Abstract
Ultrashort optical pulses have time durations around 10-12-10-15 seconds, which can provide unprecedented time resolution, spectral bandwidth, and peak intensity. They have been employed in a variety of applications, ranging from time-resolved spectroscopy, optical fiber communications, biomedical imaging, to high-field physics. As a result, there is a growing demand on measurement techniques of ultrashort optical pulses. However, there is no existing photodetector fast enough to directly resolve the envelopes of femtosecond optical pulses, not to mention the phase (or fringe density) evolution. All-optical methods relying on some nonlinear interaction of the unknown optical pulse itself to create ultrashort “gate function”, are usually required. We proposed and experimentally demonstrated the modified interferometric field autocorrelation (MIFA) method to completely retrieve the amplitude and phase profiles of ultrashort optical pulses by using thick nonlinear crystals. MIFA method is particularly attractive because of: (1) high sensitivity, (2) simplified and cost-effective configuration, and (3) free of time-consuming iterative algorithm. We have achieved an unprecedented sensitivity of 2.7 10-9 mW2, improving on the previous record of self-referenced ultrashort pulse measurement by 800 times. The method also successfully characterized 8-fs visible pulse, proving its great potential in measuring few-to-single cycle pulses.