Fundamental Limits to Mode-Locked Lasers: Toward Terawatt Peak Powers

Abstract

Most mode-locked solid-state lasers are based on soliton solutions of the cubic Ginzburg-Landau equation. Their performance is close to theoretical limits, and new design paradigms will be needed if solid-state systems are to continue to improve at their historically aggressive rates. Through comprehensive analysis of the interplay of group-velocity dispersion, nonlinear refraction, spectral filtering, and saturable absorption, we identify the factors that fundamentally limit the achievable peak power of solid-state lasers. Numerical calculations that accurately model existing solid-state lasers are used to assess new designs. In particular, we focus on normal-dispersion cavities, which support dissipative solitons. The calculations reveal that the gain bandwidth, modulation depth of the saturable absorber, and nonlinear phase accumulation present the primary limitations to the peak power. We assess these limitations in Ti:sapphire, Yb:KGW, and thin-disk oscillators. Guidelines for the optimum designs are presented, and we show that dissipative soliton pulse-shaping in cavities with net normal dispersion can fundamentally allow performance improvements of several orders of magnitude. High-performance oscillators should offer low-noise, low-cost alternatives to some current amplifier-based systems.