Optical parametric properties of ultraviolet-pumped cesium lithium borate crystals.

We report the optical parametric properties of cesium lithium borate (CLBO) crystals pumped by UV radiation of the fourth-harmonic generation at 266 nm and the third-harmonic generation at 355 nm of a picosecond Nd:YAG laser. A special optical design was used to avoid damage to the optical elements by the UV-pumped beam at 266 nm. The optical parametric generator (OPG)/optical parametric amplifier (OPA) of the 266-nm-pumped CLBO covers the tuning range from 347 nm in the UV to 1137 nm in the near IR. The 355-nm-pumped CLBO OPG/OPA, on the other hand, is tunable from 447 to 1725 nm. The experimental tuning curves for each CLBO OPG/OPA were measured and compared with the theoretical tuning curves. With a double-pass OPG configuration and a pumping intensity of approximately 6 GW/cm2, the maximum conversion efficiency, including both the signal and the idler, was approximately 11% for the 266-nm-pumped CLBO and is greater than 16% for the 355-nm-pumped CLBO without taking into account the surface losses from the uncoated elements. The bandwidth of this double-pass CLBO OPG at various wavelengths was measured and compared with other optical parametric systems. Because of the small angular dispersion of CLBO, the bandwidth of the OPG and OPA systems is exceptionally narrow, especially for the 266-nm-pumped system. Without the use of any dispersion element, the bandwidth of the 266-nm-pumped system can be as narrow as 0.22 nm at wavelengths far from the degenerate point. Comparison between the experimental bandwidth and the theoretical calculation shows that the bandwidth of the UV-pumped CLBO OPG/OPA is limited mainly by the divergence of the pump beam.