Stable, 17.5 W, Optimally-output-coupled, Yb-fiber-pumped Mid-infrared Optical Parametric Oscillator S. Chaitanya Kumar 1,* , Ritwick Das 1 , G. K. Samanta 1 and M. Ebrahim-Zadeh 1, 2 1 ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels, Barcelona, Spain 2 Institucio Catalana de Recerca i Estudis Avancats, Passeig Lluis Companys 23, Barcelona 08010, Spain E-mail: chaitanya.suddapalli@icfo.es Abstract: We report stable, continuous-wave, mid-infrared optical-parametric-oscillator based on MgO:PPLN, pumped by Yb-fiber-laser, generating total power of 17.5W at 61% extraction efficiency, in TEM 00 (M 2 Idler <1.24,M 2 Signal <1.24) spatial mode with peak-peak idler power stability of 5% over 14 hours. © 2010 Optical Society of America OCIS codes: 190.4970, 190.4360. High-power, continuous-wave (cw) mid-infrared optical parametric oscillators (OPOs) are unique sources of interest for variety of applications including photoacoustic spectroscopy and trace gas analysis, requiring wide tunability and narrow linewidth [1]. Such sources are also promising as first-stage pumps for cw OPOs in tandem, spanning the spectral coverage of these devices beyond the current practical limit of ~4 μm imposed by the onset of absorption of oxide-based nonlinear crystals. Singly-resonant OPOs (SROs) represent the most viable configuration for such applications, and using the widely established periodically-poled LiNbO 3 (PPLN), such devices have been extensively demonstrated previously. However, the generation of high mid-infrared optical powers in cw SROs is a challenging task, due to heavy thermal loading of the nonlinear crystal arising from the high intracavity signal intensities at increased pump powers. This can lead to saturation and subsequently a substantial drop in efficiency, thus limiting the available output power, as well as increased output instabilities. To date, the highest output power generated from a cw OPO is 10 W of idler at 3 μm for 50 W of pump at 20% efficiency using a SRO configuration [2]. Output coupling of SRO signal has enabled the generation of 8.6 W of total power (5.1 W signal, 3.5 W idler) for 15 W of pump, with improved extraction efficiency up to 59% [3]. Here we report the generation of 17.5 W of total power (9.8 W signal, 7.7 W idler) from an out-coupled cw SRO at 61% extraction efficiency. We also show that high output power stability and good beam quality can be maintained at such elevated output powers by careful control of crystal thermal loading effects through optimized signal out-coupling. To our knowledge, this is the highest output power and extraction efficiency reported from a cw OPO. A schematic of the experimental setup is shown in Fig. 1. The OPO is pumped by a Yb-fiber laser, delivering up to 30 W of single-frequency output at 1064 nm in linear polarization, with M 2 <1.01 and a nominal linewidth of 89 kHz. The fundamental beam is focused to a beam waist radius of 63 μm (ξ~1) at the centre of the crystal. The nonlinear crystal is a 50-mm-long, 5% MgO-doped periodically poled LiNbO 3 (MgO:PPLN), with five different grating periods ranging from 29.5 μm to 31.5 μm, in steps of 0.5 μm. The crystal is housed in an oven that can be temperature tuned from room temperature to 200 o C. The OPO is formed in a symmetric ring resonator that consists 30 W 1064 nm Yb Fiber Laser FI λ/2 λ/2 PBS Pump MgO:PPLN (in oven) M 2 M 1 Idler Signal M 3 M 4 /OC L M Fig. 1. Schematic of the Yb-fiber laser pumped MgO:PPLN OC-SRO. 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6 7 8 9 10 Λ=31 µm T=100 ºC Idler OC-SRO Output power (W) Output coupler transmission (%) Signal Fig. 2. Variation of the extracted signal and generated idler power with output coupler transmission. a704_1.pdf OSA / CLEO/QELS 2010 CThP6.pdf