Sub-100 fs Tm:MgWO_4 laser at 2017 nm mode locked by a graphene saturable absorber

Abstract

We present the first sub-100 fs bulk solid-state laser in the 2-μm spectral range employing the monoclinic Tm³⁺-dopedMgWO₄ crystal as an active medium. By applying a graphene-based saturable absorber and chirped mirrors for dispersion management, stable self-starting mode-locked operation at 2017 nm was achieved. Nearly Fourier-limited pulses as short as 86 fs featuring a bandwidth of 53 nm were generated at a repetition rate of 76 MHz. A pulse energy of 1.1 nJ was achieved at 87 MHz for a pulse duration of 96 fs. The mode-locked Tm³⁺:MgWO₄ laser exhibits excellent stability with a fundamental beat note extinction ratio of 80 dBc above noise level.