Two photon absorption in semi-insulating gallium arsenide photoconductive switch irradiated by a picosecond infrared laser

¹ Société Alliage, 75005 Paris, France
² Thomson Shorts systèmes SA, 92223 Bagneux, France
³ LGE, Université de Pau, 64000 Pau, France

Corresponding author: pascal.pignolet@univ-pau.fr

Received: 8 November 1999
Revised: 1 January 2000
Accepted: 10 July 2000
Published online: 15 September 2000

Abstract

We study gallium arsenide (GaAs) high voltage photoconductive switches triggered by a 30 ps neodymium: yttrium aluminium garnet (Nd:YAG) laser, i.e. using photons of energy smaller than the band gap. We measure optical absorption at Brewster incidence under optical pulse excitation and determine the extrinsic one photon and intrinsic two photon absorption coefficients. Analyzing the photoconductive resistance under different power densities of laser radiation, and using the absorption data, we demonstrate that only about 20% of the photons absorbed by the extrinsic process are converted into free electrons. We conclude that high efficiencies can only be obtained by using two photon absorption, which is feasible with ultrafast lasers and focussed beams.