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.

Bessel Beam Coherent Anti-Stokes Raman Scattering Spectroscopy for Turbulent Flow Diagnosis.

Coherent anti-Stokes Raman scattering (CARS) spectroscopy plays an important role in chemical analysis for transient flow dynamics. Due to the turbulent ambient conditions, the CARS spectrum often suffers from a poor signal-to-noise ratio (SNR) and cannot provide a convincing measurement. Here, we report on a CARS spectroscopic method using a Bessel beam to enhance the spectral fidelity and SNR in a quasi-turbulent environment. Compared with traditional CARS, the measurement accuracy is significantly improved by taking advantage of the anti-scattering and self-healing characteristics of the Bessel beam. Our preliminary results indicate that Bessel beam CARS could be a promising method for high precision turbulent flow measurement fields.

Extreme events in two laterally-coupled semiconductor lasers.

Rogue waves (RWs) are extreme and rare waves that emerge unexpectedly in many natural systems and their formation mechanism and prediction have been extensively studied. Here, we numerically demonstrate the appearance of extreme events (EEs) for the first time, to the best of our knowledge, in the chaotic regimes of a two-element coupled semiconductor laser array. Based on coupled-mode theory, we characterize the occurrence of EEs by calculating the probability distribution, which confirms the RW-type feature of the intensity pulses, i.e., non-Gaussian distribution. Combining with the results of the 0-1 test for chaos, we confirm that EEs originate from deterministic nonlinearities in coupled semiconductor laser systems. We show that EEs can be predicted with a long anticipation time. Furthermore, simulation results manifest that the occurrence probability of EEs can be flexibly tuned by tailoring the coupling parameter space. With the help of two-dimension maps, the effects of key parameters, i.e., the waveguide structure and the pump level, on the formation of EEs are discussed systematically. This work provides a new platform for the research of EEs in a highly integrated structure and opens up a novel investigation field for coupled semiconductor laser arrays.

Sub-nanosecond micro laser passively Q-switched by a GaAs saturable absorber.

A Nd:GdVO4/GaAs passively Q-switched laser has been demonstrated based on a microchip design. Under high pump power, the high optical intensity inside the laser cavity triggered the two photon absorption of GaAs, and the pulse duration was shortened to sub-nanosecond level. The shortest pulse of 690 ps was obtained, which we believe is the shortest pulse ever generated with a pure GaAs saturable absorber. The maximum average output power, highest repetition rate, largest pulse energy, and highest peak power were 1 W, 190 kHz, 7.5 µJ, and 10.8 kW, respectively. The results indicated that GaAs is a promising passively Q-switched saturable absorber and still has potential to explore.

High-beam-quality operation of a 2 µm passively Q-switched solid-state laser based on a boron nitride saturable absorber.

Boron nitride (BN) nanosheets were used as the material sources which were coated on a calcium fluoride mirror to achieve a saturable absorber (SA). A passively Q-switched solid-state laser at 2000.5 nm was demonstrated with a Tm,Ho:YAlO3 (Tm,Ho:YAP) crystal and a SA based on BN. An average output power of 650 mW was obtained with a minimum pulse width of 6.3 µs at the pulsed repetition frequency of 41.7 kHz, corresponding to a per pulse energy of 13 µJ. The beam quality factor was measured to be Mx2=1.06 and My2=1.07 at the maximum output power.

Semiconductor saturable absorber Q-switching of a holmium micro-laser.

We report on a Holmium micro-laser passively Q-switched by a semiconductor saturable absorber (SSA), for the first time to the best of our knowledge. It is based on a 1 at.% Ho:YAG ceramic with good energy storage capability and several commercial transmission-type SSAs with 0.24% modulation depth. Under in-band pumping by a Tm fiber laser at 1910 nm, the Ho micro-laser generated 450 mW at 2089 nm with 37% slope efficiency. Stable 89 ns, 3.2 µJ pulses are achieved at a repetition rate of 141 kHz. Further shortening of the laser pulses is feasible with the increase of the modulation depth of the SSA while power scaling may lead to Q-switching at MHz-range repetition rates.

Thulium doped LuAG ceramics for passively mode locked lasers.

Passive mode-locking of a thulium doped Lu3Al5O12 ceramic laser is demonstrated at 2022 nm. By applying different near surface GaSb-based saturable absorber mirrors, stable self-starting mode-locked operation with pulse durations between 2 and 4 picoseconds was achieved at a repetition rate of 92 MHz. The SESAM mode-locked Tm:LuAG ceramic laser exhibits an excellent stability with a fundamental beat note extinction ratio of 80 dB above the noise level. Furthermore, spectroscopic properties of Tm:LuAG ceramics at room temperature are presented.

Broadly tunable mode-locked Ho:YAG ceramic laser around 2.1 µm.

A passively mode-locked Ho:YAG ceramic laser around 2.1 µm is demonstrated using GaSb-based near-surface SESAM as saturable absorber. Stable and self-starting mode-locked operation is realized in the entire tuning range from 2059 to 2121 nm. The oscillator operated at 82 MHz with a maximum output power of 230 mW at 2121 nm. The shortest pulses with duration of 2.1 ps were achieved at 2064 nm. We also present spectroscopic properties of Ho:YAG ceramics at room temperature.

Continuous-wave tri-wavelength operation at 1064, 1319 and 1338 nm of LD end-pumped Nd:YAG ceramic laser.

We demonstrated a laser-diode (LD) end-pumped continuous-wave (CW) tri-wavelength Nd:YAG ceramic laser operating at 1064, 1319 and 1338 nm. For the 1064 nm laser, one of the Nd:YAG polished end faces was used as the output coupler. As references, Nd:YVO(4) and Nd:YAG crystal lasers were also investigated under the same structure. We found that the maximum output power came from Nd:YAG ceramic which was 1.74 W, corresponding an optical conversion efficiency of 16.3%. Using a three mirror cavity, we realized efficient multi-wavelength operation at (4)F(3/2)-(4)F(11/2) and (4)F(3/2)-(4)F(13/2) transitions for Nd:YAG ceramic, simultaneously. The maximum output power was 3.2 W, which included 1064, 1319, and 1338 nm three wavelength, and the optical conversion efficiency was 30%.

1319 nm and 1338 nm dual-wavelength operation of LD end-pumped Nd:YAG ceramic laser.

In this paper, we demonstrate the efficient 1.3 um dual-wavelength operation of LD end-pumped Nd:YAG ceramic laser. With a plano-concave cavity, a maximum continuous-wave dual-wavelength output power of 5.92 W is obtained under an incident pump power of 20.5 W, giving a slope efficiency of 30.3% and an optical-optical conversion efficiency of 29.0%. With Co(2+):LaMgAl(11)O(19) crystal as the saturable absorber, the passively Q-switched dual-wavelength operation is achieved for the first time to our knowledge. The maximum passively Q-switched average output power is 226 mW, the minimum pulse width is 15 ns, and the highest pulse repetition rate is 133 kHz.

Passively Q-switched Yb3+:NaY(WO4)2 laser with GaAs saturable absorber.

Passively Q-switched Yb(3+):NaY(WO(4))(2) lasers have been demonstrated using a GaAs saturable absorber. Under continuous wave pump mode, significant pulse shortening effects have been observed at high pump powers. At a pump power of 12 W, stable Q-switched output has been obtained with a pulse duration of 5 ns, pulse repetition rate of 83 kHz and a pulse to pulse timing jitter of less than 2%. With pulsed pump mode, much longer pulse duration and reduced pulse stability have been observed. It is proposed that the heating of GaAs may play an important role in the Q-switched operations under CW pump conditions.

High-peak-power subnanosecond passively Q-switched ytterbium-doped fiber laser.

A passively Q-switched ytterbium doped fiber laser has been demonstrated with a Cr(4+):yttrium aluminum garnet saturable absorber and distributed stimulated Brillouin scattering. A linearly polarized output with approximately 375 kW peak power and a pulse duration as short as 490 ps have been obtained. A theoretical model is developed to simulate passive Q switching with the stimulated Brillouin scattering, which shows good agreement with the experiment.

Passively Q-switched dual-wavelength laser output of LD-end-pumped ceramic Nd:YAG laser.

We reported a dual-wavelength laser with a ceramic Nd:YAG as laser material and Cr:YAG as frequency selector and saturable absorber. Continuous-wave output power was achieved to be as high as 6.19 W at 1052 nm. With Cr:YAG, the laser has dual-wavelength at 1052 and 1064 nm. The shortest pulse width, maximum pulse energy and highest peak power were 4.8 ns, 103.2 microJ, and 21.5 kW. This pulsed laser is possible to be used as a new source to generate terahertz radiation.