Unlike continuous-wave lasers, femtosecond pulsed lasers have wide spectral bandwidths and extremely high peak power.  Lasers such as Ti:Sapphire oscillators also have an adjustable center wavelength. These factors become an issue when selecting eyewear protection, as the eyewear may not protect the user from the entire laser spectrum, and the integrity of the eyewear material may be compromised by the high peak powers.  This study was a continuation of a previous study that measured the effective optical densities of commercially donated filter samples. In this study, the same samples were tested to characterize their potential modes of failure using a 1 kHz Ti:Sapphire regenerative amplifier which generated ca. 80 fs pulses with various  wavelengths, powers, repetition rates, and beam spot sizes.  For some filters, the wide bandwidth and variable center frequency of the laser caused the observed optical densities to be significantly lower than the supplier’s rating at the center frequency.  The observed modes of failure included melting, burning, bleaching, and saturable absorption behavior.  Several filters transmitted several orders of magnitude more light than the supplier’s suggested optical density ratings without any physical signs of damage.  In general, plastic lenses were considerably more likely to fail, while all glass samples tested maintained their integrity under the conditions tested.  The results of these experiments indicate that eyewear protection should be tested under the given experimental conditions to determine their efficacy before use.

Femtosecond laser eyewear protection: Measurements and precautions

255th National Meeting (2018)

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