百纳秒脉冲单频Er:YAG激光器：千兆赫兹下的高能创新

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"李尚桦等人展示了利用激光二极管泵浦的高能单频Er:YAG激光器，能够在200Hz、300Hz和500Hz的脉冲重复频率下分别获得28.6mJ、21.6mJ和15.0mJ的单频脉冲能量，这是目前Er:YAG增益介质所能达到的最高单频脉冲能量。采用环形腔设计，保持了数百纳秒的脉冲持续时间。" 本文报道了一项关于高能单频Er:YAG激光器的研究成果。Er:YAG激光器是一种掺铒钇铝石榴石激光器，其工作物质是Er:YAG晶体，其中Er（铒）作为激活离子，YAG（钇铝石榴石）作为基质材料。这种激光器的一个关键特性是其能在红外光谱区域内产生激光，特别是在1470纳米的波长，这个波长适合于激光二极管（LDs）进行泵浦。研究团队利用1470纳米的激光二极管作为泵浦源，成功地实现了高能单频脉冲的产生。在不同的脉冲重复频率下，激光器能够输出不同能量的脉冲：200Hz时能量为28.6mJ，300Hz时为21.6mJ，500Hz时为15.0mJ。这些数据表明，该激光器在保持高能输出的同时，还能维持良好的单频特性，这对于许多应用来说是非常重要的，例如精确的光学测量、医疗手术和激光加工等。采用环形腔设计是实现稳定单频激光输出的关键。环形腔可以提供更长的光路，从而增加激光在增益介质中的往返次数，这有助于减少频率漂移和多模竞争，从而确保激光的单频性。同时，这种设计还有助于控制脉冲持续时间，使其保持在数百纳秒，这在需要短脉宽但又需高能输出的应用中具有优势，例如激光打标、激光切割和医学治疗。此外，这项工作的创新点在于实现了迄今为止在Er:YAG激光器中最高的单频脉冲能量。这不仅提升了激光器的性能指标，也为未来更高功率、更高效率的单频Er:YAG激光器设计提供了参考和基础。这篇研究展示了激光技术在提高能量密度、优化脉冲特性和保持单频稳定性方面的进步，对于推动激光科学与技术的发展，尤其是在工业制造、医疗健康和科学研究等领域具有重要意义。

Laser diode pumped high-energy single-frequency Er:YAG

laser with hundreds of nanoseconds pulse duration

Shanghua Li (李尚桦)

1,2

, Qing Wang (王庆)

1,2,

*, Rui Song (宋睿)

1,2

Fangfang Hou (侯方方)

1,2

, Mingwei Gao (高明伟)

1,2

, and Chunqing Gao (高春清)

1,2

School of Optics and Photonics, Beijing Institute of Technology, Beijing 100081, China

Key Laboratory of Information Technology, Ministry of Industry and Information Technology,

Beijing Institute of Technology, Beijing 100081, China

*Corresponding author: qingwang@bit.edu.cn

Received October 27, 2019; accepted November 22, 2019; posted online February 18, 2020

We demonstrated a high-energy single-frequency erbium-doped yttrium aluminum garnet (Er:YAG) laser. With

1470 nm laser diodes (LDs) as pumping sources, single-frequency laser pulses with energy of 28.6 mJ, 21.6 mJ,

and 15.0 mJ are obtained at pulse repetition frequency of 200 Hz, 300 Hz, and 500 Hz, respectively. As far as we

know, this is the highest single-frequency pulse energy with the Er:YAG gain medium. With the ring cavity

design, pulse duration is maintained at hundreds of nanoseconds. This high-energy single-frequency laser with

hundreds of nanoseconds pulse duration is a prospective laser source for light detection and ranging applications.

Keywords: Er:YAG; injection-locking; single-frequency; high energy.

doi: 10.3788/COL202018.031401.

A single-frequency erbium-doped yttrium aluminum gar-

net (Er:YAG) laser operating at an eye-safe wavelength

has drawn much attention in various applications like

plastics processing, laser medicine, and wind measurement

light detection and ranging (Lidar)

[1–5]

. For coherent wind

measurement Lidar, range and radial velocity of aerosols

need to be measured at the same time. For long range de-

tection, a high-energy single-frequency laser is required ,

and for accurate radial velocity detection, single-frequency

laser pulses with longer pulse duration are required. So, in

coherent wind measurement Lidar systems, laser pulses

with duration of hundreds of nanoseconds are used

[6,7]

There are plenty of works on such a kind of single-fre-

quency laser system

[8–13]

. Most of the previous works on

a single-frequency pulsed laser are based on a single gain

medium, and the highest pulse energy with a single gain

medium at 1645 nm is 16 mJ, with a pulse repetition fre-

quency (PRF) of 250 Hz

[6]

For higher energy, a double gain-medium configuration

has been used in recent years

[14–17]

. Single-frequency laser

pulses with energies of 20.9 mJ

[15]

and 21 mJ

[16]

have been

obtained at a PRF of 200 Hz and 500 Hz, with pulse du-

ration of 110 ns and 93 ns, respectively.

These double gain-medium high-energy lasers produce

laser pulses with duration around 100 ns, while wind Lidar

application requires laser pulses with a duration of hun-

dreds of nanoseconds. Furthermore, for longer detection

range, a higher-energy laser pulse is needed and will lead

to shorter pulse duration, which will deteriorate the Lidar

performance.

Besides, these single-frequency Er:YAG la sers are com-

pletely or partially pumped by a 1532 nm fiber laser, with

an extra power transfer stage from a laser diode (LD) to an

Er,Yb co-doped fiber laser, resulting in lower electrical to

optical efficiency and a complicated system.

In this Letter, we demonstrate an LD pumped high-

energy single-frequency Er:YAG laser at 1645 nm, with

the pulse duration maintaining hundreds of nanoseconds.

For high-energy laser pulses generation, we compared the

common in-band pump source of a 1532 nm LD and

1470 nm LD theoretically. The analysis indicates that the

1470 nm LD outperforms the 1532 nm LD under high-

energy operation. By using two 1470 nm LDs as pump

sources and injection-locking technology, single-frequency

laser pulses with pulse energy of 28.6 mJ, 21.6 mJ, and

15.0 mJ are obtained at PRFs of 200 Hz, 300 Hz, and

500 Hz. The pulse duration is maintained at 159 ns, 191 ns,

and 263 ns, respectively, whi ch satisfies the requirement of

wind Lidar.

The center wavelengths of the in-band pump LD for the

Er:YAG system are 1470 nm and 1532 nm, respe ctively. A

simple model is used to compare the maximum upper-

state density under different pumping wavelengths

[18]

The definitions of the parameters used in this Letter

are listed in Table

Table 1. Definition of the Parameters

Item Definition

ΔN Inversion density

Pump transition upper-state Boltzmann factor

Pump transition lower-state Boltzmann factor

Upper-state population density

Lower-state population density

N Total dopant concentration

β Normalized upper-state density

COL 18(3), 031401(2020) CHINESE OPTICS LETTERS March 2020

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