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11 October 2007 Tandem OPO systems for mid-infrared generation using quasi phase-matching and volume Bragg gratings
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Efficient laser sources in the 3 - 5 μm wavelength range are needed for directed infrared countermeasures, but also have applications in remote sensing, medicine and spectroscopy. We present results and discuss the possibilities of a tandem optical parametric oscillator (OPO) scheme for converting the radiation from a 1.06 μm Nd3+-laser to the mid-infrared. Our setup uses type I quasi phase-matched (QPM) crystals in a near degenerate OPO to generate 2.13 μm radiation. The QPM crystal provides higher nonlinearity and longer interaction lengths, because walk-off is avoided, compared to conventional bulk crystals. This is an advantage especially in low pulse energy applications. To make the 2.13 μm radiation usable for pumping a second OPO a volume Bragg grating is used as a cavity mirror to limit the bandwidth, which in a conventional QPM OPO at degeneracy can be several hundred nanometers. The acceptance bandwidth for efficient OPO operation of a 14 mm long ZnGeP2 (ZGP) crystal is approximately 5 nm, which makes the need for bandwidth limiting clear. The majority of the signal energy from a periodically poled KTiOPO4 (PP KTP) OPO with a volume Bragg grating output coupler was found to be in a single longitudinal mode, whereas the idler bandwidth was measured to 19 GHz (FWHM). A volume Bragg grating resonant near 2124 nm was chosen so that the signal and idler were separated by 9 nm. This OPO output has been used as a pump source for a conventional ZGP OPO demonstrating efficient conversion and providing broadband tunable output in the mid-infrared.
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Markus Henriksson, Lars Sjöqvist, Mikael Tiihonen, Valdas Pasiskevicius, and Fredrik Laurell "Tandem OPO systems for mid-infrared generation using quasi phase-matching and volume Bragg gratings", Proc. SPIE 6738, Technologies for Optical Countermeasures IV, 673805 (11 October 2007);

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