Photoconductive Generation of Sub-Picosecond Electrical Pulses and their Measurement Applications*

Abstract

The generation of short electrical pulses via optical methods has for some time been performed by driving Auston switches (photoconductive gaps) with short laser pulses.(1) The shape of the electrical pulse depends on the laser pulseshape, the material properties of the semiconductor, the nature of the charge source, and the characteristics of the associated electrical transmission line. The same techniques can also measure the generated electrical pulses by sampling methods. An alternative measurement approach has been to use the electro-optic effect in a nonlinear crystal.(2) In this case, the field of the electrical pulse is sampled through the rotation of the polarization of the optical sampling pulse. Because it has demonstrated 460 fsec time resolution,(3) the electro-optic method is presently considered to be the fastest sampling technique. However, recent work utilizing photo-conductive switches has generated and measured subpicosecond electrical pulses.(4) This order of magnitude reduction in the generated pulsewidth demonstrates the ultrafast capability of the Auston switches and calls into question the conventional wisdom that electro-optic methods must be used to obtain ultrafast time resolution.