激光二极管抽运的Nd:YAG主振荡器功率放大器

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"Laser-diode-pumped zigzag slab Nd:YAG master oscillator power amplifier" 这篇研究报道了一种采用激光二极管（LDs）泵浦的高重复频率种子振荡器功率放大器。该系统的核心是电光Q开关的单频注入种子Nd:YAG激光器，它作为振荡器，而作为功率放大器的是一块导热冷却的Nd:YAG锯齿形晶片，采用了反弹泵浦架构。实验结果显示，该系统在1064纳米波长处实现了超过800毫焦耳的脉冲能量，在532纳米波长处达到400毫焦耳，对应的平均功率分别为200瓦和100瓦，脉冲宽度为12.6纳秒，工作频率为250赫兹。在激光技术中，种子振荡器是产生激光的第一步，它提供了初始的、低能量但高质量的激光脉冲。这里采用的电光Q开关是一种常见的调制手段，通过改变介质的光谱透过率来控制激光的输出。单频操作确保了激光的光束质量，减少了光束的色散和模式竞争，这对于需要稳定且一致输出的激光应用至关重要。激光二极管泵浦是现代固体激光器中的常见方法，因为它具有高效、紧凑和成本效益高的优点。在这个系统中，激光二极管用于激发Nd:YAG晶体内的稀土离子 Nd3+，使其处于激发状态并释放出激光。Nd:YAG（掺钕钇铝石榴石）是一种广泛使用的激光材料，因其优良的热性能和高光学效率而受到青睐。锯齿形（zigzag）晶片设计是为了优化激光增益介质的利用率和热管理。这种结构允许激光在晶体内部多次反射，增加了光子与激活离子的相互作用，从而提高放大效率。同时，导热冷却方式能有效地散发由激光产生的热量，防止热透镜效应和晶体损伤，确保系统的长期稳定运行。反弹泵浦架构是另一种优化设计，它使激光二极管的泵浦光在晶片内部多次通过，进一步提高了泵浦效率。这种方法还能减少对大尺寸激光晶片的需求，因为泵浦光可以在较短的路径长度内多次与激活离子交互。这个激光系统展示了高功率、高重复频率的性能，对于工业加工、激光雷达、医学应用以及科学研究等领域具有重要意义。通过优化激光器的设计和泵浦策略，研究人员能够实现高能量、高平均功率的激光输出，这对于提升激光技术的应用范围和性能有着重要的贡献。

COL 11(7), 071402(2013) CHINESE OPTICS LETTERS July 10, 2013

Laser-diode-pumped zigzag slab Nd:YAG master

oscillator power amplifier

Shiguang Li (

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, Xiuhua Ma (

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, Huanhuan Li (

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, Feng Li (

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Xiaolei Zhu (

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, and Weibiao Chen (

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Shanghai Key Laboratory of All Solid-State Laser and Applied Techniques,

Research Center of Space Laser Information Technology, Shanghai Institute of Optics and Fine Mechanics,

Chinese Academy of Sciences, Shanghai 201800, China

University of Chinese Academy of Sciences, Beijing 100049, China

∗

Corresponding author: maxiuhua@gmail.com

Received April 9, 2013; accepted May 13, 2013; posted online July 3, 2013

A high-repetition rate master oscillator power amplifier pumped with laser diodes (LDs) is reported. An

injection seeding single-frequency electro-optical Q-switched Nd:YAG laser is used as an oscillator, and

a conductively cooled Nd:YAG zigzag slab with a bounce- pumped architecture is utilized as a power

amplifier. Pulse energies of over 800 mJ at 1 064 nm and 400 mJ at 532 nm, corresponding to average

powers of 200 and 100 W, respectively, are achieved with a 12.6-ns pu lse width at 250 Hz. Output frequency

ﬂuctuations and single-frequency operation are further monitored. Experimental results reveal that the

proposed system, which features a single-pass amplified configuration, is a promising design for space-

based applications.

OCIS codes: 140.3280, 140.3480, 140.3515, 140.3570.

doi: 10.3788/COL201311.071402.

Conductively cooled zigzag sla bs have been the basis for

laser transmitters used in spac e -based lidar sy stems

[1−3]

Oscillator/amplifier configurations with robust designs,

long-term usability, and almost-maintenance-free o pera-

tion are generally favorablefor ﬂight-wo rthy and space-

qualified lasers

[4,5]

. However, thermal issues, such as

depolarization and aberrations, hindering in the high-

power operation of a solid-state amplifier system. Pre-

vious studies have developed a laser diode (LD)-pumped

solid-state laser with average powers of tens o f watts

[6]

corresponding to 750-mJ pulse energiesat 1 064 nm and

diﬀraction-limited output beams with co mparative pulse

energiesbased on a master oscillator power a mplifier

(MOPA)

[7]

by thermally induced phase distortion of the

gain medium. Average output powers of 235

[8]

and 250

[9]

at pulse repetition frequency (PRF) of 320 and 200

Hz, respec tively, have been obta ined. Although laser

systems with diamond-tur ned aspheric optics

[7]

, phase-

conjugated mirrors

[8]

, and angle-multiplexed ring-type

double-pass configurations

[9]

show excellent performance

in the correction of wavefronts and generation of good

beam quality with high single-pulse energies, such de-

signs add complexity and volume to prototype systems

and increase the difficulty of assembly and calibration.

Several components in such systems

[10]

may also inﬂu-

ence all qualific ation testing procedures, including opti-

cal damage and extended lifetime tes ting, in a complex

environment. Compared with conventional rod lasers,

zigzag slab lasers

[1,2,11,12]

have a rectilinear geometry

that reduces stress-induced birefringence a nd an optical

path that minimizes thermal- and stress-induced focus-

ing. Thus, zigzag slab lasers are suitable for achiev-

ing high average power levels while maintaining good

beam quality and po larization contrast. However, slab

lasers, especially side-pumped slab lasers, have low laser

efficiency, which limits their applications.

Several studies have considered fac e pumping as an

ideal slab design. Face pumping uses the same in-

terface for pumping and cooling, in which the slab

is uniformly heated throughout its volume and uni-

formly cooled through two total-internal-reﬂection (TIR)

faces

[13]

. However, face-pumped designs typically require

direct liquid cooling to satisfy the requirements of uni-

form pumping and cooling of both faces

[14,15]

. Direct liq-

uid cooling often damages the slab laser design because it

induces slab degradation and the cooling ﬂuid contami-

nates the s lab. Improvement of thermal handling requires

the reduction of slab thickness, which, in turn, reduces

the pump absorption depth in a face-pumped geometry.

The edge-pumpe d slab design

[11]

permits symmetric con-

duction cooling and efficient pump absorption and ac-

cepts large numerical aperture pump sources. Alarge as-

pect ratio (3:1) reduces the r obustness of the slab and

increases stress, resulting in crystal damage. Conduc-

tion coo ling

[16]

features benefits of mechanical stability,

protection of the TIR faces, cooling uniformity, and sep-

aration of the slab-liquid interface. However, the asym-

metries of cooling schemes cause thermal stresses in the

crystals that limit their powe r-scaling potential. The

symmetric cooling of edge-pumped slab lasers provides

a design that can be scaled to high-power levels.

A MOPA with a PRF of 100 Hz and an output en-

ergy of 800 mJ was previously investigated

[12]

. Given

that the signal-to-nois e ratio (SNR) of lidar systems is

proportional to the square root of the PRF of the laser

transmitters under certain single-pulse energ ies, higher

PRFs enable longer detection ranges and higher detec-

tion accuracy. Therefore, the PRF of lase r transmitters

must be increased. We recently success fully developed an

injection-seeded single-frequency 1 064-nm laser oscilla-

tor with a 250-Hz PRF

[17]

and high power using a highly

efficient conduction cooling technique

[18]

. In the current

1671-7694/2013/071402(4) 071402-1

 2013 Chinese Optics Letters

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