Abstract

ZnSe has been shown to be an excellent optical-limiting material for picosecond pulses at a wavelength of 532 nm.¹ Two-photon absorption (2PA) and the negative index contribution of photoexcited carriers are the primary mechanisms responsible for the limiting of the transmitted fluence. Furthermore, if the geometry is arranged so that the sample is much thicker than the depth of focus of the beam, these same mechanisms result in an internal limiting that prevents optical damage from occurring inside the bulk of the ZnSe. This mechanism may also be expected to work for longer pulses, as the carrier refraction is a cumulative effect. However, experiments with nanosecond pulses have shown that bulk damage does in fact occur. Further experiments showed that this effect is dependent on the focusing geometry, with damage observed in the bulk only for beam waists calculated to be less than 3 μm.² Until now, the source of this damage has remained unresolved.

© 1995 Optical Society of America