Appl Phys B (2011) 103: 83–88
DOI 10.1007/s00340-010-4303-4
A 200 W diode-side-pumped CW 2 μm Tm:YAG laser with water
cooling at 8°C
D. Cao · Q. Peng · S. Du · J. Xu · Y. Guo · J. Yang ·
Y. Bo · J. Zhang · D. Cui · Z. Xu
Received: 30 May 2010 / Revised version: 12 October 2010 / Published online: 20 November 2010
© Springer-Verlag 2010
Abstract A water-cooled 785 nm diode-side-pumped high-
power CW Tm:YAG laser system at 2 μm is reported. 200 W
output power is achieved with cooling water running at 8°C.
As far as we know, this is the highest output power for a
diode-pumped all solid-state 2 μm Tm:YAG laser. The out-
put corresponds to optical-to-optical conversion efficiency
of 11.2%, with a slope efficiency of about 22.8%. To make
the system structure simple, only deionized water is used as
the coolant instead of alcohol- or glycol-water mixture or
the liquid nitrogen in the reported high-power Tm rod laser
experiments, which were performed at low temperature near
the freezing point of water, or even below.
1 Introduction
In recent years, a lot of efforts have been made on 2 μm
laser systems for applications in many fields, such as med-
ical surgery, remote sensing, high speed detection, optical
communications and effective pump sources for 3 ∼ 5 μm
optical parametric oscillators (OPOs), and so on [1–5].
D. Cao · Q. Peng ( ) · S. Du · J. Xu · Y. Guo · J. Yang · Y. Bo ·
D. Cui · Z. Xu
RCLPT, Key Lab of Functional Crystal and Laser Technology,
Technical Institute of Physics and Chemistry, Chinese Academy
of Sciences, Beijing 100190, China
e-mail: pengqinjun@163.com
D. Cao · J. Yang
Graduate School of the Chinese Academy of Sciences,
Beijing 100190, China
J. Zhang
Department of Physics, Georgia Southern University, Statesboro,
GA 30460, USA
There are two main methods to realize 2 μm lasers. One
is the optical parametric method in nonlinear optical crys-
tals pumped by a near IR laser at ∼1 μm laser. Wu et al.
[6] obtained 21.4 W output at 2 μm with a pair of KTP
crystals, which are diffusion bonded together in a walk-off-
compensated configuration. The important advantage of op-
tical parametric method is that it is easier to achieve wave-
length tuning. However, limited by the nonlinear optical
crystals dimension and damage threshold, a very high level
laser output power at 2 μm is difficult to reach. So far as we
know, no output higher than 100 W has ever been reported.
Another way to achieve a high-power 2 μm laser is by means
of rare-earth ion (mostly Tm
3+
and Ho
3+
) doped crystals.
The use of these Tm- or Ho-doped materials might result in
eye safety, high reliability, long lifetime, high overall elec-
trical efficiency, etc. [3]. By far the most investigated mate-
rials are oxides (specifically garnets) [4, 5, 7–10] and fluo-
rides [1, 11–13], among which Y
3
Al
5
O
12
(YAG) and LiYF
4
(YLF) are the most popular. However, oxide crystals have
better thermomechanical properties than fluorides [14], and
this difference deserves more attention from those who pur-
suit high-power output at ∼2 μm. These differences mean
that YAG can withstand more heat, which is inevitable in
a high-power laser system. Moreover, garnets are usually
chemically stable and mechanically hard, which makes ma-
chining and optical polishing easier than fluorides. Besides,
the garnets are isotropic, making the growth and preparation
of the samples simpler than the anisotropic ones. The latter
two features make it possible to manufacture the YAG crys-
tals with high optical quality and large dimension, which is a
great advantage for achieving high-power output. In respect
of doping ions, Tm
3+
possesses an advantage over Ho
3+
, in
that it can be directly pumped by the commercial 785 nm
or 808 nm high-power diode arrays, while Ho
3+
can only
be pumped by another 2 μm band light (usually Tm laser