2005 Conference on Lasers and Electro-Optics Europe

200mW yellow laser based ona diode-pumped Nd3+: KGd(WO4)2 Raman resonator

Akihide Hamano" , Masahito Okida2 and Takashige Omatsu3

'Furukmava Co.,Ltd., AMaterials Research Laboratory,1-25-13, Kannondai, Tsukuba, 305-0856, Japan

2lnstitute ofApplied Physics, University of Tsukuba,1-1-1, Tennodai, Tsukuba, 305-8573, Japan

3Department ofInformation and Image science, Chiba University,1-33, Yayoi-cho, Inage-ku, Chiba, 263-0022, Japan

omatsufifaculty.chiba-ujp

Sub-watt compact solid-state yellow lasers have been an intense subject for applications including environmentalmonitoring, and laser therapy, etc.. Stimulated Raman scattering technology can extend efficiently a laser frequency invisible and infrared regions [1]. Thus, frequency doubling of the Raman radiation from Ijgm lasers is one solution togenerate efficient yellow radiation.A Nd doped KGd(WO4)2 (Nd:KGW) crystal is a promising candidate for compact Raman lasers, because it exhibits

attractive features such as high stimulated emission cross-section as well as a high Raman gain [2].In this paper, we report 0.2 W yellow output from a transversely diode-pumped self-stimulating Nd:KGW Raman

laser. The optical efficiency from the diode to yellow output was 3.3 %. This value is the highest, to the best of ourknowledge, obtained by diode-pumped, self-stimulating Raman lasers.A 5.0 at.% Nd doped KGW crystal used had dimensions 2 x 1 x 25 mm3. Two 2 x 1 mm2 end-faces were AR-coated

for 1067 nm, a 2 x 25 mm2 facet was AR-coated for pumping at 810 nm, and another 2 x 25 mm2 facet was 810 nmHR-coated for the pump being retro-reflected to the crystal. The crystal coating combined with fairly-high Nd dopingresulted in the highly efficient pumping. The crystal was transversely pumped by a 300 W quasi-continuous-wave(QCW) diode bar with pulse duration of 20 1ts at a pulse repetition frequency of 2 kHz. The diode output was directlydelivered to the crystal pump face as an area of 0.9 mm x 10 mm. The cavity arrangement was a piano-concaveresonator with a flat output mirror and 0.15 m curvature end mirror. The output mirror had high reflectivity (HR) for1067 nm and 20 % transmission for first Stokes radiation of 1181 nm. The end mirror had high reflectivity (HR) for1067 nm and 1181 nm. An acousto-optic modulator was used for Q-switched operation. Extra-cavity second harmonicgeneration was performed by focusing the Ramanoutput into a LiB305 (LBO) crystal. The crystal withdimensions of 3 x 3 x 15 mm3 was used for non-critical type I phase matching at room temperature.The crystal faces were anti-reflection coated for 591nm, 1067 nm, and 1181 nm. The crystal temperaturewas maintained at 20 'C with a thermoelectric cooler.A maximum Raman output power of 0.8 W was

measured at the pump power of 5.6 W. The slopeefficiency and threshold were 19 % and 1.4 W,respectively. The maximum yellow output reached upto 0.2 W, and then, the optical efficiency from thepump power to yellow output was 3.3 %. This is thehighest value, to the best of our knowledge, obtainedby diode-pumped, self-stimulating Raman lasers.

The results are summarized in Fig. 1. Furtherimprovements in power scaling of yellow output areexpected by intra-cavity second harmonic generation.

0

0~4_

a)3

1.2 * Funiamental0 Raian

1.0 * Yellow U

0.8 0

0.6-

0.4 *

0.2- * AA A

US ~~~AA A0.0- , .-I*.-

0 1 2 3 4 5 6

Pump power (V)

Fig. 1 Output power of fundamental, Raman and the yellow lasers

References[1] R.P.Mildren, M.Convey, H.M.Pask, J.A.Piper and T.Mckay, Opt.Exp.12, (2004) 785.[2] T.Omatsu, Y.Ojima, H.M.Pask, J.A.Piper, P.Dekker, Opt.Commun 232, (2004) 327.

0-7803-8974-3105l$20.00 ©2005 IEEE 61