High-power 880-nm diode-directly-pumped passively ... a semiconductor saturable absorber mirror

High-power880-nm diode-directly-pumped passively mode-locked Nd:YVO4laser at1342nm with a semiconductor saturable absorber mirror Fang-Qin Li,1,2,4Ke Liu,1Lin Han,1Nan Zong,1Yong Bo,1Jing-Yuan Zhang,1,3

Qin-Jun Peng,1,*Da-Fu Cui,1and Zu-Yan Xu1

1Research Center of Laser Physics and Technology,Key Laboratory of Functional Crystal

and Laser Technology,Technical Institute of Physics and Chemistry,

Chinese Academy of Sciences,Beijing100190,China

2Key Laboratory of Optical Physics,Institute of Physics,Chinese Academy of Sciences,Beijing100190,China 3Department of Physics,Georgia Southern University,Statesboro,Georgia30460,USA

4Graduate School of the Chinese Academy of Sciences,Beijing100190,China

*Corresponding author:pengqinjun@http://www.wendangwang.com

Received October27,2010;revised March14,2011;accepted March14,2011;

posted March15,2011(Doc.ID137263);published April15,2011

A high-power880-nm diode-directly-pumped passively mode-locked1342nm Nd:YVO4laser was demonstrated

with a semiconductor saturable absorber mirror(SESAM).The laser mode radii in the laser crystal and on the SE-SAM were optimized carefully using the ABCD matrix formalism.An average output power of2:3W was obtained with a repetition rate of76MHz and a pulse width of29:2ps under an absorbed pump power of12:1W,corresponding to an optical-optical efficiency of19.0%and a slope efficiency of23.9%,respectively.©2011Optical Society of America

OCIS codes:140.3480,140.3580,140.4050.

Light sources at1:3μm are required in many fields such

as telecommunications,remote sensing,micromachin-

ing,and data http://www.wendangwang.comser emission at1:3μm can be

obtained from fiber lasers[1],vertical-cavity surface-emitting lasers[2],diode-pumped solid-state lasers[3],

and so on.Because of the high potentiality,numerous

Nd-doped crystals have been employed to generate 1:3μm lasers at CW[4]or pulsed operation[5].For mode-locked operation at this wavelength,the neodymium-

doped vanadate Nd:YVO4crystal is favorable due to its

large stimulated cross section(6×10−19cm2)[6–8].How-ever,because of its weak thermal conductivity,the out-put power of the Nd:YVO4laser is usually limited by the thermal effects in the laser crystal.One effective method to solve this problem is to use the direct pumping,which has been widely used in1064nm lasers[9],since the di-rect pumping scheme leads to a reduced quantum defect ratio between the laser and the pump wavelengths. Recently,1342nm lasers have been reported for CW and Q-switched operation under880or888nm diode di-rect pumping[10,11].Passively CW mode-locked lasers using semiconductor saturable absorber mirrors (SESAMs)attract more interests for their inherent simpli-city,low cost,and compactness.There are enormous in-vestigations on mode-locked lasers with SESAMs at1μm [12,13].But because of the lack of proper saturable ab-sorbers for CW mode locking at1:34μm,the SESAM-based mode-locked lasers at this wavelength are seldom reported[14,15].Some Nd:YVO4oscillators generated CW mode-locked pulses at1:34μm by use of intracavity semiconductor saturable absorbers[16,17].The maxi-mum output power for1:34μm CW mode-locked lasers with SESAMs or intracavity semiconductor saturable ab-sorbers is1:05W at present[17].The major obstacle that prevents it from producing a higher output is presumably due to thermal effects by using808nm pumping.

In this Letter,we demonstrated an880-nm diode-directly-pumped passively mode-locked Nd:YVO4laser

at1342nm with a SESAM.The laser mode radii in Nd:YVO4crystal and on the SESAM were carefully de-signed to achieve good mode matching between the laser

and the pump light in the crystal for good laser beam quality and to avoid damage of the SESAM.At an ab-sorbed pump power of12:1W,a maximum mode-locked

power of2:3W was obtained with a repetition rate of 76MHz and a pulse width of29:2ps.This output corre-sponds to an optical–optical efficiency of19.0%and a slope efficiency of23.9%,respectively.

The experimental setup is illustrated in Fig.1.An a-cut Nd:YVO4crystal with a Nd concentration of0:25at:%and dimensions of3mm×3mm×8mm was used as the gain medium.Both end faces of the laser crystal were antire-flection coated at1342,880,and1064nm,and the crystal was single-end-wedged at2°to suppress potential Fabry–Perot etalon effect.The laser crystal was wrapped with indium foil and mounted in a water-cooled copper heat sink,and the water temperature was maintained at19°C. To reduce thermal effects in the laser crystal,an880nm fiber-coupled laser diode(DILAS)was used as the pump source.The fiber had a core diameter of400μm and

High-power 880-nm diode-directly-pumped passively ... a semiconductor saturable absorber mirror

a

Fig. 1.Experimental setup for the diode-directly-pumped passively mode-locked Nd:YVO4laser at1342nm.

April15,2011/Vol.36,No.8/OPTICS LETTERS1485

0146-9592/11/081485-03$15.00/0©2011Optical Society of America

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