Space radiation test of saturable absorber for femtosecond laser.

We report a space radiation test performed on a semiconductor-type saturable absorber (SA) for its use in outer space as a key mode-locking component of fiber-based femtosecond pulse lasers. Gamma-ray effects on the nonlinear transmission behavior of the SA were evaluated by configuring a pump-probe experiment with femtosecond light pulses. Test results revealed that when the total ionizing dose of gamma-ray exposure reaches 120 krad, the SA encounters a sudden failure with its modulation depth and saturation fluence deteriorating from 11% to 6% and 40 to 110 µJ/cm2, respectively. On the other hand, no notable degradation was observed in its temporal response of absorption recovery.