BaWO 4 Intracavity Pumped Eye-safe Raman Laser Karel Nejezchleb, Nickalai Kapitch, Václav Škoda a Crytur Ltd. Turnov, Czech Republic nejezchleb@crytur.cz Helena Jelínková, Lucia Koubíková, Jan Šulc b Faculty of Nuclear Sciences and Physical Engineering Czech Technical University in Prague Prague, Czech Republic Pavel Boháček c , Zdeněk Remeš c Institute of Physics Academy of Sciences of the Czech Republic Prague, Czech Republic Abstract— We present a compact Raman laser emitting short pulses with high energy in the wavelength region of 1.5 μm. We utilize intracavity conversion of giant pulses at the wavelength of 1.34 microns in a BaWO 4 Raman crystal. For pumping energy of 28 J, stable vertically polarized generation of the 1st Stokes radiation at 1528 nm was reached. The output energy of 9.7 mJ in 1.9 ns pulses was reached in single mode operation. Keywords— BaWO 4 Raman crystal, Nd:YAG Q-switched laser, V:YAG saturable absorber, eye safe wavelength. I. INTRODUCTION The fundamental wavelength of Nd:YAG can be shifted to “eye-safe” spectral region via stimulated Raman scattering. Because most of the Raman crystals have shift around 1000 cm -1 , cascading to second or third Stokes order is required to reach the “eye-safe” spectral region in vicinity of 1.5 m when pumping at the 1064 nm. In this case significant portion of pump power is lost to heat due to inelasticity of the Raman scattering [1]. It is therefore beneficial to use the 1.3 m transition in neodymium and utilize scattering only to the first Stokes order. We utilize an intracavity conversion of the 1.3 μm line of Nd:YAG laser in a BaWO 4 Raman crystal. BaWO 4 has a high Raman gain with the principal Stokes shift at 926 cm -1 , with a linewidth of 1.6 cm -1 [2]. II. MATHERIALS AND METHODS A. Laser experimental arrangement A flash-lamp pumped laser with a Nd:YAG rod 4 x 100 mm was used as a source for Raman conversion at wavelength of 1.34 m. The pump radiation oscillator consisted of a concave mirror M1 (r = 0.5 m, HR @ 1.34 μm, HT @ 1.06 μm), a flat polarizing intracavity mirror M2, and a concave mirror M4 (r = 1 m, HR @ 1.34 μm, R = 39 % @ 1.53 μm). The polarizing mirror, giving the resonator a characteristic “L” shape, ensured stable linearly polarized laser emission and prevented parasitic oscillations at 1.06 μm. The Q-switching was realized by V:YAG saturable absorber (T 0 = 37 % @ 1.34 m, AR coating @ 1.06/1.34/1.53 μm). Single mode operation was ensured by inserting of 1.5 mm aperture. Fig 1. Layout of the intracavity Raman laser of total length of 246 mm. B. BaWO 4 crystal and intracavity Raman laser BaWO 4 single crystal was grown along the a- axis using the Czochralski technique. Scattering centers in as grown BaWO 4 crystal boules were measured. AR coated BaWO 4 crystal (free of scattering centers, 18 mm long,) was used for the Raman laser oscillator, which was formed by an output coupler M4 (r = 1 m, HR@1.3 μm, R = 39 % @1.5 μm) and an intracavity mirror M3 (r = 0.5 m, HR @ 1.5 μm, HT @ 1.3 μm). III. RESULTS Vertically polarized output beam of the 1st Stokes radiation at 1528 nm with output energy of 9.7 mJ in 1.87 ns pulses was reached. The spatial beam profile was close to Gaussian structure. The generation was stable without surface damage to the BaWO 4 . IV. CONCLUSIONS A compact intracavity Raman laser generating at 1.5 m was demonstrated. With a Gaussian-like output beam profile the output energy was 9.7 mJ and the pulse duration 1.9 ns. Compactness and high energy in short pulses makes the laser suitable for a wide range of applications. REFERENCES [1] Takei, N., Suzuki, S., Kannari, F., “20-Hz operation of an eye-safe cascade Raman laser with a Ba(NO3)2 crystal”, Applied Physics B 74, 521-527 (2002). [2] Basiev, T. T., Sobol, A.A., Zverev, P.G., Ivleva, L.I., Osiko V.V. and Powell, R.C., “Raman spectroscopy of crystals for stimulated Raman scattering,” Optical Materials 11, 307-314 (1999). This research has been supported by the Grant of Czech Technological Agency TA03011141