Koichi AIZAWA, Hiroyuki AOKI, Yoshimasa ITO, Yosuke TANAKA^* and Takashi KUROKAWA

Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Naka-cho, Koganei-shi, Tokyo 184-8588, Japan

(Received October 4, 2004; Accepted January 5, 2005)

We demonstrate a novel waveform measurement system of ultra-short optical pulses based on the two-photon absorption process in a Si-image sensor. Using an interferometer with a tilt mirror in the reference path, the relative time difference between the signal and reference pulses is spatially distributed on the Si-image sensor, so the intensity auto-correlation is monitored as an image at a time without using moving parts. This system can create or remove an interference fringe pattern overlapped on the auto-correlation image by controlling the polarization states of the laser pulse, which is useful for measuring the crossing angle between the signal and reference beams as well as avoiding contamination of the interference fringe into the auto-correlation image. We successfully measured optical pulses less than 100 fs from a fiber ring laser with a temporal resolution of 0.4 fs. The obtained waveform agreed well with that observed with a conventional second harmonic generation (SHG) based auto-correlator.

Key words: pulse measurement, short optical pulse, two-photon absorption, image sensor

^*E-mail address: tyosuke@cc.tuat.ac.jp