Electron Diffraction in the Picosecond Domain Steven Williamson and Gerard Mourou and Synchronous Amplification of 70 fsec Pulses Using a Frequency-Doubled Nd: YAG Pumping Source

Abstract

With the exception of picosecond photoelectron switching recently demonstrated, streak camera tubes have been used exclusively as a fast optical and x-ray diagnostic tool. However, some of the most beautiful features of the image converter device used in the streak camera have been only partially exploited with this application. The image converter device produces a temporal and spatial monoenergetic photoelectron replica of the incident optical pulse. This replica is ultimately limited by the temporal and spatial resolution of the particular streak tube employed. Temporal and spatial resolution can be as good as subpicosecond and 100 μm respectively. It is also worth noting that this replica is accurately synchronized with the incident optical pulse. We have used this electron burst to generate an electron diffraction pattern, inferring that picosecond snap shots of laser induced structural changes in laser annealing or in the field of surface physics, can now be taken not only with a picosecond exposure, but also in picosecond synchronization with the laser induced kinetics. In the experiment (Fig.1) a demountable photochron II streak camera tube is used. The Al specimen of 150 Angstroms thickness is located in the drift space 1 cm behind the anode. The diffraction pattern is captured on a phosphor sreen and photographed using an image intensifier with a gain of 3×10⁴ lens coupled to the film.