Patent ID: 9660409
Date: 2017-05-23
CPC Classifications: G01N,G02F,H01S

Claim:
1. A laser for generating deep ultra-violet (DUV) continuous wave (CW) light, the laser comprising: a second-harmonic generator configured to convert light having a fundamental wavelength to light having a second harmonic wavelength; and a fourth-harmonic generator configured to convert the light having the second harmonic wavelength to light having a fourth harmonic wavelength, the fourth-harmonic generator including: a plurality of mirrors configured to circulate light in the fourth harmonic generator; a first non-linear optical (NLO) crystal having first optical axes that are oriented relative to the light circulated in the fourth harmonic generator such that said first NLO crystal converts a portion of the light having the second harmonic wavelength to light having the fourth harmonic wavelength and having a first astigmatism, the first NLO crystal in operative relation to the plurality of mirrors; and a pair of thin plates, each said thin plate having parallel planar surfaces, said pair of thin plates disposed in operative relation to the first NLO crystal such that the light circulated in the fourth harmonic generator passes through said planar parallel surfaces of the pair of thin plates, wherein the pair of thin plates are disposed in a tilted arrangement at substantially equal and opposite angles about respective parallel axes such that the pair of thin plates introduce a second astigmatism to the light circulated in the fourth harmonic generator that corrects for said first astigmatism while minimizing displacement of said circulated light, and wherein the first NLO crystal comprises a hydrogen-annealed cesium lithium borate (CLBO) crystal.