We present what is to our knowledge a new approach to generating tunable blue light by cascaded nonlinear frequency conversion in a single LiTaO<sub>3</sub> crystal. Simultaneous quasi-phase matching of an optical parametric generation process and a sum-frequency mixing process is achieved by means of structuring the crystal with a quasi-periodic optical superlattice. The spectral (wavelength tuning and bandwidth) and power characteristics of the blue-light generation are studied with a fixed-wavelength 532-nm picosecond laser and a wavelength-tunable nanosecond optical parametric oscillator (OPO) as the pump sources. By tuning the OPO wavelength, we could tune the blue output over ∼20 nm . Temperature tuning of the blue output at a fixed pump wavelength of 532 nm was limited to ∼1.5 nm. A maximum blue power of 15 μW was generated at a pump power of 0.5 mW, corresponding to an efficiency of 3%.
© 2004 Optical Society of AmericaPDF Article