High Power Laser Science and Engineering, (2018), Vol. 6, e18, 7 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.2018.20
High pulse energy fiber/solid-slab hybrid picosecond
pulse system for material processing on polycrystalline
diamonds
Wei Chen
1
, Bowen Liu
1
, Youjian Song
1
, Lu Chai
1
, Qianjin Cui
2
, Qingjing Liu
2
, Chingyue Wang
1
, and
Minglie Hu
1
1
Ultrafast Laser Laboratory, Key Laboratory of Opto-Electronic Information Technology, Ministry of Education, School of Precision
Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China
2
Laize Photonics Co., Ltd, Beijing 101399, China
(Received 30 December 2017; revised 23 January 2018; accepted 7 March 2018)
Abstract
We demonstrate an all polarization-maintaining (PM) fiber mode-locked laser seeded, hybrid fiber/solid-slab picosecond
pulse laser system which outputs 40 µJ, 10 ps pulses at the central wavelength of 1064 nm. The beam quality factors M
2
in the unstable and stable directions are 1.35 and 1.31, respectively. 15 µJ picosecond pulses at the central wavelength
of 355 nm are generated through third harmonic generation (THG) by using two LiB
3
O
5
(LBO) crystals, in order to get
better processing efficiency on polycrystalline diamonds. The high pulse energy and beam quality of these ultraviolet
(UV) picosecond pulses are confirmed by latter experiments of material processing on polycrystalline diamonds. This
scheme which combines the advantages of the all PM fiber mode-locked laser and the solid-slab amplifier enables
compact, robust and chirped pulse amplification-free amplification with high power picosecond pulses.
Keywords: all polarization-maintaining fiber; chirped pulse amplification free amplification; hybrid fiber/solid slab; material processing;
mode-locked laser
1. Introduction
High power, high repetition rate pulse lasers with near-
diffraction-limited beam quality have made significant con-
tributions in many applications such as X-ray generation
[1]
,
attosecond pulses generation
[2]
and material processing
[3–7]
.
In particular, the performance of material precise processing
varies largely due to different pulse durations. Generally,
with the decreasing of pulse duration, the material processing
results become better
[3]
. It can be explained that with the
ultrashort pulse duration (i.e., less than one picosecond),
laser pulse transfers almost all of its energy to the electrons,
rather than the atoms/lattice, and the pulse is shorter than
the time takes for the energy of the electronics to reach
equilibrium with the lattice, whereas the pulse machin-
ing by nanosecond or longer pulse laser may involve a
solid-state phase transformation, melting or evaporation of
the target due to thermal activation
[4]
. Although Q-switch
laser processing systems have achieved great successes for
their simple and stable schemes, the processing quality and
Correspondence to: M. Hu, Tianjin University, Tianjin 300072, China.
Email: huminglie@tju.edu.cn
scope of applications are limited, due to nanosecond pulse
durations
[4–7]
.
All polarization-maintaining (PM) fiber mode-locked
lasers have been confirmed as robust, compact and alignment-
free light sources with the output pulse duration of less than
10 ps
[8–13]
. Particularly, in most schemes of these kinds of
mode-locked lasers, the mode-locking is achieved by passive
mode-locked devices such as carbon nanotube (CNT) or
semiconductor saturable absorber mirror (SESAM), which
have simpler mode-locking mechanism than traditional
nonlinear polarization rotation (NLPR) mode-locked lasers.
On the other hand, due to the fact that lights are always
trapped in the PM fiber without any free space optical
devices, these structures are less sensitive to external
temperature and stress perturbations. As a result, this kind
of mode-locked laser shows much more robustness and less
output states, compared to traditional NLPR mode-locked
lasers, which is an ideal alternative to Q-switch laser in
material processing applications.
Another problem is how to amplify the seed pulse up to de-
sired output pulse energies. Unlike the regenerative amplifier
scheme which is hard to stay stable at high repetition rate
[14]
,
1