Characterization of high-power near-infrared ultrashort pulses of solid-state laser amplifiers using spectral phase measurements

Abstract

Ultrafast laser science relies on the characterization of ultrashort pulses, which requires determining their electric field properties. This thesis focuses on the pulse characterization of two solid-state femtosecond lasers operating in the near-infrared range using self-referenced spectral interferometry (SRSI). SRSI is a technique based on linear spectral interferometry that utilizes cross-polarized wave generation to generate a reference pulse and enables the determination of both the spectral amplitude and the spectral phase of laser pulses. The experimental setup and critical parameters were carefully analyzed to ensure accurate measurements of the electric field. In the process of determining the spectral phase, a polynomial fitting was employed to obtain dispersion terms up to order four. Experimental evidence indicates that these determined dispersion terms accurately correspond to the actual dispersion terms only within a specific validity range. A method for establishing this validity range is presented. Dispersion compensation devices were implemented to minimize pulse duration by flattening the phase across the spectral bandwidth. Consequently, a pulse duration of 38 fs was achieved for a Thales ALPHA kHz laser, while a pulse duration of 271 fs was achieved for a Light Conversion PHAROS laser. Moreover, this work implemented an extended SRSI technique that takes into account the influence of an incoherent laser output component, specifically amplified spontaneous emission (ASE). The experimental findings confirmed the predictions of the extended analytical model, which also allowed the determination of the ASE spectrum of a Thales ALPHA kHz laser.