Q-switched Pulses Research Articles

B-AsP as the saturable absorber for a mid-infrared 3 µm nanosecond laser

Black arsenic-phosphorus (B-AsP) has better stability than traditional black phosphorus (BP), and it was utilized to modulate a mid-infrared (mid-IR) 3 µm laser for what we believe to be the first time. The linear and nonlinear absorption characteristics of B-AsP at 3 µm were also investigated. The maximum continuous wave (CW) output power of the Er: SrF2 laser was 240 mW with an absorbed pump power of 2.87 W, resulting in a corresponding slope efficiency of 8.1%. During passively Q-switched (PQS) experiments, a laser pulse with a minimum duration of 188 ns was successfully generated at a repetition rate of 78 kHz, and the relevant single-pulse energy was 2.0 µJ. To the best of our knowledge, this is the narrowest passively Q-switched pulse for Er:SrF2 crystal laser. Our results indicate that B-AsP SA was a promising candidate to be the optical modulator in the mid-IR wavelength range.

1.45 ps All-solid-state Q-switched mode-locked laser based on new material Bi2Te3/Sb2Te3

In this work, the improvement of material properties and the optimization of mode-locked devices are discussed. The lateral heterojunction Bi2Te3/Sb2Te3 is prepared by a simple solvothermal method to overcome the limitation of traditional single material and improve the nonlinear optics properties. Based on a Bi2Te3/Sb2Te3 saturable absorber, the stable passive Q-switched mode-locked operation with wavelength of 1064 nm is achieved in Nd: YVO4 crystal. When the pump power reaches 5.5 W, a Q-switched mode-locked output with a maximum power of 910 mW is obtained, and the corresponding optical–optical conversion efficiency is 16.5 %. The repetition frequency of Q-switched pulse envelopes is 83.81 kHz, the pulse width is 1.8 μs, and the pulse energy is 10.8 μJ. The repetition frequency of the mode-locked pulse in the Q-switched envelope is 312.8 MHz and the pulse width is 1.45 ps. This flexible tunable laser provides high peak power, narrow pulse width, and highly stable laser output, broadening its application prospects in high-performance pulsed lasers.

Bulk-structured VTe2 as a novel low-cost saturable absorber for pulsed fiber lasers

In this work, we first investigate bulk-structured vanadium telluride (VTe2) saturable absorption properties and its application in the Q-Switched pulse generation. Bulk-structured VTe2 flakes have been obtained by the liquid phase exfoliation method. The prepared VTe2-SA has good saturable absorption characteristics whose saturable intensity is 0.24 MW/cm2, and the modulation depth is 2.73 % at 1.5 μm region. Furthermore, a Q-switched pulsed fiber laser based on VTe2-SA is constructed. The repetition rate of the Q-switched pulses can be increased from 16.3 kHz to 28.2 kHz, and the corresponding pulse duration decreases from 6.8 to 3.5 μs. The maximum Q-switched single pulse energy is 91.5 nJ. This work suggests that bulk-structured VTe2 can serve as a novel low-cost SA material and open up a new platform for expanding the applications of VTe2 for ultrafast photonics.

Passively generated Q-switched pulses fiber laser in 2 μm wavelength using MXene Ti3C2Tx and Ti2CTx saturable absorber

Abstract In this paper, Q-switched Thulium-doped fiber lasers (TDFLs) operating near the 2 µm region were demonstrated, utilizing a newly developed Thulium doped fiber as the gain medium and titanium carbide MXene as the saturable absorber (SA). The Thulium-doped fiber with a composition of SiO2-GeO2-Al2O3-HfO2-Y2O3-Bi2O3, was produced from a preform prepared using the modified chemical vapor deposition (MCVD) process. Two variations of titanium carbide MXene-based SA, Ti3C2Tx and Ti2CTx, were tested and compared, both successfully generating Q-switched pulses. When Ti3C2Tx was used, the Q-switched pulse had a center wavelength of 1934.223 nm, a repetition rate of 55.39 kHz and a pulse width and 1.942 µs. For Ti2CTx, the generated Q-switched pulse has a center wavelength of 1932.229 nm, with a repetition rate of 77.28 kHz and a pulse width of 1.608 µs. The signal-to-noise ratio (SNR) values were 45.6 dB and 50.2 dB for Ti3C2Tx and Ti2CTx respectively. Based on the experimental results, both Ti3C2Tx and Ti2CTx show promise as SAs for generating Q-switched pulses in the 2 µm region within the TDFL cavity.

A theoretical study of the output coupler reflectivity effect on the characteristics of Er+3 laser pulse at passively q-switching

The objective of this study deal the effect of the output coupler mirror reflectivity of laser system on behavior and characteristics (duration and energy) of erbium passive Q-switching laser pulse was studied theoretically. In the methods of the study, virtual passive Q-switching laser system consist of major elements such as erbium doped silica as an active medium, Cr+4: YAG crystal used as a saturable absorber, and the mirrors of resonator. Mathematical rate equations model has been used to describe the physical relationship between this element has been solved numerically by Rung - Kutta –Fehlberg method. The results showed regarding the pulse behavior, the increasing value of output coupler mirror reflectivity lead to decreasing of rising and falling time of pulse, so the emission of pulse occur in an advanced time. While regarding the pulse characteristics, the pulse was distinguishable by short duration and high energy, resulting high power of pulse when the output coupler mirror reflectivity increasing. Regarding of results discussion, the study attributes the results to a decrease of the initial and final population inversion density of active medium that results from the increasing value of output coupler mirror reflectivity. Therefore, it is possible to conclude in order to improve the characteristics of erbium passive Q-switching laser pulse; it is appropriate increase the value of output coupler mirror reflectivity within acceptable limits.

Sub-picosecond mode-locked laser operation in a femtosecond-laser-inscribed Yb:CaF2 channel waveguide

We present the successful demonstration of both Q-switched mode-locked (QSML) and continuous-wave mode-locked (CWML) operation in a femtosecond-laser-inscribed Yb:CaF2 double-track waveguide (WG) structure. A semiconductor saturable absorber output coupler (SOC) was used as the mode locker with fine tuning of the intracavity group delay dispersion (GDD) achieved through the Gires-Tournois interference (GTI) effect induced by an air gap. To ensure sufficient fluence on the saturable absorber, the cavity was extended to 50 cm by inserting two lenses between the SOC and WG, resulting in a repetition frequency of ∼300 MHz. In the QSML regime, the laser exhibited an amplitude modulation period of 65 kHz within Q-switched pulses of 3-µs duration. Notably, in the purely CWML regime, the laser generated a maximum output power of 51 mW near 1036 nm with a pulse width of 979 fs.

1.8 mJ pulses at 1560 nm based on a 55 µm core pure-erbium-doped VLMA fiber.

Despite the increasing demand for high-energy erbium lasers for LIDAR imaging applications, the scaling of the current Er-Yb co-doped technology is still hindered by a 1 µm parasitic emission. In this study, we present the first, to the best of our knowledge, utilization of the REPUSIL powder synthesis method to fabricate a 55 µm double-clad fiber with a remarkably large modal area. Doped solely with erbium and free of ytterbium, its estimated cladding absorption is 2 dB/m at 976 nm, enabling short amplification lengths. We demonstrate its potential through direct amplification of a GHz femtosecond laser (M2 = 1.12) and notably, the generation of 1.8 mJ, 37 ns Q-switched pulses in oscillator configuration (M2 = 1.46).

On the Synthesis of Graphene Oxide/Titanium Dioxide (GO/TiO2) Nanorods and Their Application as Saturable Absorbers for Passive Q-Switched Fiber Lasers.

We report passively Q-switched pulse operation through an erbium-doped fiber laser (EDFL) utilizing graphene oxide/titania (GO/TiO2) nanorods as a saturable absorber. The GO/TiO2 nanorods were fabricated using a Sol-gel-assisted hydrothermal method. The optical and physical characterization of the GO/TiO2 was then characterized using a field-emission-scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and diffuses reflectance spectroscopy (DRS). To investigate the performance of the Q-switched EDFL based on the GO/TiO2 SA, the prepared nanorods were mechanically deposited on the fiber ferrule employing adhesion effects of in-dex-matching gel. This integration of the nanorod SA resulted in a self-starting Q-switching opera-tion initiated at a pump power of 17.5 mW and sustained up to 306.9 mW. When the pump range was tuned from 17.5 to 306.9 mW, the emission wavelength varied from 1564.2 to 1562.9 nm, pulse repetition rates increased from 13.87 kHz to 83.33 kHz, and pulse width decreased from 30.27 µs to 3.75 µs. Moreover, at the maximum pump power of 306.9 mW, the laser exhibited an average output power of 0.74 mW, a peak power of 1.54 mW, and a pulse energy of 8.88 nJ. Furthermore, this study investigates the GO/TiO2 damage threshold and prolonged stability of the proposed EDFL system.

Boosting pulse characterization precision for Ho: YAP double pulse laser with back propagation neural network.

The precise energy and temporal control advantages of the 2 µm double-pulse laser have diverse applications in laser processing, biomedicine, and communications. The Ho: YAP Q-switched double pulse laser, a complex system, demands comprehensive theoretical analysis and precise experimental operations, especially when managing pulse overlap and ensuring output stability. Traditional design methods, time-consuming and labor-intensive, pose challenges in error elimination and susceptibility to environmental and device instabilities. This paper focuses on regulating the design and performance of the Ho: YAP Q-switched double-pulse laser. Critical developmental and optimization challenges are addressed by utilizing a back propagation neural network to forecast the nonlinear propagation of the laser while affirming the feasibility of bypassing intricate numerical solution models. This strategy streamlines experimental trials, ensuring reliable predictions of laser output characteristics and laying the foundation for forecasting more intricate laser systems in the future.

Dual Eu3+ and Er3+ doping in ZnO nanoporous 2D frameworks for tuning photocatalytic activity, linear and non-linear optical response

Recent days, the greater attention of research materials are focusing on the porous nano frame structure due to their distinctive properties and high photocatalytic activity. The porous defective materials revealed a significant role in numerous research fields like sensors, catalysts, energy production, magnetic memory storage, bio medical etc. In our work, pure ZnO and 4f shell shielded rare earth metals doped ZnO metal oxide nanomaterials attributed in the photocatalytic dye degradation, non-linear optical and magnetic properties. We were synthesized pure ZnO and ZnO0.1–2xEuxErxHMT0.1–2x (2x = 0.025,0.05,0.075, 0.010 wt%) nanoparticles using a straightforward hydrothermal route. The hexagonal wurtzite structure of ZnO and Eu:Er-doped ZnO (Eu:Er@ZnO) exhibited by PXRD, and the optical bandgap (Eg) range from 3.14 eV to 3.18 eV was determined by Tauc relation (αhγ)2 = 0. The porous nanoplate morphology of as-synthesized materials revealed by HR-SEM and HR-TEM techniques. All synthesized materials exposed weak ferromagnetic property nature by VSM studies. Among all the synthesized materials, the 0.0025 wt% Eu:Er@ZnO nanoparticles exhibited porous nanoplate structures capable of catalyzing the breakdown of reactive black 5 (RB5) dye, achieving a photocatalytic activity of 93.2 % after 65 min of UV light exposure. The dopant concentration significantly influenced this photocatalytic activity, with lower concentrations showing enhanced performance, particularly in acidic conditions. Moreover, all synthesized porous nano-plate materials followed pseudo-first-order kinetics. Additionally, the Z-scan technique was employed to assess the nonlinear optical properties of the synthesized materials using Q-switched nanosecond Nd laser pulses at 532 nm wavelength. The open-aperture Z-scan revealed reverse saturable absorption (RSA) in all samples. The Eu:Er@ZnO porous nano-plates exhibited promising nonlinear absorption characteristics, with a higher nonlinear absorption coefficient ranging from 5.21 to 7.84 × 10−11 m/W and a lower optical limiting threshold between 0.87 and 0.95 × 1012 W/m2.

Less is more: surface-lattice-resonance-enhanced aluminum metasurface with giant saturable absorption for a wavelength-tunable Q-switched Yb-doped fiber laser

Resonant metasurfaces provide a promising solution to overcome the limitations of nonlinear materials in nature by enhancing the interaction between light and matter and amplifying optical nonlinearity. In this paper, we design an aluminum (Al) metasurface that supports surface lattice resonance (SLR) with less nanoparticle filling density but more prominent saturable absorption effects, in comparison to a counterpart that supports localized surface plasmon resonance (LSPR). In detail, the SLR metasurface exhibits a narrower resonance linewidth and a greater near-field enhancement, leading to a more significant modulation depth (9.6%) at a low incident fluence of 25 μJ/cm2. As an application example, we have further achieved wavelength-tunable Q-switched pulse generation from 1020 to 1048 nm by incorporating the SLR-based Al metasurface as a passive saturable absorber (SA) in a polarization-maintaining ytterbium-doped fiber laser. Typically, the Q-switched pulse with a repetition rate of 33.7 kHz, pulse width of 2.1 μs, pulse energy of 141.7 nJ, and signal-to-noise ratio (SNR) of greater than 40 dB at the fundamental frequency can be obtained. In addition, we have investigated the effects of pump power and central wavelength of the filter on the repetition rate and pulse width of output pulses, respectively. In spite of demonstration of only using the Al metasurface to achieve a passive Q-switched fiber laser, our work offers an alternative scheme to build planar, lightweight, and broadband SA devices that could find emerging applications from ultrafast optics to neuromorphic photonics, considering the fast dynamics, CMOS-compatible fabrication, and decent nonlinear optical response of Al-material-based nanoplasmonics.

Nanostructured LNTO saturable absorber for generating multi-wavelength laser in Q-switched EDFL

In this paper, we propose a new and efficient ferroelectric nanostructure metal oxide lithium niobate [(Li1.075Nb0.625Ti0.45O3), (LNTO)] solid film as a saturable absorber (SA) for modulating passive Q-switched erbium-doped fiber laser (EDFL). The SA is fabricated as a nanocomposite solid film by the drop-casting process in which the LNTO is planted within polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] as host copolymer. The optical and physical characteristics of the solid film are experimentally established. The SA is incorporated within the cavity of EDFL to examine its capability for producing multi-wavelength laser. The experimental results proved that a multi-wavelength laser is produced, where stable four lines with central wavelengths at 1529.5, 1530.5, 1531.5, and 1532 nm are observed on the laser spectrum at 157 mW pumped power. Furthermore, at maximum available pumped power (157 mW), laser pulses are running with a rate of 178 kHz and pulse width of 2.64 μs. The output power of 3.7 mW is attained at pumped power of 157 mW. The result proved that the LNTO-SA could be a potential candidate for generating multi-wavelength passive Q-switched fiber laser pulses.

In-fiber waveguide-based mode-locker for generating diverse ultrafast pulses

The pursuit of an optimal mode-locker in nonlinear photonics is crucial for advancing high-performance laser technologies. Addressing the market demands and technical complexities in creating highly integrated and robust saturable absorbers, we present a femtosecond laser-inscribed in-fiber straight waveguide, seamlessly integrating a few-mode fiber segment into a single-mode fiber. This design reduces costs, simplifies fabrication, and enhances system integration and stability. As a saturable absorber, it enables nonlinear polarization rotation and multimode interference, which are essential for ultrafast pulse generation. It exhibits slight polarization-dependent loss and significant modulation depth, effectively inducing mode-locking. Based on the waveguide, 1.36 ps soliton pulses with a 2.9 nm bandwidth at a central wavelength of 1573 nm are initially achieved in an anomalous dispersion regime. Transitioning to the normal dispersion regime, at 190 mW pump power, the system produces Q-switched mode-locked pulses at 1574 nm. Increasing the pump power to 295 mW results in 712 fs noise-like pulses at 1572 nm, featuring an 8 nm bandwidth and 4.57 MHz repetition rate. This advancement in fiber lasers, facilitated by hybrid nonlinear effects in the waveguide, represents a significant milestone, promising for nonlinear optics and photonics due to its simplicity, cost-effectiveness, compactness, robustness, and high damage threshold.

Black phosphorus film as Q-switcher in neodymium-doped fiber laser

We present the successful development of a 1089.4 nm Q-switched laser employing a neodymium-doped fiber (NDF) as the active fiber and black phosphorus (BP) as the saturable absorber (SA). The BP SA was fabricated by inserting BP compound into a polyvinyl alcohol (PVA) host polymer, exhibiting a saturable absorption of 2.8 %. Integrated into an NDFL ring cavity, the SA modified the cavity loss, enabling the production of Q-switched pulses. With an increase in the 808 nm pumping power from 108.6 to 155.9 mW, the laser output pulse duration decreased from 3.74 to 3.54 μs, while the repetition rate improved from 40.6 to 51.0 kHz. The laser demonstrated a stable pulse train output, with a fundamental frequency signal to background noise ratio of 45.78 dB. The highest pulse energy of 1.3 nJ was recorded at 155.9 mW pump power. To the best of our knowledge, this represents the first utilization of BP as a SA or Q-switcher within an NDFL cavity.

Cerium oxide for L-band Q-switched pulse laser generation

Cerium oxide (CeO2), a rare earth metal oxide belonging to the lanthanide group is a mature engineered nanoparticle that has been developed for various industry applications. The nanoparticle features defects in its lattice structure, which is highly advantageous for bandgap tuning, and is acclaimed for its least cytotoxicity among other metal oxides. In this work, CeO2 is employed as a saturable absorber (CeO2-SA) in the generation of an L-band Q-switched erbium-doped fiber laser. Q-switching was attained at 33.33 mW pump power threshold with a central wavelength of 1600.512 nm. Within 33.33 mW to 153.20 mW pump power range, the Q-switched laser obtained pulse repetition rates between 11.00 to 34.48 kHz, and pulse widths between 39.0 to 12.0 µs, with a high maximum pulse energy of 410 nJ. The Q-switched fiber laser remained stable over a 45-minute observation time at 153.20 mW pump power. The room temperature and direct mechanical deposition fabrication technique of the CeO2-SA in this work demonstrates the extreme simplicity and low cost of the device, which would reduce the overall cost and facilitate a wider technology adoption of pulse laser systems.

Bandwidth modulation and pulse characterization of passively Q-switched erbium-doped fiber laser

We demonstrate the modulation of laser bandwidth by utilizing an ultranarrow tunable bandpass filter (UNTBF) in a passively Q-switched erbium-doped fiber laser. The passive Q-switch mechanism is enabled by using carbon nanotubes as saturable absorber at a Q-switched threshold of 35.5 mW. Based on spectral filtering effect introduced by the UNTBF, the 3 dB laser bandwidth can be tuned from 0.016 nm to 0.478 nm at a fixed pump power of 75.9 mW. The corresponding pulse behavior for each different bandwidth is characterized, and the results reveals that the pulse width can be as well tuned from 7.8 to 2.6 μs against the laser bandwidth, which agrees with the rule of time-bandwidth product. Correspondingly, the pulse repetition rate and the pulse energy vary from 16.23 kHz to 26.16 kHz and from 0.67 to 1.03 μJ respectively across the laser bandwidth. Further investigation of the pulse performance is performed against the pump power increment up to 107.2 mW. To the best of our knowledge, this is the first demonstration of spectrum bandwidth modulation in a passively Q-switched fiber laser, which can be useful for fully exploiting the possibilities of Q-switched pulse applications.

Co/MoS2 nanocomposite for passive Q-switched pulse operation in erbium-doped fiber lasers

Co/MoS₂ nanocomposite for passive Q-switched pulse operation in erbium-doped fiber lasers

Nonlinear optical properties of Bi2Se2Te for harmonic mode-locked and broadband Q-switched pulses generation.

The nonlinear optical properties of bismuth selenium telluride (Bi2Se2Te), a few-layer two-dimensional topological insulator material, have been investigated in this work. An erbium-doped fiber laser (EDFL) based on Bi2Se2Te (BST) nanosheets as saturable absorber (SA) was demonstrated. The BST SA with saturation intensity and modulation depth of 4.96 MW/cm2 and 2.45%, respectively, was obtained by mixing the layered BST nanosheets solution prepared by liquid phase exfoliation with a polyvinyl alcohol solution. On the basis of a 3.81 MHz fundamental repetition rate (RPR), seven types of high-order harmonic mode-locked (HML) at 300.2, 392.7, 424.2, 454.3, 516.9, 547.5 and 611.7 MHz were obtained, corresponding to 79th, 103rd, 111th, 119th, 135th, 144th and 160th harmonics, with the maximum 3-dB spectral width (2.31, 2.55, 2.55, 2.85, 2.96, 2.73 and 2.85 nm) and the narrowest pulse widths (1.11, 1.00, 1.00 ps, 896, 862, 935 and 895 fs), respectively. After reducing the cavity length by removing 30 m of single-mode fiber, a Q-switched operation with a maximum single pulse energy of 29.62 nJ and a tuning range of up to 81.91 kHz was obtained. The experimental results fully demonstrated that BST SA provided an important reference in the design of generating high RPR ultra-short pulses and Q-switched fiber lasers.

SESAM Q-switched Dy-doped fluoride fiber laser at 3.1 µm.

We report on a passive Q-switching laser operation of an in-band pumped Dy-doped zirconium fluoride fiber using a commercially available semiconductor saturable absorber mirror (SESAM). Stable Q-switching pulse trains with minimum pulse duration of 460 ns, highest repetition frequency of 206 kHz, and pulse energy up to 1.7 µJ are demonstrated.

Production of Cu/Zn Nanoparticles by Pulsed Laser Ablation in Liquids and Sintered Cu/Zn Alloy

As a preliminary step to establish technology for fabricating High-Entropy Alloys (HEAs) that can make a large-scale HEA using a pulse laser with high peak intensity and high-repetition in the future, we fabricated alloys in which two types of metal atom are mixed close together in the order of nanometers. For the method to produce the alloy, metal alloy nanoparticles were prepared by irradiating the material in liquid with focused high-repetition Q-switched laser pulses using an in-liquid laser ablation method. When brass powder was used as an original material, analysis results by TEM showed that numerous nanoparticles mixed with copper and zinc atoms could be produced. Furthermore, it was clarified by SEM EDS that copper and zinc atoms in the nanoalloy were maintained at a ratio of 3:1 in sintered alloy, and that the atoms were spatially uniformly distributed over a wide range in sintered metal.