CN103036137A - Method for generating subnanosecond mode-locked pulse laser with high stability and low repetition frequency - Google Patents
Method for generating subnanosecond mode-locked pulse laser with high stability and low repetition frequency Download PDFInfo
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Abstract
本发明提供一种产生高稳定、低重复频率、亚纳秒锁模脉冲激光的方法。采用主动电光调Q-饱和吸收体GaAs被动锁模的双损耗调制技术，通过三镜谐振腔参数优化设计，使主被动双调Q锁模激光的重复率依赖于主动电光调制的重复率、调Q包络内的锁模脉冲依赖于主动调制和被动饱和吸收；依据激活介质、饱和吸收体小信号透过率、主动调制器重复率、腔参数、泵浦功率的选择，使调Q包络的宽度小于激光往返的时间，每个调Q包络只有一个锁模脉冲振荡，锁模脉冲的重复率等于主动电光调制的几KHz重复率。本发明不仅脉冲重复率低，而且具有高度稳定性；脉冲的宽度为调Q包络内锁模脉冲的宽度为亚纳秒级，且具有高峰值功率。
The invention provides a method for generating high stability, low repetition frequency, and subnanosecond mode-locked pulse laser. The dual-loss modulation technology of active electro-optic Q-switching-saturated absorber GaAs passive mode-locking is adopted, and the repetition rate of the active-passive dual-Q-switching mode-locked laser depends on the repetition rate of the active electro-optic modulation and modulation through the optimized design of the parameters of the three-mirror resonator. The mode-locked pulse in the Q envelope depends on active modulation and passive saturable absorption; according to the selection of the active medium, saturable absorber small-signal transmittance, active modulator repetition rate, cavity parameters, and pump power, the Q-switched envelope The width is less than the round-trip time of the laser, and each Q-switched envelope has only one mode-locked pulse oscillation, and the repetition rate of the mode-locked pulse is equal to the repetition rate of several KHz of active electro-optic modulation. The invention not only has a low pulse repetition rate, but also has high stability; the width of the pulse is sub-nanosecond, and the width of the mode-locked pulse in the Q-switching envelope is high peak power.
Description
技术领域technical field
本发明涉及一种采用主被动双损耗调制技术产生高稳定、低重复频率、亚纳秒脉冲激光的方法，属于激光技术领域。The invention relates to a method for generating high-stability, low-repetition-frequency, sub-nanosecond pulsed laser light by adopting an active-passive dual-loss modulation technology, which belongs to the field of laser technology.
背景技术Background technique
全固态短脉冲激光中的脉冲宽度、重复率、稳定性、峰值功率是极为重要的几项指标。高稳定性和高峰值功率是短脉冲激光应用的必要条件；脉冲宽度和重复率决定了光与物质相互作用的时间及动力学过程，低重复率不仅提高脉冲的峰值功率，而且在诸如荧光寿命测量中能够增加寿命测量的范围。图1显示了通常激光器的四种不同运转状态，包括连续(CW)、调Q(Q-switching)、连续锁模（CW mode-locking）、调Q锁模（Q-switching andmode-locking）。Pulse width, repetition rate, stability, and peak power in all-solid-state short-pulse lasers are extremely important indicators. High stability and high peak power are necessary conditions for short-pulse laser applications; pulse width and repetition rate determine the time and dynamics of light-matter interaction. The range of life measurement can be increased in the measurement. Figure 1 shows four different operating states of a typical laser, including continuous (CW), Q-switching (Q-switching), continuous mode-locking (CW mode-locking), and Q-switching mode-locking (Q-switching and mode-locking).
一般说来，连续锁模激光能够产生皮秒(ps)和飞秒(fs)级的脉冲，脉冲的重复率依赖于腔长,在MHz~GHz量级；通过增加腔长到100m和3.8Km，在被动锁模激光和被动锁模光纤激光中最低的重复率只能到1.5MHz和77KHz，但腔长的增加无疑使激光器系统复杂，且难以获得几KHz的重复速率。主动调Q激光能够产生几纳秒到几十纳秒的脉冲，脉冲的重复率为kHz量级，并可以调控；被动调Q激光可产生纳秒级的脉冲，而微片被动调Q激光的脉冲宽度可以窄到亚纳秒级，但被动调Q激光的单脉冲能量及脉冲的重复率均不稳定；调Q技术难以获得高稳定性、高峰值功率的脉冲激光。调Q锁模是介于调Q和连续锁模之间的动力学过程，调Q包络的脉宽和重复率均与调Q激光相同，调Q包络下的锁模脉冲的脉宽为亚纳秒级，其重复率与连续锁模相同，峰值功率高于调Q激光和连续锁模激光脉冲，但调Q包络下的锁模脉冲串个数众多，单脉冲能量从包络中心向外依次减小，稳定性较差。因此，单一的连续锁模、调Q或调Q锁模技术，均难以获得低重频（几KHz）、高稳定性、高峰值功率的亚纳秒级锁模脉冲激光。Generally speaking, continuous mode-locked lasers can generate picosecond (ps) and femtosecond (fs) level pulses, and the pulse repetition rate depends on the cavity length, which is in the order of MHz~GHz; by increasing the cavity length to 100m and 3.8Km , the lowest repetition rate in passive mode-locked laser and passive mode-locked fiber laser can only reach 1.5MHz and 77KHz, but the increase of cavity length undoubtedly makes the laser system complex, and it is difficult to obtain a repetition rate of several KHz. Actively Q-switched lasers can generate pulses of a few nanoseconds to tens of nanoseconds, and the repetition rate of the pulses can be adjusted at the kHz level; passive Q-switched lasers can generate nanosecond-level pulses, and the microchip passive Q-switched laser The pulse width can be as narrow as sub-nanoseconds, but the single pulse energy and pulse repetition rate of passive Q-switched lasers are unstable; Q-switching technology is difficult to obtain pulsed lasers with high stability and high peak power. Q-switched mode-locking is a dynamic process between Q-switched and continuous mode-locked. The pulse width and repetition rate of the Q-switched envelope are the same as those of the Q-switched laser. The pulse width of the mode-locked pulse under the Q-switched envelope is Sub-nanosecond level, its repetition rate is the same as that of continuous mode-locked laser pulses, and its peak power is higher than that of Q-switched lasers and continuous mode-locked laser pulses, but there are many mode-locked pulse trains under the Q-switched envelope, and the single pulse energy is Decrease outwards successively, and the stability is poor. Therefore, it is difficult to obtain sub-nanosecond mode-locked pulsed laser with low repetition frequency (several KHz), high stability and high peak power by single continuous mode-locking, Q-switching or Q-switching mode-locking technology.
双损耗调制是将两种不同或相同的损耗调制相结合，并同时放入一谐振腔内。依据不同的结合又可分为双主动损耗调制、主-被动双损耗调制、双被动损耗调制。双主动损耗调制如主动电光（声光）和主动声光（电光）相结合，主-被动双损耗调制如主动电光（声光）与饱和吸收体（Cr4+:YAG、GaAs、SESAM等）被动吸收相结合，双被动损耗调制如饱和吸收体（Cr4+:YAG、GaAs、SESAM等）被动吸收与饱和吸收体（Cr4+:YAG、GaAs、SESAM等）被动吸收相结合。与单损耗调制的激光相比，双损耗调制的激光够产生更窄的脉冲宽度、更高的峰值功率、更稳定的脉冲。理论和实验结果表明，双调Q激光能够比单调Q激光产生更窄的脉冲宽度、更对称的波形、更高的峰值功率，主被动和双被动连续锁模激光能够产生更稳定的锁模脉冲，双调Q锁模激光峰值功率大幅度提高、稳定性大大增强。众所周知，主动损耗调Q产生的短脉冲激光重复率稳定、易于控制，而饱和吸收体被动锁模结构简单、价格低廉。因此，主-被动双损耗调制能够利用两种损耗调制的特点，产生单损耗调制难以获得的理想调制脉冲，倍受人们的青睐。Dual loss modulation is to combine two different or the same loss modulations and put them into a resonant cavity at the same time. According to different combinations, it can be divided into dual active loss modulation, active-passive dual loss modulation, and dual passive loss modulation. Dual active loss modulation such as the combination of active electro-optic (acousto-optic) and active acousto-optic (electro-optic), active-passive dual loss modulation such as active electro-optic (acousto-optic) and saturable absorbers (Cr 4+ : YAG, GaAs, SESAM, etc.) Combination of passive absorption, double passive loss modulation such as saturable absorber (Cr 4+ : YAG, GaAs, SESAM, etc.) passive absorption and saturable absorber (Cr 4+ : YAG, GaAs, SESAM, etc.) passive absorption combined. Compared with single loss modulated laser, double loss modulated laser can generate narrower pulse width, higher peak power, and more stable pulse. Theoretical and experimental results show that double Q-switched lasers can generate narrower pulse widths, more symmetrical waveforms, and higher peak power than monotonous Q-switched lasers, and active-passive and dual-passive continuous mode-locked lasers can generate more stable mode-locked pulses , The peak power of the double Q-switched mode-locked laser is greatly improved, and the stability is greatly enhanced. As we all know, the short pulse laser repetition rate generated by active loss Q-switching is stable and easy to control, while the passive mode-locking of saturable absorbers has a simple structure and low cost. Therefore, active-passive dual-loss modulation can utilize the characteristics of two loss modulations to generate ideal modulation pulses that are difficult to obtain with single-loss modulation, and is favored by people.
发明内容Contents of the invention
本发明针对现有单一的连续锁模、调Q或调Q锁模技术存在的难以获得低重频、高稳定性、高峰值功率的亚纳秒级锁模脉冲激光的问题，提供一种基于双损耗调制技术能够产生高稳定、低重复频率、亚纳秒锁模脉冲激光的方法。The present invention aims at the problems existing in the existing single continuous mode locking, Q-switching or Q-switching mode-locking technology that it is difficult to obtain sub-nanosecond level mode-locked pulsed laser with low repetition frequency, high stability and high peak power, and provides a method based on The dual-loss modulation technique is a method capable of generating highly stable, low repetition rate, sub-nanosecond mode-locked pulsed lasers.
本发明产生高稳定、低重复频率、亚纳秒锁模脉冲激光的方法，是：The present invention produces the method for high stability, low repetition rate, sub-nanosecond mode-locked pulsed laser, is:
采用主动电光调Q-GaAs饱和吸收体被动锁模相结合的双损耗调制技术，将电光调制器和GaAs饱和吸收体同时放入谐振腔内，使谐振腔内振荡的激光为双调Q锁模激光运转；所述谐振腔为三个腔镜构成的V型腔，三个腔镜为第一全反射凹面镜、第二全反射凹面镜和平面输出镜，第一全反射凹面镜和第二全反射凹面镜之间依次设有激活介质、起偏器、电光调制器和四分之一波片，电光调制器的重复率选择低重频1KHz；GaAs饱和吸收体小信号透过率为92.6％；GaAs饱和吸收体置于贴近平面输出镜处，以获得最小振荡激光光斑半径；调整谐振腔的参数:第一全反射凹面镜和第二全反射凹面镜的曲率半径及两者之间的距离L1、第二全反射镜M2和平面输出镜之间的距离L2以及平面输出镜的透过率，使双调Q锁模激光的重复率依赖于电光调制器的重复率、调Q包络内的锁模脉冲依赖于电光调制器和GaAs被动饱和吸收；由于调Q包络内相邻两锁模脉冲的时间间隔等于振荡激光在腔内往返的时间，调Q包络的宽度决定了调Q包络内锁模脉冲振荡的个数，依据激活介质、饱和吸收体小信号透过率、电光调制器的重复率、谐振腔的参数和泵浦功率的选择，使调Q包络的宽度小于激光在谐振腔内的往返时间，使每个调Q包络只有一个锁模脉冲振荡，锁模脉冲的重复率等于主动电光调制的重复率，即能产生产生高稳定、低重复频率、亚纳秒锁模脉冲激光。The dual-loss modulation technology combining active electro-optic Q-switching-GaAs saturable absorber passive mode-locking is adopted, and the electro-optic modulator and GaAs saturable absorber are placed in the resonant cavity at the same time, so that the laser oscillating in the resonant cavity is dual-Q-switched and mode-locked Laser operation; the resonant cavity is a V-shaped cavity composed of three cavity mirrors, the three cavity mirrors are the first total reflection concave mirror, the second total reflection concave mirror and the plane output mirror, the first total reflection concave mirror and the second An active medium, a polarizer, an electro-optic modulator and a quarter-wave plate are sequentially arranged between the total reflection concave mirrors. The repetition rate of the electro-optic modulator is selected as low as 1KHz; the small-signal transmittance of the GaAs saturable absorber is 92.6 %; GaAs saturable absorber is placed close to the plane output mirror, to obtain the minimum oscillation laser spot radius; adjust the parameters of the resonant cavity: the radius of curvature of the first total reflection concave mirror and the second total reflection concave mirror and the distance between the two The distance L 1 , the distance L 2 between the second total reflection mirror M 2 and the planar output mirror, and the transmittance of the planar output mirror make the repetition rate of the double Q-switched mode-locked laser depend on the repetition rate of the electro-optic modulator, modulation The mode-locked pulse in the Q envelope depends on the electro-optic modulator and GaAs passive saturation absorption; since the time interval between two adjacent mode-locked pulses in the Q-switched envelope is equal to the time for the oscillating laser to go back and forth in the cavity, the width of the Q-switched envelope The number of mode-locked pulse oscillations in the Q-switching envelope is determined. According to the selection of the activation medium, the small-signal transmittance of the saturable absorber, the repetition rate of the electro-optic modulator, the parameters of the resonant cavity, and the selection of the pump power, the Q-switching envelope The width of the envelope is smaller than the round-trip time of the laser in the resonator, so that each Q-switched envelope has only one mode-locked pulse oscillation, and the repetition rate of the mode-locked pulse is equal to the repetition rate of active electro-optic modulation, which can produce high stability and low repetition Frequency, sub-nanosecond mode-locked pulsed lasers.
谐振腔优化参数依据如下条件：The optimization parameters of the resonator are based on the following conditions:
（1）电光调制器重复率越低，调Q包络脉冲宽度越窄；(1) The lower the repetition rate of the electro-optic modulator, the narrower the Q-switched envelope pulse width;
（2）GaAs饱和吸收体小信号透过率越大，调Q锁模运转时调Q包络的重复率越大；(2) The larger the small-signal transmittance of the GaAs saturated absorber, the larger the repetition rate of the Q-switched envelope during Q-switched mode-locked operation;
（3）谐振腔越长，参与激光振荡的纵模数越多，容易实现锁模激光运转，并且相邻两锁模的时间间隔越长，但长腔调Q包络的脉宽较宽；(3) The longer the resonator, the more longitudinal modes that participate in the laser oscillation, and it is easier to realize the mode-locked laser operation, and the time interval between two adjacent mode-locked is longer, but the pulse width of the Q-switched envelope of the long cavity is wider;
（4）GaAs饱和吸收体处较小的光斑半径易达到饱和吸收，但光斑强度需小于损伤阈值；(4) The smaller spot radius at the GaAs saturable absorber can easily reach saturated absorption, but the spot intensity must be smaller than the damage threshold;
（5）由于调Q包络内相邻两锁模脉冲的时间间隔等于振荡激光在腔内往返的时间,调Q包络脉冲宽度越窄，每一个调Q包络内振荡的锁模脉冲个数越少。(5) Since the time interval between two adjacent mode-locked pulses in the Q-switched envelope is equal to the time for the oscillating laser to go back and forth in the cavity, the narrower the pulse width of the Q-switched envelope, the more mode-locked pulses oscillating in each Q-switched envelope The fewer the number.
优化谐振腔参数达到的目的：The purpose of optimizing the parameters of the resonator:
（1）谐振腔内振荡的激光为双调Q锁模激光运转，双调Q锁模激光的重复率依赖于主动电光调制的重复率、调Q包络内的锁模脉冲依赖于主动电光调制和GaAs被动饱和吸收。(1) The laser oscillating in the resonator is a dual-Q-switched mode-locked laser operation. The repetition rate of the dual-Q-switched mode-locked laser depends on the repetition rate of the active electro-optic modulation, and the mode-locked pulse in the Q-switched envelope depends on the active electro-optic modulation. and GaAs passive saturable absorption.
（2）在一定的泵浦功率下，调Q包络的宽度小于激光在腔内的往返时间，确保每个调Q包络只有一个锁模脉冲振荡。(2) Under a certain pump power, the width of the Q-switched envelope is smaller than the round-trip time of the laser in the cavity, ensuring that each Q-switched envelope has only one mode-locked pulse oscillation.
（3）实现双调Q锁模激光每个调Q包络只有一个锁模脉冲运转，锁模脉冲的重复率等于主动电光调制的重复率，脉冲宽度为亚纳秒级。(3) To realize the dual Q-switched mode-locked laser, each Q-switched envelope has only one mode-locked pulse to operate, the repetition rate of the mode-locked pulse is equal to the repetition rate of active electro-optic modulation, and the pulse width is sub-nanosecond level.
本发明利用主动电光调制的低重复率和高稳定性及饱和吸收体被动调Q锁模亚纳秒的脉冲宽度，这种脉冲激光的运转具有鲜明的特点，脉冲的重复率等于电光的重复率1kHz，不仅重复率低，而且具有高度稳定性；脉冲的宽度为调Q包络内锁模脉冲的宽度为亚纳秒级，且具有高峰值功率。The invention utilizes the low repetition rate and high stability of active electro-optic modulation and the sub-nanosecond pulse width of passive Q-switching mode-locking of saturated absorbers. The operation of this pulsed laser has distinctive characteristics, and the pulse repetition rate is equal to that of electro-optic 1kHz, not only has a low repetition rate, but also has high stability; the width of the pulse is sub-nanosecond, and the width of the mode-locked pulse in the Q-switched envelope has high peak power.
附图说明Description of drawings
图1是通常激光器的四种不同运转状态示意图。包括连续(CW)、调Q(Q-switching)、连续锁模（CW mode-locking）、调Q锁模（Q-switching andmode-locking）。Figure 1 is a schematic diagram of four different operating states of a typical laser. Including continuous (CW), Q-switching (Q-switching), continuous mode-locking (CW mode-locking), Q-switching mode-locking (Q-switching and mode-locking).
图2是本发明的三镜谐振腔装置的示意图。Fig. 2 is a schematic diagram of the three-mirror resonant cavity device of the present invention.
图3是调Q包络的脉冲宽度随泵浦功率的变化关系示意图。Fig. 3 is a schematic diagram of the relationship between the pulse width of the Q-switched envelope and the change of the pump power.
图4是示波器记录的调Q包络内锁模脉冲个数随泵浦功率的变化关系图。Fig. 4 is a relationship diagram of the number of mode-locked pulses in the Q-switched envelope recorded by an oscilloscope as a function of pump power.
图5是调Q包络内锁模脉冲宽度随泵浦功率的变化关系示意图。Fig. 5 is a schematic diagram of the relationship between the mode-locked pulse width in the Q-switched envelope and the pump power.
图6是示波器记录的泵浦功率为7.09W亚纳秒锁模脉冲序列示意图。Fig. 6 is a schematic diagram of a sub-nanosecond mode-locked pulse sequence recorded by an oscilloscope with a pump power of 7.09W.
具体实施方式Detailed ways
本发明采用主动电光调Q-饱和吸收体GaAs被动锁模的双损耗调制技术，利用电光调制开关速度快、调Q脉宽窄、性能稳定的特点，GaAs饱和吸收体光损伤阈值高及单光子、双光子、自由载流子饱和吸收被动锁模易于控制的优点，将电光调制器和GaAs饱和吸收体同时放入谐振腔内，通过谐振腔使谐振腔内振荡的激光为双调Q锁模激光运转，并依据谐振参数优化设计，使双调Q锁模激光的重复率依赖于主动电光调制的重复率、调Q包络内的锁模脉冲依赖于主动电光调制和GaAs被动饱和吸收。由于调Q包络内相邻两锁模脉冲的时间间隔等于振荡激光在腔内往返的时间，调Q包络的宽度决定了调Q包络内锁模脉冲振荡的个数，依据激活介质、饱和吸收体小信号透过率、主动调制器重复率、腔参数、泵浦功率的选择，使调Q包络的宽度小于激光在腔内的往返时间，确保每个调Q包络只有一个锁模脉冲振荡，锁模脉冲的重复率等于主动电光调制的重复率，脉冲宽度为亚纳秒级。The present invention adopts active electro-optic Q-switching-gaAs saturated absorber GaAs passive mode-locking dual-loss modulation technology, utilizes the characteristics of electro-optic modulation switching speed, narrow Q-switching pulse width, and stable performance, GaAs saturable absorber has high optical damage threshold and single photon , two-photon, free carrier saturated absorption passive mode-locking is easy to control, the electro-optic modulator and GaAs saturable absorber are placed in the resonant cavity at the same time, and the laser oscillating in the resonant cavity is double Q-switched mode-locked through the resonant cavity Laser operation, and optimized design based on resonance parameters, makes the repetition rate of the double Q-switched mode-locked laser depend on the repetition rate of active electro-optic modulation, and the mode-locked pulse in the Q-switched envelope depends on active electro-optic modulation and GaAs passive saturation absorption. Since the time interval between two adjacent mode-locked pulses in the Q-switched envelope is equal to the round-trip time of the oscillating laser in the cavity, the width of the Q-switched envelope determines the number of mode-locked pulse oscillations in the Q-switched envelope. According to the activation medium, The small-signal transmittance of the saturable absorber, the repetition rate of the active modulator, the cavity parameters, and the selection of the pump power make the width of the Q-switched envelope smaller than the round-trip time of the laser in the cavity, ensuring that each Q-switched envelope has only one lock Mode pulse oscillation, the repetition rate of the mode-locked pulse is equal to the repetition rate of active electro-optic modulation, and the pulse width is sub-nanosecond.
本发明采用图2所示的三镜谐振腔装置，三个腔镜为第一全反射凹面镜、第二全反射凹面镜和平面输出镜，第一全反射凹面镜和第二全反射凹面镜之间依次设有激光晶体（激活介质）、起偏器（偏振片）、电光（EO）调制器和四分之一波片。第一全反射镜的曲率半径为150mm，第二全反射镜的曲率半径为500mm，平面输出镜的透过率为6.5%。激光晶体（作为激光介质）为键合晶体YVO4/Nd:YVO4，采用键合晶体能减少热效应。第一全反射镜和第二全反射镜之间的距离L1为600mm，第二全反射镜与平面输出镜之间的距离L2为460mm。The present invention adopts the three-mirror resonant cavity device shown in Fig. 2, and three cavity mirrors are the first total reflection concave mirror, the second total reflection concave mirror and the plane output mirror, the first total reflection concave mirror and the second total reflection concave mirror A laser crystal (active medium), a polarizer (polarizer), an electro-optic (EO) modulator and a quarter-wave plate are arranged in sequence between them. The radius of curvature of the first total reflection mirror is 150 mm, the radius of curvature of the second total reflection mirror is 500 mm, and the transmittance of the planar output mirror is 6.5%. The laser crystal (as the laser medium) is bonded crystal YVO 4 /Nd:YVO 4 , and the use of bonded crystal can reduce the thermal effect. The distance L1 between the first total reflection mirror and the second total reflection mirror is 600mm, and the distance L2 between the second total reflection mirror and the planar output mirror is 460mm.
采用激光二极管作为泵浦源，激光二极管与第一全反射凹面镜M1之间设置两个凸透镜。光纤耦合系统，泵浦光聚焦到激活介质（激光晶体）中，聚焦后泵浦光的光斑半径与谐振腔模相匹配。电光调制器作为主动调制损耗，电光晶体为BBO晶体，电光调制器的重复率为重复速率1kHz。GaAs作为被动饱和吸收体，置于贴近平面输出镜M3处，以获得最小振荡激光光斑半径。GaAs饱和吸收体小信号透过率为92.6%。依据谐振腔参数，根据ABCD矩阵理论，优化后的GaAs饱和吸收体处的光斑半径128-135微米。激光的阈值功率0.9W-1W，泵浦光一旦超过阈值功率，便可获得稳定的双调Q锁模激光，其调Q包络的重复率等于电光调制的重复率1kHz，调Q包络内锁模脉冲的重复率依赖于谐振腔长，为114MHz。A laser diode is used as the pumping source, and two convex lenses are arranged between the laser diode and the first total reflection concave mirror M1 . In the fiber coupling system, the pump light is focused into the active medium (laser crystal). After focusing, the spot radius of the pump light matches the cavity mode. The electro-optic modulator acts as an active modulation loss, the electro-optic crystal is a BBO crystal, and the repetition rate of the electro-optic modulator is 1kHz. As a passive saturable absorber, GaAs is placed close to the flat output mirror M3 to obtain the minimum oscillating laser spot radius. The small signal transmittance of the GaAs saturable absorber is 92.6%. According to the parameters of the resonator, according to the ABCD matrix theory, the spot radius at the optimized GaAs saturated absorber is 128-135 microns. The threshold power of the laser is 0.9W-1W. Once the pump light exceeds the threshold power, a stable double Q-switched mode-locked laser can be obtained. The repetition rate of the Q-switched envelope is equal to the repetition rate of the electro-optical modulation 1kHz. The repetition rate of the mode-locked pulse depends on the cavity length and is 114MHz.
双调Q锁模激光调Q包络的脉冲宽度可用存储示波器测量，图3显示脉宽随泵浦功率的变化关系。图3表明，脉宽随泵浦功率的增加而变窄（随泵浦功率的增加，调Q包络的脉冲宽度减小）。因为调Q包络内相邻两锁模脉冲的时间间隔等于振荡激光在腔内往返的时间7ns,调Q包络的宽度决定了调Q包络内锁模脉冲振荡的个数。脉宽变窄意味着每个调Q包络内振荡的锁模脉冲个数减少。当调Q包络的宽度小于激光在腔内的往返时间时，每个调Q包络只有一个锁模脉冲振荡，锁模脉冲的重复率等于主动电光调制的1KHz重复率，脉冲宽度为亚纳秒级。在这种情况下，低重频、高稳定、亚纳秒锁模脉冲即可产生。图3中，当泵浦功率为4.65W时，调Q包络的脉冲宽度小于振荡激光在腔内往返的时间，每个调Q包络只有一个锁模脉冲，其重复率为1KHz，脉冲宽度为亚纳秒级，获得了低重复频率、亚纳秒、高稳定、锁模激光脉冲。The pulse width of the double Q-switched mode-locked laser Q-switched envelope can be measured with a storage oscilloscope. Figure 3 shows the relationship between the pulse width and the pump power. Figure 3 shows that the pulse width narrows as the pump power increases (the pulse width of the Q-switched envelope decreases as the pump power increases). Because the time interval between two adjacent mode-locked pulses in the Q-switched envelope is equal to the round-trip time of the oscillating laser 7ns in the cavity, the width of the Q-switched envelope determines the number of mode-locked pulse oscillations in the Q-switched envelope. The narrower pulse width means that the number of mode-locked pulses oscillating in each Q-modulated envelope is reduced. When the width of the Q-switched envelope is less than the round-trip time of the laser in the cavity, each Q-switched envelope has only one mode-locked pulse oscillation, the repetition rate of the mode-locked pulse is equal to the 1KHz repetition rate of active electro-optic modulation, and the pulse width is sub-nano second level. In this case, low repetition rate, high stability, sub-nanosecond mode-locked pulses can be generated. In Figure 3, when the pump power is 4.65W, the pulse width of the Q-switched envelope is less than the round-trip time of the oscillating laser in the cavity, and each Q-switched envelope has only one mode-locked pulse with a repetition rate of 1KHz and a pulse width of For the sub-nanosecond level, low repetition rate, sub-nanosecond, high stability, and mode-locked laser pulses were obtained.
图4显示了一个典型的调Q包络内锁模脉冲个数随泵浦功率的变化的示波器记录图。其中(a)的泵浦功率为2.75W，一个调Q包络内约有10个振荡的锁模脉冲；(b)的泵浦功率为4.03W，一个调Q包络内约有4个振荡的锁模脉冲，(c)和(d)的泵浦功率分别为4.65W、7.09W，每个调Q包络只有一个锁模脉冲运转。图4显示，当泵浦功率大于4.65W，能够实现单锁模激光运转（每个调Q包络只有一个锁模脉冲运转）。Figure 4 shows a typical oscilloscope recording of the number of mode-locked pulses in a typical Q-switched envelope as it varies with pump power. Among them, the pump power of (a) is 2.75W, and there are about 10 oscillating mode-locked pulses in a Q-switched envelope; the pump power of (b) is 4.03W, and there are about 4 oscillations in a Q-switched envelope The pump powers of (c) and (d) are 4.65W and 7.09W respectively, and only one mode-locked pulse operates for each Q-switched envelope. Figure 4 shows that when the pump power is greater than 4.65W, single mode-locked laser operation can be achieved (only one mode-locked pulse operation per Q-switched envelope).
图5显示图4中的四个泵浦功率锁模脉冲波形示波器记录图。其中，(a)的泵浦功率2.75W，(b)的泵浦功率4.03W，(c)的泵浦功率4.65W，(d)的泵浦功率7.09W。该图表明，锁模脉宽随泵浦功率的增加而变窄。当泵浦功率为7.09W时，锁模脉宽为580ps。Figure 5 shows the oscilloscope recordings of the four pump power mode-locked pulse waveforms in Figure 4. Among them, the pumping power of (a) is 2.75W, the pumping power of (b) is 4.03W, the pumping power of (c) is 4.65W, and the pumping power of (d) is 7.09W. The figure shows that the mode-locked pulse width narrows with increasing pump power. When the pump power is 7.09W, the mode-locked pulse width is 580ps.
图6显示了示波器记录的泵浦功率为7.09W亚纳秒锁模脉冲序列示意图，图6表明，脉冲的重复率为低重频1kHz，锁模脉冲的振幅高度稳定。Figure 6 shows a schematic diagram of the sub-nanosecond mode-locked pulse sequence recorded by an oscilloscope with a pump power of 7.09W. Figure 6 shows that the repetition rate of the pulse is low at 1kHz, and the amplitude of the mode-locked pulse is highly stable.
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