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.

Sub-60-fs, compact 1100-nm fiber laser system based on double-pass pre-chirp managed amplification.

An ytterbium-doped, single-stage, double-pass nonlinear fiber amplification system was fabricated for amplifying an 1100-nm mode-locking fiber laser. Pre-chirp managed amplification (PCMA) was applied in realizing the nonlinear amplification process with an all-polarization-maintaining (PM) fiber construction. The system can deliver 19.8-nJ, 58.7-fs, 24.4-MHz amplified signal pulses with a 10-dB spectral range spanning from 1049 nm to 1130 nm. Further experimental investigations were conducted in exploring the dynamics of the double-pass nonlinear amplification process. This compact 1100-nm ultrafast fiber laser can be implemented for multi-photon microscopy (MPM) with deep penetration depth.

Investigation of Nonlinear Optical Modulation Characteristics of MXene VCrC for Pulsed Lasers.

We report the surface morphology and the nonlinear absorption characteristics of MXene VCrC nanosheets prepared by the liquid-phase exfoliation method. The self-made MXene VCrC was applied as a saturable absorber in the Tm:YAP laser experiments, performing excellent Q-switching optical modulation characteristics in infrared range. With this absorber, a stable passively Q-switched 2 µm laser was achieved. Under an incident pump power of 3.52 W, a maximum output power of 280 mW was obtained with a T = 3% output coupler at a repetition frequency of 49 kHz. The corresponding pulse energy and peak power were 5.7 µJ and 6.6 W, respectively. The shortest pulse duration was 658 ns at the repetition rate of 63 kHz with a T = 1% output coupler.

Wavelength-tunable 1104†nm nonlinear amplifier loop mirror laser based on a polarization-maintaining double-cladding fiber.

An ytterbium-doped stretched-pulse mode-locked fiber oscillator was fabricated by applying a nonlinear amplifier loop mirror (NALM). The fiber cavity was built using a large-mode area (LMA) polarization-maintaining (PM) double-cladding (DC) fiber. The central wavelength of the generated 24.7 MHz laser can be modified from 1034 to 1104 nm by tuning the intra-cavity loss. The output power of this laser with a wavelength of 1104 nm at the transmission and reflection ports is 7.61 and 0.33 mW, respectively. The corresponding compressed pulse durations are 192 and 187 fs, which are 1.54 and 1.02 times the Fourier-transform-limited pulse duration, respectively.

Layered Metallic Vanadium Disulfide for Doubly Q-Switched Tm:YAP Laser with EOM: Experimental and Theoretical Investigations.

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.

Investigation on the optical nonlinearity of the layered magnesium-mediated metal organic framework (Mg-MOF-74).

The wavelength-related optical nonlinearities of few-layer Mg-MOF-74 nanosheets were investigated in the wavelength region around 1.08, 1.94, and 2.85 µm by the closed aperture Z-scan, open aperture Z-scan and I-scan method. Under the excitation of 100-µJ laser pulses, the nonlinear refractive index (n2) of -7.7 ± 2.6, -131 ± 5 and 4.9 ± 0.2 cm2/W were obtained, respectively. The wavelength-related optical nonlinearity of the Mg-MOF-74 nanosheet was also investigated. In 2.85 µm wavelength region, the Mg-MOF-74 nanosheets shows a stable saturable absorption property with a modulation depth of 8% and a saturation intensity of 170 mJ/cm2. In the 1.08 and 1.94 µm wavelength regions, we can observe that the Mg-MOF-74 transits from saturable absorption regime to reverse saturable absorption regime with the increasing incident laser intensity. Employed as a saturable absorber in a Er:Lu2O3 laser, Mg-MOF-74 nanosheet shows a thickness-related laser modulation performance. The shortest laser pulse of 284-ns was achieved under a repetition rate of 116 kHz with a 6-nm-thick Mg-MOF-74 nanosheet, which corresponds to a pulse energy of 3.2 µJ and a peak power of 11.4 W.

Theoretical and experimental investigations on doubly Q-switched Tm:YAP laser with EOM and Sb2Te3 nanosheets.

In this paper, two-dimensional material Sb2Te3 nanosheets are fabricated and the optical nonlinear response is investigated. A laser diode (LD) end-pumped doubly Q-switched Tm:YAP laser with electro-optic modulator (EOM) and Sb2Te3 nanosheets based saturable absorber (SA) is presented. The shortest pulse duration of 38 ns is achieved at the pulse repetition frequency of 100 Hz, corresponding to the highest peak power of 111.8 kW. The double Q-switching technique shows the advantages of pulse duration compression and peak power improvement. The coupled rate equations for the doubly Q-switched laser are developed and the corresponding numerical simulation agrees with the experimental results. We believe that the Sb2Te3 is a potential nanomaterial for the application in optoelectronic field.

Theoretical and experimental investigations on Nb2CTxMXene Q-switched Tm:YAP laser at 2µm for the nonlinear optical response.

In this paper, the Nb2CTxMXene 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 Nb2CTxMXene were also investigated. As the saturable absorber (SA), the Nb2CTxMXene was applied in the passively Q-switched Tm:YAP laser. 1.96µs 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 Nb2CTxMXene can be a good potential nanomaterial for further optoelectronic applications.

Optical nonlinearity and laser modulation performance of FeNi-LDH in the mid-infrared region.

In this Letter, we prepare FeNi-layered-double-hydroxide (LDH) nanoflakes and illustrate the corresponding microcosmic morphology. The optical response and laser modulation performance of the nanoflakes in the mid-infrared region were investigated for the first time, to the best of our knowledge. Employed as a saturable absorber in an ${\rm Er}{:}{\rm Lu}_2{\rm O}_3$ laser system, pulses with 256-ns duration were yielded at a repetition of 129 kHz under 7.8-W pump power, which corresponds to a pulse energy of 4.98 µJ.

Modulation of MXene Nb2CTx saturable absorber for passively Q-switched 2.85 µm Er:Lu2O3laser.

We proposed a passively stabilized Q-switched Er:Lu2O3 laser at 2845 nm, applying a MXene Nb2CTx nanosheets saturable absorber prepared by the liquid-phase exfoliation method. The surface morphology and nonlinear properties of this nanosheet were systematically characterized. Average output power of 542 mW for the Q-switched laser was obtained under 7.26 W of absorbed pump power. Meanwhile, the Q-switched pulse duration was measured to be 223.7 ns with 142.9 kHz repetition rate corresponding to a peak power of 16.96 W.

Room temperature watt-level 3.87†µm MgO:PPLN optical parametric oscillator under pumping with a Tm:YAP laser.

A room-temperature highly efficient Tm:YAP laser pumped MgO:PPLN optical parametric oscillator operating at 3.87 µm near degeneracy is demonstrated. The pump source is an acousto-optical (AO) Q-switched Tm:YAP laser, which delivers a maximum output power of 6.17 W with a pulse duration of 45 ns and a repetition rate of 6 kHz. The temperature dependent wavelength tuning characteristics of the PPLN-OPO is investigated, and a maximum OPO output power of 1.2 W at around 3.87 µm is achieved at 35°C, corresponding to an optical-optical conversion efficiency of 19.4%. To the best of our knowledge, this is the maximum output power ever reported from 2 µm waveband laser pumped 3-5 µm MgO:PPLN OPOs.

Passively Q-switched Er:Lu2O3 laser at 2.8 µm with TiC saturable absorber.

Titanium carbide (TiC) nanosheets of two-dimensional multilayer structure were prepared by the liquid-phase exfoliation method. By using the TiC as a saturable absorber, a stable passively Q-switched Er:Lu2O3 laser at 2.85 µm was realized. Under an absorbed pump power of 7.32 W, the obtained maximum output power was 896 mW with a slope efficiency of 15.6%. The Q-switched pulse duration was measured to be 266.8 ns with repetition rates of 136.9 kHz, corresponding to a peak power of 24.6 W.

Passively Q-switched Er:Lu2O3 laser with MXene material Ti4N3Tx (T = F, O, or OH) as a saturable absorber.

In this Letter, we report a titanium nitride (Ti4N3Tx) passive Q-switched Er:Lu2O3 laser. The homemade two-dimensional Ti4N3Tx saturable absorber shows excellent passive Q-switching performance around a 2.85 µm wavelength region. Under the absorbed pump power of 7.4 W, the passive Q-switching laser yields a maximum output power of 0.778 W at a pulse repetition rate of 113.7 kHz, corresponding to a single pulse energy of 6.84 µJ and peak power of 24.57 W.

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.

Are graphene-Bi2Te3 van der Waals heterostructure-based saturable absorbers promising for solid-state Q-switched lasers?

This Letter compared the absorption characteristics of a homemade graphene-Bi2Te3 (G-B) van der Waals heterostructure to a Bi2Te3 topological insulator (TI) with a similar preparation method and number of layers. The results indicate that the G-B heterostructure can tremendously enhance the modulation depth and saturable intensity. In addition, a passively Q-switched laser at 1.06 µm with a G-B heterostructure as a saturable absorber (SA) was demonstrated for the first time, to the best of our knowledge. Compared to Bi2Te3 TI, the G-B heterostructure Q-switched laser had better laser performance, indicating that a G-B heterostructure is a promising SA candidate for a 1 µm laser.

Silicon-nanoparticle-based broadband optical modulators for solid-state lasers.

Motivated by the tremendous success of carbon nanomaterials in acting as optical nonlinear modulators, in this Letter, the optical nonlinearity of their counterpart, silicon nanoparticles (SiNPs), is investigated. For the first time, to the best of our knowledge, the nonlinear optical property of SiNPs in 1 µm and 2 µm wavelength bands is observed. Its practical modulation performance is investigated by employing SiNPs as a saturable absorber (SA) in pulsed lasers, and the fabrication process, surface morphology, and linear and nonlinear optical response properties of the prepared SiNPs-SA are presented. Based on the SiNPs-SA, the formed Q-switched Nd:LuAG laser can generate laser pulses with the shortest duration of 490 ns at ∼1 µm and ∼2 µm laser pulses with the shortest duration of 453 ns are delivered from a Q-switched Tm:YAP laser, which shows that the SiNPs can be employed as a promising broadband SA for near- and mid-infrared spectral regions.

High-peak-power mode-locking pulse generation in a dual-loss-modulated laser with BP-SA and EOM.

In this Letter, a high-quality black phosphorus saturable absorber (BP-SA) with a multilayer structure was prepared, and its corresponding characteristics were investigated. Based on the BP-SA and an electro-optic modulator (EOM), a dual-loss-modulated mode-locked laser with a controllable repetition rate and high peak power was realized, which has the repetition rate of EOM and the mode-locking pulse width in the Q-switching and mode-locking laser. The output performances versus the pump power were measured. The maximum pulse peak power of 3.89 MW was obtained with the minimum pulse duration of 119 ps. To the best of our knowledge, this is the highest pulse peak power with BP-SA reported.

Hybrid Q-switched laser with MoS2 saturable absorber and AOM driven sub-nanosecond KTP-OPO.

Two-dimensional (2D) materials, especially transition-metal dichalcogenides, such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2), have attracted great interests due to their exceptional optical properties as saturable absorbers in laser systems. In this work, at first, we presented a diode-pumped passively Q-switched laser with MoS2 saturable absorber (MoS2-SA). At an incident pump power of 6.54 W, a maximum output power of 1.15 W with a minimum pulse duration of 70.6 ns was obtained, which is the shortest pulse duration of diode pumped passively Q-switched laser with MoS2-SA to the best of our knowledge. Then, by using a hybrid Q-switched laser with a MoS2-SA and an acousto-optic modulator (AOM) as pumping fundamental laser, a sub-nanosecond KTiOPO4 (KTP) based intracavity optical parametric oscillation (IOPO) was realized. With an incident pump power of 10.2 W and AOM repetition rate of 10 kHz, the maximum output power of 183 mW with minimum pulse duration of 850 ps was obtained. The experimental results indicate that the IOPO pumped by the hybrid Q-switched laser with AOM and MoS2-SA can generate signal wave with shorter pulse duration than those IOPOs pumped by hybrid Q-switched laser with AOM and Cr4+:YAG or single-walled carbon nanotube saturable absober (SWCNT-SA) or monolayer graphene SA.

Dual-wavelength Nd:LGGG laser intracavity pumped simultaneous OPO and SRS processes in single KTP.

Simultaneous optical parametric oscillation (OPO) and stimulated Raman scattering (SRS) in a single KTiOPO4 (KTP) intracavity pumped by a dual-wavelength Nd:LGGG laser were demonstrated for the first time, to the best of our knowledge. A maximum output power for the signal beam was 448 mW, while for the Stokes radiations it was 40 mW, corresponding to an overall conversion efficiency of about 4.65%. The shortest pulse durations for OPO and SRS waves were directly measured to be 850 ps and 1.526 ns, respectively. The highest peak power of 30.6 kW and the pulse energy of 26 µJ for the signal beam were also obtained. A set of coupled rate equations for the dual-wavelength pumped OPO and SRS was also established. The numerical solutions fit with the experimental results.

Experimental and theoretical investigation on passively Q-switched laser action in c-cut Nd:MgO:LiNbO3.

The performance of a diode-pumped c-cut Nd:MgO:LiNbO3 laser at 1093 nm was demonstrated. Under an absorbed pump power of 7.450 W, a maximum continuous wave output power of 1.570 W was obtained, corresponding to a slope efficiency of 26.0%. For passive Q-switching operation, 24 ns pulses were observed with a repetition rate of 17.1 kHz, resulting in a peak power of 1357 W. The experimental results were theoretically analyzed by a rate equation model, in which the Gaussian spatial distribution of the intracavity photon density was taken into account.