and the remaining 785nm pump light pass through the 45° beam splitter 7, part of which is transmitted, and the other Part of it is reflected outside the cavity by a 45° mirror. The 45° beam splitter 7 adopts a plane mirror structure with a surface element of Ф20mm and a thickness of 2mm. The transmittance of mirror 7 to 2010nm laser is 80%. Since most of the 785nm pump light is reflected outside the cavity, most of the 2010nm laser is transmitted through, and the transmitted 2010nm laser is then adjusted by the 1/2 wave plate 8 to obtain better mode matching. 9. The optical axis of the Glan prism 9 is parallel to the incident surface. Using the different refractive indices of the o-ray and e-ray in the Glan prism 9, a prism wedge angle of 40° is selected through calculation to make the o-ray totally reflect outside the cavity, e The light propagates in the cavity, and a linearly polarized 2010nm single-frequency laser is obtained. The linearly polarized 2010nm single-frequency laser passes through the 45° partial reflector 10 reflecting 2010nm, and a part of it is reflected on the total reflection mirror 11, and then returns to the Glan prism 9 through the total reflection mirror 11 and the 45° partial reflector 10, and then passes through the The 1/2 wave plate 8 passes through the 45° beam splitter 7 and re-enters the resonant cavity formed by the left end face of the Tm:YAG crystal 4 and the transmission volume grating (T-VBG) 6 . Among them, the 45° partial reflector 10 adopts a plane mirror structure, the plane element is Ф20mm, and the thickness is 2mm. Through calculation, it can be known that the transmittance of the 45° partial reflector 10 to the 2010nm laser is 90%, and the remaining 2010nm laser passes through the 45° partial reflector. 10. Shoot onto the total reflection mirror 11, wherein the 2010nm laser reflected by the 45° partial reflection mirror 10 is to achieve the minimum power for self-injection frequency locking, so that the induction is enough to form linearly polarized light, and passes through the 45° beam splitter 7 again Inject into the resonant cavity to form a self-injection system of seed light, inject the seed light into the resonant cavity, compete with the natural mode in the resonant cavity, and induce more single-frequency, linearly polarized 2010nm lasers, Due to the increase of 2010nm linearly polarized single-frequency lasers in the resonator, the mode competition is increased, and more 2010nm linearly polarized single-frequency laser outputs are continuously induced. Continue this process to obtain high-power, Linear polarization, single frequency 2012nm laser output. When the seed laser is not injected, the output power is 75mW. Compared with the seed laser, the power is greatly improved, and the linear polarization degree is higher than 0.95, and the beam quality is less than 1.2. Single longitudinal mode output.

Not only Tm:YAG crystals can be used in this structure, but also this self-injection structure can be used in isotropic thulium-doped lasers to obtain high-power, linearly polarized single-frequency laser output, such as Tm:LuAG crystals, At the same time, it is necessary to appropriately change the wavelength of the pumping light, the length of the cavity, and the film system of each lens according to the properties of the crystal itself.

Since the self-injected structure is a laser that forms the seed cavity and the power cavity, the mode matching between the natural mode and the seed mode will be easier than that of the externally injected structure. When sufficient injection power is achieved, the natural mode can be better. suppression. And the linearly polarized laser output obtained by the self-injection structure through the combination of the wave plate and the prism can be re-injected into the laser resonant cavity, thereby inducing more linearly polarized light to be generated. Since isotropic crystals produce circularly polarized light, but the increase in pumping power will lead to significant depolarization and seriously affect the polarization stability of laser output, so using this self-injection structure to re-inject linearly polarized light will avoid The generation of this phenomenon realizes 2μm laser polarization, single frequency and stable output. This structure of self-injecting linearly polarized light into the cavity is the outstanding feature of this patent. In addition, the 2μm laser obtained through this self-injection method has better monochromaticity and higher spectral purity.

Claims (12)

1. One kind realize isotropic medium output line polarization single-frequency laser from injecting structure, namely utilize and singly mix thulium crystal pumping end face as the input cavity mirror, and adopt F-P etalon and body Bragg grating to carry out single longitudinal mode and select, wherein the body Bragg grating is as the output cavity mirror, in conjunction with 1/2 wave plate and Glan prism, making output laser is linearly polarized light, linearly polarized light reflects through total reflective mirror, thereby linearly polarized light is re-injected in the crystal, continue vibration, formed one from the structure of injecting single frequency laser.
2. As claimed in claim 1 a kind of realize isotropic medium output line polarization single-frequency laser from injecting structure, it is characterized in that being constituted by 1/2 wave plate, Glan prism, total reflective mirror and partially reflecting mirror from injected system.
3. As claimed in claim 1 a kind of realize isotropic medium output line polarization single-frequency laser from injecting structure, it is characterized in that adopting and singly mix thulium crystal pumping end face as the resonant cavity input mirror, crystal length scope 3-180mm, doping content scope 0.1%-8%.
4. As claimed in claim 1 a kind of realize isotropic medium output line polarization single-frequency laser from injecting structure, it is characterized in that adopting two P-F etalons as the frequency-selecting element, the thickness of one of them F-P etalon is 0.1mm, and adopts red quartz material; The thickness of another F-P etalon is 1mm, and adopts the YAG material.
5. As claimed in claim 1 a kind of realize isotropic medium output line polarization single-frequency laser from injecting structure, it is characterized in that adopting transmission-type body Bragg grating (T-VBG), and as the output cavity mirror, this grating live width is less than 1nm, diffraction efficiency is greater than 99.5%, and seeing through centre wavelength is 2010nm.
6. As claimed in claim 1 a kind of realize isotropic medium output line polarization single-frequency laser from injecting structure, it is characterized in that adopting two P-F etalons as the frequency-selecting element, the thickness of one of them F-P etalon is 0.1mm, and adopts red quartz material; The thickness of another F-P etalon is 1mm, and adopts the YAG material.
7. As claimed in claim 1 a kind of realize isotropic medium output line polarization single-frequency laser from injecting structure, it is characterized in that adopting 45 ° of spectroscopes, this spectroscope is coated with the 2010nm anti-reflection film, transmitance is 60%; The 785nm film (R＞99.5%) that is all-trans.
8. As claimed in claim 2 a kind of realize isotropic medium output line polarization single-frequency laser from injecting structure, it is characterized in that adopting Glan prism, it is of a size of 9 * 9 * 10mm ³, the prism angle of wedge is 40 °.
9. As claimed in claim 2 a kind of realize isotropic medium output line polarization single-frequency laser from injecting structure, it is characterized in that the total reflective mirror that adopts being coated with the 2010nm high-reflecting film.
10. As claimed in claim 2 a kind of realize isotropic medium output line polarization single-frequency laser from injecting structure, it is characterized in that 45 ° of partially reflecting mirrors adopting, be coated with the anti-reflection film of 2010nm, transmitance is 80%.
11. 11. as claimed in claim 3 a kind of realize isotropic medium output line polarization single-frequency laser from injecting structure, it is characterized in that the centre wavelength of the LD pumping source that adopts is the center absorbing wavelength of corresponding laser medium.
12. 12. as claimed in claim 3 a kind of realize isotropic medium output line polarization single-frequency laser from injecting structure, it is characterized in that adopting Tm:YAG crystal pumping end face as the resonant cavity input mirror, crystalline size is

    

    3 * 7mm ³, doping content is 3.5%.

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