COL 11(4), 041408(2013) CHINESE OPTICS LETTERS April 10, 2013
Large-aperture end-pumped Nd:YAG thin-disk laser
directly cooled by liquid
Peilin Li (
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), Qiang Liu (
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, Xing Fu (
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Center for Photonics and Electronics, State Key Laboratory of Tribology, Department of Precision Instrument,
Tsinghua University, Beijing 100084, China
∗
Corresponding author: qiangliu@mail.tsinghua.edu.cn
Received October 25, 2012; accepted December 13, 2012; posted online March 28, 2013
A large-aperture Nd:YAG thin-disk laser directly cooled by liquid is end-pumped by two spatial self-
organized laser diode arrays. The pump coupling efficiency reaches as high as 93%. Without any complex
pump coupling components, the structure becomes simplified and compact. By optimizing the incident
angle of the pump beam, a pump power d ensity of 578 W/cm
2
is achieved with a pump uniformity of
5.52%. Up to 1 346-W peak output power with a slope efficiency of 54.9% is obtained when pumping with
a long pulse. The near-fi eld pattern of the laser output is uniform.
OCIS codes: 140.3480, 140.3580, 140.4780.
doi: 10.3788/COL201311.041408.
Recently, diode-pumped solid-state lasers (DPLs) have
attracted considerable attention because of their com-
pact structure, high efficiency, good beam quality, power
scalability, and good operation stability
[1−4]
. At present,
the thermal e ffects of laser gain medium restric t further
development of DPLs
[5−7]
. Solid laser gain medium gen-
erates heat when pumped by hig h-power diode lasers.
Thermal effects, such as thermally induced stress and
beam aberr ation, limit the output power and b e am qual-
ity of solid-state lasers , whereas extremely high thermal
intensity can cause the fracture of solid laser gain ma te-
rials. To reduce thermal effects, various configurations
of high-powe r solid-state lasers were prop osed and de-
veloped, such as heat capacity lasers
[8]
, slab lasers
[9]
,
and disk lasers
[10]
. In 2009 , Avizonis et al.
[11]
demon-
strated a 27 -kW output by combining 10 modules of a
Yb:YAG laser, in which disk-shaped gain medium was
cooled by a microchannel heat sink through one of the
flat surfaces. A thin-disk laser is an effective architec-
ture used to re duce thermal effects because of its lar ge
cooling surface and the short distance between the cool-
ing surface and the heat source. However, thermally
induced stres s and beam aberration still limit the output
power a nd beam quality of disk lasers. Controlling ther-
mal e ffects remains to be a very important task in disk
lasers. In 2008, a pa tent was granted to General Atom-
ics Corp. with the title “Laser containing a distributed
gain medium”. The patent comprised a scheme in which
coolant liquid that directly flows over the surfaces of
laser gain medium is proposed to achieve high cooling
efficiency
[12]
. In 2007, Textron Defense Inc. presented
a 27-kW output produced by a single laser module and
a 100-kW output from six laser modules by employing
Nd:YAG ceramic thin slab as gain medium and using
the scheme in which coolant liquid directly flows over
the slab s urfaces
[13]
. Based on the schemes used by
General Atomics Corp. and Textron Defense Inc., the
scheme in which coolant liquid directly flows over the
surfaces of laser gain medium has become an important
trend because it results in weakened thermal effects. In
this letter, a large-aperture end-pumped Nd:YAG thin-
disk laser directly cooled by liquid is demonstrated to
reduce the thermal effects of laser gain medium. A di-
rect pumping scheme that contains spatial self-organized
laser diode arrays (LDAs) is adopted without any opti-
cal coupling components, and good pump uniformity is
achieved together with high coupling efficiency. With-
out any optical coupling components, the ther mal effects
of high-power pump coupling components are avoided,
endowing the system with compact structure, high relia-
bility, and high stability.
The experimental setup of the large-aperture end-
pumped Nd:YAG thin-disk laser directly cooled by liquid
is depicted in Fig. 1. The laser gain medium is a 1.0-
at.-%-doped Nd:YAG disk. The dimension of the disk
is 50×30×5 (mm), with a large aperture (50×30 (mm))
for light passage. The disk is end- pumped from a single
side by two LDAs. The pump beam reaches the pump
surface of the dis k after pass ing through a 2-mm-thick
quartz window and a 2-mm-thick coolant water layer. A
coating (HR@1 064 nm, AR@808 nm) is depos ited on the
pump surface of the disk, which serves as the reflector
of the resonator , wherea s a plane output mirror (OC) of
40% transmission is positioned at a distance of 10 mm
from the disk surface.
The disk is directly pumped by two LDAs with an
emission area of 38×10 (mm). Each LDA, consisting of
20 laser diode bars, emits a peak output power of 2 500
W at a wavelength of approximately 80 8 nm at a coolant
Fig. 1. Experimental setup of large-aperture end-pumped
Nd:YAG thin-disk laser directly cooled by liquid.
1671-7694/2013/041408(4) 041408-1
c
2012 Chinese Optics Letters
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