Mid-infrared nonlinear phenomena in polycrystalline semiconductors

We have studied second-harmonic generation by 30 ps and 70 ns 10 m CO₂ laser pulses in nonlinear polycrystalline ZnSe, CdTe and GaAs samples. Second-harmonic generation in these materials can limit the amplification of high-power CO₂-laser pulses in amplifier chains sealed with these polycrystalline IR-transmission materials. On the other hand, we now demonstrate for the first time that these materials are suited as nonliner elements for autocorrelation measurements on short infrared laser pulses. For such pulse-width measurements polycrystalline materials have an advantage over single crystals, e.g. GaAs, because they are insensitive to misalignement. Furthermore, these polycrystalline optical elements are easier and cheaper to manufacture than single crystal devices. With such polycrystalline materials we were able to realize reliable autocorrelation measurements of 30–300 ps 10 m optical-free-induction-decay (OFID) laser pulses.