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

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.

SnS2 as a Saturable Absorber for Mid-Infrared Q-Switched Er:SrF2 Laser

Two-dimensional (2D) materials own unique band structures and excellent optoelectronic properties and have attracted wide attention in photonics. Tin disulfide (SnS₂), a member of group IV-VI transition metal dichalcogenides (TMDs), possesses good environmental optimization, oxidation resistance, and thermal stability, making it more competitive in application. By using the intensity-dependent transmission experiment, the saturable absorption properties of the SnS₂ nanosheet nearly at 3 μm waveband were characterized by a high modulation depth of 32.26%. Therefore, a few-layer SnS₂ was used as a saturable absorber (SA) for a bulk Er:SrF₂ laser to research its optical properties. When the average output power was 140 mW, the passively Q-switched laser achieved the shortest pulse width at 480 ns, the optimal single pulse energy at 3.78 µJ, and the highest peak power at 7.88 W. The results of the passively Q-switched laser revealed that few-layer SnS₂ had an admirable non-linear optical response at near 3 μm mid-infrared solid-state laser.

Nonlinear Optical Modulation Characteristics of MXene Cr2C for 2 μm Pulsed Lasers

MXene materials have shown numerous useful mechanical and electronic properties, and have been found to possess nice potential in the field of optical modulation. Here, we fabricated a MXene Cr₂C saturable absorber by the liquid-phase exfoliation method, and systemically analyzed the surface morphology and nonlinear properties of the Cr₂C sample. Applying the Cr₂C saturable absorber as a Q-switch in a thulium-doped yttrium aluminum perovskite (Tm: YAP) laser, the shortest single pulse was obtained with a width of 602 ns under an absorbed pump power of 3.3 W at a repetition rate of 55 kHz with a T = 1% output coupler. The maximum output power was obtained with a T = 5% output coupler at a repetition rate of 58 kHz. The obtained maximum pulse energy and peak power were 3.96 μJ and 4.36 W, separately, which reveal that the MXene Cr₂C can be applied as a promising modulation material in the near-infrared pulsed lasers.

Multi-Pulse Bound Soliton Fiber Laser Based on MoTe2 Saturable Absorber

Bound solitons have become a hot topic in the field of nonlinear optics due to their potential applications in optical communication, information processing and radar systems. However, the trapping of the cascaded bound soliton is still a major challenge up to now. Here, we propose and experimentally demonstrate a multi-pulse bound soliton fiber laser based on MoTe₂ saturable absorber. In the experiment, MoTe₂ nanosheets were synthesized by chemical vapor deposition and transferred to the fiber taper by optical deposition. Then, by inserting the MoTe₂ saturable absorber into a ring cavity laser, the two-pulse, three-pulse and four-pulse bound solitons can be stably generated by properly adjusting the pump strength and polarization state. These cascaded bound solitons are expected to be applied to all-optical communication and bring new ideas to the study of soliton lasers.

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.

Few-layer GaSe nanosheet-based broadband saturable absorber for passively Q-switched solid-state bulk lasers

In this paper, few-layer two-dimensional (2D) GaSe nanosheets were fabricated and utilized as broadband saturable absorbers (SAs) for passively Q-switched (PQS) solid-state bulk lasers operating at 1.06 and 1.99 µm. For 1.06 µm laser operation, the maximum average output power, the shortest pulse width, and the largest single pulse energy were determined to be 438 mW, 285 ns, and 2.31 µJ, respectively, while for 1.99 µm PQS laser operation, they were 937 mW, 383 ns, and 9.56 µJ. Our results identified the great potential applications of few-layer 2D GaSe nanosheets for practical optical modulators such as SAs for pulsed laser generation.

2D materials beyond graphene toward Si integrated infrared optoelectronic devices

Since the discovery of graphene in 2004, it has become a worldwide hot topic due to its fascinating properties. However, the zero band gap and weak light absorption of graphene strictly restrict its applications in optoelectronic devices. In this regard, semiconducting two-dimensional (2D) materials are thought to be promising candidates for next-generation optoelectronic devices. Infrared (IR) light has gained intensive attention due to its vast applications, including night vision, remote sensing, target acquisition, optical communication, etc. Consequently, the generation, modulation, and detection of IR light are crucial for practical applications. Due to the van der Waals interaction between 2D materials and Si, the lattice mismatch of 2D materials and Si can be neglected; consequently, the integration process can be achieved easily. Herein, we review the recent progress of semiconducting 2D materials in IR optoelectronic devices. Firstly, we introduce the background and motivation of the review. Then, the suitable materials for IR applications are presented, followed by a comprehensive review of the applications of 2D materials in light emitting devices, optical modulators, and photodetectors. Finally, the problems encountered and further developments are summarized. We believe that milestone investigations of IR optoelectronics based on 2D materials beyond graphene will emerge soon, which will bring about great industrial revelations in 2D material-based integrated nanodevice commercialization.

Molybdenum Disulfide Film Saturable Absorber Based on Sol-Gel Glass and Spin-Coating Used in High-Power Q-Switched Nd:YAG Laser

In recent years, many different kinds of nonlinear optical materials have been applied to passively Q-switched solid-state lasers. However, the average output powers of these lasers are typically limited to 1 W due to the low damage threshold of the materials. In this study, a molybdenum-disulfide-doped glass-composite absorber was synthesized using the sol-gel method and spin-coating technique. The optical damage threshold of the absorber reached 3.17 J/cm². Saturation intensity, modulation depth, and nonsaturable loss are 9.35 MW/cm², 8.41%, and 9.14%, respectively. After inserting the absorber into a linear Nd:YAG laser cavity, the maximum average output power (3.22 W) and stable Q-switched laser pulses duration (132 ns) were obtained.

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.

The energy band structure analysis and 2 μm Q-switched laser application of layered rhenium diselenide

In this paper, we prepared a high-quality multilayer ReSe₂ saturable absorber with a liquid-phase exfoliation method and characterized its saturable absorption properties around 2 μm.

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.