Semiconductor nanocrystal films form ultrafast holograms
Scientists at the Los Alamos National Laboratory (Los Alamos, NM) have demonstrated the use of solid-state films of close-packed cadmium selenide nanocrystal solids as the active material for generating dynamic holographic gratings. The gratings were formed using two 400-nm, 100-ps pump pulses that interfered at the sample plane to form an intensity grating. This, in turn, formed a population grating in the nanocrystal sample, which modulated its absorption via such mechanisms as state filling and the carrier-induced Stark effect. The real part of the refractive index was modified through Kramers-Kronig transformation, and the dynamic grating formed in the samples was probed at the Bragg angle with tunable 100-fs pulses generated by an optical parametric amplifier. A high diffraction efficiency of up to 0.5% for films of approximately 0.5 Ám was calculated as the ratio of the intensities of the diffracted and incident beams. The spectral maximum of diffraction efficiency is located in the vicinity of the lowest (1S) absorption maximum (the nanocrystal band edge) and is tunable over a wide range by varying the size of the nanocrystals used in fabricating the solid. Contact Victor Klimov at klimov@lanl.gov.

Laser Focus World May, 2001
Author(s) :   Laser Focus World Staff