ABSTRACT
Femtosecond laser pulses are much harder to measure than picosecond or nanosecond pulses. Nanosecond pulses can be easily measured using a fast photodiode and an oscilloscope. The fast photodetector produces a pulse of current that mimics the optical pulse, and an oscilloscope capable of reproducing the pulse traces it on a screen. The interferometer was used to measure picosecond and, as soon as they were first generated, femtosecond laser pulses. The laser pulses are split into the two arms of the interferometer using a partially reflecting mirror. The pulses are later recombined, and one of the arms of the interferometer can be adjusted in length. In order to make interferometers useful for pulse measurement purposes, it is important to measure a nonlinear optical signal that depends on the coherence and pulse duration of the source. The Interferometric autocorrelation (IAC) is modulated at the carrier frequency of the pulse, essentially the average optical frequency.
