WO2019028679A1 - 倍频激光器及谐波激光产生方法 - Google Patents

倍频激光器及谐波激光产生方法 Download PDF

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WO2019028679A1
WO2019028679A1 PCT/CN2017/096449 CN2017096449W WO2019028679A1 WO 2019028679 A1 WO2019028679 A1 WO 2019028679A1 CN 2017096449 W CN2017096449 W CN 2017096449W WO 2019028679 A1 WO2019028679 A1 WO 2019028679A1
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mirror
laser
harmonic
cavity
cavity mirror
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PCT/CN2017/096449
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English (en)
French (fr)
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朱宝华
方志强
陆业钊
王瑾
高云峰
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大族激光科技产业集团股份有限公司
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Priority to PCT/CN2017/096449 priority Critical patent/WO2019028679A1/zh
Priority to JP2018515266A priority patent/JP2019526924A/ja
Priority to US15/748,161 priority patent/US10630044B2/en
Priority to CN201780023062.6A priority patent/CN109643879A/zh
Priority to DE112017007839.3T priority patent/DE112017007839T5/de
Publication of WO2019028679A1 publication Critical patent/WO2019028679A1/zh

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    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H01S3/108—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
    • H01S3/109—Frequency multiplication, e.g. harmonic generation
    • H01S3/1095—Frequency multiplication, e.g. harmonic generation self doubling, e.g. lasing and frequency doubling by the same active medium
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    • H01S3/108—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
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    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
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    • H01S3/164—Solid materials characterised by a crystal matrix garnet
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    • 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
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    • G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
    • G02F1/3542—Multipass arrangements, i.e. arrangements to make light pass multiple times through the same element, e.g. using an enhancement cavity
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Definitions

  • the invention relates to a frequency doubled laser and a harmonic laser generating method, and belongs to the field of lasers.
  • the large energy lasers of the currently visible spectrum are mainly based on short or ultrashort pulsed lasers, such as Q-switched lasers.
  • short or ultrashort pulsed lasers such as Q-switched lasers.
  • the conversion efficiency is low due to the beam quality and peak power density of the fundamental light.
  • Conventional long-pulsed green laser devices using intracavity frequency doubling enhance the fundamental power optical density in nonlinear crystals by inserting a lens into the cavity.
  • this method requires that the mounting position of the nonlinear crystal is limited to a very small range, and it is easy to damage the nonlinear crystal.
  • a frequency doubled laser wherein the frequency doubled laser comprises: a first mirror, a second mirror, a gain medium, a telescope module, a polarizing element, and a nonlinear crystal; the first mirror and the second mirror are spaced apart to form a resonant cavity of the frequency doubling laser; the polarizing element, the gain medium, the telescope module, and the nonlinear crystal are disposed on In the resonant cavity, and the telescope module is disposed between the gain medium and the nonlinear crystal.
  • the gain medium, the first cavity mirror, the second cavity mirror, and the nonlinear crystal are disposed along a line.
  • the telescope module includes a first cavity mirror and a second cavity mirror, the first cavity mirror and the second cavity mirror are disposed along a laser interval emitted from the gain medium, and the gain medium and the The optical axes of the first cavity mirror and the second cavity mirror are coincident.
  • the first cavity mirror is a plano-concave lens
  • the second cavity mirror is a plano-convex lens
  • a concave surface of the plano-concave lens is disposed opposite to a convex surface of the plano-convex lens.
  • the polarizing element is disposed between the first mirror and the telescope module for converting the fundamental laser output of the gain medium into linearly polarized light.
  • the polarization direction of the polarizing element is parallel or perpendicular to the optical axis of the nonlinear crystal or forms an angle of 45[deg.].
  • a harmonic output mirror is further included, the harmonic output mirror being disposed between the gain medium and the telescope module to output a harmonic laser.
  • the harmonic output mirror has opposing first and second surfaces, the first surface facing a nonlinear crystal, the second surface facing a gain medium, the a surface is plated with a first harmonic output mirror coating for reflecting the harmonic laser light and transmitting to the fundamental frequency laser; the second surface is plated with a second harmonic output mirror coating, the second harmonic output mirror
  • the coating is a fundamental-frequency optical antireflection film for enhancing the transmission of the fundamental laser.
  • the polarizing element, the gain medium, the telescope module, and the nonlinear crystal are arranged in a zigzag pattern.
  • the telescope module includes a first cavity mirror and a second cavity mirror, and the polarization element, the gain medium and the second cavity mirror are disposed along a first line; the first cavity mirror and The nonlinear crystal is collinearly arranged along the second straight line.
  • the first cavity mirror forms an angle with the first straight line
  • the second cavity mirror The normal line forms an angle with the second line
  • the first cavity mirror is opposite to the second cavity mirror, and the first cavity mirror is a total reflection mirror, and the second cavity mirror is a harmonic output mirror for outputting a harmonic laser. And reflect the fundamental frequency laser.
  • the focusing amount ⁇ of the frequency doubling laser is L ⁇ (f 1 +f 2 ), L is the distance between the first cavity mirror and the second cavity mirror, f 1 For the focal length of the first cavity mirror, f 2 is the focal length of the second cavity mirror;
  • the excitation gain medium outputs a fundamental frequency laser and detects the light energy of the output harmonic laser
  • the above-mentioned method for generating a frequency-doubled laser and a harmonic laser, by setting a telescope resonance system in the frequency-doubled laser, has no focus in the cavity, thereby relaxing the placement position of the nonlinear crystal and reducing the probability of damage of the nonlinear crystal.
  • FIG. 1 is a schematic structural diagram of a frequency doubled laser according to a first embodiment of the present invention
  • Figure 2 is a graph of the amount of focus and the fundamental frequency laser beam quality factor
  • Figure 3 is a graph showing the relationship between the harmonic conversion efficiency and the fundamental frequency laser beam quality factor
  • FIG. 4 is a schematic flow chart of a method for generating a harmonic laser by using a frequency doubling laser according to the present invention
  • FIG. 5 is a schematic structural diagram of a frequency doubled laser according to another embodiment of the present invention.
  • the first mirror 1 and the second mirror 2 are spaced apart to form a resonant cavity of the frequency doubled laser 100, and the polarizing element 6, the gain medium 3, the telescope module 5, and the nonlinear crystal 7 are sequentially disposed in the resonant cavity.
  • the first mirror 1 and the second mirror 2 are spaced apart from each other, and the first mirror 1 is totally reflected to the fundamental laser in the resonant cavity, and the second mirror 2 is applied to both the fundamental laser and the harmonic laser.
  • the first mirror 1 may be plated with a first reflective film 11 for reflecting a fundamental frequency laser; the second mirror 2 may be plated with a second reflective film 21 for reflecting a fundamental frequency laser and a harmonic laser.
  • the gain medium 3 is disposed adjacent to the first mirror 1 for outputting a fundamental frequency laser, and
  • the pulse width of the fundamental laser can be greater than 100 ⁇ m.
  • the gain medium 3 may be an Nd:YAG crystal, and may also be other gain media such as Nd:Glass, Yb:YAG, Er:YAG, etc., wherein the two-pass light end faces of the gain medium 3 are plated with an antireflection film of 1064 nm.
  • the telescope module 5 is disposed in a resonant cavity between the gain medium 3 and the second mirror 2, and the telescope module 5 is configured to increase the equivalent cavity length of the resonant cavity to reduce the divergence of the fundamental frequency light in the nonlinear crystal 7. The angle and the area ratio of the fundamental light in the gain medium 3 and the nonlinear crystal 7 are increased.
  • the telescope module 5 includes a first cavity mirror 51 and a second cavity mirror 52. The first cavity mirror 51 and the second cavity mirror 52 are disposed along the laser light emitted from the gain medium 3, and the gain medium 3 and the first cavity are disposed. The optical axes of the mirror 51 and the second mirror 52 coincide.
  • the first cavity mirror 51 may be a plano-convex lens
  • the second cavity mirror 52 may be a plano-concave lens
  • the concave surface of the plano-concave lens may be disposed opposite to the convex surface of the plano-convex lens.
  • the distance between the plano-concave lens and the plano-convex lens may be L
  • the focal length of the plano-concave lens may be f 1
  • the focal length of the plano-convex lens may be f 2
  • the equivalent cavity length of the resonant cavity is increased, which is advantageous for obtaining a higher beam quality, thereby obtaining a higher frequency doubling efficiency.
  • the plano-concave lens and the plano-convex lens are only specific embodiments, and the first cavity mirror 51 and the second cavity mirror 52 can also be selected according to actual needs, as long as the function of increasing the equivalent cavity length of the resonant cavity can be performed. .
  • the nonlinear crystal 7 is disposed between the telescope module 5 and the second mirror 2, which is used to generate secondary and/or higher harmonics.
  • the optical axis of the nonlinear crystal 7 may coincide with the optical axes of the first cavity mirror 51 and the second cavity mirror 52.
  • the gain medium 3, the first cavity mirror 51, the second cavity mirror 52, and the nonlinear crystal 7 are arranged along a line.
  • the nonlinear crystal 7 converts the fundamental frequency light in the resonant cavity into frequency-doubled light by nonlinear action.
  • the polarizing element 6 is disposed between the first mirror 1 and the telescope module 5 for converting the fundamental laser output of the gain medium 3 into linearly polarized light, thereby facilitating the arrangement of the polarizing element 6, and facilitating the protection of the polarizing element 6. Avoid damage.
  • the polarizing element 6 can be disposed along the same line as the gain medium 3, the first cavity mirror 51, the second cavity mirror 52, and the nonlinear crystal 7. Further, the polarization direction of the polarizing element 6 is parallel or perpendicular to the optical axis of the nonlinear crystal 7 (Class I phase matching), or an angle of 45° (Class II phase matching) is formed to achieve phase matching. It can be understood that the polarizing element 6 can also be disposed at other positions in the resonant cavity.
  • the frequency doubled laser 100 further includes a harmonic output mirror 8 which is disposed between the gain medium 3 and the nonlinear crystal 7 for outputting harmonic lasers and can effectively avoid harmonic output
  • the mirror 8 is damaged and can reduce losses with higher harmonic output efficiency.
  • the harmonic output mirror 8 can be disposed between the gain medium 3 and the telescope module 5.
  • the surface normal of the harmonic output mirror 8 and the optical axis of the resonant cavity can form a certain angle for reflecting the harmonic laser, so that the harmonic laser outputs the resonant cavity.
  • the harmonic output mirror 8 has two opposite surfaces.
  • the opposite surfaces of the harmonic output mirror 8 are provided with a coating.
  • the harmonic output mirror 8 includes a first surface and a second surface.
  • the first surface faces the direction of the nonlinear crystal 7, which is disposed facing the gain medium 3.
  • the first surface is plated with a first harmonic output mirror coating 81, which is a harmonic reflection film for reflecting harmonic lasers and transmitting to the fundamental laser for reflection harmonics
  • the harmonic output resonator is formed;
  • the second surface is plated with a second harmonic output mirror coating 82, and the second harmonic output mirror coating 82 is a fundamental frequency light antireflection film for enhancing the fundamental frequency laser in the harmonic output mirror Transmission in 8.
  • the position of the harmonic output mirror 8 can also be set at other positions between the nonlinear crystal 7 and the first mirror 1, and can be adjusted according to actual needs.
  • the frequency doubling laser 100 further includes a pumping unit 4 for outputting the pumping light excitation gain medium 3 to generate a fundamental frequency laser.
  • the pump unit 4 may include a flash lamp or a semiconductor laser.
  • the fundamental laser light output from the gain medium 3 is trapped and oscillated and amplified between the first mirror 1 and the second mirror 2.
  • the nonlinear crystal 7 converts a part of the fundamental frequency laser in the cavity into a frequency doubled harmonic laser by nonlinear action.
  • the harmonic output mirror 8 couples the frequency-doubled harmonic laser converted by the nonlinear crystal 7 into the cavity.
  • the efficiency of harmonic conversion of the frequency doubled laser 100 is related to three parameters: crystal length, effective nonlinear coefficient, and area ratio of the fundamental light in the gain medium and the nonlinear crystal (A 1 /A 2 ). Since the change of the first two parameters is difficult, a large A 1 /A 2 can be obtained by adjusting the cavity structure to improve the frequency doubling efficiency. In addition, reducing the divergence angle of the fundamental frequency light in the nonlinear crystal is also advantageous for improving the frequency doubling efficiency. The invention can simultaneously obtain a large A 1 /A 2 and reduce the divergence angle cavity structure of the fundamental frequency light in the nonlinear crystal through the telescope module.
  • the beam quality of the fundamental frequency light can be finely adjusted by fine-tuning the focusing amount of the telescope system.
  • the telescope module system consists of two sets of lenses, which are arranged between the gain medium and the nonlinear crystal, and the distance between the lenses is L. It is assumed that the focal length of the lens group close to the gain medium is f 1 and the focal length of the lens group close to the nonlinear crystal is f 2 .
  • the amount of focus ⁇ is defined as L-(f 1 +f 2 ).
  • harmonic conversion efficiency can be adjusted over a wide range by fine tuning the beam quality.
  • the frequency doubled laser 100 provided by the above embodiment has the following beneficial effects by introducing the telescope module to the harmonic conversion device:
  • the frequency multiplication efficiency is optimized, and the harmonic laser output efficiency is improved;
  • the telescope module can achieve higher beam quality and smaller divergence angle, which is beneficial to achieve high frequency conversion efficiency.
  • the present invention also provides a method for generating a harmonic laser by a frequency doubled laser, comprising:
  • step S10 the focus amount ⁇ is set to zero.
  • step S11 the excitation gain medium outputs a fundamental laser and detects the optical energy of the output harmonic laser.
  • the energy of the fundamental laser is set to the harmonic light energy that is detected by the energy meter.
  • step S12 the focus amount ⁇ is adjusted in the forward or reverse direction, and the focus amount is changed until the harmonic laser output stops.
  • the amount of change in the amount of focusing should ensure that the harmonic output energy does not change too much.
  • step S13 the position where the harmonic output energy is the largest is selected, the position of the optimal focus amount is obtained, and the harmonic laser is output.
  • the positions of the first cavity mirror 51 and the second cavity mirror 52 in the telescope module 5 are obtained, thereby obtaining the position of the optimal focus amount.
  • the above-mentioned frequency doubling laser generates a harmonic laser method, and by adjusting the focusing amount of the telescope module, the frequency doubling efficiency of the frequency doubling laser can be improved.
  • a frequency doubling laser 200 including a first mirror 1, a second mirror 2, a gain medium 3, a telescope module 5, a polarizing element 6, and a nonlinear crystal 7 .
  • the first mirror 1 and the second mirror 2 are spaced apart to form a resonant cavity of the frequency doubling laser 100, and the gain medium 3, the telescope module 5, the polarizing element 6 and the nonlinear crystal 7 are disposed in the resonant cavity, and the gain medium 3, the telescope
  • the module 5, the polarizing element 6, and the nonlinear crystal 7 are arranged in a zigzag shape.
  • the frequency doubled laser 200 provided by the second embodiment of the present invention is basically the same as the first embodiment, except that the gain medium 3, the telescope module 5, the polarizing element 6, and the nonlinear crystal 7 are arranged in a zigzag shape, and the telescope module 5 Simultaneously as a harmonic output mirror to output harmonic laser.
  • the first mirror 1 and the second mirror 2 are dislocated, that is, the first mirror 1 and the second mirror 2 are non-collinearly disposed.
  • the polarizing element 6, the gain medium 3 and the first mirror 1 are arranged in line along the first line; the nonlinear crystal 7 and the second mirror 2 are arranged along the second line, so that the gain medium 3, the telescope module 5, and the polarization
  • the element 6 and the nonlinear crystal 7 are arranged in a zigzag shape as a whole.
  • the fundamental laser outputted from the gain medium 3 is reflected by the telescope module 5, passes through the nonlinear crystal 7, is incident on the second mirror 2, and then returns to the first mirror 1 along the original optical path through the second mirror 2, thereby The first mirror 1 and the second mirror 2 oscillate and amplify back and forth.
  • the telescope module 5 includes a first cavity mirror 51 and a second cavity mirror 52, and the normal of the first cavity mirror 51 and the second cavity mirror 52 forms an angle with the transmission direction of the laser light in the resonant cavity; the second cavity mirror 51 Coaxially arranged with the first mirror 1, the polarizing element 6, and the gain medium 4 for reflecting the fundamental frequency laser to the first cavity mirror 51 and outputting the harmonic laser; the first cavity mirror 51 can be combined with the nonlinear crystal 7
  • the second mirror 2 is arranged in line for reflecting the fundamental laser beam and the harmonic laser light reflected by the second mirror 2 to the second cavity mirror 52 to output the harmonic laser light, and the base mirror 52 is used to The frequency laser light is reflected to the first mirror 1 to form an oscillation and amplification between the first mirror 1 and the second mirror 2.
  • the first cavity mirror 51 and the second cavity mirror 52 are oppositely disposed.
  • the first cavity mirror 51 is a total reflection mirror for reflecting the fundamental frequency laser and the harmonic laser; the second cavity mirror 52 is simultaneously used as a harmonic output mirror.
  • the harmonic laser is output and the fundamental laser is reflected.
  • a first mirror coating 511 is disposed on the surface of the first cavity mirror 51 opposite to the second cavity mirror 52 to reflect the fundamental frequency laser and the harmonic laser; the second cavity mirror 52 is opposite to the first cavity mirror 51.
  • the surface is provided with a second mirror coating 521 for transmitting a harmonic laser for output and reflecting the fundamental laser.
  • the fundamental laser light reflected by the first mirror 1 passes through the gain medium 3 and is incident on the second mirror 52. After being reflected by the second cavity mirror 52, it is incident on the first cavity mirror 51.
  • the fundamental laser light is reflected by the first cavity mirror 51, incident on the nonlinear crystal 7, and then reflected by the second mirror 2, and then incident on the nonlinear crystal 7.
  • the fundamental laser then passes through the nonlinear crystal 7, the first cavity mirror 51 and the second cavity mirror 52, back to the gain medium 3.
  • the fundamental laser passes through the gain medium 3 again and reaches the first mirror 1, completing one transmission in the cavity.
  • the fundamental light is confined in the cavity formed by the first mirror 1 and the second mirror 2 and the first mirror 51 and the second mirror 52, and is reciprocated by the gain medium 3 to obtain amplification.
  • the second cavity mirror 52 is transmissive to the harmonic laser light, as the harmonic output mirror, the harmonic laser light is output.
  • the frequency doubled laser 100 provided by the above embodiment has the following beneficial effects by introducing the telescope module to the harmonic conversion device:
  • the frequency multiplication efficiency is optimized, and the harmonic laser output efficiency is improved;
  • the telescope module can obtain higher beam quality and smaller divergence angle under the same cavity length, which is beneficial to obtain high frequency conversion efficiency
  • the resonant cavity mirror of the telescope module as the harmonic output cavity mirror, it is not necessary to separately set the harmonic output cavity mirror, and the structure is more compact, which can further reduce the influence of the separately arranged output cavity mirror on the transmission of the laser in the resonant cavity, and improve Output efficiency.

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Abstract

一种倍频激光器及谐波激光产生方法，倍频激光器包括第一反射镜（1）、第二反射镜（2）、增益介质（3）、望远镜模块（5）、偏振元件（6）以及非线性晶体（7），第一反射镜（1）及第二反射镜（2）间隔设置形成倍频激光器的谐振腔，偏振元件（6）、增益介质（3）、望远镜模块（5）以及非线性晶体（7）设置于谐振腔中，且望远镜模块（5）设置于增益介质（3）与非线性晶体（7）之间。倍频激光器及谐波激光产生方法放宽了非线性晶体（7）的放置位置，减少了非线性晶体（7）的损伤几率。

Description

倍频激光器及谐波激光产生方法 技术领域
本发明涉及一种倍频激光器及谐波激光产生方法，属于激光器领域。
背景技术
随着电动汽车的兴起和新能源产业的蓬勃发展，对高功率电路和电池技术提出了迫切的需求。铜作用一种重要的导电材料，其高效、稳定的焊接成为近年来关注的一个热点。由于铜的热导率很高且对近红外激光的吸收率在常温下很低而在熔点附近会突然升高，使得激光焊接过程容易受到工件表面质量的影响。铜的激光焊接当前仍是一个极具挑战性的课题。
铜材激光焊接中存在问题可以通过采用长脉冲(脉冲宽度大于100μs)绿光解决。在绿光波段，铜对激光的吸收率可以达到40％，同时绿光聚焦后焦点更小、功率密度更高，易于获得高质量的焊点。因此，采用长脉冲绿激光作为焊接光源，可以大幅度提高铜材焊接的产率和质量。
当前可见光谱的大能量激光主要基于短或超短脉冲激光器，比如调Q激光器。对于准连续的大能量固体激光器***，受限于基频光的光束质量和峰值功率密度，转换效率较低。传统的采用腔内倍频的长脉冲绿光激光器装置，通过在谐振腔内***一片透镜来提高非线性晶体中的基频光功率密度。然而，这一方法需要将非线性晶体的安装位置限定在一个非常小的范围内，并且很容易损伤非线性晶体。
发明内容
综上所述，确有必要提供一种非线性晶体设置位置灵活、减少非线性晶体损伤的倍频激光器及谐波激光的产生方法。
一种倍频激光器，其中，所述倍频激光器包括：第一反射镜、第二反射镜、 增益介质、望远镜模块、偏振元件以及非线性晶体；所述第一反射镜及第二反射镜间隔设置形成倍频激光器的谐振腔；所述偏振元件、增益介质、望远镜模块以及非线性晶体设置于谐振腔中，且所述望远镜模块设置于所述增益介质与所述非线性晶体之间。
在其中一个实施例中，所述增益介质、第一腔镜、第二腔镜、非线性晶体沿一直线设置。
在其中一个实施例中，所述望远镜模块包括第一腔镜及第二腔镜，所述第一腔镜及第二腔镜沿从增益介质出射的激光间隔设置，且所述增益介质与所述第一腔镜及第二腔镜的光轴重合。
在其中一个实施例中，所述第一腔镜为平凹透镜，所述第二腔镜为平凸透镜，且所述平凹透镜的凹面与所述平凸透镜的凸面相对设置。
在其中一个实施例中，所述偏振元件设置于第一反射镜与望远镜模块之间，用于将增益介质输出的基频激光转换为线偏振光。
在其中一个实施例中，所述偏振元件的起偏方向与非线性晶体的光轴平行或垂直或形成45°夹角。
在其中一个实施例中，还包括谐波输出镜，所述谐波输出镜设置于增益介质与望远镜模块之间，以输出谐波激光。
在其中一个实施例中，所述谐波输出镜具有相对的第一表面及第二表面，所述第一表面面对非线性晶体设置，所述第二表面面对增益介质设置，所述第一表面镀有第一谐波输出镜镀膜，用于反射谐波激光，而对基频激光为透射；所述第二表面镀有第二谐波输出镜镀膜，所述第二谐波输出镜镀膜为基频光增透膜，用于增强基频激光的透射。
在其中一个实施例中，所述偏振元件、增益介质、望远镜模块以及非线性晶体呈Z字形排布。
在其中一个实施例中，所述望远镜模块包括第一腔镜及第二腔镜，所述偏振元件、增益介质与第二腔镜沿第一直线共线设置；所述第一腔镜与非线性晶体沿第二直线共线设置。
在其中一个实施例中，所述第一腔镜与第一直线形成夹角，所述第二腔镜 的法线与第二直线形成夹角。
在其中一个实施例中，所述第一腔镜与第二腔镜相对设置，且第一腔镜为全反射镜，所述第二腔镜为谐波输出镜，用于输出谐波激光，并反射基频激光。
一种利用如上所述的倍频激光器产生谐波激光的方法，其中，所述方法包括：
将倍频激光器的调焦量Δ置为0，其中，所述调焦量Δ为L-(f1+f2)，L为第一腔镜与第二腔镜之间的距离，f1为第一腔镜的焦距，f2为第二腔镜的焦距；
激励增益介质输出基频激光，并探测输出的谐波激光的光能；
将调焦量Δ沿正向或反向调节，改变调焦量，直到谐波激光输出停止；
选取谐波输出能量最大的位置，获得最优调焦量的位置，输出谐波激光。
上述倍频激光器及谐波激光的产生方法，通过在倍频激光器中设置望远镜谐振***，使得谐振腔内无焦点，从而放宽了非线性晶体的放置位置，减少了非线性晶体的损伤几率。
附图说明
图1为本发明第一实施例提供的倍频激光器的结构示意图；
图2为调焦量与基频激光光束质量因子的曲线图；
图3为谐波转换效率与基频激光光束质量因子的关系图；
图4为本发明提供的利用倍频激光器产生谐波激光的方法的流程示意图；
图5为本发明另一实施例提供的倍频激光器的结构示意图。
主要元件符号说明
倍频激光器 100
第一反射镜 1
第一反射膜 11
第二反射镜 2
第二反射膜 21
增益介质 3
泵浦单元 4
望远镜模块 5
第一腔镜 51
第一腔镜镀膜 511
第二腔镜 52
第二腔镜镀膜 521
偏振单元 6
非线性晶体 7
谐波输出镜 8
第一输出镜镀膜 81
第二输出镜镀膜 82
具体实施方式
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
可以理解，本发明所使用的术语“第一”、“第二”等可在本文中用于描述各种元件，但这些元件不受这些术语限制。这些术语仅用于将第一个元件与另一个元件区分。
请一并参阅图1，本发明提供的倍频激光器100包括第一反射镜1、第二反射镜2、增益介质3、望远镜模块5、偏振元件6以及非线性晶体7。第一反射镜1及第二反射镜2间隔设置形成倍频激光器100的谐振腔，偏振元件6、增益介质3、望远镜模块5以及非线性晶体7依次设置于谐振腔中。
第一反射镜1及第二反射镜2相互之间间隔设置，该第一反射镜1对谐振腔中的基频激光为全反射，该第二反射镜2对基频激光及谐波激光均为全反。该第一反射镜1可镀有第一反射膜11，用于反射基频激光；该第二反射镜2可镀有第二反射膜21，用于反射基频激光及谐波激光。
增益介质3靠近第一反射镜1设置，该增益介质3用于输出基频激光，且 基频激光的脉宽可大于100μm。增益介质3可为的Nd：YAG晶体，还可以为Nd：Glass、Yb：YAG、Er：YAG等其它增益介质，其中，增益介质3的两通光端面镀有1064nm的增透膜。
望远镜模块5设置于增益介质3与第二反射镜2之间的谐振腔中，该望远镜模块5用于增大谐振腔的等效腔长，以减小非线性晶体7中基频光的发散角，并提高基频光在增益介质3及非线性晶体7中的面积比。所述望远镜模块5包括第一腔镜51及第二腔镜52，所述第一腔镜51及第二腔镜52沿从增益介质3出射的激光间隔设置，且增益介质3与第一腔镜51及第二腔镜52的光轴重合。进一步，所述第一腔镜51可为平凸透镜，所述第二腔镜52可为平凹透镜，该平凹透镜的凹面可与该平凸透镜的凸面相对设置。该平凹透镜与平凸透镜之间的距离可为L，平凹透镜的焦距可为f1，该平凸透镜的焦距可为f2，则望远镜模块5的调焦量Δ＝L-(f1-f2)。通过调节望远镜模块5调焦量，可以优化倍频效率。通过设置该望远镜模块5，增大了了谐振腔的等效腔长，有利于获得较高的光束质量，从而获得较高的倍频效率。可以理解，平凹透镜及平凸透镜仅为具体的实施例，该第一腔镜51及第二腔镜52还可以根据实际需要进行选择，只要能够起到增加谐振腔等效腔长的作用即可。
非线性晶体7设置于望远镜模块5与第二反射镜2之间，该非线性晶体7用于产生二次和/或更高次的谐波。该非线性晶体7的光轴可与第一腔镜51和第二腔镜52的光轴重合。进一步，该增益介质3、第一腔镜51、第二腔镜52、非线性晶体7沿一直线设置。非线性晶体7通过非线性作用将谐振腔内的基频光转换为倍频光。
该偏振元件6设置于第一反射镜1与望远镜模块5之间，用于将增益介质3输出的基频激光转变为线偏振光，从而方便偏振元件6的设置，有利于保护偏振元件6，避免损伤。所述偏振元件6可与该增益介质3、第一腔镜51、第二腔镜52、非线性晶体7沿同一直线设置。与进一步，所述偏振元件6的起偏方向与非线性晶体7的光轴平行或垂直(I类相位匹配)，或形成45°夹角(II类相位匹配)，以实现相位匹配。可以理解，该偏振元件6也可设置于谐振腔中的其他位置
进一步，该倍频激光器100还包括谐波输出镜8，该谐波输出镜8可设置于增益介质3和非线性晶体7之间，用于输出谐波激光，并且能够有效的避免谐波输出镜8的损伤，并且能够减少损耗，具有更高的谐波输出效率。具体的，该谐波输出镜8可设置于增益介质3与望远镜模块5之间。该谐波输出镜8的面法线与谐振腔的光轴可形成一定夹角，用于反射谐波激光，使谐波激光输出谐振腔。该谐波输出镜8具有相对的两个表面，另外，该谐波输出镜8相对的两个表面均设置有镀膜，具体的，该谐波输出镜8包括第一表面及第二表面，该第一表面面对非线性晶体7的方向设置，该第二表面面对增益介质3设置。该第一表面镀有第一谐波输出镜镀膜81，该第一谐波输出镜镀膜81为谐波反射膜，用于反射谐波激光，而对基频激光为透射，用于反射谐波使谐波输出谐振腔；该第二表面镀有第二谐波输出镜镀膜82，该第二谐波输出镜镀膜82为基频光增透膜，用于增强基频激光在谐波输出镜8中的透射。可以理解，该谐波输出镜8的位置还可以设置在非线性晶体7与第一反射镜1之间的其他位置，可以根据实际需要进行调整。
另外，该倍频激光器100还包括泵浦单元4，用于输出泵浦光激励增益介质3，产生基频激光。该泵浦单元4可包括闪光灯或半导体激光器。
上述倍频激光器100在工作时，增益介质3输出的基频激光被束缚在第一反射镜1和第二反射镜2之间振荡和放大。非线性晶体7通过非线性作用将腔内的一部分基频激光转换为倍频谐波激光。谐波输出镜8将非线性晶体7转换的倍频谐波激光由谐振腔内耦合输出。
倍频激光器100的谐波转换的效率与三个参数相关：晶体长度、有效非线性系数和基频光在增益介质和非线性晶体中的面积比(A1/A2)。由于前两个参数的改变比较困难，可通过调整谐振腔结构来获得较大的A1/A2以提升倍频效率。此外，减小非线性晶体中基频光的发散角也有利于提升倍频效率。本发明通过望远镜模块，能够同时获得较大的A1/A2和减小非线性晶体中基频光的发散角谐振腔结构。
另外，请一并参阅图2及图3，对于望远镜模块，通过微调调节望远镜***的调焦量可以实现基频光的光束质量微调。望远镜模块***由两组透镜组成， 设置于增益介质和非线性晶体之间，设透镜间的距离为L。假设靠近增益介质的透镜组焦距为f1，靠近非线性晶体的透镜组焦距为f2。将调焦量Δ定义为L-(f1+f2)。对于给定的非线性晶体和谐振腔结构，谐波转换效率可以通过微调光束质量来进行大范围调节。
上述实施例提供的倍频激光器100，通过将望远镜模块引入到谐波转换装置，具有以下有益效果：
首先，谐振腔内无焦点，从而放宽了非线性晶体的放置位置，减少了非线性晶体的损伤几率；
其次，可通过调节望远镜模块离焦量，优化倍频效率，提高谐波激光输出效率；
再次，在相同的谐振腔长度下，望远镜模块可以获得更高的光束质量和更小的发散角，有利于获得高的倍频转换效率。
进一步，请一并参阅图2，为更有效的输出谐波激光，本发明还提供一种通过倍频激光器产生谐波激光的方法，包括：
步骤S10，将调焦量Δ置为0。
步骤S11，激励增益介质输出基频激光，并探测输出的谐波激光的光能。
基频激光的能量设置为谐波光能被能量计探测。
步骤S12，将调焦量Δ沿正向或反向调节，改变调焦量，直到谐波激光输出停止。
在调整望远镜模块的调焦量的过程中，调焦量的改变量应保证谐波输出能量不会出现过于剧烈的变化。
步骤S13，选择谐波输出能量最大的位置，获得最优调焦量的位置，输出谐波激光。
通过对输出的谐波的能量进行检测，选择谐波输出能量最大的时候，望远镜模块5中的第一腔镜51及第二腔镜52所在的位置，从而获得最优调焦量的位置。
上述倍频激光器产生谐波激光的方法，通过调节望远镜模块的调焦量，能够提高倍频激光器的倍频效率。
请一并参阅图3，本发明另一实施例提供一种倍频激光器200，包括第一反射镜1、第二反射镜2、增益介质3、望远镜模块5、偏振元件6以及非线性晶体7。第一反射镜1及第二反射镜2间隔设置形成倍频激光器100的谐振腔，增益介质3、望远镜模块5、偏振元件6以及非线性晶体7设置于谐振腔中，且增益介质3、望远镜模块5、偏振元件6以及非线性晶体7呈Z字形排布。
本发明第二实施例提供的倍频激光器200与第一实施例基本相同，其不同在于，该增益介质3、望远镜模块5、偏振元件6以及非线性晶体7呈Z字形排布，该望远镜模块5同时作为谐波输出镜以输出谐波激光。
具体的，该第一反射镜1与第二反射镜2错位设置，即第一反射镜1与第二反射镜2非共线设置。偏振元件6、增益介质3与第一反射镜1沿第一直线共线设置；非线性晶体7与第二反射镜2沿第二直线共线设置，使增益介质3、望远镜模块5、偏振元件6以及非线性晶体7整体上呈Z字形排布。从增益介质3输出的基频激光经过望远镜模块5反射之后，经过非线性晶体7，入射到第二反射镜2；然后经过第二反射镜2沿原光路返回至第一反射镜1，从而在第一反射镜1和第二反射镜2之间来回振荡和放大。
该望远镜模块5包括第一腔镜51及第二腔镜52，且第一腔镜51与第二腔镜52的法线与激光在谐振腔中的传输方向形成夹角；第二腔镜51与第一反射镜1、偏振元件6、增益介质4共线设置，用于将基频激光反射至第一腔镜51，并输出谐波激光；第一腔镜51可与非线性晶体7及第二反射镜2共线设置，用于将第二反射镜2反射的基频激光和谐波激光再次反射至第二腔镜52，以输出谐波激光，并通过第二腔镜52将基频激光反射至第一反射镜1，从而在第一反射镜1和第二反射镜2之间形成振荡和放大。
该第一腔镜51和第二腔镜52相对设置，该第一腔镜51为全反射镜，用于反射基频激光及谐波激光；第二腔镜52同时作为谐波输出镜，用于输出谐波激光，并反射基频激光。具体的，第一腔镜51与第二腔镜52相对的表面上，设置有第一腔镜镀膜511，以反射基频激光及谐波激光；第二腔镜52与第一腔镜51相对的表面设置有第二腔镜镀膜521，用于透射谐波激光以输出，对基频激光进行反射。
第二实施例提供的倍频激光器200在工作时，由第一反射镜1反射的基频激光通过增益介质3，并入射向第二腔镜52。经过第二腔镜52反射后，入射到第一腔镜51。基频激光由第一腔镜51反射后，入射到非线性晶体7，随后由第二反射镜2反射后，入射到非线性晶体7。随后基频激光再次通过非线性晶体7、第一腔镜51和第二腔镜52，回到增益介质3。基频激光再次穿过增益介质3并到达第一反射镜1，完成谐振腔内的一次传输。这样基频光就被约束在由第一反射镜1和第二反射镜2以及第一腔镜51和第二腔镜52构成的谐振腔中，往返通过增益介质3获得放大。同时，由于第二腔镜52对于谐波激光为透射，因此，作为谐波输出镜，输出谐波激光。
上述实施例提供的倍频激光器100，通过将望远镜模块引入到谐波转换装置，具有以下有益效果：
首先，谐振腔内无焦点，从而放宽了非线性晶体的放置位置；
其次，可通过调节望远镜***离焦量，优化倍频效率，提高谐波激光输出效率；
再次，在相同的谐振腔长度下，望远镜模块可以获得更高的光束质量和更小的发散角，有利于获得高的倍频转换效率；
最后，通过将望远镜模块的谐振腔镜作为谐波输出腔镜，无需单独设置谐波输出腔镜，结构更加紧凑，可进一步降低单独设置的输出腔镜对激光在谐振腔中传输的影响，提高输出效率。
以上所述实施例仅表达了本发明的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对本发明专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本发明构思的前提下，还可以做出若干变形和改进，这些都属于本发明的保护范围。因此，本发明专利的保护范围应以所附权利要求为准。

Claims (13)

  1. 一种倍频激光器，其特征在于，所述倍频激光器包括：第一反射镜、第二反射镜、增益介质、望远镜模块、偏振元件以及非线性晶体；所述第一反射镜及第二反射镜间隔设置形成倍频激光器的谐振腔；所述偏振元件、增益介质、望远镜模块以及非线性晶体设置于谐振腔中，且所述望远镜模块设置于所述增益介质与所述非线性晶体之间。
  2. 根据权利要求1所述的倍频激光器，其特征在于，所述增益介质、第一腔镜、第二腔镜、非线性晶体沿一直线设置。
  3. 根据权利要求1所述的倍频激光器，其特征在于，所述望远镜模块包括第一腔镜及第二腔镜，所述第一腔镜及第二腔镜沿从增益介质出射的激光间隔设置，且所述增益介质与所述第一腔镜及第二腔镜的光轴重合。
  4. 根据权利要求3所述的倍频激光器，其特征在于，所述第一腔镜为平凹透镜，所述第二腔镜为平凸透镜，且所述平凹透镜的凹面与所述平凸透镜的凸面相对设置。
  5. 根据权利要求1所述的倍频激光器，其特征在于，所述偏振元件设置于第一反射镜与望远镜模块之间，用于将增益介质输出的基频激光转换为线偏振光。
  6. 根据权利要求5所述的倍频激光器，其特征在于，所述偏振元件的起偏方向与非线性晶体的光轴平行或垂直或形成45°夹角。
  7. 根据权利要求1所述的倍频激光器，其特征在于，还包括谐波输出镜，所述谐波输出镜设置于增益介质与望远镜模块之间，以输出谐波激光。
  8. 根据权利要求7所述的倍频激光器，其特征在于，所述谐波输出镜具有相对的第一表面及第二表面，所述第一表面面对非线性晶体设置，所述第二表面面对增益介质设置，所述第一表面镀有第一谐波输出镜镀膜，用于反射谐波激光，而对基频激光为透射；所述第二表面镀有第二谐波输出镜镀膜，所述第二谐波输出镜镀膜为基频光增透膜，用于增强基频激光的透射。
  9. 根据权利要求1所述的倍频激光器，其特征在于，所述偏振元件、增益 介质、望远镜模块以及非线性晶体呈Z字形排布。
  10. 根据权利要求9所述的倍频激光器，其特征在于，所述望远镜模块包括第一腔镜及第二腔镜，所述偏振元件、增益介质与第二腔镜沿第一直线共线设置；所述第一腔镜与非线性晶体沿第二直线共线设置。
  11. 根据权利要求10所述的倍频激光器，其特征在于，所述第一腔镜与第一直线形成夹角，所述第二腔镜的法线与第二直线形成夹角。
  12. 根据权利要求10所述的倍频激光器，其特征在于，所述第一腔镜与第二腔镜相对设置，且第一腔镜为全反射镜，所述第二腔镜为谐波输出镜，用于输出谐波激光，并反射基频激光。
  13. 一种利用权利要求1-12中任意一项所述的倍频激光器产生谐波激光的方法，其特征在于，所述方法包括：
    将倍频激光器的调焦量Δ置为0，其中，所述调焦量Δ为L-(f1+f2)，L为第一腔镜与第二腔镜之间的距离，f1为第一腔镜的焦距，f2为第二腔镜的焦距；
    激励增益介质输出基频激光，并探测输出的谐波激光的光能；
    将调焦量Δ沿正向或反向调节，改变调焦量，直到谐波激光输出停止；
    选取谐波输出能量最大的位置，获得最优调焦量的位置，输出谐波激光。
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