High Power Laser Science and Engineering, (2018), Vol. 6, e58, 9 pages.
© The Author(s) 2018. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/
licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
doi:10.1017/hpl.2018.52
Design and experimental demonstration of a high
conversion efficiency OPCPA pre-amplifier for petawatt
laser facility
Xiao Liang
1,2
, Xinglong Xie
1
, Jun Kang
1
, Qingwei Yang
1
, Hui Wei
1
, Meizhi Sun
1
, and Jianqiang Zhu
1
1
National Laboratory on High Power Laser and Physics, Shanghai Institute of Optics and Fine Mechanics,
Chinese Academy of Sciences, Shanghai 201800, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
(Received 12 July 2018; revised 3 September 2018; accepted 28 September 2018)
Abstract
We present the design and experiment of a broadband optical parametric chirped-pulse amplifier (OPCPA) which
provides high conversion efficiency and good beam quality at 808 nm wavelength. Using a three-dimensional spatial
and temporal numerical model, several design considerations necessary to achieve high conversion efficiency, good
beam quality and good output stability are discussed. To improve the conversion efficiency and broaden the amplified
signal bandwidth simultaneously, the nonlinear crystal length and OPCPA parameters are analyzed and optimized with
the concept of dissipating amplified idler between optical parametric amplification (OPA) of two crystals configuration.
In the experiment, an amplifier consisting of two OPCPA stages of ‘L’ type configuration was demonstrated by using
the optimized parameters. An amplified signal energy of 160 mJ was achieved with a total pump-to-signal efficiency of
35% (43% efficiency for the OPCPA stage 2). The output bandwidth of signal pulse reached 80 nm and the signal pulse
was compressed to 24 fs. The energy stability reached 1.67% RMS at 3% pump energy variation. The optimized OPCPA
amplifier operates at a repetition rate of 1 Hz and is used as a front-end injection for the main amplifier of SG-II 5PW
laser facility.
Keywords: BBO; nonlinear optics; optical parametric chirped-pulse amplifier; petawatt laser
1. Introduction
Optical parametric chirped-pulse amplification (OPCPA) has
been a popular technique to amplify a broadband optical
pulse in recent years
[1, 2]
. This is mainly due to some
important advantages of OPCPA. Most notably, for different
wavelengths, from visible to infrared, OPCPA can support
wide gain bandwidth by choosing appropriate nonlinear
crystals and satisfying its phase-matching conditions. Mean-
while, OPCPA provides a high gain in a relatively short
path length, which can minimize the B-integral and reduce
spatial aberration caused by thermal loading effects
[3, 4]
. In
the front-end parts of large high-intensity ultrashort pulse
laser systems, many prominent works have been done with
OPCPA. Picosecond or even femtosecond pumped OPCPA
can deliver a sufficiently broad spectrum and greatly improve
the pulse contrast
[5–8]
. Diode pumped laser or thin disk laser
Correspondence to: J. Zhu and M. Sun, No. 390 Qinghe Road, Jiading
District, Shanghai 201800, China. Email: jqzhu@siom.ac.cn (J. Zhu);
eric913@siom.ac.cn (M. Sun).
pumped OPCPA has been successfully demonstrated at a
variety of repetition rates
[9–11]
.
Before the main amplifier of a petawatt level laser, a
pre-amplifier is required to provide signal pulses of tens to
hundreds millijoules of energy. Many articles have reported
OPCPA amplifier at different wavelengths based on different
crystals, and the output energy is from millijoules to sub-
joule level
[12–14]
. Maximizing the pulse energy from a
broadband pre-amplifier reduces the total gain narrowing
in the system and yields the shortest available transform-
limited compressed pulses. Carefully designed signal and
pump spatial–temporal profiles and the properly set ratio
of pump and seed pulse durations are naturally beneficial
to the conversion efficiency and bandwidth and simultane-
ously suppress the super-fluorescence
[15, 16]
. However, the
conversion efficiency cannot easily increase to over 40%
in the traditional OPCPA amplifier of one crystal scheme.
The gain bandwidth narrowing and back conversion effect
caused by phase mismatching of the pump and signal are the
crucial obstacle to improve conversion efficiency further. To
inhibit these effects, Ma et al. used a Sm
3+
-doped yttrium
1