Q-switched Oscillator Research Articles

Low-Timing Jitter Single-Frequency Pulse Output from a Passively Q-Switched Monolithic Non-Planar Ring Oscillator

A low-timing jitter passively Q-switched monolithic non-planar ring oscillator (NPRO) with diffusion-bonded Cr4+: YAG in a single-frequency operation was realized. The pulse parameters were controlled by a Cr4+: YAG saturable absorber, while the single-frequency operation was ensured by the unidirectional ring cavity structure. The pulse trigger was actively provided by a gain switcher utilizing a composite pumping scheme. The dependence of the timing jitter between the output pulse and the trigger signal on the parameters of the composite pumping scheme was investigated both theoretically and experimentally. Using this approach, we achieved a single-frequency pulsed laser output with a timing jitter of 14.568 ns (RMS) at a repetition rate of 100 Hz corresponding to a pulse width of 5.99 ns. This novel Q-switched monolithic NPRO, which integrates the benefits of both active and passive Q-switching, results in a simple and reliable structure that achieves a low-timing jitter single-frequency pulse output.

Real-time spectral transient dynamics measurement of mode-locked semiconductor disk lasers with DFT

The real-time measurement of transient dynamics of a semiconductor disk laser (SDL) was demonstrated using the dispersive Fourier transform (DFT) technology. Operating in a stable mode-locking state with a repetition rate of 425 MHz and a pulse width of 2.18 ps, the SDL exhibits significant changes in both spectral shape and pulse profile in the process of the establishment and extinction of mode locking. The pulse-resolved spectral evolution was captured, which includes relaxation oscillation, Q-switched oscillation and mode-locking states. Notably, we observed a progressive shift in the central wavelength—from 983.8 nm during initial mode-locking to 982.5 nm in the stabilization phase, and finally to 980 nm at extinction. The shift of mode locked wavelength can be attributed to thermal effect. To the best of our knowledge, this is the first time to observe the mode-locked dynamics in SDLs using a DFT technology.

3.8 µm pulse burst self-optical parametric oscillator utilizing a programmable step-active Q-switch with Nd:MgO:PPLN crystal.

This paper reports a 3.8 µm pulse burst self-optical parametric oscillator (SOPO) employing the Nd:MgO:PPLN crystal, achieving programmable mid-infrared pulse burst output based on step-active Q-switching technology. Building on the intracavity optical parametric oscillator (IOPO) theory, a theoretical model for the step-active Q-switched self-optical parametric oscillator is developed by introducing idler photon and step loss terms. The simulation results elucidate the evolution of population inversion and photon numbers and determine step-active Q-switching loss values for different sub-pulse numbers. Additionally, a 3.8 µm pulse burst laser output with a repetition rate of 10 kHz is experimentally achieved using the step-active Q-switching signal designed from the theoretical simulation. The effective programming of the step-active Q-switching signal achieves control over 2-4 sub-pulses, 260-1000 ns intervals, and any amplitude ratios. The experimental and simulation results demonstrate consistency, offering valuable insights for optimizing the Q-switching technology in other SOPO systems.

The effects of thermalization on the performance of passively Q-switched IC-OPOs

In this paper, we report a new model for passively Q-switched intracavity optical parametric oscillators (IC-OPOs), using Cr:YAG as a Q-switch crystal. The model considers the effects of thermalization in the Nd:YAG laser crystal, excited state absorption in the Cr:YAG saturable absorber, nonlinear loss due to pump depletion in the nonlinear crystal, the thermal lens effect and the mode overlap of the fields within the nonlinear crystal. The calculated pulse width for the 1,064 nm pump light was 6.2 ns compared to the experimental result of 6 ns, while the signal wave was calculated to have a pulse width of 1.75 ns compared to the experimental result of 2 ns. The model is shown to accurately calculate both the temporal and output power characteristics of the IC-OPO, which has not been previously reported to the best of our knowledge.

Deep ultraviolet laser at 223.8 nm with adjustable repetition rate and narrow pulse width.

We presented the first, to our knowledge, demonstration of an ultraviolet (UV) laser at 223.8 nm by six-harmonic generation of an electro-optic Q-switched cavity dumping 1342 nm Nd:YVO4 laser. It offers high power, constant short pulse duration, and adjustable pulse repetition rate. The pulse duration is independent of the pump power and repetition rate compared to classical Q-switched oscillators. The output efficiency of the UV laser is optimized by adjusting the focusing lens. With the incident pump power of 30 W, an maximum average output power of 249 mW was obtained at 13 kHz. The pulse width maintained 3.4-3.5 ns from 5 to 20 kHz. The maximum pulse energy of 28.1 µJ was obtained at 5 kHz, and the corresponding peak power was up to 8.1 kW.

Investigations on saturable absorption characteristic of PdS2 and its application to high-peak-power sub-nanosecond intracavity OPO

In this work, a unique pentagonal TMD material, palladium disulfide (PdS2) nanosheets were fabricated by the liquid-phase exfoliation (LPE) process, and the physical characteristics were also investigated. The nonlinear transmittance is measured by the power scanning method and the modulation depth is fitted to be 15.3%. Based on the transmittance curve, the saturable absorption parameters of PdS2 are calculated, including 5.85 × 10−19 cm2 ground-state absorption cross-section, 1.63 × 10−19 cm2 excited-state absorption cross-section, and 683.5 μs excited-state lifetime. By employing both PdS2 as a saturable absorber (SA) and an acousto-optic modulator (AOM), a doubly Q-switched and mode-locked (QML) laser-pumped intracavity KTiOPO4 (KTP) optical parametric oscillator (OPO) was realized. The pulse energy and the pulse width of the Q-switched envelope for signal wave have been measured. At higher pump power, the high-peak-power low-repetition-rate sub-nanosecond mode-locking pulse of signal wave is generated, in which there is only one mode-locked pulse underneath a Q-switched envelope. The measured shortest signal pulse duration is 530 ps, corresponding to a peak power of 337 kW, at an incident pump power of 9.81 W and an acousto-optic modulator (AOM) repetition rate of 1 kHz. In addition, by considering the Gauss distribution of intracavity photon density, a set of coupled rate equations for a doubly QML laser-pumped intracavity OPO was given and the numerical simulations agreed with the experimental results. These results indicate that PdS2 is a promising nonlinear optical material for optical applications in the near-infrared (NIR) region.

Passively Q-switched mode-locked fiber laser with 1-GHz fundamental repetition rate based on zeolite-fabricated Yb–Mg-doped silica glass

We successfully demonstrated a pulse laser with a fundamental repetition rate of 1 GHz in passively Q-switched mode-locked oscillation by using Yb–Mg-doped silica glass fiber (YbMgSGF). The YbMgSGF core glass, fabricated by the zeolite method, showed a Yb2O3 content of 5.46 wt%. To the best of our knowledge, our laser is the first silica-glass-based, Yb-doped fiber laser operating at a fundamental repetition rate of gigahertz. The laser cavity was constructed by a 102-mm-long YbMgSGF as a laser medium and a semiconductor saturable-absorber mirror as a mode-locker. The laser output power reached 5.93 mW, and its slope efficiency and lasing threshold power were 3.6% and 5.3 mW, respectively. The peak wavelength of the oscillation was 1039 nm. We also discuss the conditions to transition from Q-switched mode-locked operation to continuous-wave mode-locked operation. The proposed fiber laser can serve as a seed laser for a master oscillator power amplifier for a high-power, high-efficiency pulsed fiber laser source.

1.5 μm passively Q-switched self frequency conversion optical parametric oscillator based on Nd3+ doped MgO:PPLN with the multi-focus end-face coupling pumping mode

A 1.5 μm passively Q-switched self frequency conversion optical parametric oscillator based on Nd3+ doped MgO:PPLN with the multi-focus end-face coupling pumping mode is reported. The reason for the generation of dual-wavelength fundamental frequency laser is explained by Nd:MgO:PPLN laser characteristics and energy level theory, and a multi-focus pumping thermal model is established to numerically simulate the temperature field distribution under different pumping injection modes. Compared with the traditional single-focus pumping mode, the multi-focus coupling pumping mode effectively disperses the thermal effect of the Nd:MgO:PPLN crystal, the oscillation of the σ-polarized 1093 nm laser is suppressed, the single-wavelength output of the π-polarized 1084 nm laser is realized. Thereby the more efficient 1514 nm signal light is obtained. In the experiment, the 1514 nm signal light with an average output power of 183 mW is obtained when the repetition frequency is 5.4 kHz, the pulse width is 6.8 ns and the pulse energy is 34 μJ in the double-focus pumping mode. In the triple-focus pumping mode, the 1514 nm signal light with an average output power of 165 mW is obtained when the repetition frequency is 5.6 kHz, the pulse width is 7.2 ns and the pulse energy is 30 μJ. Overall evaluation of the experimental effects of the two kinds of pumping modes shows that the double-focus pumping mode is superior to the triple-focus pumping mode.

400 W average power Q-switched Yb:YAG thin-disk-laser

We report on producing up to 403 W average power directly from an acousto-optically Q-switched Yb:YAG thin-disk laser (TDL). To achieve this power, it has theoretically and experimentally been shown that the laser stability border could be shifted toward higher repetition rates by engineering of the output coupler transmittance. This allows for stable operation of the laser at higher frequencies and a further increase in the power extraction from the active medium. Using an output coupler with 93% reflectivity, a maximum average power of 403 W at the repetition rate of 12.0 kHz has been recorded under the pump power of 1220 W. Furthermore, the maximum pulse energy of 57 mJ was produced at the repetition rate of 1.00 kHz and the pump power of 520 W. The characteristics of the laser at various Q-switching rates and the pump powers have been investigated. In addition, a numerical study for supporting the experimental results has been proposed here. To the best of our knowledge, the achieved average power and the pulse energy are the highest values reported to date from a Q-switched Yb:YAG TDL. The results pave the way to further power scaling of solid-state Q-switched oscillators.

1 kHz, 12 MW, 300 ps microchip oscillator power amplifier system

We report a diode-pumped passively Q-switched (PQS) sub-nanosecond master oscillator power amplifier system. The master oscillator is a PQS Nd:YAG/Cr:YAG monolithic microchip laser, yielding a pulse duration of ∼300 ps and pulse energy of 33 μJ at repetition frequency of 1 kHz. After passing two stages end pumped Nd:YVO4 amplifier, the pulse energy is boosted to 3.6 mJ and pulse peak power up to 12 MW with excellent stability (root mean square ∼ 0.14%) and high beam quality (M 2 < 1.22).

High-energy Q-switched 16-core tapered rod-type fiber laser system.

High-energy Q-switched master oscillator power amplifier systems based on rod-type 4 × 4 multicore fibers are demonstrated, achieving energy up to 49 mJ in ns-class pulses. A tapered fiber geometry is tested that maintains low mode order in large multimode output cores, improving beam quality in comparison to a similar fiber with no taper. The tapered fiber design can be scaled both in the number of amplifying cores and in the dimensions of the cores themselves, providing a potential route toward joule-class fiber lasers systems.

Demonstration of a compact, multi-joule, diode-pumped Tm:YLF laser.

We report the demonstration of a diode-pumped Tm:YLF laser operating at 1.88 µm that produces pulse energies up to 3.88 J in 20 ns. The compact system consists of a Q-switched cavity-dumped oscillator generating 18 mJ pulses, which are then amplified in a four-pass power amplifier. Energies up to 38.1 J were obtained with long-pulse amplifier operation. These results illustrate the high energy storage and extraction capabilities of diode-pumped Tm:YLF, opening the path to high peak and average power mid-infrared solid-state lasers.

2.6-GHz fundamental repetition rate, Q-switched mode-locking Nd[formula omitted]-doped single-mode silica fiber laser, fabricated by zeolite method

We successfully constructed a pulse laser whose fundamental repetition rate is 2.6-GHz in Q-switched mode-lock oscillation. To the best of our knowledge, this is the highest repetition rate among silica glass fiber lasers. The laser cavity was constructed by a 40-mm-long Nd3+-doped single-mode silica glass fiber (Nd-SMF) and a SESAM as a saturable absorber. The core glass of the Nd-SMF was fabricated by a zeolite method and its concentration of Nd2O3 was 1.25 wt%. The maximum laser power reached 27.2 mW, and its slope efficiency and lasing thresholds were 19.6% and 7.3 mW. The peak wavelength of the oscillation was 1062.7 nm. The RF spectrum and the time-dependent waveform from a 20-GHz-bandwidth oscilloscope show a 2.6-GHz repetition rate of an Nd-SMF laser. We also discuss the conditions for achieving a CW-mode-lock (CML) oscillation, which is critical laser output Pout of 180 mW. Such a simple multi-GHz repetition rate laser will be available to make a compact frequency comb or a laser oscillator that will achieve ablation-cooled material removal in laser processing.

High-pulse-energy passively Q-switched sub-nanosecond MOPA laser system operating at kHz level.

A passively Q-switched sub-nanosecond master oscillator power amplifier (MOPA) laser system at 1064 nm has been reported in this paper. The master oscillator was a passively Q-switched YAG/Nd:YAG/Cr4+:YAG microchip laser, yielding a pulse energy of 0.14 mJ and a pulse width of ∼490 ps at repetition rates of 500 Hz and 1 kHz. After passing a double-pass side-pumped Nd:YAG amplification system, the pulse energy reached 7.6 mJ and 1.7 mJ at 500 Hz and 1 kHz, respectively. The spatial beam deformation caused by the thermally induced birefringence was investigated numerically and experimentally.

Linearly-polarized pulsed Nd-doped fiber MOPA at 905 nm and frequency conversion to deep-UV at 226 nm.

We present the first frequency-quadrupled linearly-polarized Q-switched neodymium-doped fiber laser generating > 500 mW average power at 226 nm. For this purpose, an amplified Q-switched oscillator using novel large-mode-area (LMA) fibers and generating up to 24 W average power (15 kW peak power) at 905 nm was developed. Two nonlinear frequency conversion stages using a LBO crystal for SHG and a BBO crystal for FHG generate respectively up to 4.9 W average power in the deep blue at 452 nm and a maximum of 510 mW average power in the deep ultra-violet (DUV) at 226 nm. Performance limitations and further improvements are discussed.

Experimental optimization and dynamics solution of active-passive Q-switched intracavity optical parametric oscillator based on EO modulator and layered-WSe2 SA

By applying a prepared 3 nm-thick tungsten diselenide (WSe2) saturable absorber to an electro-optic (EO) modulated fundamental-light laser, an active and passive Q-switched intra-cavity optical parametric oscillator (IOPO) has been experimentally realized. Benefiting from the saturable absorption property of WSe2, the output characteristics of Q-switched IOPO with signal-light oscillating are obviously improved, including the 93.7%-increased peak power, 54.6%-compressed pulse width, 30.1%-improved conversion efficiency, 60.1%-improved pulse-train stability, 17.8%-improved beam quality, and 27.4%-shortened linewidth. With the values of absorption parameters calculated from the measured nonlinear-transmittance curve of WSe2, the rate equations for dual-loss Q-switched IOPO with WSe2 saturable absorber and electro-optic modulator are numerically solved. The theoretical values correspond to the experimental data well.

Characterization of multi-wavelength Q-switched fiber laser by changing wavelength separation of filter

Abstract In this paper, we present a simple compact and low threshold laser that has characteristics of Q-switched and multi-wavelength oscillation simultaneously. Multi-wavelength Q-switched oscillation is realized by inserting a Sagnac filter as a multi-wavelength filter and a section of unpumped erbium-ytterbium co-doped fiber (EYDF) into the laser cavity as a saturable absorber (SA). The characteristics of multi-wavelength Q-switched fiber laser affected by wavelength separation of filter and pump power are investigated. The number of Q-switched wavelengths increases and the wavelength separation of the laser reduces with wavelength separation of the filter decreasing. Stable multi-wavelength oscillations at wavelength separation of 0.4–0.8 nm were obtained by increasing the length of polarization maintaining fiber (PMF) in the Sagnac filter. Moreover, the number of wavelengths and wavelength separation are increased by increasing the pump power when the filter is fixed. Further, the multi-wavelength laser is verified to have Q-switched properties at each wavelength, which is filtered from laser output through a narrow-band tunable filter outside of the cavity.

Modeling of a Q-switched master oscillator power amplifier fiber laser and gain saturation properties

Here, a model is developed for a master oscillator power amplifier of a Q-switched double-clad ytterbium–doped fiber laser, based on time-dependent coupled rate equations by virtue of the finite difference method. At first, the master oscillator is modeled with various rise times and its effect on the output peak power and pulse duration is investigated. The output pulse is characterized in terms of input pump power, dopant concentration, fiber length and core diameter. Then, the power amplifier (PA) is modeled to determine the input/output signals via the numerical solution of the coupled rate equations. The best fitting of data is performed over the analytical amplification relation by making use of the least squares method in order to find the gain and saturation parameters. Eventually, the small signal gain and saturation power are obtained under various parameters such as input pump power, dopant concentration, fiber length and core diameter. The dominant effect of filling factors are also discerned versus core diameters to attain the single mode operation. Finally, the power extracted from a single stage PA is envisaged versus various parameters.

Modeling of intracavity-pumped Q-switched terahertz parametric oscillators based on stimulated polariton scattering

In this paper, the rate equations describing the operation of intracavity-pumped Q-switched terahertz parametric oscillators based on stimulated polariton scattering are given for the first time. The rate equations are obtained under the plane-wave approximation, the oscillating fundamental and Stokes waves are supposed to be round uniform beam spots. Considering the fact that the terahertz wave nearly traverses the pump and Stokes beams and using the coupled wave equations, the terahertz wave intensity is expressed as the function of the fundamental and Stokes intensities. Thus, the rate equations describing the evolution processes of the fundamental and Stokes waves are obtained in the first step. The THz wave properties are then obtained. Several curves based on the rate equations are generated to illustrate the effects of the nonlinear coefficient, the THz wave absorption coefficient, and pulse repetition rate on the THz laser characteristics. Taking the intracavity-pumped Mg:LiNbO3 TPO as an example, the THz frequency tuning characteristic and the dependences of the fundamental, Stokes, and THz wave powers on the incident diode pump power are calculated. The theoretical results are in agreement with the experimental results on the whole.

An active and passive dual-loss Q-switched intracavity OPO based on few-layer WS2 saturable absorber

A 2.5 nm-thickness tungsten disulfide (WS2) saturable absorber (SA) was successfully fabricated by the electron beam evaporation (EBE) combined with post vulcanization. By applying the prepared WS2 SA to an acousto-optic (AO) Q-switched fundamental laser, a dual-loss-modulated Q-switched intracavity optical parametric oscillator (IOPO) has been experimentally realized. Because of the participation of WS2 SA, the problem of output decline was alleviated when the pump power was between 8.6 W and 10.8 W. The pulse width could be maximally compressed by 73% in WS2 SA based active-passive Q-switched IOPO with 10 kHz pulse-repetition rate, and the shortest pulse width in experiment was 1.098 ns. Benefiting from the pulse compression, the maximum pulse peak power in dual-loss-modulated Q-switched IOPO was 427% higher than that in AO active Q-switched IOPO. The application of WS2 SA also contributed to the stability of signal pulse train whose root mean square error (RMS) was efficiently lowered from 0.01776 to 0.00954. The nonlinear conversion efficiency was improved by approximate 38.2% in the dual-loss-modulated Q-switched IOPO.