Simultaneous operations at 1125 nm, 1161 nm, and
1567 nm from a single KTiOPO
4
crystal
pumped by a passively Q-switched Nd:GGG laser
Hongwei Chu, Shengzhi Zhao,* Kejian Yang, Yufei Li, Guiqiu Li, Dechun Li, Jia Zhao, Wenchao Qiao, and Tao Li
School of Information Science and Engineering, Shandong University, Jinan 250100, China
*Corresponding author: shengzhi_zhao@sdu.edu.cn
Received November 5, 2013; revised January 2, 2014; accepted January 2, 2014;
posted January 3, 2014 (Doc. ID 200609); published January 31, 2014
A multiwavelength operation generated from an intracavity optical parametric oscillator (OPO) pumped by a pas-
sively Q-switched Nd:GGG laser with a Cr
4
:YAG saturable absorber is demonstrated. KTiOPO
4
simultaneously
worked as nonlinear OPO and Raman crystal. Maximum output powers of 302 mW at 1566.8 nm and 115 mW
at 1124.9∕1160.7 nm were obtained at a diode power of 10.5 W, corresponding to the optical-to-optical conversion
efficiencies of 2.88% and 1.1%, respectively. The measured shortest pulse duration at 1566.8 nm was 1.61 ns, while
the obtained minimum pulse duration at 1124.9∕1160.7 nm was 2.88 ns. © 2014 Optical Society of America
OCIS codes: (190.4410) Nonlinear optics, parametric processes; (190.4970) Parametric oscillators and amplifiers;
(140.3550) Lasers, Raman; (140.3540) Lasers, Q-switched.
http://dx.doi.org/10.1364/OL.39.000723
Simultaneous multiwavelength operation has attracted a
lot of attention because of the applications in various
fields, such as differential spectroscopy, enviro nmental
monitoring, and nonlinear optics, especially in terahertz
(THz) generation [
1]. There are several approaches to
obtain multiwavelength operation. Among these ap-
proaches, the frequency conversion based on nonlinear
crystals has been verified to be an efficient way. Based on
second-order nonlinearity χ
2
[2] and third-order nonli-
nearity χ
3
[3], the multiple radiations have been realized.
Nowadays, the combination of χ
2
and χ
3
has become
an interested research field in the spotlight [
4–7].
KTiOPO
4
(KTP) crystal is a commonly used non-
linear medium for the effects arising from χ
2
nonlinear-
ity, such as second-harmonic generation (SHG),
sum-frequency mixing (SFM), difference frequency gen-
eration (DFG), and parametric amplification. The spon-
taneous Raman spectra of KTP crystal indicated also
that KTP could be used in a practical stimulated Raman
scattering (SRS) converter and the strongest Raman
scattering near 270 cm
−1
was observed [8]. By combining
the effects from χ
2
and χ
3
, Y. Chen once reported an
efficient second Stokes conversion with simultaneous
self-SFM and self-SHG in a single KTP crystal [
9]. In
addition, another combination of χ
2
and χ
3
, i.e., simul-
taneous OPO and SRS nonlinear processes from a
single nonlinear crystal, has raised increasing interests.
By using a periodically poled KTP (PPKTP) crystal,
Pasiskevicius et al. have demonstrated a simultaneous
optical parametric and Raman oscillation [
10]. Further-
more, coexistent Raman and parametric conversion for
the same fundamental wave has been realized. Using
KTiOAsO
4
a single KTA crystal, Liu et al. once reported
a dual-wavelength simultaneous oscillation at the first
Stokes line and the signal wavelength [
11]. Based on a
KTP crystal, a dual-wavelength operation at the first
Stokes radiation of 1096 nm and signal wave of 1572 nm
has been reported [
7].
In order to obtain the laser radiation in the eye-safe
region (∼1.5–1.6 μm), SRS nonlinear conversion is a
common approach [
12,13]. However, the obtained optical
efficiencies are low, and the required threshold pump
power intensities are very high [
13]. On the contrary,
OPO process pumped by a 1.06 μm laser is an attractive
way to access this spectral region with a high con version
efficiency [
14].
Actually, spectral wavelengths at the range from 1120
to 1160 nm have attracted a lot of attentions owing to the
capabilities to pump Tm-Ho-doped fiber lasers [
15] and
Raman lasers or amplifiers at 1178 nm [
16]. It is a poten-
tial technique to generate the corresponding pump
sources with high peak powers from the all-solid-state
laser systems. Because of the advantages of the KTP
crystal such as the high nonlinear coefficient and damage
threshold, it is attractive and expected to obtain the
diverse wavelengths at the second and the third SRS
radiations near 1120 and 1160 nm as well as the signal
wavelength around 1570 nm from a compact, simple
and efficient laser system.
In this Letter, based on the simultaneous OPO and SRS
processes, we demonstrate a multiwavelength operation
at 1124.9, 1160.7, and 1566.8 nm pumped by a passively
Q-switched Nd:GGG laser with Cr
4
:YAG saturable
absorber. A 5 mm × 5 mm × 20 mm KTP crystal is simul-
taneously employed as the OPO and Raman crystal. The
second Stokes wavelength at 1124.9 nm, the third Stokes
line at 1160.7 nm, and the signal wavelength of the intra-
cavity OPO at 1566.8 nm were obtained. Under the diode
power of 10.5 W, a maximum output power of 302 mW at
1566.8 nm, 115 mW at 1124 .9∕1160 .7 nm were achieved,
corresponding to the conversion efficiencies 2.88% and
1.1%, respectively. The shortest pulse durations for
OPO and SRS were 1.61 and 2.88 ns, respectively.
The experimental setup of the KTP intracavity OPO
and SRS conversions pumped by a passively Q-switched
Nd:GGG laser with Cr
4
:YAG saturable absorber is
shown in Fig.
1. The pump source was a fiber-coupled
laser-diode (FAP-I system, Coherent Inc., USA) with
central wavelength at 808 nm. The pump beam was
collimated and focused into the Nd:GGG crystal with
a spot of 400 μm in diameter by an optics system.
The Nd:GGG crystal (5 mm × 5 mm × 5 mm, 1 at.
February 1, 2014 / Vol. 39, No. 3 / OPTICS LETTERS 723
0146-9592/14/030723-04$15.00/0 © 2014 Optical Society of America
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