Deep ultraviolet laser using strontium tetraborate for frequency conversion

An inspection system comprising:

• a light source configured to generate light having a wavelength in a range between 180 nm and 200 nm;
• and
• an optical system configured to direct the light onto a sample,
• wherein the light source comprises:
• a first fundamental laser configured to generate a fundamental laser beam having a corresponding fundamental frequency;
• one or more intermediate frequency conversion stages collectively configured to generate an intermediate frequency light using the fundamental laser beam, the intermediate frequency light having an associated intermediate frequency and a corresponding intermediate wavelength between 360 nm and 400 nm;
• a final frequency doubling stage configured to pass the intermediate frequency light through a nonlinear crystal,
• wherein the nonlinear crystal includes a plurality of strontium tetraborate (SBO) crystal plates disposed in a stacked configuration such that each first SBO crystal plate is adjacent to at least one second crystal plate, and
• wherein the plurality of SBO crystal plates are cooperatively configured to form a periodic structure that achieves quasi-phase-matching (QPM) of the intermediate frequency light such that light exiting the nonlinear crystal includes laser output light having an output frequency with a corresponding wavelength in the range of approximately 180 nm to approximately 200 nm.