Based on two theorems, the importance of the root-mean-square (rms) width for the characterization of ultrashort optical pulses is demonstrated. First, it is shown that one can directly determine the rms width from the autocorrelation without making any assumptions about the specific form of the pulse envelope. Second, it is shown that a bandwidth-limited (unchirped) wave packet has the smallest possible rms time–bandwidth product. This reveals a natural definition for a rms chirp that is easily accessible to experimental measurement and that presents a useful measure for the quality of pulse compression techniques.
© 2000 Optical Society of America
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