Microsecond duration free carrier induced gratings in CdMnTe

Very efficient gratings can be recorded in semiconductor media due to thc hugc dependance of the rcfrilctive index with respect to carrier density. However. due to the fast diffusion of thc photogenerated carriers, the lifetime of these gratings is small (from the picosecond to the nanosecond range). In this paper. wc show that long-lived (T > Ips) gratings can bc recorded in CdMnTe awing to the efficient trapping of electrons on mangancse sitcs [I], which generates U grating of fixed ncgativc chnigcs whcn the crystal is illuminated by an interference patlcrn. Neutrality requiring the existencc of a hole grating then c~eates a hole induced refractive index grating. Griltinga were recorded ~n a 3 mrn thick CdMnTc ramplc by the interference pattern of two "write" pulsesdslivered by the same dye laser pumped by a frequency doubled Q-switched KdYAG laser. The time evolution of the diffracted signal obuined from B ~ontin~ous "read" lacr diode WE rcgistcrcd for various grating wavelcngths A (sce figure i(a) as an example). The corrcsponding inverse of the grating lifetime 11% is plotted in figure I(b) as B function of A-?