Unstable and Multiple Pulsing Can Be Invisible to Ultrashort Pulse Measurement Techniques

Abstract

Multiple pulsing occurs in most ultrashort-pulse laser systems when pumped at excessively high powers, and small fluctuations in pump power in certain regimes can cause unusual variations in the temporal separations of sub-pulses. Unfortunately, the ability of modern intensity-and-phase pulse measurement techniques to measure such unstable multi-pulsing has not been studied. Here we report calculations and simulations finding that allowing variations in just the relative phase of a satellite pulse causes the second pulse to completely disappear from a spectral interferometry for direct electric field reconstruction (SPIDER) measurement. We find that, although neither frequency-resolved optical gating (FROG) nor autocorrelation can determine the precise properties of satellite pulses due to the presence of instability, they always succeed in, at least, seeing the satellite pulses. Also, additional post-processing of the measured FROG trace can determine the correct approximate relative height of the satellite pulse and definitively indicate the presence of unstable multiple-pulsing.

100% reliable algorithm for second-harmonic-generation frequency-resolved optical gating

“…This inversion problem is actually significantly simpler and much less ill-posed. The function s(t) can then be trivially found in terms of the frequency marginal, M SHG (w): (5) where, of course, at every point in time, t, the square root has two complex roots, s±(t), where we define s+(t) to be the root with positive real component, and s-(t) to be the root with negative real component, corresponding to phase values of f(t) and f(t) + p, respectively.…”

Dispersion Scan Frequency Resolved Optical Gating For Evaluation of Pulse Chirp Instability

“…A prominent variation of the pulse electric field on a short time scale leads to the appearance of a narrow feature in the recorded nonlinear signal, which is called a "coherent artifact". This artifact can confuse interpretation of the autocorrelation or SPIDER measurements, including of the pulse length and temporal structure 12,13 . On the contrary, the spatial and temporal chirp variations manifest themselves in the standard FROG setup as a discrepancy between the measured and the retrieved FROG traces 6,11 .…”

High-Sensitivity, Simple Frequency-Resolved-Optical-Gating Device

“…Measuring pulses directly from a laser requires a selfreferenced technique, and the most reliable and general such technique is frequency-resolved optical gating (FROG) [2]- [5]. FROG, like essentially all other pulse-measurement techniques, however, was designed for measuring pulses from relatively high-power fs lasers.…”