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A doubly Q-switched Nd:GGG laser emitting 1064 nm wavelength with an acousto-optic modulator (AOM) and a monolayer graphene saturable absorber (SA) is presented to study the pulse characteristics. In comparison with singly passive Q-switched laser (SPQSL) with grapheme SA, the doubly Q-switched laser (DQSL) can effectively shorten the pulse width and improve the pulse peak power. The existence of the ramping behavior of pulse characteristics versus modulation frequency in DQSL is shown. The average output power, the pulse width, the pulse energy and the peak power are related to modulation frequency of AOM, and the point of inflection is dominated by pump power. [ABSTRACT FROM AUTHOR]

By simultaneously employing electro-optic (EO) modulator and Graphene saturable absorber (SA) in a dual-loss-modulated Q-switched and mode-locking (QML) Nd:Lu 0.15 Y 0.85 VO 4 /KTP green laser, the sub-nanosecond single mode-locking green laser is demonstrated with high peak power, low repetition rate and high stability. The monolayer and 3-layer graphene sheets grown by chemical vapor deposition (CVD) method were used as SAs in the experiment. When the pump power reached 10.72 W, the maximum peak power obtained from the doubly QML laser with EO and monolayer graphene-SA was 1.38 MW, corresponding to a pulse duration of 480 ps. The shortest pulse width of 340 ps was obtained with a 3-layer graphene-SA. [ABSTRACT FROM AUTHOR]

An intracavity KTiOPO 4 (KTP) optical parametric oscillator (IOPO) pumped by a doubly Q-switched YVO 4 /Nd:YVO 4 laser with an acousto-optic modulator (AOM) and a monolayer graphene saturable absorber has been realized for the first time. The average output power, the pulse duration, single pulse energy and the peak power of signal light versus incident pump power have been measured. At an incident pump power of 11.7 W and an AOM repetition rate of 10 kHz, the shortest pulse duration of 1.24 ns was obtained, corresponding to a single pulse energy of 9.5 μJ and a peak power of 7.9 kW. In comparison, the doubly IOPO (DIOPO) pumped by doubly Q-switched laser with AOM and graphene saturable absorber can generate pulses with narrower pulse width and higher peak power than the singly IOPO (SIOPO) pumped only by AOM Q-switched laser. [ABSTRACT FROM AUTHOR]

Abstract The saturable absorption properties of molybdenum tungsten disulfide (MoWS 2) near 1.6 μm were investigated. Passively Q-switched Er:YAG laser at 1645 nm with a home-made MoWS 2 as saturable absorber was realized. Under an absorbed pump power of 10.75 W, a maximum average output power of 1.62 W was achieved with a pulse duration of 1 μs at a repetition rate of 43 kHz, corresponding to a pulse energy of 37.7 μJ. Highlights • MoWS 2 alloy has outstanding absorption properties. • MoWS 2 alloy possesses great potential for the optical modulation of laser operation at 1.6 μm. • We realized stable laser operation by utilizing MoWS 2 alloy as saturable absorber. [ABSTRACT FROM AUTHOR]

• The Bi 2 Te 3 nanoflakes was fabricated by liquid-phase exfoliation and characterized. • Applying the Bi 2 Te 3 SA, a dual-loss-modulated QML IOPO laser was realized, resulting in the generation of sub-nanosecond single mode-locking pulses. • The rate equations for IOPO driven by the QML laser with Bi 2 Te 3 SA were numerically solved. By utilizing the ultrasound-assisted liquid phase exfoliation process, Bi 2 Te 3 nanosheets are synthesized and deposited onto a quartz plate to form a saturable absorber (SA), in which nonlinear absorption characteristics around 1 μm are investigated with a home-made Q-switched laser. With the as-prepared Bi 2 Te 3 SA employed, a sub-nanosecond KTiOPO 4 (KTP) based intracavity optical parametric oscillator (IOPO) pumped by a dual-loss-modulated Q-switched and mode-locked (QML) laser is successfully realized. With a short duration of sub-nanosecond and a repetition rate of several kilohertz (kHz), the signal wave's single mode-locking pulse existed underneath a Q-switched envelope can be formed. At an incident pump power of 8.92 W and an acousto-optic modulator (AOM) repetition rate of 2 kHz, a signal wave's single mode-locking pulse underneath a Q-switching envelope with a measured minimum pulse duration of 520 ps is accomplished. It is the first demonstration of such Bi 2 Te 3 SA utilized in a solid-state QML IOPO laser, to the best of our knowledge. According to the experimental results, this provides an efficient and straightforward approach to acquire sub-nanosecond OPO signal wave pulses. Additionally, the relevant coupled rate equations are established, and the simulation results match the experimental results, revealing the potential of Bi 2 Te 3 as a nanomaterial for optoelectronic applications. [ABSTRACT FROM AUTHOR]

In this paper, the Nb2CTx MXene nanosheets were fabricated and the corresponding microstructures were investigated. The nonlinear optical response was illustrated by open aperture Z-scan and I-scan methods. The ground and the excited state absorption cross-sections of 2D Nb2CTx MXene were also investigated. As the saturable absorber (SA), the Nb2CTx MXene was applied in the passively Q-switched Tm:YAP laser. 1.96 μs Q-switched pulses with 3.97 W peak power were achieved at the repetition frequency of 80 kHz. Further theoretical model was built by using the coupled rate equations in simulating the dynamic process of the passively Q-switched Tm:YAP laser. The numerical simulation results are fundamentally in agreement with the experimental results, which proves the Nb2CTx MXene can be a good potential nanomaterial for further optoelectronic applications. [ABSTRACT FROM AUTHOR]

• 2D MoTe 2 nanosheets were fabricated and characterized. • A sub-nanosecond IOPO pumped by a hybrid Q-switched laser has been realized. • Simulation results agreed with the experimental results well. In this paper, few-layered molybdenum ditelluride (MoTe 2) nanosheets are synthesized with a liquid-phase exfoliation method. Its appearance, the spectra and the saturated absorption characteristics are measured. By using MoTe 2 as saturable absorber (SA), a passively Q-switched YVO 4 /Nd:YVO 4 laser is realized. At an incident pump power of 6.64 W, a maximum output power of 1.14 W with a minimum pulse duration of 66.2 ns is obtained. To our knowledge, this is the shortest pulse width ever achieved from a passively Q-switched laser with a MoTe 2 -SA at 1.06 μm. Based on this, a sub-nanosecond KTiOPO 4 (KTP) based intracavity optical parametric oscillation (IOPO) pumped by a hybrid Q-switched laser with a MoTe 2 -SA and an acousto-optic modulator (AOM) is realized. At an incident pump power of 10.4 W and an AOM repetition rate of 10 kHz, a maximum output power of 195 mW with a minimum pulse duration of 835 ps for signal wave is obtained. To solve the IOPO rate equations, the ground-state and excited-state absorption cross sections of MoTe 2 are rationally calculated to be 1.32 × 10−18 cm2 and 9.15 × 10−19 cm2 according to the observed transmittance curve, respectively, and the excited-state lifetime is 376.2 µs. The numerical solution of the equations matches well with the experimental data. [ABSTRACT FROM AUTHOR]

• MoTe 2 nanoflakes were successfully exfoliated by liquid phase exfoliation. • The saturable absorption property of the film at ~3 μm was characterized. • Q-switched laser at ~3 μm based on the MoTe 2 film was realized. • 2 dimensional MoTe 2 film is an outstanding passive modulator at ~3 μm. The stable nano-seconds pulsed Er:Lu 2 O 3 laser were realized by employing a molybdenum ditelluride (MoTe 2) saturable absorber (SA), which was fabricated with the liquid phase exfoliation (LPEx) method. Under the absorbed power of 7.24 W, the maximum average output power of 0.52 W was achieved in a repetition rate of 105 kHz and a pulse duration of 317 ns at 2.85 μm, corresponding to a pulse energy of 4.94 μJ and a peak power of 15.6 W. [ABSTRACT FROM AUTHOR]

In this paper, a sub-nanosecond KTiOPO 4 (KTP)-based intracavity optical parametric oscillator (IOPO) pumped by a dual-loss modulated Q-switched and mode-locked (QML) laser with an acousto-optic modulator (AOM) and a Cr 4+ :YAG saturable absorber (Cr 4+ :YAG-SA) has been demonstrated. By changing the initial transmission of Cr 4+ :YAG-SA and the transmission of the output coupler at the signal wavelength, the signal pulse width compression can be realized. At an incident pump power of 8.3 W and an AOM repetition rate of 15 kHz, a single signal pulse underneath Q-switched envelope with the shortest pulse width of 220 ps was obtained. The experimental results reveal that this is a simple and effective way to obtain the sub-nanosecond OPO signal pulses. In addition, the related coupled rate equations have been set up and the simulation results agreed with the experimental results well. [ABSTRACT FROM AUTHOR]

2D MoWS 2 is fabricated by the chemical-vapor transport and liquid-phase exfoliation method. Its nonlinear optical response is measured. By using MoWS 2 SA and EOM, an LD-pumped doubly Q-switched mode-locked (QML) Tm:YAP laser at 2 μ m waveband is presented. The average output power, the pulse width, and the pulse peak power of the Q-switched envelope are measured. In comparison to the singly QML laser with MoWS 2 SA or EOM, the doubly QML laser can generate shorter pulse duration and higher peak power. Based on the fluctuation mechanism, a developed rate equation model under plane wave approximation is proposed to describe the doubly QML dynamic process. The pulse characteristics of QML laser are numerically simulated and the theoretical simulations are in agreement with the experiment results. Both the experiments and numerical simulations show that MoWS 2 is a promising nanomaterial, and the dual-loss-modulated QML laser displays well performance in pulse width compression and peak power enhancement. • Two-dimensional MoWS 2 is fabricated and its optical response is measured. • Doubly Q-switched mode-locked Tm:YAP laser with MoWS 2 and EOM is realized. • A developed rate equation model is proposed to describe Q-switched mode-locking. [ABSTRACT FROM AUTHOR]

Highlights: [•] The fabricate process of GO and CNTs dispersions was demonstrated. [•] Q-switching performance of GO and CNTs dispersions was reported. [•] The GO and CNTs dispersions are suitable for solid-state lasers. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, by considering Gaussian distribution of the intracavity photon density, the coupled rate equations for the diode-pumped doubly Q-switched and mode-locked (QML) laser with EO modulator and GaAs saturable absorber are presented. These equations are numerically solved, and the key parameters of an optimally coupled doubly QML laser have been determined. These key parameters include parameters of the gain medium, the small-signal transmission of saturable absorber as well as the modulation frequency of EO modulator, which can maximize the pulse energy of singly Q-switched envelope. A diode-pumped doubly QML Nd:Lu0.15Y0.85VO4 laser with EO modulator and GaAs saturable absorber is constructed, the experimental results have verified numerical simulation applicable. [Copyright &y& Elsevier]

In the current study, layered metallic vanadium disulfide (VS2) is fabricated by a liquid-phase exfoliation method, and its microstructures as well as optical characteristics are investigated. Based on first-principles calculations, the band structure and density of the states of both bulk T-VS2 and monolayer H-VS2 are illustrated, showing the metallic behavior with a zero band gap. By using VS2 as the saturable absorber in a doubly Q-switched Tm:YAP laser with an EOM, the Q-switching laser pulses at 2 μm with 22 ns and 200 Hz are generated, corresponding to the single pulse energy of 755 μJ and the peak power of 34.3 kW. The coupled rate equations of the doubly Q-switched laser are given, and the numerical simulations agree with the experimental results. The results indicate that VS2 is a promising nanomaterial due to its nonlinear optical property. The doubly Q-switched laser demonstrates a high level of performance in reducing pulse width and enhancing pulse peak power. [ABSTRACT FROM AUTHOR]

Ternary chalcogenides possess a promising prospect for their superior nonlinear optical response, offering new opportunities in future photonic devices. Ta 2 NiS 5 and Ta 2 NiSe 5 nanoflakes fabricated by liquid-phase exfoliation were investigated. Based on Tm:YAG ceramic and Tm,Ho:Ca(Gd,Lu)AlO 4 crystal as gain media, the doubly passively Q-switched lasers with Ta 2 NiS 5 and Ta 2 NiSe 5 saturable absorbers were realized. The shortest pulse duration was 391 ns, which was realized in Tm,Ho:Ca(Gd,Lu)AlO 4 laser. And the highest peak power 17.73 W was obtained in Tm:YAG ceramic laser. The results demonstrate that the Ta 2 NiS 5 and Ta 2 NiSe 5 nanomaterials have the potential to generate a short-pulsed laser. Doubly Q-switching technology can compress pulse duration and enhance peak power. • The Ta 2 NiS 5 and Ta 2 NiSe 5 nanoflakes was fabricated by liquid-phase exfoliation. • Ternary chalcogenide nanomaterials performed well for pulsed laser generation. • The shortest pulse duration of 391 ns was realized in Tm,Ho:Ca(Gd,Lu)AlO 4 laser. • The highest peak power of 17.73 W was obtained in Tm:YAG ceramic laser. [ABSTRACT FROM AUTHOR]

• Two-dimensional MXene Ti 3 C 2 T x was fabricated. • A doubly Q-switched Tm:LuAG laser was realized with MXene Ti 3 C 2 T x and AOM. • The narrowest pulse width was 178 ns and highest peak power was 1062 W. MXene Ti 3 C 2 T x (T = F, O, or OH) was fabricated by aqueous acid etching and liquid phase exfoliation method. Its appearance, the spectra and the saturated absorption characteristics were measured. By using MXene Ti 3 C 2 T x as saturable absorber (SA) and an acousto-optic modulator (AOM), a doubly Q-switched Tm:LuAG laser at 2 μm waveband was realized. Under the incident pump power of 9.5 W at modulated repetition rate 1 kHz of AOM, the narrowest laser pulse width of 178 ns was obtained, corresponding to the highest pulse peak power of 1062 W. To our knowledge, this is the shortest pulse width and highest peak power obtained in the Q-switched lasers with MXene Ti 3 C 2 T x as SA. In comparison to the singly Q-switched laser with only MXene Ti 3 C 2 T x or AOM, the doubly Q-switched laser can generate shorter pulse width and higher peak power. The maximum compression ratio of pulse width 6.0 and the highest enhancement factor of peak power 205 were achieved. The experimental results show that MXene Ti 3 C 2 T x is an excellent SA in 2 μm waveband laser system and the doubly Q-switched laser can compress pulse width and improve pulse peak power. [ABSTRACT FROM AUTHOR]

• Tm:Ca(Gd,Lu)AlO 4 is used as laser medium. • CVD-grown WS 2 is used as saturable absorber. • Doubly Q-switch compresses pulse width and improves peak power. A two-dimensional WS 2 grown by chemical vapor deposition (CVD) is employed as saturable absorber. Using a novel crystal of Tm:Ca(Gd,Lu)AlO 4 , doubly Q-switched laser with acousto-optic modulator (AOM) and WS 2 saturable absorber is presented. The shortest pulse width of 91 ns corresponding to a highest peak power of 1.2 kW is obtained when the modulation rate (MR) of AOM is 1 kHz. In comparison to the singly Q-switched lasers with WS 2 or AOM, the maximum pulse width compression ratio is 15.38 and the highest peak power enhancement factor is 511.30. The experiment results show a promising saturable absorption of WS 2 and that the doubly Q-switched laser is beneficial for compressing the pulse width and improving the peak power. [ABSTRACT FROM AUTHOR]

By simultaneously inserting MoS 2 and WS 2 saturable absorbers (SAs) into laser resonator, a doubly passively Q-switched Tm:YAP laser at 2 μm was realized. Measurements of the average output power, the pulse width and the pulse repetition frequency (RF) have been undertaken. In comparison to singly Q-switched laser using MoS 2 or WS 2 , the doubly Q-switched laser using both MoS 2 and WS 2 can generate more stable pulse trains with shorter pulse width and higher peak power. At the absorbed pump power of 6.04 W, the maximum peak power of 22.4 W and the shortest pulse width of 249.4 ns were obtained. While for singly Q-switched laser using MoS 2 or WS 2 , they were 10.7 W, 528.4 ns and 14.4 W, 458.8 ns. The experimental results hit at a conclusion that the doubly passively Q-switched operation is an efficient way to compress the pulse width, improve the peak power and enhance the stability of pulse trains at 2 μm waveband laser. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) graphitic carbon nitride (g-C 3 N 4) was fabricated as saturable absorber (SA) and the nonlinear optical absorption properties were measured. A laser-diode (LD) pumped doubly Q-switched Tm-doped yttrium-aluminium perovskite YAlO 3 (Tm:YAP) laser at 2 μm with g-C 3 N 4 and acousto-optic modulator (AOM) is presented for the first time to the best of our knowledge. Under an absorbed pump power of 5.34 W, the minimum pulse width of 239 ns and the maximum peak power of 1146 W were obtained by the doubly Q-switched laser. In comparison with the singly Q-switched laser using g-C 3 N 4 SA or AOM, the dual-loss-modulated Q-switched laser could generate shorter pulse width and higher peak power. The maximum pulse width compression ratio was 4.48 and the highest peak power enhancement factor was 241. The experimental results indicated that 2D g-C 3 N 4 SA is potential in Q-switched laser at 2 μm and the doubly Q-switched technology is a useful way to compress the pulse width and improve the peak power. • 2D g-C 3 N 4 SA was fabricated and the nonlinear optical absorption properties were measured. • A laser-diode (LD) pumped doubly Q-switched Tm:YAP laser at 2 μm with g-C 3 N 4 SA and AOM is realized for the first time. • The pulse width of the Q-switched laser is compressed greatly. • The pulsed peak power is improved evidently. [ABSTRACT FROM AUTHOR]