Wave mixing analysis in photorefractive quantum wells in the Franz–Keldysh geometry under a moving grating

On the mobility-lifetime products in photorefractive GaAs-AlGaAs quantum wells structures determined by moving grating technique measurements

“…As a result, the superposition of writing waves of intensities of I 1 and I 2 gave the interference pattern: I(x ,t)=(I 1 + I 2 )[1 + mcos(Kx  t)], describing the light pattern with the fringe contrast m moving with the velocity v = /K, where K = 2/ denotes the grating constant. For a given frequency  =  res one obtains the enhancement of the PR response with the resonant frequency  res increasing linearly with the average light intensity (I 0 = I 1 + I 2 ) [3,4]. In order to obtain theoretical relationships for quantities of interest we refer to the system of material equations given in [2,5], where both bipolar carrier transport and hot electrons nonlinear transport are included.…”

“…for small fringe contrast (m << 1). Neglecting the diffusion currents for large applied electric fields, one obtains [4] …”

“…For SI-MQW with a quadratic electro-optic effect, the diffraction efficiency, and hence the diffracted signal intensity, are proportional to the square of the amplitude of a refractive index grating, i.e. I diff (t)  [n(t)] 2  [E 0 + E sc (t)] 4 . Therefore, the time response of an optical signal is not equal to the space-charge field response time given by Eq.…”