Photoconductive Generation of Subpicosecond 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.[l] 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 alternate measurement approach has been to use the electro-optic effect in a 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 photoconductive switches has generated and measured subpicosecond electrical pulses.[4] This large reduction in the generated pulsewidth demonstrates the ultrafast capability of the Auston switches and challenges the ultrafast time resolution of the electro-optic methods. We will now discuss subpicosecond pulse generation using photoconductive gaps,[4] together with the initial interpretation of these experimental results. In addition, we will present some recent measurements, which will allow us to conclude with a relatively complete description of the pulse generation process.