Active Q-switching Research Articles

A cellular automata model of a laser reproducing laser passive and active Q-Switching

A cellular automata model of a laser reproducing laser passive and active Q-Switching

Few ns Pulse Duration of Gain-Switched Ho:YAG Laser Pumped by an Active Q-Switched Tm:YLF Laser

This paper describes a gain-switched Ho:YAG laser that emitted at 2089 nm, driven by an actively Q-switched Tm:YLF laser as the pumping source. The laser attained few ns short pulse durations with high energies at controlled repetition rates due to the active Q-switch pump source. Using the gain-switch method, stable short pulse durations ranging from 3.5 to 7.2 ns, with an energy per pulse of 0.4 to 0.52 mJ, were achieved at repetition rates of up to 2.5 kHz. This design can have significant advantages in various fields, where accuracy in the repetition rate is essential and a passive Q-switch cannot be implemented due to its accuracy limitations, including sensing, LIDAR, medical procedures, and material processing.

30-100 kHz, 2 ns passively Q-switched laser for fast and efficient photoacoustic microscopy.

Actively Q-switched (AQS) fiber laser and solid-state laser (SSL) are widely used for photoacoustic microscopy (PAM). In contrast, passively Q-switched (PQS) SSL not only maintains most of the merits of AQS lasers, but also exhibits unique advantages, including the pulse width (PW), pulse repetition rate (PRR) tunability, wavelength, compactness, and cost. These advantages all benefit the PAM. However, there are few reports demonstrating the performance of PQS-SSL on PA imaging. Here, we demonstrate a compact PQS-SSL for fast and efficient PA imaging. The laser uniquely maintains a constant PW (~2 ns) and pulse energy (~3 μJ) during the PRR variation (30-100 kHz), which is valuable for preserving a stabilized imaging performance at different scanning rates. The PA imaging performance is compared by a resolution target and showcased by whole-body scanning of an embryonic zebrafish in vivo. The performance indicates that PQS-SSL is a promising candidate for PAM.

Single-frequency pulsed fiber laser based on an electro-optic modulator with injection seeding technique.

A single-frequency linearly polarization pulsed fiber laser based on an electro-optic modulator with injection seeding technique is demonstrated. The single-frequency performance of the fiber ring-cavity laser is guaranteed by the seed source, which is a distributed-feedback fiber laser based on the π-phase-shifted fiber Bragg grating. The electro-optic modulator triggers active Q-switching of the laser for pulse generation. The devices used in the fiber laser are all polarization-maintaining to ensure linear polarization laser output. Through parameter optimization, the laser generates a single-frequency linearly polarization pulsed laser with a central wavelength of 1064.22nm, linewidth of 35MHz, and polarization extinction ratio of better than 40dB. This type of fiber laser can be applied in lidar, beam combining, nonlinear frequency conversion, and other fields.

Contagious photons: Laser dynamics and the susceptible-infected-recovered model.

We explore a complete analogy between the classic susceptible-infected-recovered epidemiological model with natural birth and death rates, and class-B laser equations. As a result, recently derived asymptotic formulas in the former context can be used to describe the switch-on intensity pulse of a laser suddenly brought well above the lasing threshold, as in active Q-switching. Conversely, the well-studied laser relaxation oscillations find a companion behavior in epidemiology, emphasizing nontrivial timescales. Finally, we discuss the possible correspondence between multistrain outbreaks and multimode lasing.

Q-switching of an optical tweezer phonon laser

We theoretically investigate the active Q-switching of an optical tweezer phonon laser Pettit et al (2019 Nat. Photon. 13 402) operating in a coupled-mode configuration. One of the modes is lasing and outcouples to the second mode. The coupling is induced via asymmetric modulation of the trap potential in the transverse plane of the trapped nanoparticle. We show that a time-modulated coherent coupling between two transverse modes of oscillation of an optically levitated nanoparticle holds the key to coherent pulsed phonon transfer between them. Our analytical and numerical results on the position dynamics, phonon dynamics as well as second-order coherence confirms pulsed phonon lasing transfer between the transverse modes. Our work on Q-switched operation of the optical tweezer phonon laser enhances understanding of the analogies between optical and mechanical lasers, and is relevant to levitated phonon transport, acoustic imaging, sensing and information processing technologies.

Review of the Yb3+:ScBO3 Laser Crystal Growth, Characterization, and Laser Applications

Passive Q-switching is an effective approach for generating pulsed lasers, owing to its compact and additional modulation-free design. However, to compare favorably with active Q-switching and multi-stage amplification, the output energy needs to be enhanced for practical applications. Kramers Ytterbium ion (Yb3+)-doped borate crystals, with their excellent energy storage capacity, have been proven to be high-potential laser gain mediums for achieving pulsed lasers with moderate and high output energy using passive Q-switching technology. In this study, the growth, characterization, and laser generation of one Yb3+-doped borate crystal, the Yb3+:ScBO3 crystal, are systematically reviewed. The continuous-wave and passive Q-switching laser characteristics are presented in detail, and the self-pulsations derived from intrinsic ground-state reabsorption are also demonstrated. The specific characteristics and experiments confirm the potential of the Yb3+:ScBO3 crystal for future pulsed laser applications with moderate or even high energy output.

Three-nanosecond-equal interval sub-pulse Nd:YAG laser with multi-step active Q-switching

We demonstrate a three-nanosecond equidistant sub-pulse multi-step Q-switched Nd:Y3Al5O12 (Nd:YAG) laser. In the time interval of 100–1000 ns, three pulses with the same nanosecond interval and the same peak power are obtained at the pulse width of 24 ns, 28 ns, and 36.6 ns, respectively. The energy is 32.5 mJ, and the optical efficiency is 10.8%. The multi-step Q-switched method does not require the insertion of other optical elements into the traditional Q-switched laser, and it is very suitable to obtain pulse group output with several nanosecond pulse intervals.

Compact actively Q-switched laser for sensing applications

Current active Q-switching is mainly generated by acousto-optical modulators (AOMs) or electro-optical modulators (EOMs). However, EOMs make the setup bulky, while AOMs require the radiofrequency (RF) signal and water-cooling. We present a novel approach to active Q-switching of an integrated waveguide chip laser by utilizing a deformed helix ferroelectric liquid crystal cell (6mm×6mm) with a thickness of 2 mm. This device can be directly integrated onto the Ytterbium-doped waveguide chip and controlled by the electrical signal. In experiments, with an electrical signal with a pulse duration of 2 μs and a magnitude from 10 V to 84 V, the Q-switched lasers can be observed at a repetition rate ranging from 0.1 kHz to 20 kHz. The shortest pulse duration and the maximum slope efficiency is 38 ns and 22% respectively. This novel integrated and low-cost laser source is a promising tool for a broad range of applications such as gas sensing and LIDAR.

Theoretical studies of the generation of picoseconds pulses with two-section blue-violet semiconductor lasers

We report the results of theoretical investigations of the generation of sub-10 ps pulses by a blue-violet InGaN two-section laser. The principle of pulse generation is active Q-switching. We study numerically the influence of the length of the switching section and the emission wavelength on the steady-state and dynamic behaviour. We investigate also the impact of the gain-compression factor on peak power, pulse energy and pulse width and compare the numerical results with semi-analytic expressions.

Efficient high-power orthogonally-polarized dual-wavelength Nd:YLF laser at 1314 and 1321 nm

We demonstrate an 806 nm laser diode end-pumped continuous-wave (CW) and actively Q-switched (AQS) orthogonally-polarized dual-wavelength Nd:YLF laser operating at 1314 and 1321 nm. Benefitting from the small difference of the stimulated emission cross sections at 1314 and 1321 nm in Nd:YLF crystal, the power equalized emissions at both wavelengths were achieved by simply titling the output coupler. A maximum CW output power of 9.2 W was obtained with the incident pump power of 32.5 W, giving an optical-to-optical conversion efficiency of approximately 28% and a slope efficiency of approximately 33%. Furthermore, active Q-switching was realized by inserting a Brewster-cut acousto optic modulator. For an incident pump power of 30 W, this oscillator delivered an average power of 6.5 W at a pulse repetition frequency (PRF) of 20 kHz, and a pulse energy of 2.6 mJ with a peak power of approximately 72 kW at a PRF of 1 kHz.

Q-Switched Bismuth-Doped Fiber Laser at 1330 nm

We report on, to the best of our knowledge, the first Q-switched bismuth-doped fiber laser operating at ~1.3 μm. An acousto-optic modulator (AOM)-based active Q-switching was realized in a ring cavity with a bismuth-doped phosphosilicate fiber as an active medium. Stable pulsing in the range from 1310 to 1350 nm was achieved using various fiber Bragg gratings. The dependence of the laser operation on the unsaturable loss of the active fiber was studied. Optimization of the scheme and selection of an appropriate bismuth-doped fiber provided maximum pulse energy of ~11.5 μJ at the output of the laser. Using the data obtained, the evaluation of the extractable energy and the concentration of the bismuth active centers in the fiber samples under investigation was performed.

Numerical modelling and optimization of actively Q-switched waveguide lasers based on liquid crystal transducers.

We have recently experimentally demonstrated that a novel liquid crystal-based photonic transducer for sensing systems could be utilized as an active Q-switch in a miniaturised and integrated waveguide laser system. In this paper, we now present a comprehensive numerical modelling study of this novel laser architecture by deriving a set of equations that accurately describe the temporal optical response of the liquid crystal cell as a function of applied voltage and by combining this theoretical model with laser-rate equations. We validate the accuracy of this model by comparing the results with previously obtained data and find them in excellent agreement. This enables us to predict that under realistic conditions and moderate pump power levels of 500 mW, the laser system should be capable of generating peak power levels in excess of 1.1 kW with pulse widths of about 20 ns, corresponding to pulse energies > 20 μJ. We believe that such a low-cost and ultra-compact laser source could find applications ranging from trace gas sensing and LIDAR to material processing.

Theoretical investigation of anti-index guiding inactively Q-switched two-section diode lasers

We present a new theoretical design for diode lasers which should be capable of generating sub-100-ps pulses with pulse energies of more than 10 nJ per 100-μm-contact width by active Q-switching. We show that the carrier-induced reduction of the refractive index in the active layer, i.e. the vertical anti-index guiding effect, results in a dependence of the optical confinement factor on the carrier density which can be exploited for a further enhancement of the pulse energy and a reduction of the pulse length.

A Hybrid Q-switched Yb<sup>3+</sup>s-doped All-fiber Laser Based on the Acousto-optic Q-switch and SBS Effect

In the past 30 years, the studies on Q-switched fiber lasers have made great progress in both theoretical and experimental fields. So far there have been many reports about the acousto-optic active Q-switched fiber lasers. At the same time, there are many reports about the passive Q-switched pulse output using SBS effect in optical fibers, and this Q-switched mechanism based on SBS effect has become a simple and feasible scheme to narrow the pulse width. However, there are few reports about the Q-switched all-fiber lasers which have the two advantages mentioned above simultaneously. Theoretically the active and passive hybrid Q-switch can make the laser pulse stable and narrow. In this paper, by using the acousto-optic Q-switch and the SBS effect, the operation of a hybrid Q-switched Yb3+-doped all-fiber laser is realized. The pulse width 150ns is obtained at the repetition rate 50kHz. Furthermore, the output wavelength is 1083nm, with the pulse energy 0.02mJ and the peak power 133W achieved. In this experiment, the acousto-optic Q-switch and single-mode fiber play the role of Q-switching at the same time. The active acousto-optic Q-switch plays the role of frequency stabilization. The SBS effect in single-mode fiber plays the role of compressing pulse width. Hence the advantages of active and passive Q-switching modes are reflected.

Power scaling of an actively Q-switched orthogonally polarized dual-wavelength Nd:YLF laser at 1047 and 1053 nm.

We report a high average power actively Q-switched (AQS) orthogonal polarization dual-wavelength Nd:YLF laser at 1047 and 1053nm. The gain-to-loss balance of dual wavelengths was realized via an uncoated quartz etalon. A maximum continuous wave (CW) output power of 14.2W was obtained under the incident pump power of 41.7W, corresponding to an optical-to-optical conversion efficiency of 34.1% and a slope efficiency of 38.3%. Active Q-switching was accomplished by inserting an acousto-optic modulator in the cavity. Under the incident pump power of 40W, this setup delivered a maximum average output power of 10W at the pulse repetition frequency (PRF) of 30kHz and the largest pulse energy of 3.4mJ at the PRF of 1kHz, respectively. To the best of our knowledge, these are the highest average output powers for both CW and AQS orthogonally polarized dual-wavelength lasers based on laser crystals.

Q-switching and quasi-phase-matching using a domain structured LiNbO3 crystal

We report a device that acts as an active Q-switch and a quasi-phase-matching structure. It is a domain-structured LiNbO3 crystal, where the Q-switching is performed by electro-optic deflection and the wavelength conversion is produced by quasi-phase-matched optical parametric generation. By introducing this device into a diode-pumped Nd:YAG laser we obtained pulses at 1064 nm (~10 ns FWHM, 195 µJ) and 1617 nm (~3 ns, 15 µJ).

Temperature Effects on the Optical Parameters of a Passively Q-Switched Diode-Side Pumped Yb,Er-Laser

Temperature effects on photoluminescence and absorption spectra of the active medium (LGS-DE erbium phosphate glass) and passive Q-switch (MgAl2O4:Co2+ crystal) of a diode-side pumped Yb,Er-laser are studied. The obtained data are applied to an analysis of the spectral and energetic characteristics of compact erbium emitters. It is established that the dominant generation channel in the temperature range 233–328 K is the optical transition between lower Stark sublevels of Er3+ states 4I13/2 and 4I15/2 (λ = 1532.0–1533.9 nm). A rate-equation system taking into account thermal population of Stark sublevels of states 4I13/2 and 4I15/2 is proposed to describe the experimental temperature dependence of the threshold absorbed power of the pumping radiation. This system and the lasing threshold enable modeling of Yb,Er-emitter output energetic and temporal characteristics.

Q-switching of an all-fiber ring laser based on in-fiber acousto-optic bandpass modulator

Active Q-switching of an all-fiber ring laser utilizing a novel in-fiber acousto-optic tunable bandpass filter (AOTBF) is reported. The transmission characteristics of the AOTBF are controlled by amplitude modulation of the acoustic wave; the device exhibits a 3-dB power insertion loss, 0.91-nm optical bandwidth, and 28-dB nonresonant light suppression. Cavity loss modulation is achieved by full acousto-optic mode re-coupling cycle induced by traveling flexural acoustic waves. When the acoustical signal is switched on, cavity losses are reduced, and then, laser emission is generated. In addition, by varying the acoustic wave frequency, a wide wavelength tuning range of 30.7 nm is achieved from 1542 to 1572.7 nm. The best Q-switched pulses were obtained at 1.1-kHz repetition rate, with a pump power of 242 mW, at the optical wavelength of 1569.4 nm. A maximum pulse energy of 8.3 μJ at an average output power of 9.3 mW was achieved, corresponding to optical pulses of 7.8-W peak power and 1-μs temporal width.

Eye-Safe KGd(WO4)2:Nd Laser: Nano- and Subnanosecond Pulse Generation in Self-Frequency Raman Conversion Mode with Active Q-Switching

The shape of the multimode Stokes pulse generated by an eye-safe KGd(WO4)2:Nd laser with self-frequency Raman conversion and active Q-switching was shown to depend on the inhomogeneity of the active-medium pump. The laser generated a short and undistorted Stokes pulse of length ~2.5 ns that increased with increasing laser cavity length for a moderately inhomogeneous pump characterized by a higher population inversion in the center of the active element. The energy of the Stokes pulse (~11.5 mJ) varied little as the output-mirror reflectivity varied in the range 5–45%. The Raman pulse became distorted if the inhomogeneity of the pump was increased considerably. The degree of pump inhomogeneity was negligible with fundamental TEM00 mode selection. The laser generated subnanosecond Stokes pulses with peak power in the MW range.