Roles of resonance and dark irradiance for infrared photorefractive self-focusing and solitons in bipolar InP:Fe

Abstract

This paper shows experimental evidence of photorefractive steady state self-focusing in InP:Fe for a wide range of intensities, at both 1.06 and 1.55µm. To explain those results, it is shown that despite the bi-polar nature of InP:Fe where one photocarrier and one thermal carrier are to be considered, the long standing one photocarrier model for photorefractive solitons can be usefully applied. The relationship between the dark irradiance stemming out of this model and the known resonance intensity is then discussed.

Experimental control of steady state photorefractive self-focusing in InP:Fe at infrared wavelengths

“…The experimental results presented in this paper allow us to point out the origin of the different behaviors reported in the literature [30,36]. In fact, we are able to reproduce the two main types of self focusing (with and without a transition from defocusing to focusing, as presented in [30] and [36] respectively) in the same crystal by using a uniform background illumination.…”

“…In fact, we are able to reproduce the two main types of self focusing (with and without a transition from defocusing to focusing, as presented in [30] and [36] respectively) in the same crystal by using a uniform background illumination. Further on, we show how beam bending and self focusing itself can be controlled by tuning various parameters: iron doping, temperature and background illumination.…”

“…A 10 kV/cm external electric field is applied along the < 001 > axis. Note that this is the same configuration as the one used in references [30,36,37]. The crystal is thermally stabilized with a Peltier cell.…”

“…This is equally true for materials with 2 types and 1 type of charge carriers. In previous theoretical models, self focusing is characterized by two specific parameters: the dark intensity (I d ) in [36] and the (resonance intensity (I res ) in [30].…”

“…Moreover, they are considering the steady state of the self focusing only. A later model [28,36] does take into account the transient regime of the self focusing, but it does not explain the electric field amplification observed experimentally. Also, in [36] no transition from self defocusing to self focusing is observed when the intensity of the beam is increased.…”