Widely tunable optical parametric oscillator using urea

A singly resonant urea optical parametric oscillator is discussed. With a pump source at 355-nm wavelength, the oscillator has been shown to generate radiation easily for the entire range of wavelengths between 498 nm and 1.23 microns, almost continuously tunably. Further, through second-harmonic generation of the signal wave, the tuning curve has been extended from 498 nm to wavelengths as short as 249 nm. The oscillator linewidth, conversion efficiency, temporal profile, and spatial-mode profile have been characterized, and are all found to be favorably comparable with other sources of tunable radiation, such as pulsed dye lasers. Spontaneous parametric fluorescence in urea is reported for the first time.