THE BULK PHOTOVOLTAIC EFFECT OF PHOTOREFRACTIVE LINBO3-FE CRYSTALS AT HIGH LIGHT INTENSITIES

摘要

Direct measurements of the bulk photovoltaic current density j(phv) in photorefractive LiNbO3:Fe,LiNbO3:Mg,Fe and LiNbO3:Zn,Fe crystals were performed at high light intensities. Illumination of the crystals with light pulses of a Q-switched frequency-doubled Nd:YAG laser (pulse duration 20 ns; light wavelength 532 nm) yielded a photovoltaic current through the crystals which charged a capacitor. Afterwards an electrometer measured the voltage of the charged capacitor. From this voltage and from capacity and exposure time the current density j(phv) was deduced. For intensities above 10(7) W m(-2) a contribution to j(phv) which increased quadratically with light intensity/appeared for LiNbO3:Fe crystals. Go-doping with Mg and Zn lowered the quadratic component. Our results are in good qualitative and quantitative agreement with previous holographic measurements and support the claim that the intrinsic defect Nb-Li(4+/5+) acts as a secondary photorefractive centre in LiNbO3 at high light intensities. [References: 26]