Abstract

Recent progress in femtosecond pulse-shaping technology¹,² drives a strong impetus to try to find novel operations that a tailored optical waveform can achieve and that would be impossible with transform-limit one. In this paper, we propose a scheme to map an amplitude profile of an optical waveform on THz radiation that is generated via optical rectification in nonlinear crystals³. The present study was motivated by an anticipation that if chirp can be optically coded on the THz radiation, it could compensate for spreading of the THz wavepacket that propagates under group-velocity-dispersion (GVD). The idea is close to recently demonstrated "wavepacket focusing"⁴. In an arrangement that we envision, two independent optical waveforms, E₀ and E_S, are directed into an E-O medium, and they overlap both in time and space to form a fringe pattern in the medium as shown in Fig. 1. Source polarization P_NL ∝ E_O E_S emits THz radiation along the direction of difference wavevector, by which we define z-axis. We denote amplitude of wavepacket propagating in (± z) direction by U_±. If E₀ is a monochromatic light and E_S has some tailored waveform, P_NL is expected to replicate the amplitude profile of E_S instead of its intensity profile. Detailed analysis⁵ reveals features proper to the present configuration; i) spectral bandwidth of U_± is limited by spatial monochromaticity, of the fringe pattern, ii) when a chirped pulse is used as E_S, U_± carries an opposite chirp to each other, and cancellation of material GVD with the coded chirp occurs in either one direction. Also, arrival time of the wavepackets are shifted from that for E_S with no chirp. The time shift is in advance in one direction and in retardence in the other. Objective of the experiment is to see such asymmetry.

© 1996 Optical Society of America