4.1 W continuous-wave and broadly wavelength tunable Tm-doped laser in 2.1-2.4 µm spectral region based on vibronic and electronic transitions.

Efficient diode-pumped continuous-wave (CW) and wavelength tunable Tm:YAP lasers based on the vibronic and electronic transitions are investigated. A total maximum output power of 4.1 W is achieved with multi-wavelength output around 2162 nm and 2274 nm, corresponding to a slope efficiency of 29.8% for a 3 at. % Tm:YAP crystal. A maximum output power of 2.48 W with a slope efficiency of 25.4% is obtained at 2146 nm for a 4 at. % Tm:YAP crystal. Using a birefringent filter (BF), the emission wavelengths of the Tm:YAP laser are tuned over spectral ranges of 59 nm from 2115 nm to 2174 nm and 127 nm from 2267 nm to 2394 nm, respectively, which is the first demonstration of wavelength tunable Tm:YAP laser based on the electronic transition 3H4→3H5 and vibronic transition 3F4→3H6, to the best of our knowledge. The results show great potentials of the Tm:YAP crystal for realizing efficient lasers in the spectral range of 2.1-2.4 µm.

67†mJ, 137†ns narrow bandwidth 355†nm UV laser.

A high-efficiency, high-energy, narrow bandwidth, hundred-nanosecond pulse width 355 nm ultraviolet (UV) laser was realized. A high-energy single-frequency 1064 nm fundamental laser was demonstrated firstly with multistage end-pumped preamplifiers and side-pumped main amplifiers. The corresponding pulse energy, repetition rate, pulse duration, bandwidth, and beam quality factor M2 were determined to be 221 mJ, 100 Hz, 156 ns, 2.25 MHz, and 1.23, respectively. By using type-I phase-matching LBO crystal for second harmonic generation (SHG) and type-II phase-matching LBO crystal for the sum frequency generation of the third harmonic, 67 mJ, a narrow bandwidth 355 nm UV laser was obtained with a pulse width of 137 ns and an energy stability of RMS < 1.2%@2 h. The fundamental to UV optical conversion efficiency was 30.3%. Our results provided a new way for generating high-energy, narrow bandwidth hundred-nanosecond 355 nm UV lasers used for direct-detection Doppler wind lidar (DWL) system.

Modified Frantz-Nodvik equation and numerical simulation of a high-power Innoslab picosecond laser amplifier.

A modified Frantz-Nodvik (F-N) equation and a simple one-dimensional unfolded slicing model for numerically simulating high-power Innoslab picosecond amplifier are developed for the first time. The anisotropic stimulated emission cross-section of laser crystal, the influence of the tilted optical path, the spatial overlap of the seed and pump laser, as well as the pump absorption saturation effect are considered. Based on the as-developed model, 4-, 6- and 8-pass schemes high-power Nd:YVO4 Innoslab picosecond amplifiers are designed with output powers of 76.2 W, 81.4 W, and 85.5 W, respectively. The experimental results agree well with that of numerical simulation, indicating that our model is a powerful tool and paves a new way for designing and optimizing high-power Innoslab picosecond laser amplifier.

Cascade MIR Ho:YLF laser at 2.1†µm and 2.9 µm.

Cascade transitions of Ho3+:5I6→5I7 and 5I7→5I8 provide a platform for a dual-wavelength mid-infrared (MIR) laser. In this paper, a continuous wave cascade MIR Ho:YLF laser operating at 2.1 and 2.9 µm is realized at room temperature. The total output power of 929 mW with 778 mW at 2.9 µm and 151 mW at 2.1 µm is obtained under the absorbed pump power of 5 W. Compared to the non-cascade mode, 2.9-µm lasing threshold is reduced by 10.3% and the slope efficiency is increased by 76.1% with the supports of cascade lasing at 2.1 µm. However, 2.9-µm lasing is the key population accumulation of the 5I7 level, which thus efficiently reduces the threshold and improves the output power of the 2.1-µm laser. Our results put forward a way for generating cascade dual-wavelength MIR lasing in Ho3+-doped crystals.

Highly Stable Passively Q-Switched Erbium-Doped All-Fiber Laser Based on Niobium Diselenide Saturable Absorber.

A saturable absorber (SA) based on niobium diselenide (NbSe2), which is a layered transition metal dichalcogenide (TMD) in the VB group, is fabricated by the optically driven deposition method, and the related nonlinear optical properties are characterized. The modulation depth, saturable intensity, and nonsaturable loss of the as-prepared NbSe2 nanosheet-based SA are measured to be 16.2%, 0.76 MW/cm2, and 14%, respectively. By using the as-fabricated NbSe2 SA, a highly stable, passively Q-switched, erbium-doped, all-fiber laser is realized. The obtained shortest pulse width is 1.49 µs, with a pulse energy of 48.33 nJ at a center wavelength of 1560.38 nm. As far as we know, this is the shortest pulse duration ever obtained by an NbSe2 SA in a Q-switched fiber laser.

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.

Generation of a square-shaped pulse in mode-locked fiber lasers with a microfiber-based few-layer Nb2C saturable absorber.

Niobium carbide (Nb2C), a novel two-dimensional MXene material, has attracted much attention due to its outstanding electronic and optical properties. In this work, a microfiber-based few-layer Nb2C saturable absorber (SA) is fabricated by the magnetron sputtering deposition technique. The reverse saturable absorption (RSA) response of few-layer Nb2C nanosheets is observed with I-scan measurements. The square-wave pulses (SWPs) are generated by using the as-prepared microfiber-based few-layer Nb2C SA in an erbium-doped fiber laser. The SWP width increases from 0.33 to 2.061 ns with the single pulse energy increases linearly up to 0.89 nJ while the amplitude remains as a constant. In addition, nonlinear polarization rotation mode-locking fiber lasers with different cavity lengths are constructed to explore the formation conditions of SWP. Our results indicate that the RSA effect of the few-layer Nb2C nanosheets plays a decisive role in the formation of the SWP.

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.

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.

High-repetition-rate kHz electro-optically Q-switched Ho, Pr: YLF 2.9 µm bulk laser.

In this study, we operated a novel bulk laser: a dual-end-pumped electro-optically (EO) Q-switched Ho, Pr:YLF laser at 2945.9 nm with a repetition rate of kHz level. The shortest pulse duration of 25.2 ns was obtained at the repetition rate of 500 Hz, corresponding to a single pulse energy of 0.4 mJ and a peak power of 15.9 kW. A maximum output power of 268 mW was delivered at the repetition rate of 1.5 kHz. The beam quality factors of the EO Q-switched Ho, Pr:YLF laser at the maximum output power were Mx 2 = 1.50 and My 2 = 1.54 in x- and y- directions, respectively. The long-term output power instability was measured to be ± 1.5% (RMS) within five hours. The achieved results indicated the promising potential of Ho, Pr: YLF crystals for high repetition rate Q-switched mid-infrared laser pulse generation very well.

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.

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.

High-efficiency watt-level continuous-wave 2.9 µm Ho,Pr:YLF laser.

The bottleneck in Ho3+:I65→I752.9 µm laser emission, where the upper-level lifetime (I65) is significantly shorter than that of the lower-level (I75) lifetime, is overcome by co-doping Ho3+ and Pr3+ ions. A novel kind of Ho3+,Pr3+:YLIF4 (Ho,Pr:YLF) crystal is fabricated by optimizing the doping concentration ratios. By using as-grown Ho,Pr: YLF crystals with doping concentrations of 0.498 at. % Ho3+, 0.115 at. % Pr3+ and 0.489 at. % Ho3+, 0.097 at. % Pr3+ as gain media, both high-efficiency and continuous-wave 2.9 µm laser operations are realized under 1150 nm fiber laser pumping, respectively. With the 0.498 at. % Ho3+, 0.115 at. % Pr3+: YLF crystal, a maximum output power of 1.27 W with a corresponding slope efficiency of 28.3% is yielded under a 4.48 W absorbed pump power, which is the highest output power among the Ho3+-doped 2.9 µm lasers ever reported, to the best of our knowledge. The results well reveal the great potential of Ho,Pr:YLF crystals in developing high-power, high-efficiency 2.9 µm mid-infrared lasers.

Few-layer TiSe2 as a saturable absorber for nanosecond pulse generation in 2.95 µm bulk laser.

1T-phase titanium diselenide (1T-TiSe2), a model two-dimensional (2D) transition metal dichalcogenide, has attracted much attention due to its intriguing electrical and optical properties. In this work, a 1T-TiSe2-based high-quality large-area saturable absorber (SA) (1T-TiSe2-SA) was successfully fabricated with the liquid-phase exfoliation method. With the as-prepared 1T-TiSe2-SA, a stable, passively Q-switched laser operating at 2.95 µm was first realized. Under an absorbed pump power of 3.35 W, the maximum average output power was 130 mW with a slope efficiency of 5%. A pulse width of 160.5 ns was obtained, which is the shortest among 3.0 µm passively Q-switched lasers ever achieved with 2D materials as SAs, to the best of our knowledge. The results indicate that 1T-TiSe2 is a promising alternative as a nonlinear optical modulator for short-pulse laser generation near the 3.0 µm mid-infrared region.

Passively Q-switched mid-infrared laser pulse generation with gold nanospheres as a saturable absorber.

High-quality gold (Au) nanospheres (Au-NPs) with a diameter of 52 nm were prepared by the seeded growth method. The mid-infrared (MIR) nonlinear saturable absorption properties were measured by a balanced twin-detector measurement technique. With the as-prepared Au-NPs saturable absorber (SA), an efficient passively Q-switched laser was realized at 2.95 µm for the first time, to the best of our knowledge. Under an absorbed pump power of 4.0 W, a maximum output power of 268 mW was obtained with the shortest pulse width of 734 ns and repetition rate of 91 kHz, corresponding to the pulse energy up to 2.95 µJ. The results indicate that Au-NPs are promising candidates as SAs for MIR laser pulse generation.

Few-layer Ti3C2Tx (T = O, OH, or F) saturable absorber for a femtosecond bulk laser.

Few-layered titanium carbide (Ti3C2Tx), a novel two-dimensional (2D) Van der Waals material in the MXene family, was fabricated with a liquid-phase method and applied as a saturable absorber for a continuous-wave mode-locked femtosecond bulk laser. Pulses as short as 316 fs with a repetition rate of 64.06 MHz and maximum output power of 0.77 W were achieved at the central wavelength of 1053.2 nm, demonstrating the first known, to the best of our knowledge, application of MXene in an all-solid-state laser. Considering the flexible band gap for different surface functional groups of Ti3C2Tx, these results may promote the development of ultrafast photonics and further applications of 2D optoelectronic layered materials in the infrared and mid-infrared regions.

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.

Passively mode-locked 1.34 µm bulk laser based on few-layer black phosphorus saturable absorber.

By using few-layer black phosphorus (BP) as saturable absorber, an efficient mode-locked Nd:GdVO4 bulk laser operating at 1.34 µm was realized. An average output power of 350 mW was achieved with a slope efficiency of 15%. The corresponding mode-locking pulse repetition rate, pulse duration and pulse energy were 58.14 MHz, 9.24 ps and 3.0 nJ, respectively. To the best of our knowledge, the pulse width is the shortest among the mode-locked 1.34 µm neodymium lasers ever obtained with other two-dimensional materials saturable absorber. The results clearly indicate the few-layered BP is a kind of promising saturable absorber for ultrafast 1.34 µm lasers.

Few-layered ReS2 as saturable absorber for 2.8 µm solid state laser.

A novel two-dimensional (2D) material member in the transition metal dichalcogenides family, few-layered rhenium disulfide (ReS2) was prepared by liquid phase method successfully. By using the open-aperture Z-scan method, the saturable absorption properties at 2.8 µm were characterized with a saturable fluence of 22.6 µJ/cm2 and a modulation depth of 9.7%. A passively Q-switched solid-state laser at 2.8 µm was demonstrated by using the as-prepared ReS2 saturable absorber successfully. Under an absorbed pump power of 920 mW, a maximum output power of 104 mW was obtained with a pulse width of 324 ns and a repetition rate of 126 kHz. To the best of our knowledge, this is the first demonstration of applying ReS2 in an all-solid-state laser. Moreover, this represents the shortest pulses in Q-switched MIR lasers based on a 2D material as the saturable absorber, which demonstrated the superiority of ReS2 acting as an optical modulator for generating short-pulsed lasers. The results well prove that 2D ReS2 is a reliable optical modulator for MIR solid-state lasers.

83.4 W, 17.69 kHz spectral bandwidth, continuous-wave, beam densely folded Innoslab amplifier.

Combined with the advantages of the narrow bandwidth of a non-planar ring oscillator seed laser and the structure of a direct pumped Innoslab amplifier, a high-efficiency and high-power continuous-wave (CW) single-frequency laser was obtained by densely folding the seed laser beam in an Innoslab amplifier with a wedged multi-folded configuration. A maximum output power of 83.4 W of a single-frequency amplifier with a bandwidth of 17.69 kHz was obtained under a pump power of 234 W, corresponding to an optical-to-optical conversion efficiency of 33.2%. The beam quality factor M2 at the maximum output power in horizontal and vertical directions was measured to be 1.15 and 1.24, respectively. The long-term power instability in 2 h was less than 1.63%.