Junpeng Qiao

WS 2 as a saturable absorber for Q-switched 2 micron lasers

We prepared WS2 nanosheets by using the thermal decomposition method and demonstrated for the first time its nonlinear saturable absorption property at around 2 μm. With the as-prepared WS2 nanosheets as saturable absorber (SA), a passively Q-switched Tm:LuAG laser was realized successfully, and 660 ns laser pulses with an average output power of 1.08 W and pulse peak power of 26 W at a repetition rate of 63 kHz were obtained for an incident pump power of 7 W. Our experimental results definitely demonstrate that WS2 could be a kind of promising SA for solid-state 2 μm lasers.

High-Peak Power Passively Q-Switched 2-μm Laser With MoS 2 Saturable Absorber

The passive Q-switching characteristics of a diode-pumped Tm,Ho:YAP laser at 2 μm based on a MoS2 saturable absorber (SA) is presented for the first time. Pulses as short as 435 ns under a repetition rate of about 55 kHz were generated at the incident pump power of 8.4 W, corresponding to the pulse peak power up to 11.3 W. This is, to the best of our knowledge, the highest pulse peak power, ever obtained from MoS2 based passively Q-switched 2-μm lasers. The experimental results sufficiently validated the feasibility of MoS2 as SA for solid-state 2-μm lasers.

Hybrid Q-switched laser with MoS 2 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.

Diode-pumped Nd:Gd3Ga5O12–KTiOPO4 green laser doubly passively Q-switched mode-locked by GaAs and Cr4+:YAG saturable absorbers

By simultaneously employing GaAs and Cr4+:YAG saturable absorbers, a diode-pumped doubly passively Q-switched and mode-locked (DP-QML) Nd:Gd3Ga5O12 (Nd:GGG)/KTiOPO4 (KTP) green laser has been presented. At the maximum incident pump power of 7.69 W, the obtained average output power, the pulse duration of the Q-switched envelope, the mode-locked pulse width and the pulse repetition rate are 62 mW, 16.8 ns, 352 ps, and 15.5 kHz, respectively, corresponding to a pulse energy of 4.2 µJ and a peak power of 0.25 kW. In comparison with singly passively Q-switched and mode-locked (SP-QML) green laser with GaAs or Cr4+:YAG saturable absorbers, the DP-QML green laser can generate shorter pulse width, deeper modulation depth and higher peak power. The coupled equations for diode-pumped doubly passively QML Nd:GGG/KTP green laser are given and the numerical simulations are in good agreement with the experimental results.

Sub-nanosecond KTP-OPO pumped by a hybrid Q-switched laser with WS 2 saturable absorber and AOM

By using a few-layered tungsten disulfide (WS2) nanosheet based saturable absorber (SA) prepared with the ultrasonic assisted vertical evaporation method, a diode-pumped singly Q-switched laser is demonstrated. At an incident pump power of 6.54 W, a maximum output power of 1.18 W with a minimum pulse duration of 53 ns is obtained from the singly WS2-SA Q-switched laser. To the best of our knowledge, this is the shortest pulse duration ever achieved from a diode-pumped solid-state passively Q-switched laser with a WS2-SA at 1.06 μm. Based on this, a sub-nanosecond KTiOPO4 (KTP) based intracavity optical parametric oscillation (IOPO) pumped by a hybrid Q-switched laser with a WS2-SA and an acousto-optic modulator (AOM) is realized. At an incident pump power of 10.2 W and an AOM repetition rate of 10 kHz, a maximum output power of 233 mW with a minimum pulse duration of 810 ps for signal wave is obtained. The experimental results indicate that the IOPO pumped by the hybrid Q-switched laser with an AOM and a WS2-SA can generate a signal wave with a shorter pulse duration and a higher peak power than that pumped by the Q-switched laser with an AOM and a graphene-SA or a molybdenum disulfide SA (MoS2-SA).

High peak power, 28 ns Q-switched Tm:LuAG laser at a 2 μm wavelength by dual-loss-modulation

By employing output couplers (OCs) with different transmissions T and GaAs saturable absorbers (SAs) with different modulation depth ΔR in a passively Q-switched Tm:LuAG laser at 2 μm, the optimal parameters of OCs and SAs for obtaining short pulse width and high peak power were investigated. By inserting an electro-optical modulator (EOM) into the optimized passively Q-switched Tm:LuAG laser (T = 2%/ΔR = 19%), a dual-loss-modulated Q-switched Tm:LuAG laser with an EOM and GaAs was realized. The experimental results show that the dual-loss-modulated Q-switched laser can generate a shorter pulse width and higher peak power than the single-loss-modulated case. At an incident pump power of 8.4 W, the shortest pulse width achieved was 28 ns and the highest peak power reached 74 kW.

Doubly Q-Switched Laser With AOM- and SWCNT-SA-Driven KTP Intracavity OPO

By simultaneously using an acousto-optic modulator (AOM) and a single-walled carbon nanotube saturable absorber, an intracavity optical parametric oscillation (IOPO) in KTiOPO4 pumped by a dual-loss-modulated Q-switched laser has been demonstrated. With an incident pump power of 8.3 W and an AOM modulation rate of 20 kHz, the maximum output power of 375 mW for signal waves was obtained, corresponding to an optical-conversion efficiency of 4.5%. In comparison with IOPO pumped by a singly Q-switched laser with an AOM, the IOPO pumped by doubly Q-switched laser can generate signal light with shorter pulse width and higher peak power as well as better pulse stability.

High-peak-power sub-nanosecond intracavity KTiOPO4 optical parametric oscillator pumped by a dual-loss modulated laser with acousto-optic modulator and single-walled carbon nanotube

A high-peak-power low-repetition-rate sub-nanosecond intracavity KTiOPO4 (KTP) optical parametric oscillator (OPO) pumped by a doubly Q-switched and mode-locked (QML) YVO4/Nd:YVO4 laser with an acousto-optic modulator (AOM) and a single-walled carbon nanotube saturable absorber (SWCNT-SA) has been demonstrated. A maximum output power of 373 mW at a signal wavelength of 1570 nm was obtained. The smallest pulse width, highest pulse energy, and greatest peak power of mode-locking pulses were estimated to be 119 ps, 124 µJ, and 1.04 MW, respectively, under a maximum incident pump power of 8.3 W and an AOM repetition rate of 2 kHz. This OPO operation paves a simple way to produce eye-safe laser sources at 1570 nm with low repetition rates, small pulse widths, and high peak powers.

Modulation frequency characteristics of the Q-switched envelope in a doubly Q-switched and mode-locked laser with acousto-optic modulator and Cr4+:YAG saturable absorber

Abstract. The modulation frequency characteristics of the Q-switched envelope in a doubly Q-switched and mode-locked Nd:GGG laser with an acousto-optic modulator (AOM) and Cr4+:YAG saturable absorber are given. At a fixed incident pump power, the repetition rates of the Q-switched envelope and the related laser characteristics versus the modulation frequency of AOM for different small signal transmissions of Cr4+:YAG saturable absorbers have been measured. The experimental results show that the repetition rates of the Q-switched envelope, the average output power, the average peak power, and the pulse widths of the Q-switched envelopes are subharmonics of the modulation frequency at a fixed incident pump power. Furthermore, the mechanism for these behaviors is discussed.