Wide-band low-noise tunnel current measurements in laser assisted experiments

A composite current-to-voltage converter that shows a superior bandwidth an d signal-to-noise ratio (bandwidth similar to 50 MHz at 410 k Omega transim pedance) was designed. Two options for the input stage were tested: a high input impedance wide-band operational amplifier (OP) OPA655 (Burr-Brown) an d a differential cascade which is based on the junction field effect transi stors SST440 (Siliconics). By using a wideband current feedback OPA658 in t he second stage the achieved bandwidth gain product is similar to 10 GHz. A method for testing the performance of the preamplifier by using laser indu ced electron emission is described. The technique's possibility for measure ments of laser induced acoustic waves with high sensitivity and nanometer l ocal resolution is demonstrated. For further applications the design of a w ide-bandwidth, low-noise, single tunneling electron counting capable preamp lifier is discussed. (C) 1999 American Institute of Physics. [S0034-6748(99 )00507-9].