CORRELATION METHOD FOR FEMTOSECOND OPTICAL PULSES

A correlation method for accurate measurement of ultrafast optical pulses of femtosecond resolution is presented. It uses a lock-in amplifier and a variable mixing method of reference frequencies in a Michelson interferometer. The read-out system consists of an X-Y plotter or a computer monitor. This technique does not require high-speed photodetectors but is sufficiently sensitive to plot femtosecond pulses at low optical power level (about 10 muW average power). The measurement of 320 fs FWHM light pulses from an actively mode-locked semiconductor laser and a contrast ratio of 80 were demonstrated. The resolution of this technique is believed to be a few femtoseconds.