Efficient generation of coherent blue light by frequency-tripling single 1.32-μm beam in two separate KTP and Ce:KTP crystals

Abstract

Summary form only given. By frequency mixing of 1.064 /spl mu/m and 0.809 /spl mu/m radiation in a KTiOPO/sub 4/ (KTP) crystal, it is possible to generate blue light, however, in the presence of two pump beams. By cascading second-harmonic generation (SHG) and sum-frequency generation (SFG) in two separate LiNbO/sub 3/ and KTP crystals, coherent blue light can be generated by using a single pump beam from Nd:YAG laser. However, this scheme has not been implemented solely in KTP crystals. KTP is one of a few important nonlinear optical materials because it is highly resistant to laser damage. In addition, it possesses large nonlinear optical coefficients with broad angular and temperature phase-match acceptance width-length products. However, it has noticeable absorption in the blue domain. 1. Here we report our results of reducing absorption of flux-grown KTP crystals in the blue domain by doping them with cerium atoms (replacing /spl sim/9% of titanium atoms). In the blue to green region the absorption coefficients of the Ce-doped KTP are significantly less than those of the undoped KTP. Therefore, we can achieve a relatively higher conversion efficiency in this domain by using a Ce:KTP crystal while minimizing the effect of laser heating. We have then used an undoped KTP crystal to generate a coherent beam at 0.66 /spl mu/m via SHG from a pump beam at 1.32 /spl mu/m. The 1.32-/spl mu/m pump beam is the output of a nanosecond optical parametric oscillator pumped by a frequency-tripled Nd:YAG laser, with the tunable output wavelength. By mixing the residual pump beam with the SH beam in a Ce-doped KTP crystal via type-II SFG, we have successfully generated coherent blue light at 0.44 /spl mu/m by using a single pump beam.