DETERMINATION OF ULTRASHORT PULSE WIDTHS BY TWO-PHOTON FLUORESCENCE PATTERNS

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Abstract
The extent that characteristics of intense, ultrashort duration pulses can be determined using the two‐photon fluorescence (TPF) display technique is examined within the framework of a simple model of partial laser mode‐locking. It is found that the contrast ratio in the TPF pattern can give a reliable estimate of the degree of mode‐locking, thereby allowing the fraction of laser beam energy contained in intense pulses and the width of these pulses to be inferred. However, the width of the peak in the TPF pattern varies nonmonotonically with the width of the pulses, and is not a sensitive measure of pulse width. It is argued that a direct measurement of the laser beam intensity profile by a relatively low‐resolution photodiode‐oscilloscope system gives a misleading estimate of the intense pulse content of the beam.