Optics Communications 435 (2019) 81–87
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Optics Communications
journal homepage: www.elsevier.com/locate/optcom
Passively Q-switched laser based on Nd:YAG/YAG Polygonal Active Mirror
with timing jitter improvement
Ye Lang
a,b
, Yanzhong Chen
b,
∗
, Hongbo Zhang
b,c
, Jianguo Xin
d
, Wenqi Ge
b,c
, Lifen Liao
b,c
,
Zhongwei Fan
b,c,
∗
a
China Electronics Technology Group Corporation, No.3 Research Institute, Beijing 100015, China
b
Academy of Opto-Electronics, Chinese Academy of Science, Beijing, 100094, China
c
Harglo Applied Laser Technology Institute Co. Ltd., Tianjin, 300304, China
d
School of Information and Electronics, Beijing Institute of Technology, Beijing 100081, China
A R T I C L E I N F O
Keywords:
Solid state lasers
Q-switched lasers
Diode-pumped lasers
A B S T R A C T
We demonstrate a passively Q-switched laser based on Polygonal Active Mirror (PAM). Cr:YAG with different
initial transmittance were used as saturable absorber (SA). To improve the output timing jitter, an intracavity
aperture was used. Without the intracavity aperture, the maximum average output power of 726 mW was
obtained with SA initial transmittance of 98%, and the corresponding optical-to-optical efficiency was 23.3%.
With 92% initial transmittance SA, the maximum slope efficiency of 49.9% was obtained, and the maximum
single pulse energy was 132.8 uJ. By applying the intracavity aperture, the output beam quality and timing
jitter were improved. With 98% initial transmittance Cr:YAG SA, the beam quality (M
2
) was improved from
1.40×1.22 to 1.33×1.19 after applying the aperture, while timing jitter was improved from 18.4 μs(31.68%) to
4.8 μs(8.61%).
1. Introduction
Stable, high beam quality passively Q-switched (PQS) lasers with
high peak power are good laser sources for many applications, such as
ranging [1], pollution monitoring [2], laser ignition [3], and so on. Laser
diode (LD) pumped passively Q-switched lasers have the advantages
of, compactness, low cost and simplicity. Unlike active Q-switch such
as electro-optical (EO) or acousto-optical (AO) Q-switch, a passive Q-
switch usually does not need any external drive. The PQS laser based
on microchip scheme could achieve compact package with short cavity
length, which is preferred for short pulse width of several nanoseconds
or even picoseconds [2,4–8]. However, a significant disadvantage of
PQS lasers is the instability of their pulse repetition rate (PRR), which
resulting in timing jitter.
Nd:YAG/YAG polygonal active mirror (PAM) has been demonstrated
with good beam quality and high efficient laser operation, even without
using any active cooling configuration [9,10]. Due to the large mode size
inside the PAM gain medium, the thin-disk scheme of PAM allows easy
power scaling. But large mode size could be an obstacle to fundamental
transverse mode laser operation, resulting in multi-mode lasing and
degeneration of beam quality. What is worse, in PQS laser, multi-
mode oscillation usually exhibits large timing jitter and fluctuation on
peak power [11–13], which is undesirable for many applications. For
these reasons, the cavity must be carefully designed for fundamental
∗
Corresponding authors.
E-mail addresses: aoecyz@163.com (Y. Chen), fanzhongwei@aoe.ac.cn (Z. Fan).
transverse mode laser operation. Methods must be addressed to suppress
high order mode and improving the timing jitter in PQS laser.
In this paper, for the first time we report a PQS laser based on
PAM gain medium, with Cr:YAG as SA. Comparing with other saturable
absorber (SA), Cr:YAG crystal possesses several desirable features, as
good chemical and mechanical property, could be easily diffusion
bonded to YAG or Nd/Yb:YAG, etc. So Cr:YAG has been widely exploited
in both Nd-ions [14,15] and Yb-ions [16–18] lasers, and applied in
many compact passively Q-switched lasers [11,16,17]. The cavity was
carefully designed for effectively bleaching the SA. At the same time,
the cavity also meets the need of overlap between pump and laser mode
in gain medium, for fundamental laser operation. Employing different
initial transmittance (𝑇
0
) Cr:YAG SA in the cavity, the output pulse
properties were investigated, including pulse energy, PRR, pulse width
and timing jitter. With SA of 𝑇
0
= 98%, maximum output power of
726 mW was obtained under maximum absorbed pump power of 3.1
W, and the corresponding pulse width and single pulse energy were
221.8 ns and 17.93 kHz. The output laser pulse timing jitter under
maximum power operation was about 18.4 μs (31.68%). For the purpose
of improving the timing jitter, an intra-cavity aperture was used. With
SA of 𝑇
0
= 98%, the output beam quality (M
2
) was improved from 1.40
× 1.22 to 1.33 × 1.19, and timing jitter was improved from 18.4 μs
(31.68%) to 4.8 μs (8.61%). Two more experiments with different
https://doi.org/10.1016/j.optcom.2018.11.009
Received 25 May 2018; Received in revised form 2 November 2018; Accepted 5 November 2018
Available online 9 November 2018
0030-4018/© 2018 Elsevier B.V. All rights reserved.