Ruijun Lan

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

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.

Broadly tunable mode-locked Ho:YAG ceramic laser around 2.1 µm

A passively mode-locked Ho:YAG ceramic laser around 2.1 µm is demonstrated using GaSb-based near-surface SESAM as saturable absorber. Stable and self-starting mode-locked operation is realized in the entire tuning range from 2059 to 2121 nm. The oscillator operated at 82 MHz with a maximum output power of 230 mW at 2121 nm. The shortest pulses with duration of 2.1 ps were achieved at 2064 nm. We also present spectroscopic properties of Ho:YAG ceramics at room temperature.

Semiconductor saturable absorber Q-switching of a holmium micro-laser

We report on a Holmium micro-laser passively Q-switched by a semiconductor saturable absorber (SSA), for the first time to the best of our knowledge. It is based on a 1 at.% Ho:YAG ceramic with good energy storage capability and several commercial transmission-type SSAs with 0.24% modulation depth. Under in-band pumping by a Tm fiber laser at 1910 nm, the Ho micro-laser generated 450 mW at 2089 nm with 37% slope efficiency. Stable 89 ns, 3.2 μJ pulses are achieved at a repetition rate of 141 kHz. Further shortening of the laser pulses is feasible with the increase of the modulation depth of the SSA while power scaling may lead to Q-switching at MHz-range repetition rates.

Thulium doped LuAG ceramics for passively mode locked lasers

Passive mode-locking of a thulium doped Lu3Al5O12 ceramic laser is demonstrated at 2022 nm. By applying different near surface GaSb-based saturable absorber mirrors, stable self-starting mode-locked operation with pulse durations between 2 and 4 picoseconds was achieved at a repetition rate of 92 MHz. The SESAM mode-locked Tm:LuAG ceramic laser exhibits an excellent stability with a fundamental beat note extinction ratio of 80 dB above the noise level. Furthermore, spectroscopic properties of Tm:LuAG ceramics at room temperature are presented.

Efficient near-infrared, multiwavelengths PbWO4 Raman laser

Abstract. We report on a near-infrared, multiwavelength-stimulated Raman scattering (SRS) laser source based on the PbWO4 crystal, pumped by a pico-second Nd:YAG laser. At a high pump level, simultaneous two phonon modes SRSs are obtained, including 901 and 323  cm−1 Raman shifts, presenting six Raman spectral lines distributing in 1- to 1.5-μm waveband. The largest Raman output energy is 0.72 mJ, corresponding to an optical conversion efficiency of 37.9% and a slope efficiency of 80.4%. This work manifests that, as a low cost, large size, and high damage threshold crystal, PbWO4 is an efficient, convenient SRS material to enrich near-infrared laser wavelengths.

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

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.