WS2 as a saturable absorber for Q-switched 2 micron lasers

Multi-Functional Applications of H-Glass Embedded with Stable Plasmonic Gold Nanoislands

Metal nanoparticles (MNPs) are synthesized using various techniques on diverse substrates that significantly impact their properties. However, among the substrate materials investigated, the major challenge is the stability of MNPs due to their poor adhesion to the substrate. Herein, it is demonstrated how a newly developed H-glass can concurrently stabilize plasmonic gold nanoislands (GNIs) and offer multifunctional applications. The GNIs on the H-glass are synthesized using a simple yet, robust thermal dewetting process. The H-glass embedded with GNIs demonstrates versatility in its applications, such as i) acting as a room temperature chemiresistive gas sensor (70% response for NO2 gas); ii) serving as substrates for surface-enhanced Raman spectroscopy for the identifications of Nile blue (dye) and picric acid (explosive) analytes down to nanomolar concentrations with enhancement factors of 4.8 × 106 and 6.1 × 105 , respectively; and iii) functioning as a nonlinear optical saturable absorber with a saturation intensity of 18.36 × 1015 W m-2 at 600 nm, and the performance characteristics are on par with those of materials reported in the existing literature. This work establishes a facile strategy to develop advanced materials by depositing metal nanoislands on glass for various functional applications.

Development of a 2 μm Solid-State Laser for Lidar in the Past Decade

The 2 μm wavelength belongs to the eye-safe band and has a wide range of applications in the fields of lidar, biomedicine, and materials processing. With the rapid development of military, wind power, sensing, and other industries, new requirements for 2 μm solid-state laser light sources have emerged, especially in the field of lidar. This paper focuses on the research progress of 2 μm solid-state lasers for lidar over the past decade. The technology and performance of 2 μm pulsed single longitudinal mode solid-state lasers, 2 μm seed solid-state lasers, and 2 μm high power solid-state lasers are, respectively, summarized and analyzed. This paper also introduces the properties of gain media commonly used in the 2 μm band, the construction method of new bonded crystals, and the fabrication method of saturable absorbers. Finally, the future prospects of 2 μm solid-state lasers for lidar are presented.

High performance 1.9 µm passively Q-switched bulk laser with germanene as a saturable absorber

Germanene is an analog of graphene, and its independent novel low-bending honeycomb structure gives outstanding advantages such as environmental stability and significant low-frequency optical absorbance. In this paper, the few-layer germanene was successfully prepared by the liquid phase exfoliation method. The saturable absorption characteristics of germanene in the infrared waveband were detected by the open-aperture Z-scan method. With germanene as a saturable absorber, a high-performance passively Q-switched bulk laser was realized at 1.9 µm. The shortest pulse width of 60.5 ns was obtained from continuous-wave pumping, corresponding to a single pulse energy of 6.7 µJ and peak power of 110 W. By utilizing the pulse pumping style with a repletion rate of 10 Hz, the single pulse energy and peak power increased to 45.8 µJ and 328 W, respectively, which exceeded all two-dimensional SA materials reported before. This research manifests that germanene is an excellent SA material for mid-infrared solid-state lasers.

Generation of High Peak Power Mode-Locked Green Pulses Based on WS2 and EOM: Experiment and Theory

Based on an as-prepared high-quality WS₂ film and an electro-optic modulator (EOM), a dual-loss-modulated low repetition rate mode-locking laser at 0.53 μm with high peak power is presented for the first time. The laser characteristics versus the pump power are investigated experimentally and theoretically. At a pump power of 10.67 W, the shortest pulse duration of 305 ps can be measured, corresponding to the highest peak power of 931 kW, which is much higher than those of the single passive modulated lasers with WS₂-SA. A simple rate equation simulation was used to describe this dual-loss-modulated mode-locking green laser based on WS₂ and EOM. The results of the numerical simulation are basically in accordance with the experimental values.

Nickel-vanadium layered double hydroxide nanosheets as the saturable absorber for a passively Q-switched 2 µm solid-state laser

Nickel-vanadium (NiV)-layered double hydroxide (LDH) was fabricated into a novel saturable absorber (SA) by the liquid phase exfoliation method and utilized as the laser modulator for the first time, to our best knowledge. We investigated a passive Q-switched Tm:YAG ceramic laser at 2 µm with the NiV-LDH SA. Under an absorbed pump power of 7.2 W, the shortest pulse width of 398 ns was obtained with an average output power of 263 mW and a pulse repetition frequency of 101.8 kHz, corresponding to a single pulse energy at 2.30 µJ. The results indicate that the NiV-LDH SA has great research potential in the field of laser modulation.

Self-Q-switched and multicolor operation of a Tm:LuAG laser

In this paper, we report self-Q-switched (SQS) and three-color operation of an all-solid-state Tm:LuAG laser for the first time to our knowledge. In the experiments, a low-cost 3 W AlGaAs laser diode was used to end-pump the Tm:LuAG crystal inside a four-mirror x cavity. In typical continuous-wave (cw) operation, as high as 754 mW output power was obtained with 49% power efficiency at 2023 nm. Three-color and SQS operations were initiated by fine tuning of the curved mirror separation within the stability range of the resonator. In the three-color regime, the Tm:LuAG laser produced two extra, i.e., 2019 and 2033 nm, wavelength oscillations in addition to on at 2023 nm. As high as 542 mW output power was observed in this regime. To the best of our knowledge, this is the first stable three-color laser operation obtained with an isotropic gain medium without having any birefringent elements in the cavity. Furthermore, the SQS operations were also observed at other curved mirror separations. In the SQS regime, the Tm:LuAG laser produced as fast as 13.3 kHz repetition rate pulses and as high as 42.5 µJ pulse energy. Analysis of power-dependent repetition rate data gave an estimated value of 2% for the round-trip saturable loss of the crystal. As far as we know, this is the first cw-pumped stable SQS 2 µm laser that contains an ordered isotropic gain medium as well as the highest pulse energy obtained in any cw-pumped SQS laser.

Saturable absorption characteristics of Bi2Se3 in a 2 µm Q-switching bulk laser

We investigate the saturable absorption properties of Bi₂Se₃ in a bulk laser operating at 2 µm wavelength region. The Bi₂Se₃ saturable absorber (SA) is prepared with the liquid-phase exfoliation method, which gives a saturable input flux of 4.3 mJ/cm², a modulation depth of ∼10%, and a non-saturable absorption of 10.2%. With the Bi₂Se₃ saturable absorber, a passive Q-witching Tm:YAG ceramic laser is realized with a shortest pulse duration of 355 ns, a single pulse energy of 6.76 µJ and peak power of 19 W. We believe that this is the first report on Bi₂Se₃ Q-switched 2 µm bulk laser.

2D materials towards ultrafast photonic applications

Two-dimensional materials are now excelling in yet another arena of ultrafast photonics, including optical modulation through optical limiting/mode-locking, photodetectors, optical communications, integrated miniaturized all-optical devices, etc.

Synthesis of WS1.76Te0.24 alloy through chemical vapor transport and its high-performance saturable absorption

Layered transitional metal dichalcogenides (TMDs) are drawing significant attentions for the applications of optics and optoelectronics. To achieve optimal performances of functional devices, precisely controlled doping engineering of 2D TMDs alloys has provided a reasonable approach to tailor their physical and chemical properties. By the chemical vapor transport (CVT) method and liquid phase exfoliation technique, in this work, we synthesized WS_1.76Te_0.24 saturable absorber (SA) which exhibited high-performance of nonlinear optics. The nonlinear saturable absorption of the WS_1.76Te_0.24 SA was also measured by the open aperture Z-scan technique. Compared to that of the binary component WS₂ and WTe₂, WS_1.76Te_0.24 SA has shown 4 times deeper modulation depth, 28% lower saturable intensity and a much faster recovery time of 3.8 ps. The passively Q-switched laser based on WS_1.76Te_0.24 was more efficient, with pulse duration narrowed to 18%, threshold decreased to 28% and output power enlarged by 200%. The promising findings can provide a method to optimize performances of functional devices by doping engineering.

Ternary chalcogenide Ta2NiS5 as a saturable absorber for a 1.9 μm passively Q-switched bulk laser

In this Letter, a high-quality saturable absorber (SA) based on a multilayered two-dimensional ternary chalcogenide Ta₂NiS₅ with a narrow bandgap, has been successfully fabricated and used as a SA in a 1.9 μm spectral region. The nonlinear saturable absorption properties of the as-prepared SA have been investigated by using an open-aperture Z-scan method. A passively Q-switched all-solid-state laser operating at 1.9 μm has been realized with the Ta₂NiS₅ SA. The maximum average output power, shortest pulse width, pulse energy, and pulse peak power from the passively Q-switched (PQS) laser are 1.1 W, 313 ns, 22.0 μJ, and 71.0 W, respectively. This is the first demonstration of the saturable absorption property of Ta₂NiS₅, to the best of our knowledge. The results indicate well the promising potential of Ta₂NiS₅ as a broadband SA in realizing pulsed mid-infrared lasers with high performance.

Passively Q-switched 1.989 μm all-solid-state laser based on a WTe2 saturable absorber

In this paper, the novel two-dimensional (2D) tungsten ditelluride (WTe₂) was successfully fabricated by the liquid phase exfoliation method and used as a saturable absorber (SA) for a diode-end-pumped passive Q-switching Tm:YAP laser operating at the 2.0 μm wavelength band. The saturable fluence and the modulation depth of the prepared WTe₂ SA were determined to be 5.1  μJ/cm² and 7.2%, respectively. The maximum average output power of 0.64 W was obtained with the shortest pulse width of 368 ns at a pulse repetition rate of 78 kHz. The corresponding highest single pulse energy and largest pulse peak power were calculated to be 4.8 μJ and 12.7 W, respectively. To the best of our knowledge, this is the first time that WTe₂ has been used as the SA for 2.0 μm solid-state bulk lasers. The results indicate that WTe₂ should be an excellent SA for generating 2.0 μm pulsed lasers.

Bilayer platinum diselenide saturable absorber for 2.0 μm passively Q-switched bulk lasers

A noble transition metal dichalcogenide, bilayers platinum diselenide (PtSe₂), has a narrow bandgap (0.21 eV) and high charge carrier mobility. This metal was manufactured for use as a saturable absorber via the chemical vapor deposition method. The saturable absorption properties of samples, at a wavelength of 2.0 μm, were characterized by the open aperture Z-scan method. An all-solid-state 2.0 μm passively Q-switched laser was achieved experimentally based on the as-prepared bilayers PtSe₂ saturable absorber. The maximum average output power, shortest pulse width, highest single-pulse energy, and highest pulse peak power of this laser were 1.41 W, 244 ns, 24.3 μJ, and 99.6 W, respectively.

Broadband 1T-titanium selenide-based saturable absorbers for solid-state bulk lasers

1T-titanium selenide (1T-TiSe2), a representative of 1T phase transition metal dichalcogenides (TMDs), exhibits semimetallic behaviour with a nearly zero bandgap structure, which makes it a promising photoelectric material. A high-quality multilayer 1T-TiSe2 saturable absorber (SA) is successfully fabricated by a combination of liquid phase exfoliation and the spin coating method. The broadband nonlinear saturable absorption properties of the prepared 1T-TiSe2 SA are investigated by using the open aperture (OA) Z-scan method. Passively Q-switched (PQS) all-solid-state lasers with different bulk crystals at the wavelengths of 1.0, 1.3, 2.0 and 2.8 μm are realised based on the 1T-TiSe2 SA. To the best of our knowledge, this is the first presentation of the application of a 1T-TiSe2 material to all-solid-state bulk lasers. The results indicate that 1T-TiSe2 could be an alternative broadband SA for solid-state pulsed lasers and exhibits promising potential applications in mode-locked ultrafast lasers.

Passive Q-switching induced by few-layer MoTe2 in an Yb:YCOB microchip laser

We report on passive Q-switching action induced by a few-layer MoTe₂ saturable absorber in an Yb:YCa₄O(BO₃)₃ (Yb:YCOB) microchip laser. With a sapphire-based few-layer MoTe₂ incorporated into the 4 mm long plane-parallel resonator of the Yb:YCOB microchip laser, efficient stable passively Q-switched operation was achieved under output couplings of 40%-70%, producing, at an incident pump power of 5.0 W, an average output power of 1.58 W at a repetition rate of 704 kHz with a slope efficiency of 36%; the pulse energy and peak power were respectively 2.25 μJ and 40.8 W, while the shortest pulse duration obtained was 52 ns.

Multi-watt sub-30 ns passively Q-switched Yb:LuPO4/WS2 miniature laser operating under high output couplings

We report on a miniature Yb:LuPO₄ crystal laser at 1.01 μm that is passively Q-switched with a sapphire-based few-layer WS₂ saturable absorber, and that can be operated under very high output couplings (≥80%). With 12.6 W of pump power absorbed, an average output power of 4.35 W is generated at a repetition rate of 1.33 MHz with a slope efficiency of 47%. The maximum pulse energy and highest peak power achieved are 3.41 μJ and 110 W, respectively; while the shortest pulse duration obtained is 28.6 ns. To the best of our knowledge, these results represent the highest output power and shortest pulse duration ever achieved in the 1 μm region from solid-state lasers passively Q-switched by using two-dimensional saturable absorbers.

High-power passively Q-switched 2.0 μm all-solid-state laser based on a MoTe2 saturable absorber

In this article, a high-power diode-end-pumped passively Q-switched (PQS) Tm:YAP laser is reported with novel two-dimension (2D) molybdenum ditelluride (MoTe₂) as a saturable absorber (SA). By using the open-aperture Z-scan method, the saturable absorption properties around 2.0 μm was characterized with a saturable fluence of 2.26 μJ∕cm² and a modulation depth of 6.0% for the as-prepared MoTe₂ SA. The band structure of MoTe₂ with the introduction of Te vacancies is simulated by the DFT method, and the results indicate that the bandgap can be reduced with the vacancies in a suitable range. The shortest pulse width of 380 ns was obtained with an average output power of 1.21 W at a repetition rate of 144 kHz, corresponding to a maximum single pulse energy of 8.4 µJ and peak power of 22.2 W. It is the first presentation of MoTe₂ as the saturable absorber in 2.0 μm solid-state pulse laser generation and the pulse width is the shortest among 2.0 μm solid-state lasers passive Q-switched with transitional metal dichalcogenides (TMDs) SAs to the best of our knowledge. The results indicated that MoTe₂ should be an excellent optical modulator for high repetition rate and short pulsed laser generation in a broadband spectral range.

Diode-wing-pumped electro-optically Q-switched 2 μm laser with pulse energy scaling over ten millijoules

Characteristics of diode-wing-pumped highly efficient Tm:LuAG lasers running both in continuous wave (CW) and electro-optical Q-switching regimes have been investigated. Using a simple plane-plane cavity, a maximum CW output power of 8.5 W has been achieved with a corresponding slope efficiency of 44.5% by "wing pumping" at 790 nm. With a V-shaped cavity, a diode-wing-pumped MgO:LiNbO₃ crystal based electro-optically Q-switched Tm:LuAG laser at 2022.9 nm delivered a maximum pulse energy of 10.8 mJ and a minimum pulse width of 52 ns at a corresponding repetition rate of 100 Hz. To the best of our knowledge, the achieved CW output power and Q-switched pulse energy have both set records for all-solid-state Tm:LuAG lasers, which well reveals an efficient way to generate high-power and high-energy lasers at 2 μm wavelength.

High performance of a passively Q-switched mid-infrared laser with Bi2Te3/graphene composite SA

We report passively Q-switched ∼2 and ∼3  μm mid-infrared (MIR) solid-state lasers with a self-assembly solvothermal-synthesized Bi₂Te₃/graphene heterostructure saturable absorber (SA) for the first time. Based on the oxidation resistance and high thermal conductivity of graphene, and large modulation depth of Bi₂Te₃ nanosheets, two high-performance Q-switching lasers were realized. One is a Tm:YAP laser with a maximum average output power of 2.34 W and a pulse width of 238 ns at ∼2  μm. The corresponding maximum pulse peak power was 91 W, which was much improved in comparison with the pure graphene-based Tm laser. The other one is an Er:YSGG laser producing a pulse width of 243 ns, which is the shortest among the 2D SAs-based ∼3  μm solid-state lasers, as far as we know. Our results indicate that such a composite Bi₂Te₃/graphene material is a promising SA for generating high-performance mid-infrared pulse lasers.

A 2 micron passively Q-switched bulk state pulsed laser based on WS2

We report a 2 micron passively Q-switched bulk state pulsed laser with a pulse of 430 ns based on graphene-like 2D WS₂ nanosheets.