Abstract
In laser–matter interaction experiments, it is of paramount importance to characterize the laser pulse on target (in situ) and at full power. This allows pulse optimization and meaningful comparison with theory, and it can shed fundamental new light on pulse distortions occurring in or on the target. Here we introduce and demonstrate a new technique based on dispersion-scan using the concurrent third harmonic emission from the target that permits the full (amplitude and phase), in situ, in-parallel characterization of ultrashort laser pulses in a gas or solid target over a very wide intensity range encompassing the 10 13 – 10 15 W c m − 2 regime of high harmonic generation and other important strong-field phenomena, with possible extension to relativistic intensities presently inaccessible to other diagnostics.
Highlights
Great progress has been made over the last 20 years in the development of techniques such as FROG [1], SPIDER [2], MIIPS [3], and more recently, dispersion-scan (d-scan) [4], to fully characterize femtosecond laser pulses, that is, to measure the amplitude and phase of the optical field
0.13 mJ, and the on-target peak intensity was estimated to be 2 × 1014 Wcm−2. This is in agreement with the peak intensity calculated from the ≈55 eV cutoff in the Ar high harmonic generation (HHG) spectrum shown in Fig. 2(a) using the Ip + 3.2Up rule [50,51] for the cutoff energy, where Ip is the ionization potential of the gas atoms, and Up is the ponderomotive potential of the focused laser beam
The Ar HHG spectrum was recorded under identical conditions to the d-scan measurement by moving the third harmonic (TH) pick off mirror out of the beam path
Summary
Great progress has been made over the last 20 years in the development of techniques such as FROG [1], SPIDER [2], MIIPS [3], and more recently, dispersion-scan (d-scan) [4], to fully characterize femtosecond laser pulses, that is, to measure the amplitude and phase of the optical field. By directing the TH out of the chamber and recording its spectrum as a function of dispersion introduced onto the laser beam by the existing pulse compressor in the laser system, a d-scan measurement can be made In cases such as for our experiment, where the target thickness is small compared to the confocal parameter of the focused laser beam, the generation volumes for the TH and high harmonics will overlap, ensuring the laser pulse is measured in the HHG interaction region. We show that this new method is capable of accurately characterizing intense pulses of 4 fs in duration under conditions optimized for HHG
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