A Method for Measurement of the Duration of Picosecond Pulses by Beat Frequency Detection of Laser Output

Two methods for determining the duration of picosecond pulses have been reported. The earlier method, which utilizes second harmonic generation (SHG) in nonlinear crystals, was reported independently and almost simultaneously by M. Maier, W. Kaiser and J. A. Giordmaine; 1 J. A. Armstrong; 2 and H. P. AVeber.3 The second method, which utilizes the two-photon fluorescence (TPF) in certain dyes, was first reported by J. A. Giordmaine4 and his co-workers. Measurements of pulse durations based on these methods have been reported by numl 2 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1971 erous authors. Extensive references to these papers are included in a review article by A. J. DeMaria, W. H. Glenn, Jr., JI. J. Brienza and M. E. Mack. 5 Neither of these methods measures pulse duration directly. Both, in fact, measure the autocorrelation function C?(T) of the intensity /(£), namely G(r) = J -- 00 f /(/)/(/ + r) dt.