Single-walled carbon nanotubes oust graphene and semiconductor saturable absorbers in Q-switched solid-state lasers at 2 μm

Abstract

Lasers emitting around 2 μm (eye-safe spectral range) are of practical importance for remote sensing, spectroscopy and medicine. Such emission is typically achieved from Tm3+ (3F 4 →3H 6 transition) and Ho3+ ions (5I 7 → 5I 8 transition). The search for appropriate saturable absorbers (SAs) for passive Q-switching (PQS) of ∼2 μm lasers is still ongoing. While “slow” SAs, e.g. Cr2+:ZnS, are well-established, “fast” SAs for high-repetition-rate (MHz-range) PQS or mode-locking are still under investigation. The technology of semiconductor saturable absorbers (SESAs) at ∼2 μm is far from being mature. In the present work, we studied the potential of carbon nanostructures (single-walled carbon nanotubes, SWCNTs, [1] and graphene) as possible alternatives to SESAs.