Development of a Picosecond Cryo-Sampler Using Electro-Optic Techniques C.R. Cykaar l ,2, T.Y. HSiang l , and G.A. Mourou 2 1Department of Electrical Engineering, University of Rochester, Rochester NY 14627, USA 2Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, NY 14623, USA 1. Introduction The first all-superconducting sampler, with a rise time of 26 ps, was reported by Faris in 1980 [11. Recently, an improved version was developed by Wolf et al. with a 2.1 ps response [21. In this approach, a Faris pulser [11 is used to superimpose a fast current spike on an unknown waveform. This sum signal is then applied to a sense junction. whose dc bias is adjusted to reach the switching threshold. By sweeping the fast pulse in time, the unknown signal can be replicated. The speed of these systems was limited by the response time of the superconducting Josephson junctions, although junctions with switching speeds on the order of one picosecond are possible. Electro-optic sampling can also be used to study these high speed phenomena. Previously we reported on a picosecond electro-optic sampling system used to characterize Josephson devices [31. A block diagram is shown in Figure 1. The sampler [4,51 was driven by a colliding-pulse mode-locked (CPM) laser, which produced two 100 fs FWHM pulses at 100 MHz. One pulse train was used to generate an electrical signal of adjustable height and width. This was accomplished using a photoconductive switch and a resistively-charged section of microstrip transmission line. In addition, a long, looping wire bond was used to connect the switch output to ground. This prevented dc charging of the output transmission line, while preserving the shape of the switch output. delay -- L... _________ J photoconductive switch detectors Figure 1. Schematic of experimental setup This signal was used to excite the test device placed in the cryogenic environment. The resultant electrical transient was then sampled with the second CPM laser pulse train using a birefringent lithium tantalate crystal. By changing the relative delay between the optical excitation and sampling pulses, the temporal development of the electrical transient was recorded using conventional slow speed electronics. The limitations on the response of this system were found to be due to the several meters of cable required to move signals into and out of the cryogenic environment. 249 G. A. Mourou et al. (eds.), Picosecond Electronics and Optoelectronics © Springer-Verlag Berlin Heidelberg 1985