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.
Highlights
Ultrashort laser pulses are playing an ever-increasing role in important scientific experiments and applications
To understand how the pulse is retrieved from a spectral interferometry for direct electric field reconstruction (SPIDER) trace, this equation may be rewritten in terms of the spectral amplitude | E(ω )| and the derivative of the spectral phase
We show that, in the presence of double-pulsing, the SPIDER
Summary
Ultrashort laser pulses are playing an ever-increasing role in important scientific experiments and applications. Most molecular processes occur on ultrafast timescales and so their study requires ultrashort laser pulses using methods like excite-probe spectroscopy [3,4]. For all such applications, it is crucial to be able to measure ultrashort pulses in time, or at least measure their length, complexity, and pulse-to-pulse stability. Variations in the pulse shape from shot to shot introduce uncertainty in the temporal resolution of excite-probe measurements and yield inconsistent peak power, adding noise to measurements in all techniques that use ultrashort pulses. To understand the effect of multiple pulsing, we consider the SPIDER trace of a double pulse comprising two identical pulses with a temporal separation ts and a relative phase θ. The SPIDER trace of this double pulse is : SSPIDER ∝
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