Passively Q-switched 2 μm Tm:YAP laser based on graphene saturable absorber mirror

WSe2/BN heterostructure as saturable absorber for a diode-pumped passively Q-switched 2 µm solid-state laser

We have successfully achieved the synthesis of heterojunction consisting of WSe2 and BN, by using a liquid phase exfoliation method, and characterization of the prepared materials under the microstructure. The WSe2/BN heterojunction was used as a saturable absorber in the Tm:YAP laser for passively Q-switched operation, and a pulsed laser with an output wavelength around 2 µm range was successfully obtained. After comparing the effects of resonators composed of different cavity mirrors, it is concluded that when the curvature radius of the input mirror is 250 mm and the transmittance of the output coupler is 2.5%, the best output performance was obtained. The maximum average output power of 834 mW was achieved, with a pulsed repetition frequency of 43.51 kHz and a minimum pulse duration of 1.28 µs, corresponding to a peak power of 14.97 W and a maximum single pulse energy of 19.17 µJ.

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-peak-power Q-switched 1988 nm bulk laser based on an electro-optical La3Ga5SiO14 modulator

An electro-optically (EO) $Q$Q-switched Tm:YAP laser with high peak power was demonstrated based on a ${{\rm La}_3}{{\rm Ga}_5}{{\rm SiO}_{14}}$La₃Ga₅SiO₁₄ (LGS) crystal. The EO modulator was operated in a pulse-on mode driven by a 1/4 wave voltage of 2400 V, which was the lowest voltage designed for LGS-based EO modulators at 2 µm, to the best of our knowledge. At a repetition rate of 200 Hz, a maximum single-pulse energy of 3.15 mJ was obtained with a minimum pulse duration of 17 ns, corresponding to a peak power as high as 185.3 kW.

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.

Sb2Te3 as the saturable absorber for the ∼2.0 μm passively Q-switched solid state pulsed laser

We demonstrated a passively Q-switched Tm:YAP solid state pulsed laser based on an Sb₂Te₃ saturable absorber. This saturable absorber was prepared by a facile hydrothermal method. The maximum pulse energy was up to 5.366 μJ at the absorbed pump power of 6.6 W. The corresponding pulse width, output power and repetition rate were 533 ns, 542 mW and 101 kHz, respectively. The results indicated that the hydrothermally synthesized Sb₂Te₃ nanosheet was a promising saturable absorber for near-infrared pulsed lasers.

We demonstrated a passively Q-switched Tm:YAP solid state pulsed laser based on an Sb₂Te₃ saturable absorber.

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.

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.

Highly efficient passively Q-switched Tm:YAP laser using a Cr:ZnS saturable absorber

We describe a diode-pumped, passively Q-switched 2 μm Tm:YAP laser generating 10.5 W of average power. The laser utilized a Cr²⁺:ZnS saturable absorber with a nonsaturated transmission (T₀) of 90% and exhibited a record 46% optical slope efficiency and a 42% overall optical conversion efficiency, both measured relative to the incident 794 nm pump power. At maximum average output power, the laser generated 0.6 mJ Q-switched pulses with a maximum peak power of 32 kW. Pulse duration varied between 20 and 53 ns, depending on operating wavelength and pump power. A laser with a T₀=80% saturable absorber generated 1.45 mJ Q-switched pulses with a peak power of 138 kW.

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.

High Power Q-Switched Thulium Doped Fibre Laser using Carbon Nanotube Polymer Composite Saturable Absorber

We have proposed and demonstrated a Q-switched Thulium doped fibre laser (TDFL) with a 'Yin-Yang' all-fibre cavity scheme based on a combination of nonlinear optical loop mirror (NOLM) and nonlinear amplified loop mirror (NALM). Unidirectional lasing operation has been achieved without any intracavity isolator. By using a carbon nanotube polymer composite based saturable absorber (SA), we demonstrated the laser output power of ~197 mW and pulse energy of 1.7 μJ. To the best of our knowledge, this is the highest output power from a nanotube polymer composite SA based Q-switched Thulium doped fibre laser.

Dual-loss-modulated Q-switched Tm:LuAG laser with AOM and monolayer graphene

A laser-diode-pumped dual-loss-modulated Q-switching Tm:LuAG laser with an acousto-optic modulator (AOM) and monolayer graphene saturable absorber (SA) around 2 μm is presented for the first time to the best of our knowledge. The average output power and the pulse widths for different repetition rates have been measured. In comparison with the singly Q-switching laser with AOM or with monolayer graphene SA, the dual-loss-modulated Q-switching laser could generate shorter pulse width and higher peak power. The maximum pulse width compression ratio was found to be 3.11, and the highest peak power was enhanced 97.4 times. The experimental results show that the dual-loss-modulated technology is an efficient method for compressing the pulse width, improving the peak power, and enhancing the pulse stability for the Q-switched lasers at 2 μm.

Passively Q-switched mode locking performance of Nd:GdTaO4 crystal by MoS2 saturable absorber at 1066 nm

Passively Q-switched mode-locking performance of Nd:GdTaO₄ crystal using molybdenum disulfide (MoS₂) as a saturable absorber at 1066 nm was demonstrated for the first time. The MoS₂ saturable absorber was prepared simply by transferring the MoS₂ suspension onto a quartz substrate. By inserting the MoS₂ saturable absorber into the Nd:GdTaO₄ laser, stable Q-switched modelocked operation can be achieved. At the pump power of 4 W, the maximum average output power of 0.156 W was obtained with the optical conversion efficiency of 3.9%.

Passively Q-switched mode-locking of Tm:YAP laser based on Cr:ZnS saturable absorber

Using a Cr:ZnS wafer as the saturable absorber, diode-pumped passively Q-switched mode-locking of a Tm:YAP laser at 1976 nm has been realized for the first time, to the best of our knowledge, and nearly 100% modulation depth of Q-switched mode-locking was achieved. The width of the mode-locked pulse was estimated to be about 980 ps with a repetition rate of 350 MHz within a roughly 300-ns-long Q-switched pulse envelope. A maximum output power of 940 mW was obtained, corresponding to the Q-switched pulse energy of 0.55 mJ. The emission wavelength evolution between the continuous-wave and Q-switched mode-locked operations was presented and discussed. The experimental results indicate that the Cr:ZnS absorber is a promising saturable absorber for passively Q-switched mode-locking operation around 2 μm.

Diode end-pumped passively Q-switched Tm:YAP laser with 1.85-mJ pulse energy

Passive Q switching of a Tm:YAP solid-state laser at 1935 nm with Cr:ZnSe and Cr:ZnS polycrystalline saturable absorbers is demonstrated for the first time, to the best of our knowledge. With Cr:ZnS, a maximum pulse energy of 1.85 mJ is obtained for a pulse duration of 35.8 ns, resulting in a peak power of 51.7 kW. With Cr:ZnSe, the achieved pulse energy of 1.55 mJ with a pulse duration of 42.2 ns leads to 36.7-kW peak power. These high pulse energies, together with the unique lasing wavelength at 1935 nm, make this laser a promising tool for biomedical and microsurgery applications.