Compact in-line temporal measurement of laser pulses with amplitude swing

Abstract

A method of ultrashort laser pulse reconstruction is presented, consisting on the analysis of the nonlinear signal obtained from the interference of the pulse with a replica of itself at a given time delay while varying the relative amplitude between the pulses. The resulting spectral traces are analyzed both analytically and numerically, showing the encoding of the input pulse spectral phase. A reconstruction algorithm is discussed and applied to extract the spectral phase and, jointly to the measured spectral amplitude, reconstructing the pulse. In order to validate the technique, an experimental in-line implementation of the characterization concept is compared to the results from a stablished technique, obtaining a good agreement at different input pulse cases. In sum, a new technique is presented, showing the capability to reconstruct a broad range of temporal pulse durations while its implementation is robust and straightforward, able to be easily adapted to diverse pulse duration and central wavelength ranges.

Robustness and capabilities of ultrashort laser pulses characterization with amplitude swing

“…The simulated spectral phase of the pulse, , consisted in a combination of second- and third-order dispersion of—8000 fs 2 and + 20,000 fs 3 , respectively, thus the pulse duration corresponded to = 179.8 fs (FWHM). The choice of these dispersion values is motivated by the previously reported fact that for very high chirp values may more subtle encoded in the amplitude swing trace 12 , so that we decided to perform the study under adverse conditions.…”

“…In the last decade, more compact schemes have been introduced, as in MIIPS 9 , d-scan 10 or chirp-scan 11 . Recently, we have proposed and demonstrated the amplitude swing concept to measure ultrashort laser pulses 12 . In this technique, two delayed replicas of the input pulse are created with different relative amplitudes, while the spectrum of their second harmonic (SH) generation is measured for the different amplitudes, thus resulting in a two-dimensional trace.…”

“…In the amplitude swing technique 12 , two delayed replicas of the input pulse are created, then their relative amplitude is varied, and they experiment a nonlinear process (e.g., SH generation), being the amplitude of the nonlinear signal resolved in frequency with a spectrometer. A rotating birefringent material combined with a linear polarizer is used to perform the shaping of the replicas in the pulse manipulation described before.…”

“…The trace given in Eq. ( 1 ) encodes the spectral phase of the pulse, which can be retrieved with a proper algorithm 12 . Here, we also use iterative optimization by means of the Levenberg–Marquardt algorithm.…”

“…From the comparison between the experimental and the simulated SH traces it is defined a merit function, which is minimized to retrieve the spectral phase of the pulse. Previously 12 , the amplitude swing was used to retrieve pulses with a flat and complete spectral response of the SH.…”