Electronically controllable shaping of femtosecond pulses using a 128-element liquid-crystal phase modulator

Abstract

Femtosecond pulses with nearly arbitrarily controllable pulse shapes can be generated by spatial masking of individual optical frequency components within a generalized grating compressor.1 Although our original pulse shaping work was performed using fixed, microlithographically patterned masks, we have recently demonstrated programmable femtosecond pulse shaping by using a 32-element liquid crystal phase modulator.2 With this apparatus we demonstrated switching of the optical pulse shape on a 10 ms time scale and achieved gray-level (continuous) control of the individual spectral phases. In the current paper we describe pulse shaping with a new, 128-element modulator. The device is a nematic-liquid-crystal phase modulator controlled by a linear array of individually addressed electrodes on 40-µm centers (with a gap of 1.5-µm between electrodes). Although this 128-element modulator offers improved spectral resolution comparable to the best we have obtained with fixed masks defined by microlithography, full utilization of this spectral resolution will also impose more stringent requirements on the uniformity and accuracy of the phase response. In a preliminary test using binary (0 or π) phase control, we have already demonstrated the ability to perform programmable pulse shaping over a temporal window in excess of 10 ps. We intend in our talk to present the results of a more complete evaluation of pulse shaping with the 128-element modulator, including an evaluation of the ability to utilize full gray- level phase control.