STEADY STATE MODE-LOCKING OF Nd:YVO 4 LASERS OPERATING ON THE 1.34 µm TRANSITION Hristo Iliev 1 ,Valentin Petrov 2 and Ivan Buchvarov 1* 1 Department of Physics, Sofia University, 5 James Bourchier Blvd., BG-1164 Sofia, Bulgaria 2 Max-Born-Institute for Nonlinear Optics and Ultrafast Spectroscopy, 2A Max-Born-Str., Berlin, Germany *Corresponding author: ivan.buchvarov@phys.uni-sofia.bg Passive mode-locking of Nd-lasers operating on the 4 F 3/2 → 4 I 13/2 transition around 1.34 μm has been demonstrated using either saturable absorbers [1,2] or intracavity frequency doubling [3]. Currently saturable absorbers at 1.34 μm are mostly based on semiconductor saturable absorber mirrors (SESAMs) [1] or single-walled carbon nanotubes (SWCNT) [2]. The SWCNT technique is a promising approach but it is under development and still not appropriate for multi-Watt operation. Although SESAMs are widely used for passive mode- locking around 1 µm, their fabrication for longer wavelengths is much more difficult and shows relatively high residual absorption and nonsaturable losses which limits the laser output power. Average output powers ~1 W were demonstrated only recently [1] using AlGaInAs based SESAM, but the obtained pulse duration from this Nd:YVO 4 laser is relatively long, 26.4 ps. The intracavity frequency-doubling technique based on type-I SHG provides two different types of passive mode-locking mechanisms: The first one is amplitude modulation based on the intensity dependent reflectivity of the frequency-doubling nonlinear mirror (FDNLM) and the second one is phase modulation based on χ (2) -nonlinear phase shift of the fundamental wave, i.e. χ (2) -lens mode-locking. The same technique has been previously demonstrated on Nd-lasers emitting at 1.06 μm [3]. It is not only practically free of spectral limitation but also enables easier power scaling to the multi-Watt level and in contrast to the Kerr-lens mode-locking and in addition is easily applicable to narrow bandwidth laser materials such as Nd-doped crystals. In this work we present our experimental results on passive mode-locking of Nd:YVO4 lasers operating at 1.34 μm using birefringent or periodically poled SHG nonlinear crystals. Bismuth triborate BiB 3 O 6 (BIBO) has been proposed as a promising SHG material for this application. Using 7-mm-long BiB 3 O 6 nonlinear crystal an average output power of 0.9 W was achieved. The measured FWHM of the autocorrelation trace (5.7 ps) corresponds to pulse duration of 3.7 ps assuming sech 2 pulse shape. Similar performance has been observed when 20-mm-long and 1-mm-thick periodically-poled Mg-doped stoichiometric lithium tantalate (PPMgSLT) was used for intracavity SHG. The maximum average output power reached 0.8 W and the pulse durations were ~3.6 ps. In both cases the pulse repetition rate was ~120 MHz. In comparison to previously reported results [1], for the first time high average power and short pulse durations are simultaneously available from a passively mode-locked 1.34-μm diode pumped laser source. Acknowledgements: We acknowledge financial support under grant D02-134/2009 of the Bulgarian Ministry of Education, Youth and Science and by DAAD (Germany) #50448357. References: 1. S. L. Huang, H. L. Cheng, Y.-F. Chen, K. W. Su, Y. F. Chen, and K. F. Huang, Opt. Lett. 34, 2348-2350 (2009). 2. S. V. Garnov, S. A. Solokhin, E. D. Obraztsova, A. S. Lobach, P. A. Obraztsov, A. I. Chernov, V. V. Bukin, A. A. Sirotkin, Y. D. Zagumennyi, Y. D. Zavartsev, S. A. Kutovoi, and I. A. Shcherbakov, Laser Phys. Lett. 4, 648 (2007) 3. H. Iliev, I. Buchvarov, S. Kurimura, V. Petrov, Europhoton 2010, Hamburg, Germany, Aug. 29 - Sep. 3, 2010, paper TuP23, Europhysics Conference Abstract Volume 34C.