WO2018010288A1 - 一种亚稳态气体激光的共振增强横向光泵浦装置及方法 - Google Patents

一种亚稳态气体激光的共振增强横向光泵浦装置及方法 Download PDF

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WO2018010288A1
WO2018010288A1 PCT/CN2016/098238 CN2016098238W WO2018010288A1 WO 2018010288 A1 WO2018010288 A1 WO 2018010288A1 CN 2016098238 W CN2016098238 W CN 2016098238W WO 2018010288 A1 WO2018010288 A1 WO 2018010288A1
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laser
cavity
resonance
pump
pumping
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高俊
王新兵
左都罗
陆培祥
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Huazhong University of Science and Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping

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  • the invention belongs to the field of laser technology, and more particularly to a resonance enhanced lateral optical pumping device and method for a metastable gas laser.
  • LPP Laser Produced Plasma
  • EUV lithography is one of the core technologies of next-generation lithography.
  • gas lasers particularly CO 2 lasers
  • CO 2 lasers are used for laser driving of extreme ultraviolet lithography sources.
  • the electro-optical efficiency of the CO 2 laser is low and the volume is large, which results in high energy consumption and large space of the EUV lithography light source system, which limits the mass production and application of the EUV lithography light source.
  • Optically Pumped Metastable Gas Laser is a new type of gas laser that combines discharge excitation and optical pumping. It uses gas-induced metastable particles generated by electrical excitation as a gain medium. The pump achieves a population inversion to emit laser light. With its high quantum efficiency, good flow pattern and uniformity of gas medium, this type of laser can convert high-power semiconductor laser with small volume and high electro-optic efficiency into high-power output with high beam quality. It has compact structure and electro-optical light. The advantages of high efficiency and great potential for high power output with high beam quality.
  • the pump light and the exiting laser share the optical component (dual color mirror) and pass through
  • the polarization device separates and detects the laser.
  • This pumping method has the following problems: high beam quality requirements for optical components and pump light, which may increase cavity loss; extraction of laser light by polarization characteristics will directly lead to a decrease in laser power; in addition, two-way pumping
  • the limited absorption path may result in incomplete absorption of pump light, which is not conducive to improving the electro-optical efficiency of the optically pumped metastable gas laser system.
  • an object of the present invention is to provide a resonance-enhanced lateral optical pumping device for a metastable gas laser, which aims to solve the problem that the absorption path of the pump light is limited due to the use of a polarizing prism in the prior art.
  • Technical problems that result in low laser output power and low electro-optic efficiency.
  • the invention provides a resonance enhanced lateral optical pumping device for a metastable gas laser, comprising a pump laser module, a resonance enhanced pump cavity, a laser cavity and a discharge excitation module; an optical axis of the pump laser module
  • the axis of the resonance-enhanced pumping chamber coincides, the axis of the resonance-enhancing pumping chamber, the axis of the laser cavity, and the direction of the electric field of the discharge excitation module are orthogonal to each other and intersect with the discharge excitation module
  • the center of the discharge region; the pump laser module is used to pump the gain medium to achieve particle number inversion;
  • the resonance-enhanced pump cavity increases the pump power and pump light in the cavity by using a resonance enhancement method
  • the absorption path which in turn increases the efficiency of absorption of the pump light;
  • the laser cavity is used to achieve a laser output; and the discharge excitation module is used to generate a gain medium (meta-stable particles).
  • the pump laser and the exit laser are separated from each other, and the separation of the polarizer is not required, the insertion loss can be reduced, and the extraction power of the emitted laser can be improved; optical components such as a two-color mirror are not required.
  • the absorption in the pump cavity and the absorption path of the pump light are increased by the resonance enhancement to promote absorption, and the laser line component in the laser induced fluorescence is not amplified and lasing in the pump cavity.
  • the pump laser module includes a pump laser, an optical isolator and a pattern matching unit which are disposed coaxially in sequence; the optical isolator is used to block between the resonance enhanced pumping chamber and the pump laser intrinsic cavity Coupling, the pattern matching unit is used to achieve transverse mode matching between the pump laser and the resonance enhanced pumping cavity.
  • the resonance-enhanced pumping chamber includes a piezoelectric ceramic, a voltage controller, a detector, a first concave mirror and a second concave mirror; the piezoelectric ceramic, the first concave mirror and the second concave mirror are along the pump The laser laser propagation direction is sequentially coaxially placed, the first concave mirror and the second concave mirror are opposite to each other, the first concave mirror is mounted on the piezoelectric ceramic, and the second concave mirror is fixed on the optical platform via the frame; A first concave mirror and a second concave mirror are used to build a pumping chamber, and the piezoelectric ceramic, the voltage controller, and the detector are used to feedback adjust a cavity length of the pumping chamber to achieve resonance enhancement.
  • the laser cavity includes: a third concave mirror and an output coupling mirror; a concave surface of the third concave mirror faces the cavity and is placed coaxially with the output coupling mirror; the output coupling mirror is used for Achieve laser output.
  • the discharge excitation module includes a high voltage electrode and a ground electrode; a gain medium (meta-stable particle) required for laser operation is generated between the high voltage electrode and the ground electrode.
  • the lateral pumping method can be extended to multiple transverse pumps.
  • the lateral pumping method is applicable not only to the intrinsic oscillating exit laser but also to the seed injection type main oscillating power amplifier structure.
  • the use of resonance-enhanced lateral pumping methods to promote absorption of pump light is also applicable to other optically pumped gas lasers such as optically pumped oxygen iodine lasers.
  • the optically pumped metastable gas laser can be used as a driving laser for an extreme ultraviolet lithography source by virtue of its more compact volume and high electro-optical efficiency.
  • the present invention also provides a resonance-enhanced lateral optical pumping method for realizing a metastable gas laser according to the resonance-enhanced lateral optical pumping device described above, comprising the steps of:
  • the cavity length control method includes: an open loop length scanning step and a closed loop length control step.
  • step of scanning the open loop length is specifically:
  • the step size and the number of steps of the scanning are set according to the resolution of the piezoelectric ceramic and the wavelength of the pump laser, and the step size is larger than the resolution of the piezoelectric ceramic, and the value of the product of the step size and the step number is greater than Half of the wavelength of the pump laser;
  • the step size set in the first step is converted into a voltage step according to the relationship between the displacement of the piezoelectric ceramic and the driving voltage, and a one-way increasing driving voltage signal is given to the piezoelectric ceramic, so that the cavity length of the pumping chamber is made.
  • the driving voltage signal at each scanning point and the light intensity signal detected by the detector are recorded and compared to find the maximum light intensity signal Imax and the corresponding driving voltage signal Vmax.
  • closed loop length control step is specifically:
  • control step size in the closed loop cavity length scanning control program is set, and the control step size is satisfied: the control step size is larger than the resolution of the piezoelectric ceramic, and is less than or equal to the scanning step length of the open loop scanning program;
  • the step size set in the first step is converted into a voltage step according to the relationship between the displacement of the piezoelectric ceramic and the driving voltage, and the driving voltage of the maximum light intensity obtained in the scanning step of the open-loop cavity is introduced in the program.
  • the signal Vmax and the light intensity signal Imax, the driving voltage signal Vmax is applied to the piezoelectric ceramic and the light intensity signal I under the voltage signal is collected;
  • the third step is to compare I with Imax. If I and Imax are not equal, enter the closed loop system:
  • Add a voltage step that is, after the cavity length is increased by one step: if the light intensity signal increases, continue to increase a voltage step, and if the light intensity signal decreases, decrease a voltage step;
  • Decrease a voltage step that is, reduce the cavity length by one step: if the light intensity signal increases, continue to reduce a voltage step, and if the light intensity signal decreases, increase a voltage step.
  • the invention adopts the transverse pumping method of separating the pump laser and the outgoing laser, and extracts the outgoing laser without using the polarizing element, thereby improving the output power under the same pumping condition; without using the optical component in the cavity, the insertion loss is reduced;
  • the use of a two-color mirror reduces the requirement for optical components; by using resonance enhancement to the pumping chamber, the pump laser power and pump absorption path in the pumping chamber can be increased, and the absorption efficiency of the pump light and the entire laser system can be improved. Electro-optic efficiency.
  • the present invention can be extended to multiple lateral pumping to reduce power and beam quality requirements for a single semiconductor laser pumping unit.
  • FIG. 1 is a schematic structural view of a resonance-enhanced lateral optical pumping device for a metastable gas laser according to an embodiment of the present invention.
  • 1 is pump laser
  • 2 optical isolator
  • 3 is pattern matching unit
  • 4 is piezoelectric ceramic
  • 5 is voltage controller
  • 6 is detector
  • 7 is first concave mirror
  • 8 is second concave mirror
  • 9 is a third concave mirror
  • 10 is a laser output coupling mirror
  • 11 is a high voltage electrode
  • 12 is a ground electrode.
  • FIG. 2 is a flow chart showing the flow of an open loop length scanning step in a resonance enhanced lateral optical pumping method of a metastable gas laser according to an embodiment of the present invention.
  • FIG. 3 is a flow diagram of a closed loop cavity length control step in a resonance enhanced lateral optical pumping method of a metastable gas laser according to an embodiment of the present invention.
  • the present invention provides a resonance enhanced lateral pumping apparatus including a pump laser module, a resonance enhanced pumping chamber, a laser cavity, and a discharge excitation module.
  • the pump laser module is coaxial with the resonance-enhanced pump cavity, the resonance-enhanced pump cavity, the axis of the laser cavity, and the electric field of the discharge excitation module are orthogonal to each other and intersect at the center of the discharge region.
  • Separating the pump laser and exiting the laser by lateral pumping avoids the use of dichroic mirrors and polarizing elements, Reducing the use of intracavity optical components and increasing the extraction power; based on the coherent superimposed resonance enhancement cavity, increasing the intracavity power and absorption path to promote absorption, improving the absorption efficiency of the pump laser and the electro-optical efficiency of the laser system.
  • the pump laser module includes a pump laser 1, an optical isolator 2, and a pattern matching unit 3.
  • the optical isolator 2 serves to prevent coupling between the pump laser eigen cavity and the resonance enhanced pumping cavity, and the mode matching unit 3 is used to achieve transverse mode matching between the pump laser and the pumping cavity.
  • the pattern matching unit 3 may be a lens or a lens group.
  • the resonance-enhanced pumping chamber includes a first concave mirror 7, a second concave mirror 8, a piezoelectric ceramic 4, a voltage controller 5, and a detector 6.
  • the first concave mirror 7 and the second concave mirror 8 are used to form a symmetric confocal cavity or a stable cavity, and the concave surface and the other surface of the two concave mirrors are respectively plated with a narrow-band high-reflection film and a broadband anti-reflection film corresponding to the pump laser.
  • a piezoelectric ceramic 4 is placed on one of the concave mirrors.
  • the detector 6 monitors the exit signal of the pumping chamber, and performs feedback control on the voltage controller 5 of the piezoelectric ceramic 4, thereby adjusting the cavity length of the pumping chamber to achieve resonance enhancement.
  • the piezoelectric ceramic 4 may be a ring-shaped piezoelectric ceramic, or a piezoelectric ceramic with an outer inner circle, or a combination of a plurality of ( ⁇ 3) piezoelectric ceramics uniformly distributed along the circumference. .
  • the laser cavity includes a third concave mirror 9 and an output coupling mirror 10.
  • the concave surface of the third concave mirror 9 is plated with a high-reflection film corresponding to the wavelength of the emitted laser light, and the shape of the other surface of the third concave mirror 9 and whether or not the film is coated are not required.
  • the transmittance acting as the laser output coupling mirror 10 can be obtained according to the optimum transmittance formula: Where T m is the optimum transmittance, ⁇ is the laser frequency, g 0 ( ⁇ ) is the small signal gain coefficient at the laser frequency, l is the length of the gain medium along the optical axis, and a is the round-trip net loss rate.
  • the discharge excitation module includes a high voltage electrode 11 and a ground electrode 12 for generating a gain medium (metastasis atom or molecule) required for the laser.
  • the electrodes may be two plate electrodes placed in parallel; the high voltage electrode may be a strip electrode array, the ground electrode is a plate electrode, and the plane composed of the strip electrode array and the plane of the plate electrode are parallel.
  • the discharge can be DC pulse
  • radio frequency discharge, and microwave discharge, field emission can also be used.
  • the above technical solution conceived by the present invention can achieve the following beneficial effects as compared with the existing two-way longitudinal pumping method: a lateral pumping method using a separate pumping laser and an outgoing laser without using polarization
  • the component extracts the laser to improve the output power under the same pumping condition; it can avoid the use of the two-color mirror and reduce the requirements on the optical components; it does not need to use the optical component in the cavity to reduce the insertion loss; and the resonance enhancement is applied to the pumping cavity. It can increase the pump power and pump absorption path in the cavity, improve the absorption efficiency of the pump light and the electro-optical efficiency of the entire laser system.
  • the present invention can be extended to multiple lateral pumping to reduce power and beam quality requirements for a single semiconductor laser pumping unit.
  • the laser cavity in the direction perpendicular to the direction of the pump cavity and the electric field, the laser cavity is built by the third concave mirror 9 and the laser output coupling mirror 10 to ensure that the optical axis of the resonant cavity passes through the center of the discharge region;
  • S5 Monitor the laser output at the laser output coupling mirror 10, and fine-tune the cavity of the laser cavity to maximize the laser output power or energy.
  • a semiconductor laser pumped metastable argon laser is taken as an example:
  • a 811.53 nm narrow linewidth semiconductor pump laser (OptiGrate, SEOP Laser811-20 GHz-30W) was passed through an optical isolator 2 (Throlabs, IO-5-TIS2-HP) and a pattern matching unit 3 (Throlabs, LB1779- B) After introduction into the confocal cavity built in (2).
  • a silicon photodetector 6 (Throlabs, PDA 8A) is placed at the exit of the second concave mirror 8 to monitor the laser output signal (it is noted that the laser needs to be greatly attenuated before entering the silicon photodetector).
  • the piezoelectric ceramic 4 is driven by a piezoelectric controller 4 (PI, PD080.30, ring) voltage controller 5 (PI, E-753.1CD), and the optimal cavity is found by combining the computer and the cavity length control program required for resonance enhancement. long.
  • the cavity length control program consists of two parts: the open loop length scan program and the closed loop length control program.
  • the displacement step size and the number of steps of the cavity length scanning are set to 2 nm and 300, respectively, and the displacement step size of 2 nm is converted into a voltage step.
  • a one-way increasing sawtooth voltage signal is applied to the piezoceramic 4 by the voltage controller 5 to linearly increase the cavity length of the cavity.
  • the transmitted light intensity at each scanning point that is, the signal of the silicon photodetector 6, is acquired and compared to obtain a maximum transmitted signal Imax and a corresponding voltage signal Vmax .
  • the open loop control program quickly positions the chamber length near the optimum operating point of the pump chamber.
  • the closed-loop cavity length control program mainly uses the climbing method to control the cavity length of the pumping chamber in real time to lock in the vicinity of the optimal cavity length.
  • I 1 ⁇ I 2 continue to increase the voltage of one step; if I 1 >I 2 , reduce the voltage of one step.
  • the transmitted light intensity increases, continue to increase by one step, if the transmitted light intensity decreases, reduce one step voltage; if one step voltage is decreased, if it is transmitted
  • the increase in light intensity continues to decrease by one step. If the transmitted light intensity decreases, the closed-loop control that increases the voltage of one step stabilizes the cavity length within a cell near the optimal cavity length.
  • the third concave mirror 9 flat concave mirror, the concave surface faces the discharge region, and the concave surface faces the 912 nm all-inversion) and the laser output coupling mirror 10 (both sides are polished)
  • the plane mirror builds an unstable cavity (also can be built with the 532 nm laser described in (2) as the indicator light).
  • the power of the laser beam at the plane mirror 10 is monitored by a power meter. Fine-tuning the laser cavity maximizes the power of the exiting laser.
  • the present invention is not limited to the contents disclosed in the embodiment and the drawings.
  • the discharge mode it is not limited to parallel plate discharge of radio frequency, and is suitable for the case of DC pulse discharge, microwave (including array) discharge, and cathode field emission (including array) to generate metastable particles.
  • the resonance-enhanced pumping chamber is not limited to the symmetric confocal cavity, but also includes a stabilizing cavity, and the cavity mirror of the pumping cavity is not limited to a plano-concave mirror, and the radius of curvature does not need to be uniform.
  • the output mirror of the laser cavity is not limited to a plane mirror, and may be a concave mirror.
  • the laser exit is not limited to the intrinsic oscillating shown in the embodiment, but is also applicable to the seed injection type main oscillating power amplifier structure.
  • the method of promoting absorption of pump light by the resonance-enhanced lateral pumping method is also applicable to other optical pumping gas lasers such as optically pumped oxygen-iodine lasers.

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Abstract

一种亚稳态气体激光的共振增强横向光泵浦装置及方法，通过共振增强技术，可增大对泵浦光的吸收从而提高光光效率和整个系统的电光效率。通过将泵浦激光和出射激光分离，可克服使用偏振器件带来的激光提取功率的下降和相应的插入损耗，避免了双色镜的使用，降低了对单个泵浦激光模块的功率和光束质量的要求。该泵浦方案还可扩展至多路横向泵浦的本征激励及种子注入式的主振荡功率放大器结构，有利于推动光泵浦亚稳态气体激光实现更高功率的激光输出及其在激光诱导等离子体等领域的应用。此外，共振增强的横向泵浦方法也适用于光泵浦氧碘激光器等其他光泵浦气体激光器。

Description

一种亚稳态气体激光的共振增强横向光泵浦装置及方法 【技术领域】
本发明属于激光技术领域，更具体地，涉及一种亚稳态气体激光的共振增强横向光泵浦装置及方法。
【背景技术】
激光诱导等离子体(Laser Produced Plasma，LPP)极紫外光刻光源是下一代光刻的核心技术之一。目前，气体激光器特别是CO2激光器用于极紫外光刻光源的激光驱动。但是，CO2激光器的电光效率低，体积大，导致极紫外光刻光源系统的能耗高、占用空间大，限制了极紫外光刻光源的大规模量产和应用。
光泵浦亚稳态气体激光(Optically Pumped Metastable Gas Laser，OPMGL)是一种放电激励和光泵浦相结合的新型气体激光器，它采用电激励产生的气体亚稳态粒子作为增益介质，再利用激光泵浦实现粒子数反转以出射激光。凭借自身极高的量子效率、气体介质良好的流动型和均匀性，该型激光可将小体积、高电光效率的高功率半导体激光转化为具有高光束质量的高功率输出，具有结构紧凑、电光效率高的优势和实现高光束质量的高功率输出的巨大潜力。
目前，光泵浦亚稳态气体激光的实验研究均采用双程纵向的泵浦方式(J.D.Han，et al.，“Demonstration of a diode-pumped metastable Ar laser”，Optics letters，38(2013)，W.T.Rawlins，et al.“Optically pumped micro plasma rare gas laser”，Optics express，23(2015)，Paul J.Moran，et al.，“Plasma and Laser Kinetics and Field Emission from Carbon Nanotube Fibers for an Advanced Noble Gas Laser(ANGL)”，Proc.SPIE 9729，9729C(2016))。在双程纵向泵浦实验中，泵浦光和出射激光共用光学元件(双色镜)，并通 过偏振器件对激光进行分离和探测。此种泵浦方法存在以下问题：对光学元件和泵浦光的光束质量要求较高、可能增加腔内损耗；利用偏振特性提取出射激光将直接导致激光功率的下降；此外，双程泵浦的吸收路径有限，可能会造成对泵浦光的吸收不完全，不利于提升光泵浦亚稳态气体激光系统的电光效率。
【发明内容】
针对现有技术的缺陷，本发明的目的在于提供一种亚稳态气体激光的共振增强横向光泵浦装置，旨在解决现有技术中由于采用了偏振棱镜、对泵浦光的吸收路径有限导致激光出射功率和电光效率低的技术问题。
本发明提供了一种亚稳态气体激光的共振增强横向光泵浦装置，包括泵浦激光模块、共振增强泵浦腔、激光谐振腔和放电激励模块；所述泵浦激光模块的光轴与所述共振增强泵浦腔的轴线重合，所述共振增强泵浦腔的轴线、所述激光谐振腔的轴线和所述放电激励模块的电场方向三者彼此正交且相交于所述放电激励模块的放电区域的中心；所述泵浦激光模块用于泵浦增益介质以实现粒子数反转；所述共振增强泵浦腔通过采用共振增强方法增大腔内的泵浦功率和泵浦光的吸收路径，进而提高对泵浦光的吸收效率；所述激光谐振腔用于实现激光输出；所述放电激励模块用于产生增益介质(亚稳态粒子)。
本发明中，泵浦激光和出射激光相互分离，不需使用偏振器分离，可降低插入损耗，提高出射激光的提取功率；不需使用双色镜这类光学元件。通过共振增强增大泵浦腔腔内功率和泵浦光的吸收路径以促进吸收，而激光诱导荧光中的激光谱线成分不会在泵浦腔中放大而激射。
更进一步地，所述泵浦激光模块包括依次同轴设置的泵浦激光器、光隔离器和模式匹配单元；所述光隔离器用于阻止共振增强泵浦腔与泵浦激光器本征腔之间的耦合，所述模式匹配单元用于实现泵浦激光和共振增强泵浦腔之间的横模匹配。
更进一步地，所述共振增强泵浦腔包括压电陶瓷、电压控制器、探测器、第一凹镜和第二凹镜；所述压电陶瓷、第一凹镜和第二凹镜沿泵浦激光传播方向依次同轴放置，所述第一凹镜和第二凹镜的凹面相对，第一凹镜装在压电陶瓷上，第二凹镜经镜架固定于光学平台上；所述第一凹镜和所述第二凹镜用于搭建泵浦腔，所述压电陶瓷、所述电压控制器和所述探测器用于反馈调节泵浦腔的腔长以实现共振增强。
更进一步地，所述激光谐振腔包括：第三凹镜和输出耦合镜；所述第三凹镜的凹面朝向腔内，且与所述输出耦合镜同轴放置；所述输出耦合镜用于实现激光输出。
更进一步地，放电激励模块包括高压电极和接地电极；在所述高压电极和所述接地电极之间产生激光运转所需的增益介质(亚稳态粒子)。
在本发明实施例中，该横向泵浦方法可向多路横向泵浦扩展。该横向泵浦方法不仅适用于本征起振出射激光，还可用于种子注入式的主振荡功率放大器结构。利用共振增强的横向泵浦方法促进对泵浦光的吸收也适用于光泵浦泵浦氧碘激光器等其他光泵浦气体激光器。该光泵浦亚稳态气体激光可凭借其更为紧凑的体积、高电光效率作为极紫外光刻光源的驱动激光器。
本发明还提供了一种根据上述的共振增强横向光泵浦装置实现亚稳态气体激光的共振增强横向光泵浦方法，包括下述步骤：
(1)利用所述放电激励模块产生增益介质(亚稳态粒子)；
(2)利用所述第一凹镜和第二凹镜在与放电电场方向垂直的方向搭建泵浦激光腔；
(3)将所述泵浦激光模块与所述泵浦激光腔同轴放置，并将泵浦激光引入至泵浦激光腔，利用腔长反馈控制元件和腔长控制方法对腔长进行控制以实现共振增强；
(4)在与放电电场方向和泵浦增强腔轴线均垂直的方向搭建激光谐振 腔；
(5)监测激光输出耦合镜处的激光输出，微调激光谐振腔的腔镜使激光输出功率或能量最高。
更进一步地，在步骤(3)中，所述腔长控制方法包括：开环腔长扫描步骤和闭环腔长控制步骤。
更进一步地，所述开环腔长扫描步骤具体为：
第一步，根据压电陶瓷的分辨率和泵浦激光的波长来设置扫描的步长和步数，并满足：步长大于压电陶瓷的分辨率，步长与步数的乘积的值大于泵浦激光波长的一半；
第二步，将第一步中设置的步长根据压电陶瓷位移和驱动电压的关系换算成电压步长，给压电陶瓷一个单向增大的驱动电压信号，使得泵浦腔的腔长单向增加；
第三步，记录每个扫描点下的驱动电压信号和探测器探测到的光强信号并比较，找出最大光强信号Imax及相应的驱动电压信号Vmax。
更进一步地，所述闭环腔长控制步骤具体为：
第一步，设置闭环腔长扫描控制程序下的控制步长，控制步长满足：控制步长大于压电陶瓷的分辨率，小于等于开环扫描程序的扫描步长；
第二步，将第一步中设置的步长根据压电陶瓷位移和驱动电压的关系换算成电压步长，在程序中引入所述开环腔长扫描步骤中获得的最大光强的驱动电压信号Vmax和光强信号Imax，给压电陶瓷施加驱动电压信号Vmax并采集该电压信号下的光强信号I；
第三步，比较I与Imax，若I与Imax不等，则进入闭环系统：
增加一个电压步长，即腔长增加一个步长后：若光强信号增大，则继续增加一个电压步长，若光强信号减小，则减小一个电压步长；
减小一个电压步长，即腔长减少一个步长后：若光强信号增大，则继续减小一个电压步长，若光强信号减小，则增加一个电压步长。
本发明采用分离泵浦激光和出射激光的横向泵浦方式，不需使用偏振元件提取出射激光，提高同等泵浦条件下的出射功率；不需在腔内使用光学元件，降低插入损耗；能够避免双色镜的使用，降低对光学元件的要求；通过对泵浦腔采用共振增强可增大泵浦腔内的泵浦激光功率和泵浦吸收路径，提高对泵浦光的吸收效率和整个激光系统的电光效率。此外，本发明还可扩展至多路横向泵浦，降低对单个半导体激光泵浦单元在功率和光束质量方面的要求。
【附图说明】
图1为本发明实施例提供的亚稳态气体激光的共振增强横向光泵浦装置的结构示意图。
其中，1为泵浦激光器，2为光隔离器，3为模式匹配单元，4为压电陶瓷，5为电压控制器，6为探测器，7为第一凹镜，8为第二凹镜，9为第三凹镜，10为激光输出耦合镜，11为高压电极，12为接地电极。
图2为本发明实施例提供的亚稳态气体激光的共振增强横向光泵浦方法中开环腔长扫描步骤的流程实现图。
图3为本发明实施例提供的亚稳态气体激光的共振增强横向光泵浦方法中闭环腔长控制步骤的流程实现图。
【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。
为实现上述目的，本发明提供了一种共振增强的横向泵浦装置，装置包括泵浦激光模块、共振增强泵浦腔、激光谐振腔和放电激励模块。泵浦激光模块与共振增强泵浦腔等高同轴，共振增强泵浦腔、激光谐振腔的轴线和放电激励模块的电场三者彼此正交并相交于放电区域的中心。
通过横向泵浦分离泵浦激光和出射激光避免使用双色镜和偏振元件， 减少腔内光学元件的使用并提高提取功率；基于相干叠加的共振增强腔，增大腔内功率和吸收路径进而促进吸收，提高对泵浦激光的吸收效率和激光系统的电光效率。
如图1所示，泵浦激光模块包括泵浦激光器1、光隔离器2和模式匹配单元3。光隔离器2用于阻止泵浦激光器本征腔和共振增强泵浦腔之间的耦合，模式匹配单元3用于实现泵浦激光和泵浦腔之间的横模匹配。
作为本发明的一个实施例，模式匹配单元3可以为透镜或者透镜组。
共振增强泵浦腔包括第一凹镜7、第二凹镜8，压电陶瓷4，电压控制器5，探测器6。第一凹镜7、第二凹镜8用于构成对称共焦腔或稳定腔，两凹镜的凹面和另一面均分别镀有与泵浦激光相应的窄带高反膜和宽带增透膜，且其中一凹镜上放置压电陶瓷4。通过探测器6监测泵浦腔的出射信号，对压电陶瓷4的电压控制器5进行反馈控制，进而调节泵浦腔的腔长以实现共振增强。作为本发明的一个实施例，压电陶瓷4可以采用环形压电陶瓷，也可采用外方内圆的压电陶瓷，还可以采用多块(≥3)压电陶瓷沿圆周均匀分布的组合形式。
激光谐振腔包括第三凹镜9和输出耦合镜10。第三凹镜9的凹面镀有与出射激光波长相应的高反膜，第三凹镜9的另一面的形状以及是否镀膜则不做要求。充当激光输出耦合镜10的透射率可根据最佳透射率公式获得：
Figure PCTCN2016098238-appb-000001
其中Tm为最佳透射率，ν为激光频率，g0(ν)为激光频率处的小信号增益系数，l为增益介质沿光轴方向的长度,a为往返净损耗率。
放电激励模块包括高压电极11和接地电极12，放电激励模块用于产生激光所需的增益介质(亚稳态原子或分子)。
在本发明实施例中，所述电极可以是平行放置的两平板电极；也可以是高压电极为条状电极阵列，接地电极为平板电极，条状电极阵列组成的平面和平板电极的平面平行。在放电方式的选择上，放电可以采用直流脉 冲放电、射频放电、微波放电，还可以采用场发射的方式。
总体而言，通过本发明所构思的以上技术方案与现有的双程纵向泵浦方法相比，能够取得以下有益效果：采用分离泵浦激光和出射激光的横向泵浦方式，不需使用偏振元件提取出射激光，提高同等泵浦条件下的出射功率；能够避免双色镜的使用，降低对光学元件的要求；不需在腔内使用光学元件，降低插入损耗；通过对泵浦腔采用共振增强可增大腔内的泵浦功率和泵浦吸收路径，提高对泵浦光的吸收效率和整个激光系统的电光效率。此外，本发明还可扩展至多路横向泵浦，降低对单个半导体激光泵浦单元在功率和光束质量方面的要求。
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。
具体的操作实施步骤为：
S1：利用放电激励模块(11，12)产生增益介质(亚稳态粒子)；
S2：将两块凹镜(7和8)的凹面相对放置，将泵浦激光引入泵浦腔、搭建泵浦腔，保证泵浦腔的光轴穿过放电区域中心并与电场方向垂直；
S3：结合模式匹配单元3、利用压电陶瓷4、电压控制器5和探测器6反馈控制调节泵浦腔的腔长，使泵浦激光和泵浦腔共振；
S4：在与泵浦腔和电场方向均垂直的方向，利用第三凹镜9和激光输出耦合镜10搭建激光谐振腔，保证谐振腔的光轴穿过放电区域中心；
S5：监测激光输出耦合镜10处的激光输出，微调激光谐振腔的腔镜使激光输出功率或能量最高。
下面结合实施例及前述实施步骤，对本发明作进一步详细说明。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。
下面的实施例中，以半导体激光泵浦亚稳态氩气激光为例：
(1)利用射频平行平板放电的方式实现氩气和氦气混合气体(氩气含 量为2％)在大气压下的稳定辉光放电以获得激光运转的亚稳态氩原子。
(2)利用两块完全相同的平凹镜(凹面对811.53nm附近窄带反射率为99％，平面对811.53nm宽带增透，曲率半径R＝150mm)7和8搭建对称共焦腔，保证共焦腔的轴线和放电区域中心等高并与电场方向垂直。搭建中可利用可见光波段的激光(如长春新产业光电技术有限公司的532nm的绿光激光器，MGL-III-532)作为指示光辅助调整。
(3)将811.53nm的窄线宽半导体泵浦激光(OptiGrate,SEOP Laser811-20GHz-30W)经过光隔离器2(Throlabs，IO-5-TIS2-HP)和模式匹配单元3(Throlabs，LB1779-B)后引入(2)中搭建的共焦腔内。在第二凹镜8的出口处放置硅光探测器6(Throlabs，PDA8A)监测激光输出信号(需要指出的是，激光在进入硅光探测器之前需大幅度衰减)。利用压电陶瓷4(PI，PD080.30，环形)的电压控制器5(PI，E-753.1CD)驱动压电陶瓷4，结合计算机和实现共振增强所需的腔长控制程序寻找最佳腔长。
腔长的控制程序包括两部分：开环腔长扫描程序和闭环腔长控制程序。
如图2所示，在开环腔长扫描程序中设置腔长扫描的位移步长和步数分别为2nm和300，将2nm的位移步长换算成电压步长。通过电压控制器5给压电陶瓷4施加一个单向增大的锯齿波电压信号使谐振腔的腔长线性增加。在此过程中，采集每一个扫描点下的透射光强即硅光探测器6的信号并进行比较，以获得最大透射信号Imax和对应的电压信号Vmax。通过开环控制程序可迅速将腔长定位至泵浦腔的最佳工作点附近。
在开环腔长扫描程序后，进入闭环腔长控制程序。如图3所示，闭环腔长控制程序主要是利用爬坡法对泵浦腔的腔长进行实时控制以锁定在最佳腔长附近。闭环控制程序开始时，设置腔长控制的位移步长为1nm并换算成电压扫描步长，将开环扫描程序中的Vmax赋值给电压控制器5，采集此时的透射光强I1,应有I1＝Imax。若I1≠Imax，则增大电压使腔长增加，采集 此时的透射光强I2：
若I1<I2，继续增大一个步长的电压；若I1>I2，则减小一个步长的电压。如此，按照：增大一个步长电压后，若透射光强增大则继续增大一个步长，若透射光强减小则减小一个步长电压；减小一个步长电压后，若透射光强增大则继续减小一个步长，若透射光强减小则增大一个步长电压的闭环控制将腔长稳定在最佳腔长附近的一个小区间内。
具体控制程序的编写参照图2和图3所示的腔长控制程序流程图。
(4)在与泵浦腔和电场方向均垂直的方向，利用第三凹镜9(平凹镜，凹面朝向放电区域，且凹面对912nm全反)和激光输出耦合镜10(两面均抛光的平面镜)搭建非稳定谐振腔(同样可借助(2)中所述532nm激光作为指示光搭建)。
(5)激光谐振腔搭建后，利用功率计监测平面镜10处的出射激光功率。微调激光谐振腔使得出射激光功率最高。
以上所述为本发明的较佳的实施例而已，但本发明不局限于该实施例和附图所公开的内容。例如在放电方式的选择上，并不局限于射频的平行平板放电，而且适用于直流脉冲放电、微波(含阵列)放电、阴极场发射(含阵列)产生亚稳态粒子的情况。共振增强的泵浦腔不限于对称共焦腔，还包括稳定腔，而且泵浦腔的腔镜不限于平凹镜，曲率半径也无需一致。激光谐振腔的输出镜不限于平面镜，也可以是凹面镜。激光出射不局限于实施例中所展示的本征起振，还适用于种子注入式的主振荡功率放大器结构。此外，利用共振增强的横向泵浦方法促进对泵浦光的吸收的方法也适用于光泵浦氧碘激光器等其他光泵浦气体激光器。
本领域的技术人员容易理解，以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。

Claims (9)

  1. 一种亚稳态气体激光的共振增强横向光泵浦装置，其特征在于，包括泵浦激光模块、共振增强泵浦腔、激光谐振腔和放电激励模块；
    所述泵浦激光模块的光轴与所述共振增强泵浦腔的轴线重合，所述共振增强泵浦腔的轴线、所述激光谐振腔的轴线和所述放电激励模块的电场方向三者彼此正交且相交于所述放电激励模块的放电区域的中心；
    所述泵浦激光模块用于泵浦增益介质以实现粒子数反转；所述共振增强泵浦腔通过采用共振增强方法增大腔内的泵浦功率和泵浦吸收路径，进而提高对泵浦光的吸收效率；所述激光谐振腔用于实现激光输出；所述放电激励模块用于产生增益介质。
  2. 如权利要求1所述的共振增强横向光泵浦装置，其特征在于，所述泵浦激光模块包括依次同轴设置的泵浦激光器(1)、光隔离器(2)和模式匹配单元(3)；
    所述光隔离器(2)用于阻止共振增强泵浦腔与泵浦激光器本征腔之间的耦合，所述模式匹配单元(3)用于实现泵浦激光和共振增强泵浦腔之间的横模匹配。
  3. 如权利要求1或2所述的共振增强横向光泵浦装置，其特征在于，所述共振增强泵浦腔包括压电陶瓷(4)、电压控制器(5)、探测器(6)、第一凹镜(7)和第二凹镜(8)；
    所述压电陶瓷(4)、第一凹镜(7)和第二凹镜(8)沿泵浦激光传播方向依次同轴放置，所述第一凹镜(7)和第二凹镜(8)的凹面相对，第一凹镜(7)装在压电陶瓷(4)上，第二凹镜(8)经镜架固定于光学平台上；
    所述第一凹镜(7)和所述第二凹镜(8)用于搭建泵浦腔，所述压电陶瓷(4)、所述电压控制器(5)和所述探测器(6)用于反馈调节泵浦腔 的腔长以实现共振增强。
  4. 如权利要求1-3任一项所述的共振增强横向光泵浦装置，其特征在于，所述激光谐振腔包括：第三凹镜(9)和输出耦合镜(10)；
    所述第三凹镜(9)的凹面朝向腔内，且与所述输出耦合镜(10)同轴放置；所述输出耦合镜(10)用于出射激光。
  5. 如权利要求1-4任一项所述的共振增强横向光泵浦装置，其特征在于，所述放电激励模块包括高压电极(11)和接地电极(12)；在所述高压电极(11)和所述接地电极(12)之间产生激光运转所需的增益介质。
  6. 一种根据权利要求1-5任一项所述的共振增强横向光泵浦装置实现亚稳态气体激光的共振增强横向光泵浦方法，其特征在于，包括下述步骤：
    (1)利用所述放电激励模块产生增益介质；
    (2)利用所述第一凹镜和第二凹镜在与放电电场方向垂直的方向搭建泵浦激光腔；
    (3)将所述泵浦激光模块与所述泵浦激光腔同轴放置，并将泵浦激光引入至泵浦激光腔，利用腔长反馈控制元件和腔长控制方法对腔长进行控制以实现共振增强；
    (4)在与放电电场方向和泵浦增强腔轴线均垂直的方向搭建激光谐振腔；
    (5)监测激光输出耦合镜处的激光输出，微调激光谐振腔的腔镜使激光输出功率或能量最高。
  7. 如权利要求6所述的共振增强横向光泵浦方法，其特征在于，在步骤(3)中，所述腔长控制方法包括：开环腔长扫描步骤和闭环腔长控制步骤。
  8. 如权利要求7所述的共振增强横向光泵浦方法，其特征在于，所述开环腔长扫描步骤具体为：
    (1)根据泵浦激光波长和压电陶瓷的分辨率设置开环腔长扫描的步长 和步数；
    其中，所述步长大于压电陶瓷的分辨率，所述步长与所述步数的乘积的值大于泵浦激光波长的一半；
    (2)根据压电陶瓷位移和驱动电压的关系将所述步长换算成电压步长，并给压电陶瓷施加单向增大的驱动电压信号，使得泵浦腔的腔长单向增加；
    (3)记录每个扫描点下的驱动电压信号和探测器探测到的光强信号并比较，找出最大光强信号Imax下的扫描点对应的驱动电压信号Vmax。
  9. 如权利要求8所述的共振增强横向光泵浦方法，其特征在于，所述闭环腔长控制步骤具体为：
    (1)设置闭环腔长扫描的控制步长；
    其中所述控制步长大于压电陶瓷的分辨率，且小于等于所述开环腔长扫描步骤中的扫描步长；
    (2)根据压电陶瓷位移和驱动电压的关系将所述扫描步长换算成电压步长，在程序中引入所述开环腔长扫描步骤中获得的最大光强的驱动电压信号Vmax和光强信号Imax，给压电陶瓷施加驱动电压信号Vmax并采集该电压信号下的光强信号I；
    (3)比较I与Imax，若I与Imax不等，进入闭环控制；
    所述闭环控制具体包括：
    增加一个电压步长，即腔长增加一个步长后：若光强信号增大，则继续增加一个电压步长，若光强信号减小，则减小一个电压步长；
    减小一个电压步长，即腔长减小一个步长后：若光强信号增大，则继续减小一个电压步长，若光强信号减小，则增加一个电压步长。
PCT/CN2016/098238 2016-07-15 2016-09-06 一种亚稳态气体激光的共振增强横向光泵浦装置及方法 Ceased WO2018010288A1 (zh)

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