Patent ID: 7627008
Filing Date: 2009-12-01
Classification: G02F

Abstract:
1. A laser apparatus for generating a second harmonic laser beam at a second harmonic frequency of a fundamental frequency of a fundamental frequency laser beam, for use with a laser source that generates the fundamental laser beam at the fundamental frequency, the laser apparatus comprising: a second harmonic generator (SHG) crystal receptive of the fundamental beam which converts a portion of the light energy of the fundamental beam into a second harmonic beam of light energy at the second harmonic frequency with each pass of the fundamental beam through the SHG crystal; the SHG crystal having a characteristic angle for propagation of the fundamental beam and second harmonic beam which achieves critical phase matching of the fundamental and second harmonic beams; and an optical transmission element oriented with respect to the SHG crystal to propagate the fundamental beam through the SHG crystal in four parallel optical passes and to propagate the fundamental beam and the second harmonic beam resulting from each pass in an optical path; the optical transmission element propagating each pass of the fundamental beam and the second harmonic beam through the SHG crystal at the characteristic angle to achieve critical phase matching of the fundamental and the second harmonic beams; the optical transmission element including a plurality of mirrors positioned in the optical path to reflect the fundamental beam to the SHG crystal in first, second, third and fourth passes of the fundamental beam through the SHG crystal and to reflect the second harmonic beam resulting from passing the fundamental beam through the SHG crystal coincidentally with the fundamental beam; the optical transmission element also including a dichroic device oriented with respect to the SHG crystal to filter the second harmonic beam from the fundamental beam; and wherein: the portion of the fundamental frequency beam converted to the second harmonic beam adds energy of the second harmonic beam with each pass of the fundamental beam through the SHG crystal.