An example:

Ultrashort Pulse Techniques

Ultra-short pulse generation

We propose a novel technique for measuring the waveform and the temporal phase variation of ultrashort optical pulses. In the proposed method, we measure the spectrogram or sonogram of the pulse under test using the time gate or frequency gate which is characterized in advance. The pulse amplitude and phase are retrieved from the spectrogram or sonogram by using a newly derived formula, which can retrieve the pulse amplitude and phase uniquely without iterative calculations. The proposed method is experimentally demonstrated in the optical communication band.
(http://www.ginjo.rcast.u-tokyo.ac.jp/research01/pulse.html)

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