Approaching the microjoule frontier with femtosecond laser oscillators: theory and comparison with experiment

Abstract

A detailed numerical analysis of heavily chirped pulses in the positive-dispersion regime (PDR) is presented on the basis of the distributed cubic–quintic generalized complex nonlinear Ginzburg–Landau equation. It is demonstrated that there are three main types of pulse spectra: truncated parabolic-top, Π- and M-shaped profiles. The strong chirp broadens the pulse spectrum up to 100 nm for a Ti:Sa oscillator, which provides compressibility of the picosecond pulse down to sub-30 fs. Since the picosecond pulse has a peak power lower than the self-focusing power inside a Ti:Sa crystal, the microjoule energies become directly available from a femtosecond oscillator. The influence of the third- and fourth-order dispersions on the pulse spectrum and stability is analysed. It is demonstrated that the dynamic gain saturation plays an important role in pulse stabilization. The common action of dynamic gain saturation, self-amplified modulation (SAM) and saturation of the SAM provides pulse stabilization inside the limited range of the positive group-delay dispersions (GDDs). Since the stabilizing action of the SAM cannot be essentially enhanced for a pure Kerr-lens mode-locking regime, a semiconductor saturable absorber is required for pulse energies of >0.7 μJ inside an oscillator. The basic results of the numerical analysis are in an excellent agreement with experimental data obtained from oscillators with repetition rates ranging from 50 to 2 MHz.

Investigation of a 200-nJ chirped-pulse Ti:Sapphire oscillator for white light generation

“…This dispersion behavior is mainly limited by the dispersion of the 2" Herriott-cell mirrors since a higher number of bounces magnifies any detrimental effect resulting from their spectral GDD oscillations. The measured spectrum is also in accordance with simulations since the effect of the non-vanishing mirror TOD can be obviously seen in the observed asymmetric spectrum as supported by detailed simulations of Kalashnikov et al [8]. It is expected that by the usage of more carefully dispersion-engineered mirrors with more accurately matched GDD oscillations one could get rid of this unwanted feature.…”

Towards a Compact Thin-Disk-Based Femtosecond XUV Source

“…Depending on the mode-locking parameters, the spectrum can exhibit strong non-linear chirp at the edges, a common feature of the positive dispersion regime. The autocorrelation with pedestal may be due to an uncompensated non-linear chirp [137]. The spectral shapes in Fig.4.17 have relatively smooth edges as a result of the narrow gain bandwidth and the relatively large net loss, (see [31], [21]) and become more truncated with the growth of the GDD.…”

Tm^3+-doped CW fiber laser based on a highly GeO_2-doped dispersion-shifted fiber

“…The dashed curve in Fig. 7 demonstrates that the all-normal-dispersion (ANDi) regime of modelocking [14,15] is feasible for very small core radii. Such regime is of interest for generation of the energy-scalable femtosecond pulses [16].…”