Q-switched Research Articles

Influence of Opening Time Interval of Gate Signals on Suppression of Horizontally Polarized Signal of Infrared Pulsed Laser

Since the beginning of the 21st century, infrared Nd:YVO4 pulsed lasers have been widely applied, especially in some actual industrial processes. In the working process of a laser-aided etching device, the “match-head” effect must be effectively controlled by suppressing the first giant pulse for a solid-state Q-switched laser. In the process of optimizing the infrared Nd:YVO4 pulsed laser by adjusting the slope parameters of the radio frequency (RF) modulation to suppress the first giant pulse, it has been found that an abnormal horizontally polarized emission with a very short time appears before the formal vertically polarized emission when the gate signal is artificially started. Actually, abnormal horizontally polarized emissions will bring some unexpected machining traces during the production process and even greater dangers. The experimental results show that with the increase in the slope duration of an RF signal, the existence time of abnormal output horizontally polarized light will be shortened, and the horizontal giant pulse and vertical giant pulse are well suppressed. When the slope duration is greater than 0.18 ms, both horizontal and vertical giant pulses will disappear. The horizontally polarized light can be thoroughly suppressed when the slope duration is greater than 13.7 ms. Compared with the method of adding a polarizer to eliminate abnormal output horizontally polarized light, this method does not add elements in the laser, ensuring that the laser volume is relatively small, and does not affect the quality of the normal output laser. The research conclusion is thought to be of great practical significance, especially for processing transparent materials.

Tarnish tattoos - localised cutaneous argyria from sterling silver in fresh piercings: a case series.

Tarnish tattoo is a form of localised cutaneous argyria resulting from the deposition of silver into the skin following exposure to silver jewellery in fresh piercings. This report presents the clinical presentation, diagnosis, and management of 4 female patients with tarnish tattoos on the nose and ear from wearing silver jewellery. All four patients wore silver studs or rings immediately following the piercing. Two of the four patients underwent treatment with nanosecond Q-switched 1064nm Neodymium: Yttrium Garnet laser (QS Nd: YAG) and Q-switched Alexandrite 755nm lasers with minimal improvement. Tarnish tattoos are an under-recognized side-effect of wearing silver jewellery in fresh piercings. The grey-blue discolouration from tarnish tattoos can be challenging to treat with nanosecond QS lasers.

1.4 W Passively Q-Switched Mode-Locked Tm:CALGO Laser with a MoS2 Saturable Absorber

The passively Q-switched mode-locked (QML) operation of a Tm:CaGdAlO4 (Tm:CALGO) bulk laser pumped by a wavelength-tunable Ti:sapphire oscillator using molybdenum disulfide (MoS2) as a saturable absorber was demonstrated. By using an output coupler with 3% transmittance, Q-switched mode-locked operation can be achieved with 3.56 W absorbed pump power. At a pump power of 6.77 W, laser pulses with the maximum average power of 1.44 W were obtained, corresponding to a slope efficiency of 21.3%. The laser delivered pulses centered at 1927 nm with a repetition frequency of 131.6 MHz. The experimental results confirm the promising application of the MoS2 in high-power Q-switched mode-locked solid-state lasers at 2 µm.

1.36-um passively Q-switched laser by a Nd3+-doped double cladding phosphate glass fiber

1.36-um passively Q-switched laser by a Nd3+-doped double cladding phosphate glass fiber

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.

Melasma Revisited: National Survey Reveals How Dermatologists Diagnose and Treat This Complex Skin Condition.

Melasma is a chronic condition characterized by dark patches on the facial skin. It has a known female gender dominancy, and women usually think of melasma as being a serious cosmetic problem. Treatment of melasma can be seriously challenging, thus, dermatologists may employ different approaches for melasma. This study aimed to investigate how dermatologists diagnose and treat patients with melasma and to present the general characteristics of patients with melasma. A survey was conducted using Google Forms targeting dermatologists in Turkiye. A total of 199 dermatologists (142 females/57 males) participated in the study. Most of the participants (52.3%) were residents. Majority gender of the patients was female and most common age range of patients with melasma was 30-40 years. Mixed melasma was the most common type (57.4%). Malar region was the most frequent location (58.6%). Wood's lamp examination was used by 25.6% of the participants. Topical treatment was the first-line choice for melasma therapy (95%), with Kligman's formula being the most used topical agent (69.8%). Oral therapy was not used by 70.8% of the participants. Tranexamic acid was the first choice for oral treatment (23.4%). Only 24.9% of the dermatologists used laser/light therapy, and Q-switched Nd-YAG laser was the most preferred device (58%). The most common recurrence rate was 41%-60% (45.9%). The findings of the current study investigating the melasma management in Turkiye revealed a female predominance and peak prevalence in the 30-40 years age group. Kligman's formula is the preferred topical treatment, whereas oral tranexamic acid remains underutilized. Recurrence rates are high, highlighting the need for preventative strategies. This study emphasizes the importance of personalized approaches and ongoing research for effective melasma management.

All Fiber Passively Q-Switched Mode-Locked Laser at 1195 nm Based on Ho3+-Doped ZBYA Fibers

All Fiber Passively Q-Switched Mode-Locked Laser at 1195 nm Based on Ho³⁺-Doped ZBYA Fibers

Ultrafast laser triggering nanocrystallization inside Nd-doped photo-thermo-refractive glass and its application in Q-switched laser

Ultrafast laser triggering nanocrystallization inside Nd-doped photo-thermo-refractive glass and its application in Q-switched laser

Formation and conversion of high-peak-power structured beams by an Nd:YVO4/Cr4+:YAG laser subject to tight-focusing off-axis pumping

A compact Nd:YVO4/Cr4+:YAG passively Q-switched laser in a near-hemispherical resonator is exploited to realize high-peak-power pulsed beams with high spatial degrees of freedom. Beneficial from the advantages of strong intracavity beam focusing as well as the point-like excitation condition for the proposed cavity design, various high-order structured pulses as coherent superpositions of multiple degenerate eigenmodes are stably generated under different off-axis pump schemes. Besides, by employing external-cavity astigmatic mode conversion (AMC), the oval-shaped and chessboard-like structured pulses under on-axis and 1D off-axis pumping are transformed into exotic modes with polygonal and figure-eight-shaped envelopes to further enrich the spatial complexity of the generated fields. With well-defined beam structures that are reconstructed using the analytical resonant wave functions of the resonator, the phase structures of AMC pulsed fields are numerically resolved to present a variety of singularity arrays. Experimental results reveal that the overall peak power of the on-axis and off-axis generated structured pulses respectively exceeds 600 W and 1 kW while maintaining good pulse train stability with peak-to-peak amplitude fluctuation to be less than 10% and 15%.

Integrated mid-infrared sensing and ultrashort lasers based on wafer-level Td-WTe2 Weyl semimetal

There is an urgent need for infrared (IR) detection systems with high-level miniaturization and room-temperature operation capability. The rising star of two-dimensional (2D) semimetals with extraordinary optoelectronic properties can fulfill these criteria. However, the formidable challenges with regard to large-scale patterning and substrate-selective requirements limit material deposition options for device fabrication. Here, we report a convenient and straightforward eutectic-tellurization transformation method for the wafer-level synthesis of 2D type-II Weyl semimetal WTe2. The non-cryogenic WTe2/Si Schottky junction device displays an ultrawide detection range covering 10.6 μm with a high detectivity of ∼109 Jones in the mid-infrared (MIR) region and a short response time of 1.3 μs. The detection performance has surpassed most reported IR sensors. On top of that, on-chip device arrays based on Schottky junction display an outstanding MIR imaging capability without cryogenic cooling, and 2D WTe2 Weyl semimetal can serve as a saturable absorber for stable Q-switched and mode-locked laser operation applications. Our work offers a viable route for wafer-scale vdW preparation of 2D semimetals, showcasing their intriguing potential in on-chip integrated MIR detection systems and ultrafast laser photonics.

Optimized-selenization preparation and laser Q-switching characteristics of layered PtSe2

Abstract PtSe2 has high carrier mobility, excellent electrical and optical properties, and high potential in the field of optoelectronic devices. In this paper, the conventional selenization method is optimized and a single-temperature zone preparation is used to prepare large-area and homogeneous PtSe2 thin-film materials on sapphire substrates in a shorter time and at a lower temperature. The prepared sample is characterized by optical microscopy, atomic force microscopy, Raman spectroscopy and Z-scan method. The saturable absorption properties of layered PtSe2 as a passive Q-switched are investigated in a solid-state laser. The results show that the PtSe2 thin film material is synthesized at 400 °C for 1 h to cover the entire one-inch sapphire wafer with a thickness of about 25 nm and the surface roughness is 13.1 nm. The modulation at 1064 nm yielded an output pulse with a maximum repetition frequency of 688.47 kHz, corresponding to a pulse width of 202.5 ns, a peak power of 7.35 W, a single-pulse energy of 1.51 μJ, and a stable pulse train.

Evolution of Single Photon Lidar: From Satellite Laser Ranging to Airborne Experiments to ICESat-2

In September 2018, NASA launched the ICESat-2 satellite into a 500 km high Earth orbit. It carried a truly unique lidar system, i.e., the Advanced Topographic Laser Altimeter System or ATLAS. The ATLAS lidar is capable of detecting single photons reflected from a wide variety of terrain (land, ice, tree leaves, and underlying terrain) and even performing bathymetric measurements due to its green wavelength. The system uses a single 5-watt, Q-switched laser producing a 10 kHz train of sub-nanosecond pulses, each containing 500 microjoules of energy. The beam is then split into three “strong” and three “weak” beamlets, with the “strong” beamlets containing four times the power of the “weak” beamlets in order to satisfy a wide range of Earth science goals. Thus, ATLAS is capable of making up to 60,000 surface measurements per second compared to the 40 measurements per second made by its predecessor multiphoton instrument, the Geoscience Laser Altimeter System (GLAS) on ICESat-1, which was terminated after several years of operation in 2009. Low deadtime timing electronics are combined with highly effective noise filtering algorithms to extract the spatially correlated surface photons from the solar and/or electronic background noise. The present paper describes how the ATLAS system evolved from a series of unique and seemingly unconnected personal experiences of the author in the fields of satellite laser ranging, optical antennas and space communications, Q-switched laser theory, and airborne single photon lidars.

Melasma removal using Q-Switched Neodymium-doped Yttrium Aluminium Garnet laser toning and high-intensity focussed ultrasound.

To evaluate the effectiveness of combining high-intensity focussed ultrasound and a Q-switched neodymium-doped yttrium aluminium garnet 1064nm low-fluence toning laser in the treatment of melasma. The experimental study was conducted from November 2020 to August 2021 at the medical physics laboratory, College of Medicine, Mustansiriyah University, Baghdad, Iraq, and comprised individuals of either gender aged >25 years having mixed form melasma in malar and forehead areas. Each participant received high-intensity focussed ultrasound treatment on the right side. After 2 weeks, Q-switched neodymium-doped yttrium aluminium garnet 1064nm low-fluence toning laser was applied to the melasma patches 4 times at one-week intervals. Melasma area and severity index scores were noted at baseline and at each visit for each patient. Visual analogue scale was used for objective evaluation. After the 4 laser sessions, all the patients completed a 3-month follow-up. Data was analysed using SPSS 24. Of the 25 subjects, 15(60%) were females and 10(40%) were males. The overall mean age was 41.6±8.46 years (range: 22-60 years). There was a significant improvement with high-intensity focussed ultrasound (p<0.05). In the 3rd laser session, there was a significant difference in melasma area and severity index score of 2.48 for the right side and 3.12 for the left side (p<0.05). In the 4th session, there was a significant difference in melasma area and severity index score of 1.68 for the right side and 2 for the left side (p<0.05). No post-inflammatory hyperpigmentation or rebound was noted. High-intensity focussed ultrasound combined with toning laser was more effective than Q-switched neodymium-doped yttrium aluminium garnet 1064nm low-fluence laser alone in removing difficult melasma from the malar area in the 2nd, 3rd and 4th sessions, and from the forehead in the 3d and 4th sessions.

Platelet-Rich Plasma Injection Combined With Q-Switched Ruby Laser in the Treatment of Periorbital Hyperpigmentation.

Periorbital hyperpigmentation is a prevalent skin condition that represents a large quantity of cases seen in cosmetic dermatology. Patients tend to be left with pigmentation after Q-switched ruby laser treatment, especially the perioribital area. The study is conducted to compare the effect of PRP injection combined with laser therapy versus laser alone for periorbital hyperpigmentation treatment. In this single-center, case-control study, 30 patients with periorbital hyperpigmentation were allocated to receive PRP injection injection after Q-switched ruby laser or Q-switched ruby laser only, followed by a 12-week and 24-week follow-up visit. Visual analogue scale, Sadick tear trough rating scale, and patients' self-evaluation were used to evaluate the therapeutic effect. The combined group achieved a better improvement in long-term effect and had effect on facial rejuvenation. Patient satisfaction was higher in the combined group. Erythema and mild pain were the most common adverse reactions of both groups. Combining with PRP injection can improve the therapeutic effect of Q-switched ruby laser in treating periorbital hyperpigmentation and lessen the risk of post-inflammatory hyperpigmentation, indicating a new option for POH treatment.

1.3 μm higher order LP11 mode pulses in praseodymium-doped fluoride fiber laser

Abstract This work demonstrated an LP11 mode pulse laser at O-band using praseodymium-doped fluoride fiber as a gain medium. The Q-switched laser was initially generated using antinomy-telluride/polyvinyl-alcohol (Sb2Te3/PVA) thin film, and the LP11 modes were analyzed using a beam profiler. The pulse laser was achieved at a pumped power of 273–303 mW. With the increase in pump power, the pulse repetition rate increased to a maximum of 60.2 kHz, and the pulse width decreased to a minimum of 2.86 μs. The operating wavelength of the Q-switched output was 1303.2 nm. The corresponding pulse energy and peak power also increased with the increase in pump powers to the maximum of 12.12 nJ and 4.24 mW. The higher-order modes were obtained after the fiber was offset between the single-mode fiber and the two-mode fiber (TMF). The TMF output was then connected to the multimode fiber, a collimator, and the scanning-slit optical beam profiler to observe the higher-order modes. A uniform two-lobe structure of higher-order LP11 modes was observed.

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.

Simultaneously achieving high repetition rate and high peak power in Er,Yb:YAl3(BO3)4 microchip laser

This study presents a dual-ended pumped 1.5 µm Er,Yb:YAl3(BO3)4 (Er,Yb:YAB) passively Q-switched microchip laser, designed to address the challenge of achieving high peak power and high repetition rates simultaneously. The dual-ended pumping method significantly reduces the thermal gradient within the crystal, allowing for higher pump incident power compared to single-ended pumping. Under quasi-continuous-wave (QCW) pumping conditions, the laser achieved a pulse energy of 14.33 µJ, a repetition rate of 470.08 kHz, and a peak power of 2.53 kW. Additionally, we conducted a detailed investigation of the pulse bifurcation phenomenon observed during the experiments, uncovering the underlying mechanisms and their potential impact on laser performance. The results not only demonstrate the effectiveness of dual-ended pumping in enhancing laser performance but also provide valuable insights into thermal management in Er,Yb:YAB crystals. These findings could serve as a foundation for developing more efficient and powerful Er,Yb:YAB lasers, which hold promise for applications in lidar, remote sensing, and range finding.

Interlayer engineered bilayered V₂O₅ NPs as saturable absorbers for infrared ultrashort pulse generation

Interlayer engineering offers a promising approach to modifying the structure of layered vanadium-based oxides, enhancing their saturable absorption effect and making them a desirable choice for developing infrared wavelength-range photonics devices. This experimental work synthesizes interlayer vanadium pentoxide (V2O5) using hydrothermal techniques to produce an excellent saturable absorber (SA). The interlayer engineering strategy enhances strong saturable absorption and self-defocusing effects in V2O5-based SA, enabling the generation of ultrashort pulses in the infrared region. Their superior nonlinear optical characteristics are demonstrated by a modulation depth of 13.9 % and saturation intensity of 0.42 GW cm−1, respectively. By utilizing a transmission coupling fiber-based V2O5-SA inside an Er-doped fiber laser cavity, a passively Q-switched (PQS) laser with a narrow pulse width of 2.78 μs and signal-to-noise ratio (SNR) ∼50 dB is realized for the first time. Furthermore, we explore a V2O5 NPs-SA long-term stability and high damage threshold. The results not only offer additional proof of the capable potential of interlayer V2O5 as a photo-bleaching absorber for realizing pulsed lasers in the NIR band but also cover the method for advancing their probable applications in optoelectronic devices.