Femtosecond pulse laser beam shaping and power control for free-space optical material properties measurements

With the development of lasers, laser sources have been well adopted in spectrophotometry and optical material measurement. Especially in the ultraviolet range, ultraviolet laser has broad application prospects in the fields of optical data storage, lithography, micromachining, photobiology and medical treatment. The previously used xenon lamps have limited reliability, high energy consumption, and poor beam direction stability. NIM's new facility uses Ti: sapphire lasers as a source of monochromatic beams. Femtosecond pulse lasers can be tuned in a wide spectral range via parametric oscillation and high efficiency frequency conversions. For (280-340) nm femtosecond pulses generated via two nonlinear conversion of a (680-1080) nm Ti:Sapphire laser, the average power can be well controlled from 1 mW to sub-nW level using a polarizer-based attenuator. The laser beam quality was significantly improved using a spatial filter consists of an objective lens, a silica optical fiber, and an off-axis parabolic reflective collimator. The spatial filter was mounted on a two-dimension linear stage to accommodate the spatial beam shift. A spatially stabilized, quality beam over (280-340) nm spectral range was obtained and suitable for free-space optical materials measurements.