Passive Q-switching of microchip lasers based on Ho:YAG ceramics

Abstract

A Ho:YAG ceramic microchip laser pumped by a Tm fiber laser at 1910 nm is passively Q-switched by single- and multi-layer graphene, single-walled carbon nanotubes (SWCNTs), and Cr²⁺:ZnSe saturable absorbers (SAs). Employing SWCNTs, this laser generated an average power of 810 mW at 2090 nm with a slope efficiency of 68% and continuous wave to Q-switching conversion efficiency of 70%. The shortest pulse duration was 85 ns at a repetition rate of 165 kHz, and the pulse energy reached 4.9 μJ. The laser performance and pulse stability were superior compared to graphene SAs even for a different number of graphene layers (n=1 to 4). A model for the description of the Ho:YAG laser Q-switched by carbon nanostructures is presented. This modeling allowed us to estimate the saturation intensity for multi-layered graphene and SWCNT SAs to be 1.2±0.2 and 7±1 MW/cm², respectively. When using Cr²⁺:ZnSe, the Ho:YAG microchip laser generated 11 ns/25 μJ pulses at a repetition rate of 14.8 kHz.

Graphene Q-switched Tm:KY(WO4)2waveguide laser

“…The number of graphene layers (one) was confirmed by Raman spectroscopy with the ratio (~0.2) between the integral intensities of the G and 2D Raman bands, see figure 3(b). According to our previous studies, the saturation intensity of the studied graphene for ns pulse duration is I sat = 0.6 MW cm −2 and the saturable absorption α' S = 0.12% [22].…”

“…The output characteristics of the graphene-SA PQS Tm:KYW laser were modeled with a 'fast' SA model, see details in [19,22]. The parameters of the active material [7,11,12] and the SA [22] used for the calculations are summarized in table 1.…”

“…The parameters of the active material [7,11,12] and the SA [22] used for the calculations are summarized in table 1. Here for the active layer, we used the spectroscopic Figure 5.…”

“…Graphene PQS Tm:KYW waveguide laser: (a) pulse duration Δτ (FWHM), (b) pulse energy E out , (c) pulse repetition frequency (PRF) and (d) peak power P peak versus the absorbed pump power: symbols-experimental data, curves-modelling. [7] τ( 3 F 4 ) 0.8 ms Quantum efficiency [12] η q 1.66 Refractive index [11] n AM 1.995 Length t AM 5.0 mm Graphene-SA Initial absorption α′ 2.3% Saturable absorption [22] α′ S 0.12% Saturation intensity [22] I sat 0.6 MW cm…”

“…In this way, different nanostructured SAs, e.g. based on single-walled carbon nanotubes [22] or few-layer MoS 2 [27], which are known for their relatively low non-saturable losses, could be an alternative.…”