Femtosecond Laser Eyewear Protection: Measurements and Precautions for Amplified High Power Applications

Ultrafast lasers have become increasingly important as research tools in laboratories and commercial enterprises suggesting laser safety, personal protection and awareness become ever more important. Laser safety eyewear are typically rated by their optical densities (OD) over various spectral ranges, but these measurements are usually made using low power, large beam size, and continuous beam conditions. These measurement scenarios are vastly different than the high power, small beam size, and pulsed laser beam conditions where ultrafast lasers have extremely high peak powers and broad spectra due to the short pulse durations. Many solid-state lasers are also tunable over a broad wavelength range, further complicating the selection of adequate laser safety eyewear. Eighteen laser eyewear filter samples were tested under real-world conditions using a Ti:Sapphire regenerative amplifier with output pulses centered at 800 nm running from 2 Hz to 1 KHz repetition rate. The typical maximum peak laser irrandiance employed was ca. 3 TW/cm² (800 nm wavelength, 450 uJ/pulse with 80 fs FWHM pulse duration) or less when damage occurred, depending on the sample. While many samples maintained their integrity under these test conditions, many plastic samples showed signs of failure which reduced their OD, in some cases transmitting 4 to 5 orders of magnitude higher than expected. In general, glass filters performed significantly better than plastic filters, exhibiting less physical damage to the substrate and less absorber degradation.