Parabolic mirror optics for collimation of a crescent blue laser beam radiated from channel waveguide Čerenkov second-harmonic generation.

Parabolic mirror optics to collimate the crescent-shaped blue laser beam that radiates from Čerenkov second-harmonic generation (SHG) in a channel waveguide configuration is proposed. Mirror collimation optics has a large tolerance to the variations of SHG element parameters, such as the laser source wavelength, as well as to mirror displacement. The anisotropy of a nonlinear crystal in which the waveguide is fabricated has been taken into account. The optimum mirror alignment to obtain a collimated blue laser beam is evaluated in terms of Marechal's criterion. The minimum wave-front aberration with beam intensity weighted is 0.054 λSH. The convergence of the collimated beam is less than 1.6 mrad, and, by using an objective lens, the collimated beam can be focused to a diameter of less than 1 µm, which is 1.27 times the diffraction-limited focusing point.