Passive Q-switching Research Articles

Ti2AlC-based saturable absorber for passive Q-switching of a fiber laser

We report the feasibility of a MAX-phase material for implementation as a saturable absorber. Our saturable absorber was fabricated as a composite of Ti2AlC particles and polyvinyl alcohol (PVA) using a sandwich-structured fiber-ferrule platform. The saturation intensity and modulation depth of the prepared SA were measured at ∼31.5 MW/cm2 and ∼6.3%, respectively. Using the Ti2AlC/PVA composite-based SA within an erbium-doped fiber laser ring cavity, stable Q-switched pulses were readily obtained at a wavelength of 1.56 µm. This experimental demonstration unveils the potential of micrometer-sized MAX-phase particles for implementation as low-cost, practical, saturable absorbers.

A 2.22-W Passively Q-Switched Tm3+-Doped Laser With a TiC2 Saturable Absorber

A TiC2 solution was prepared by using an ultrasonic decomposition and nonlinear saturable absorption characteristics at about 2 μ m were evaluated. A passively Q-switched (PQS) Tm:YAP laser was developed using the TiC2 material as a saturable absorber, and a 2220-mW average output power with a 579-ns pulse duration at 255 kHz was achieved in PQS mode, corresponding to 8.4% optical conversion efficiency. Also, an 8.7- μ J per pulse energy and a 15.0-W peak power were achieved from this PQS Tm:YAP laser. Furthermore, quality factors of vertical and horizontal beams from the Tm:YAP laser were less than 1.2 under two different modes of operation.

Development of a subsurface LIBS sensor for in situ groundwater quality monitoring with applications in CO2 leak sensing in carbon sequestration

Sub-surface activity such as geologic carbon sequestration (GCS) has the potential to contaminate groundwater sources with dissolved metals originating from sub-surface brines or leaching of formation rock. Therefore, a Laser Induced Breakdown Spectroscopy (LIBS) based sensor is developed for sub-surface water quality monitoring. The sensor head is built using a low cost passively Q-switched (PQSW) laser and is fiber coupled to a pump laser and a gated spectrometer. The prototype sensor head was constructed using off the shelf components and a custom monolithic, PQSW laser and testing has verified that the fiber coupled design performs as desired. The system shows good calibration linearity for tested elements (Ca, Sr, and K), quick data collection times, and Limits of Detection (LODs) that are comparable to or better than those of table top, actively Q-switched systems. The fiber coupled design gives the ability to separate the PQSW LIBS excitation laser from the pump source and spectrometer, allowing these expensive and fragile components to remain at the surface while only the low-cost, all optical sensor head needs to be exposed to the hostile downhole environment.

Evaluating Laser-Induced Breakdown Spectroscopy Sensor Technology for Rapid Source Characterization of Rare Earth Elements

A prototype laser-induced breakdown spectroscopy (LIBS) sensor is tested for the determination of rare earth elements (Eu and Yb) in liquid and solid samples. The sensor head, built using a monolithic passively Q-switched (PQSW) Nd:YAG laser, produced a 1064 nm laser beam with ns pulses and an energy of 4.2 mJ. The measurements show good calibration linearity for both Eu and Yb with R2 values above 0.99 for all analyzed spectral lines in liquid and solid samples. Limits of detection (LODs) obtained were as low as 1 ppm, which are comparable to or better than those reported previously by using table top actively Q-switched systems. This study aims to develop a high sensitivity, field deployable sensor for characterizing existing and new sources of rare earth elements.

Aluminum nanoparticles saturable absorber as a passive Q-switcher for erbium-doped fiber laser ring cavity configuration

We report on the generation of a passively Q-switched erbium-doped fiber laser (EDFL) at 1567.6 nm, using aluminum nanoparticles (AlNPs) as a saturable absorber (SA). The synthesized film was fabricated by implanting AlNPs into polyvinyl alcohol as a host matrix. The SA thin film has a modulation depth of 7% and saturable intensity of 0.0015 MW cm−2. A small piece of composite film was inserted between two fiber ferrules to initiate Q-switching in the EDFL. Upon reaching a pump threshold of 156 mW, a stable Q-switching was achieved. As the pump power is steadily tuned from 156–300 mW, the repetition rate changes from 34.13–48.8 kHz, while the corresponding pulse duration varies from 3.4–2.17 µs. To the best of the authors’ knowledge, this the first demonstration of passive Q-switching employing an AlNP-based saturable absorber.

A 3.3-W passive Q-switched 2-µm laser with a MoS2-based saturable absorber

Using a new MoS2-based nanosheets as a saturable absorber (SA), a passively Q-switched (PQS) Tm, Ho:YAP laser at 2000.4 nm was proved in the paper. Under PQS mode, an average output power of over 3 W and per pulse energy of over 23 μJ were obtained in the experiment. Also, the beam quality factors were less than 1.1 in PQS mode.

Generation of controllable Ince – Gaussian modes in a passively Q-switched microchip laser under truncated decentred Gaussian beam pumping

We report a passively Q-switched (PQS) Nd : YAG/Cr4+: YAG microchip laser pumped by a truncated decentred Gaussian beam for controllable Ince – Gaussian (IG) mode generation. IGe(n, n) modes (n = 0, …, 4) are obtained experimentally by choosing the appropriate truncation parameter, which is defined as a ratio of the radius of the aperture to the beam waist. The IGe(4, 4) mode is produced in the PQS Nd : YAG/Cr4+: YAG microchip laser under decentred Gaussian beam pumping at a pump power of 2.6 W, the mode selection being achieved by reducing the truncation parameter. The threshold pump powers for different IGe(n, n) modes are theoretically calculated to illustrate the mode selection process. The pulsed IGe(n, n) (n ≥ 1) mode generation with a peak power exceeding 1 kW and a nanosecond pulse width is obtained in the PQS microchip laser, which is a potential laser source for forming flexible vortex arrays for optical tweezers.

Single-Frequency Side-Diode-Pumped Monopulse Nd:YAG-Laser with a Ring Cavity

The formation features of the single-frequency unidirectional monopulse lasing mode of a Nd:YAG laser with a triple-mirror ring cavity and a side diode-pump with injection of external narrow-band optical radiation into the cavity are studied. The asymmetric layout of the intracavity elements relative to the output mirror and depolarization effects in them cause the energy and polarization of the monopulse Nd:YAG ring laser to differ depending on the input direction (clockwise or counterclockwise) of the injected radiation. The difference in the output characteristics of the single-frequency unidirectional monopulse Nd:YAG ring laser is most evident for a change from active to passive Q-switching.

Application of few-layer WSe2/Sapphire in passively Q-switched solid-state lasers as saturable absorber and output coupler

We demonstrate that it is possible for a few-layer WSe2/Sapphire to act in specific high-gain solid-state lasers as both saturable absorber for passive Q-switching and as etalon mirror for output coupling. A passively Q-switched Yb:LuPO4 microchip laser formed in this manner is realized. With 11.5 W of pump power absorbed, a maximum output power of 1.8 W is produced at a pulse repetition rate of 1.2 MHz with a slope efficiency of 25%; the resulting pulse energy, duration, and peak power are, respectively, 1.5 μJ, 30 ns, and 50 W. Our work provides a simple way of making compact, reliable, high-repetition-rate pulsed microchip or miniature solid-state lasers based on 2D saturable absorbers.

Modeling of a pulsed, single cavity Yb–Bi fiber laser taking mode field area mismatch into consideration

A theoretical model concerning a pulsed, single cavity Yb–Bi fiber laser is established. A Q-switching rate equation is derived for mode field area mismatch operations. A stable Q-switching wavelength range and corresponding pump range of this laser system is explored, and the detailed population transition processes are described. Further, the pulse characteristics of the laser system are investigated with different pump powers at 1120 nm. The simulations show that, for a single cavity Yb–Bi fiber laser, stable passive Q-switching could be attained in a relatively wide wavelength range, and a relatively larger coupling ratio is more favorable for laser design. At a fixed wavelength, a steady region— where the pulse energy, peak power and pulse duration show little variation with the change of the pump power—exists, and the main cause is the relatively steady effective pump energy in this region.

MoSSe Saturable Absorber-Based High-Power Passively Q-Switched <inline-formula> <tex-math notation="LaTeX">$2.0~\mu$ </tex-math> </inline-formula>m Bulk Laser

A ternary transitional metal dichalcogenides alloy material, molybdenum sulphoselenide (MoSSe), has been successfully fabricated and used as a saturable absorber (SA) for a passively Q-switched (PQS) Tm:YAP bulk laser operating at $2.0~\mu \text{m}$ for the first time, to best of our knowledge. The open aperture Z-scan method was used to characterize the saturable absorption properties of the prepared MoSSe SA. The maximum average output power and pulse repetition rate, shortest pulse width, highest single pulse energy, and highest pulse peak power of this laser were 2.26 W, 95 kHz, 303 ns, $24.2~\mu \text{J}$ , and 80 W, respectively. The results are distinguished from other two-dimensional materials-based $2.0~\mu \text{m}$ PQS lasers, indicating that MoSSe could be a promising material for generating high power and short pulse width lasers in the $2.0~\mu \text{m}$ spectral range.

Dual-wavelength Q-switched laser based on a lens-shaped Nd : YAG active element and a Cr4+: YAG passive Q-switch

Dual-wavelength Q-switched lasing at wavelengths of 1047 and 1053 nm is achieved in a longitudinally diode-pumped laser with a lens-shaped Nd:YLF active element and a Cr4+ : YAG passive Q-switch. Dual-wavelength lasing is achieved as a result of transverse mode locking due to the choice of a cavity length corresponding to the close-to-semiconfocal configuration, which provides identical gains for the two laser wavelengths.

A passively Q-switched Ho:SSO laser with a Cr2+:ZnSe saturable absorber

Represented here is a continuous-wave (CW) operation laser and a passively Q-switch (PQS) Ho:SSO microchip laser with a Cr2+:ZnSe saturable absorber (SA). An end-pumped Tm:YAP laser pumping was employed, which operated at room temperature. Up to our knowledge, it is the first time to report a PQS microchip Ho:SSO laser. A maximum 418 mW CW laser output was realized with an absorbed pump power of 2.5 W. The slope efficiency was 59.4%. In the PQS mode, the maximum output power was 332 mW, at the same time the slope efficiency was down to 57.1%. The maximum repetition frequency was 0.69 kHz. The maximum pulse energy of 481 μJ was realized corresponding to the pulse width of 103 ns. The pulsed characteristics were studied in this work. The output wavelength for different modes were also investigated.

Rhenium diselenide as the broadband saturable absorber for the nanosecond passively Q-switched thulium solid-state lasers

The feasibility of using rhenium diselenide (ReSe2) as the saturable absorber for the broadband passively Q-switched (PQS) thulium solid-state lasers was demonstrated in this paper. In the short wavelength of 2 μm region, the combination of Tm:YLF and ReSe2 was used to achieve the PQS operation with multi-wavelength around 1900 nm. A maximum average output power of 862 mw, a shortest pulse width of 527.9 ns and a repetition rate of 54 kHz were obtained. In the long wavelength of 2 μm region, a ReSe2-based PQS multi-wavelength Tm:Y2O3 laser around 2050 nm was realized, generating a maximum average output power of 1.04 W, a shortest pulse width of 727 ns and a repetition rate of 106 kHz. The output performance of the ReSe2-based pulsed laser is competitive among these PQS thulium solid-state lasers using the emerging two-dimensional materials as SAs, indicating that ReSe2 is a promising broadband SA for the 2 μm solid-state lasers.

Passively Q-switched operation of a Tm:YAlO3 laser with a BN saturable absorber mirror

A passively Q-switched (PQS) Tm:YAlO3 (Tm:YAP) laser was perfectly implemented with boron nitride (BN) nanosheets as a saturable absorber mirror. In PQS mode, an average output power of 1.54 W with a pulse duration of 349 ns was achieved, corresponding to an optical–optical conversion efficiency of 5.78%. Also, a pulse peak power of 14.6 W was acquired with an output wavelength of 1937.40 nm from the PQS Tm:YAP laser, and the beam quality factors were measured to be and at a physical cavity of 27 mm.

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 1.9μm 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 1.9μm 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 1.1W, 313ns, 22.0μJ, and 71.0W, 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.

Effects of Cr4+ ions on forming Ince–Gaussian modes in passively Q-switched microchip solid-state lasers

The effects of Cr4+ ions on forming Ince–Gaussian (IG) laser modes in a tilted pumped Cr4+:YAG passively Q-switched (PQS) Nd:YAG microchip lasers has been studied experimentally and theoretically. The formation of Cr4+-ion domains in Cr4+:YAG crystal has been proposed based on the spatial distribution of Cr4+ ions in Cr4+:YAG crystal. The spatial modulation effect of Cr4+-ion domains on selecting a transverse mode has been investigated based on their periodic distribution and nonlinear absorption of the Cr4+ saturable absorber. The formation of IG modes in the Nd:YAG/Cr4+:YAG PQS microchip laser under tilted pumping has been demonstrated theoretically with the spatial modulation of the Cr4+-ion domains in Cr4+:YAG crystal and the inversion population distribution, by taking account of the thermal lens effect. The IG modes selected theoretically in the Nd:YAG/Cr4+:YAG PQS microchip laser are in good agreement with experimentally obtained IG modes. This work provides a theoretical model of the selection of IG modes with Cr4+-ion domains in a tilted beam pumped Nd:YAG/Cr4+:YAG PQS microchip laser to produce efficient, stable and controllable IG laser modes.

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.

Few-layer ReS2(1−x)Se2x nanoflakes for noise-like pulse generation in a mode-locked ytterbium-doped fiber laser

We investigated the ternary ReS2(1−x)Se2x alloys and fabricated few-layer ReS1.02Se0.98 nanoflakes to realize passive Q-switch and noise-like pulses operating at 1 μm wavelength.

Anomalous passive Q-switching induced by Cr4+:YAG: with pulse repetition rate approaching up to 1 MHz

Anomalous passive Q-switching behavior was demonstrated in an Yb:KLu(WO4)2 laser, with a Cr4+:YAG crystal plate acting as saturable absorber whose initial transmission amounted to 99.3%. In stable Q-switched operation realized under high output coupling of 80%, 1.83 W of average output power was produced at a pulse repetition rate of 0.97 MHz, far beyond the upper limit imposed by the recovery time of the saturable absorber. The largest pulse energy, shortest pulse duration, and highest peak power were, respectively, 1.89 µJ, 39 ns, and 48.5 W. The high-repetition-rate passive Q-switching performance shows a close similarity to some Yb-ion lasers passively Q-switched by 2D saturable absorbers.