Diffraction-limited collimation optics for a channel waveguide Cerenkov frequency doubler for diode lasers

Optical path analysis applying diffraction theory and geometrical ray tracing, and with collimation experiments shows that a hemiconic lens can convert the arc of blue radiation formed by Cerenkov second-harmonic generation to a parallel plane wave. To obtain an aberration-free plane wave, we modified the apex angle of the cone according to the birefringence of the waveguide. To correct chromatic aberration, we needed to have diode laser wavelength tuning with the aid of an achromatic cone lens doublet.