Minimum Pulse Duration Research Articles

Tunable and switchable multi-wavelength pulsed fiber laser based on a nonlinear optical loop mirror and an improved Sagnac filter.

We propose and experimentally demonstrate a tunable and switchable multi-wavelength erbium-doped fiber ring pulsed laser based on a nonlinear optical loop mirror (NOLM) and an improved Sagnac filter. To achieve multi-wavelength pulsed laser output, we adopt a NOLM as a quasi-saturable absorber and an improved Sagnac loop as a wavelength selected filter. The constructed laser has a maximum output wavelength number of five with a pulse repetition frequency of 40.45kHz and pulse duration of 108ns. The laser can output single-wavelength and dual-wavelength pulsed lasers within a certain wavelength tuning range and a five-wavelength pulsed laser with a constant wavelength interval of 3nm by adjusting the polarization controller. Dual-wavelength, three-wavelength, and four-wavelength pulsed lasers with various wavelength intervals are also obtained. The output performance of the constructed laser is tested with a maximum average output power of 127.45µW and minimum pulse duration of 52ns, and the stability of the laser output is also tested with a maximum power fluctuation of 0.62dB and minimum wavelength drift of 0.51nm with pump power of 350mW.

Passively Q-switched Er3+-doped fiber laser based on double-transition metal MAX phase TiNbAlC saturable absorber

We demonstrated a stable passively Q-switched fiber laser operation at 1531.57 nm using a double-transition metal MAX phase TiNbAlC saturable absorber. The prepared saturable absorber’s modulation depth, saturation intensity, and non-saturation loss are 1.75%, 0.089 MW/cm2, and 32.81%, respectively. Using the TiNbAlC saturable absorber within an erbium-doped fiber laser ring cavity, stable Q-switched pulses with a central wavelength of 1531.57 nm, and a 3-dB bandwidth of 1.43 nm are acquired. The minimum pulse duration and the maximum single pulse energy are 3.18 μs and 51.56 nJ, respectively. Furthermore, the maximum repetition rate is 37.9 kHz with a signal-to-noise ratio of 50 dB. Our results indicate that double-transition metal MAX phase TiNbAlC can be an excellent saturable absorber candidate for an ultrashort pulse fiber laser.

Direct temporal characterization of sub-3-fs deep UV pulses generated by resonant dispersive wave emission.

We report on the complete temporal characterization of ultrashort pulses, generated by resonant dispersive wave emission in gas-filled hollow-capillary fibers, with energy in the microjoule range and continuously tunable from the deep-ultraviolet to the ultraviolet. Temporal characterization of such ultrabroad pulses, particularly challenging in this spectral region, was performed using an all-in-vacuum setup for self-diffraction frequency resolved optical gating (SD-FROG). Sub-3-fs pulses were measured, tunable from 250 nm to 350 nm, with a minimum pulse duration of 2.4 ± 0.1 fs.

High-damage-threshold mid-infrared saturable absorber enabled by tantalum carbide nanoparticles.

A stable mid-infrared saturable absorber with a high damage threshold is urgently required for high-performance optical modulation in the mid-infrared regime. Here, we demonstrate stable mid-infrared erbium-doped fiber laser generation modulated by tantalum carbide nanoparticles (TaC NPs) experimentally. The TaC NPs show high physicochemical stability, obvious nonlinear optical absorption, and a high damage threshold. By introducing the TaC-based saturable absorber into an erbium-doped fiber laser, stable nanosecond pulses can be successfully delivered with a minimum pulse duration of 575 ns and signal-to-noise ratio of over 40 dB. The experimental results show that TaC NPs can act as a stable mid-infrared pulse modulator, and may make inroads for developing highly stable broadband optoelectronic devices.

Passive Q-switched Dy:ZBLAN fibre laser at 3.1 µm

The passive Q-switching performance of an in-band pumped Dy-doped fluorozirconate fibre laser emitting around 3.1 µm is investigated. Passively Q-switched laser operation is demonstrated employing semi-conductor saturable absorber mirrors. Stable operation is achieved, with a minimum pulse duration of 464 ns, a highest repetition frequency of 210 kHz and peak pulse powers up to 3 W.

Broadband saturable absorption responses of few-layered MoSe2 nanosheets for all-solid-state Q-switched lasers

Few-layered molybdenum diselenide (MoSe2) nanosheets were successfully fabricated by the ultrasound-assisted liquid phase exfoliation (UALPE) method. It exhibits broadband nonlinear optical (NLO) responses with optical modulation depths of 12.4% and 9.3% at 1.3 and 2 μm, respectively. Based on this, it was transferred onto a quartz substrate, acting as a saturable absorber (SA) to initiate solid-state pulsed lasers. The Q-switched Nd: GdVO4 laser with a minimum pulse duration of 366 ns and a repetition rate of 196 kHz was generated at around 1.3 μm. Meanwhile, the Q-switched Tm: YLF laser with a minimum pulse duration of 200 ns and a repetition rate of 43 kHz was obtained at around 2 μm. The experimental results indicate that few-layered MoSe2 nanosheets have a significant development prospect as a SA in optical modulation with a broad spectral band range at the near-infrared (NIR) band.

Nonlinear optical properties of porous monoclinic BiVO4 at 2.3 µm for the passively Q-switching laser

In this work, we report the nonlinear optical response of porous monoclinic bismuth vanadate (m-BiVO4) at 2.3 µm for the first time. We adopted the conventional open/closed aperture (OA/CA) Z-scan techniques to systematically investigate the nonlinear optical (NLO) behavior. The effective nonlinear absorption coefficient βeff was −6.4 ± 0.02 cm MW−1, the nonlinear refractive index n2 was 9.88 ± 0.08 × 10-1 cm2 GW−1, and the NLO third-order susceptibility |χ(3)| was 2.69 × 10-7 esu. These NLO properties allowed it to be used as a fantastic saturable absorber for the generation of mid-infrared (MIR) pulses. As an application, we implemented a passively Q-switched Tm:YAP laser with the prepared porous m-BiVO4 saturable absorber for the first time. A minimum pulse duration of 349 ns and a maximum pulse repetition frequency of 193 kHz were achieved, resulting in a maximum pulse energy of 1.18 µJ. Our findings suggest that the porous m-BiVO4 could provide a route to the MIR optoelectronic applications.

Generation of High Peak Power Pulses With Controllable Repetition Rate in Doubly Q-Switched Laser With AOM/SnSe2

By simultaneously employing self-made SnSe2 saturable absorber (SA) and an acous-to-optic modulator (AOM), a dual-loss-modulated Q-switched Nd:YVO4 laser with short pulse width, high peak power and adjustable pulse repetition rate is presented. The maximum pulse peak power of 37.57 KW with the minimum pulse duration of 5.52 ns were obtained under the pump power of 8 W and the pulse repetition rate of 5 kHz. The experimental results demonstrate that the dual-loss modulation technology with AOM and SnSe2 SA is a simple and efficient method to generate short pulses with high peak power and adjustable low repetition rates.

Third-order harmonic mode-locked and Q-switched Er-doped fiber laser based on a Cr2Ge2Te6 saturable absorber.

This paper reports the generation of fundamental solitons and third-order solitons in an erbium-doped fiber laser (EDFL) by a Cr2Ge2Te6-polyvinyl alcohol (CGT-PVA) saturable absorber (SA). Stable fundamental solitons at 1559.09 nm at a repetition frequency of 5.1 MHz were detected, and third-order solitons with a maximum output power of 6.807 mW and narrowest monopulse duration of 615.2 fs were obtained under a repetition frequency of 15.3 MHz by changing pump power. To the best of our knowledge, it is the first time to achieve a Q-switched pulse with a minimum pulse duration of 2.2 µs and maximum single pulse energy of 12.11 nJ in EDFL based on CGT-PVA SA after reducing the cavity length. Its repetition rate monotonically increased from 18.8 kHz to 61.8 kHz with a tuning range of about 43 kHz. The experimental results sufficiently demonstrate that CGT has enormous potential as an ultrafast photonics device.

Acetone PLIF visualization of the fuel distribution at plasma-enhanced supersonic combustion

This study examines the mixing and flameholding characteristics of a plasma stabilized planewall supersonic combustor. Fuel injection, ignition, and flameholding are provided by Plasma Injection Modules (PIMs) installed in a M = 2, 76.2 × 76.2 mm duct. Two configurations were explored: the first involves a plasma filament collocated within a single transverse fuel jet, while the second involves combustion stabilization using a series of three PIMs. Unburned fuel distributions were assessed with acetone planar laser induced fluorescence (PLIF), where acetone vapor was seeded into the gaseous fuel. PLIF measurements were performed for both streamwise and spanwise laser sheet orientations. Supporting datasets were collected including schlieren imaging, chemiluminescent imaging, and pressure distributions. PIM actuation is found to increase jet penetration, crossflow expansion, and initiate fuel jet breakup. The average jet cross sectional area is shown to increase by >20% with the addition of plasma. PLIF imaging at PIM stabilized combustion revealed a significant unburned fuel concentration in a local separation region near the PIMs, and identified the minimum plasma pulse duration for flowfield transition from initial conditions to the combustion pattern.

Mid-IR tunable CW and passively Q-switched laser operation of Dy-doped fluoride fiber

We report a comprehensive characterization of tunable continuous-wave (CW) and passive Q-switching laser performance of Dy-doped zirconium fluoride fiber emitting around 3 µm. The in-band pumped CW laser operation is investigated for pump wavelengths varying from 2.7 µm to 2.825 µm, for fiber lengths ranging from 0.4 m to 2 m, and for output coupling efficiency from 10% to 50%, leading to a maximum laser slope efficiency of 44% and a tuning range larger than 300 nm. With Findlay-Clay analysis and Rigrod analyses, optimal cavity parameters are retrieved, paving the way for further optimizations in performance. The passively Q-switched laser operation of Dy-doped fluoride fiber is achieved employing a semiconductor saturable absorber mirror for the first time, demonstrating a stable operation with a minimum pulse duration of 580 ns, a highest repetition frequency of 103 kHz and a pulse energy up to 300 nJ.

High-power yellow DSR pulses generated from a mode-locked Dy:ZBLAN fiber laser.

Ultrafast yellow lasers are in high demand in recent biomedical and medical applications; however, direct emission of mode-locked pulses in yellow at the high-power level still presents a huge technical challenge to date. By integrating the nonlinear polarization rotation (NPR) scheme into a Dy:ZBLAN fiber laser, dissipative soliton resonance pulses at ∼575 nm are demonstrated for the first time, to the best of our knowledge. The average output power reaches ∼240 mW at maximum, which is an improvement of almost two orders of magnitude over those reported from the latest mode-locked visible fiber lasers. The laser scheme combines a piece of large-core Dy:ZBLAN gain fiber and free-space NPR components designated at the yellow bandwidth. The maximal pulse energy is 2.4 nJ at the repetition rate of ∼100 MHz and the minimal pulse duration is 83 ps. The achieved wavelength of 575 nm is the shortest ever reached from a fiber-based mode-locked laser to date.

Nanosecond Q-switched laser with PEDOT: PSS saturable absorber.

We demonstrate deployment of the nonlinear saturable absorption property of the organic material poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) for pulse generation in the near-infrared region. The saturable absorber (SA) film was made using a straightforward process of depositing a layer of the PEDOT: PSS material onto a polyvinyl alcohol (PVA) film. The prepared SA was inserted into an erbium-doped fiber laser cavity as a Q-switcher to produce laser pulses with a maximum pulse rate of 92.75 kHz, minimum pulse duration of 912 ns, and highest pulse energy of 222.83 nJ. Results showed that PEDOT: PSS/PVA SA could become a promising SA for various laser applications. To our knowledge, this is the first time that PEDOT: PSS/PVA has been utilized as a SA to produce a stable Q-switched laser in 1.55 µm.

Third-order optical nonlinearity in Ti2C MXene for Q-switching operation at 1–2 μm

Two-dimensional (2D) transition metal carbides/nitrides (MXene) possess the peculiar physical and electronic properties. In this paper, we reported the wideband third-order optical nonlinearities in Ti2C MXene from 1 to 2 μm. The maximum effective nonlinear absorption coefficients were −0.56 cm/MW, −0.702 cm/MW and −0.62 cm/MW at 1, 1.3 and 2 μm, respectively. Moreover, two-photon absorption effect was also investigated. Based on the Ti2C MXene saturable absorber, passively Q-switched bulk lasers operating at 1, 1.34 and 2 μm were realized for the first time. The minimum pulse duration was obtained as 128 ns at 1064 nm.

Indium Tin Oxide Nanowire Arrays as a Saturable Absorber for Mid-Infrared Er:Ca0.8Sr0.2F2 Laser.

We demonstrated a passively Q-switched Er:Ca0.8Sr0.2F2 laser with indium tin oxide nanowire arrays as an optical modulator in the mid-infrared region. In the Q-switched regime, the maximum output power of 58 mW with a slope efficiency of 18.3% was acquired. Meanwhile, the minimum pulse duration and highest repetition rate of the stable pulse trains were 490 ns and 17.09 kHz, corresponding to single pulse energy of 3.4 μJ and peak power of 6.93 W, respectively. To the best of our knowledge it was the first time that indium tin oxide nanowire arrays were employed as a saturable absorber to make pulse lasers carried out at 2.8 μm. The experimental data show that indium tin oxide nanowire arrays can be employed as a competitive candidate for saturable absorber in the field of mid-infrared solid-state lasers.

A 1625 nm Q‐Switched All‐Fiber Laser

A Q‐switched all‐fiber Er‐doped laser operated at a wavelength up to 1625 nm is proposed and demonstrated. A self‐developed, element hybridization (Al, Ge, La, P, and Er in the core, Si and P in the cladding region) glass fiber with gain extended to U‐band is employed as gain medium. The compact laser cavity contains a fiber Bragg grating which was manufactured by means of point‐by‐point femtosecond laser inscription technique. Stable Q‐switched laser pulse train is successfully achieved using a semiconductor saturable absorber mirror at a low pump threshold of 29 mW. The laser has a maximum single pulse energy of 746 nJ and a minimum pulse duration of 26.8 μs. The pulse repetition rate can be gradually tuned from 6.47 to 11.87 kHz by increasing the pump power. In particular, the laser wavelength of the Q‐switched all‐fiber laser can be as long as 1625 nm. This is, to the best of our knowledge, the longest wavelength for the Q‐switched Er‐doped fiber lasers at this waveband.

Therapeutic Effects of New Pulsed-Type Microneedling Radiofrequency for Refractory Facial Pigmentary Disorders.

Numerous treatments for pigmentary disorders have been used with variable outcomes. Recently, a new radiofrequency (RF) device with minimal pulse duration has been introduced. The aim of this study was to evaluate the efficacy and safety of a pulsed-type microneedling RF device for treatment of facial pigmentary disorders. Forty-four patients diagnosed with facial melasma or Riehl melanosis received 5 treatments with RF at 2-week intervals, and evaluation was performed at each visits, including 4 and 8 weeks after the last treatment. Treatment outcomes were evaluated by investigator global assessment, patient global assessment score, and skin biophysical parameters of erythema index, melanin index (MI), and transepidermal water loss. Gene array and immunohistochemical staining including melan-A, Fontana silver, CD44, basic fibroblast growth factor (bFGF), and periodic acid-Schiff were performed. Most of the patients showed clinical improvement. Erythema index, MI, and transepidermal water loss decreased after the first treatment. Histopathologic examination showed decrease of melanin pigment, melanophages, and blood vessel proliferation but thickened basement membrane after treatment. Expression of CD44 and b-FGF was decreased after treatment. There were no serious adverse events reported during the study. Pulsed-type microneedling RF could be a treatment option for facial pigmentary disorders.

Effect of laser ignition on combustion and performance of internal combustion engine: A Review

• Laser ignition system as a prominent alternative to spark plug ignition has been reviewed. • Laser ignition is superior in context of ignition, combustion, and emission characteristics. • Effect of laser parameters on the performance of internal combustion engines have been studied. • Feasibility of laser ignition with respect to varying ignition location and possibility of multipoint combustion initiation has been reviewed. Internal combustion engines have undergone many technological advancements over the period keeping in mind economic aspects and stringent emission norms in context of global environment changes. Research in this field mainly emphasizes performance enhancement. Improved performance can be in terms of efficiency improvement, emission reduction or higher power output keeping inputs variables unchanged. The key process that can affect all mentioned perspectives is combustion. The ignition system initiates the combustion process and ensures that it happens in an organized manner as per expectations. Laser ignition systems have numerous benefits over spark ignition systems like superior lean burn capacity, excellent control over ignition timings, flexible ignition locations and improved performance and emission characteristics. Majority of studies have used Q-switched Nd: YAG lasers for their research. Laser ignition system comprises different attributes like minimum ignition energy (MIE), wavelength, pulse duration and focal length of lens and focal spot size which has a vital influence on engine combustion characteristics. The purpose of this article is to examine the scope and current level of research towards implementing laser ignition systems in real-world automobiles. Compactness, cost, and misalignment of the laser system due to real-time vibration of engines are a few of the major hurdles. Further research into these important issues, together with the improved benefits of laser ignition, could result in a significant contribution in the automobile sector, with the goal of commercialization.

Ti3C2 MXene as an optical modulator in a Thulium/Holmium-doped fiber laser

A Ti3C2 MXene based saturable absorber (SA) was demonstrated as an optical modulator to enable Q-switching and mode-locking in a Thulium-Holmium doped fiber laser (THDFL) cavity. Two different SA configurations were studied, with one SA in the form of a polyvinyl alcohol (PVA) polymer host thin film and the other one with the Ti3C2 MXene deposited along with a D-shaped fiber. For the case of the Ti3C2-PVA SA, only Q-switched was obtained at the threshold pump power of 126.4 mW. The generated Q-switched pulses had a center wavelength of 1961.4 nm with a maximum repetition rate and pulse energy of 42.5 kHz and 37.4 nJ and a minimum pulse duration of 2.4 μs. For the Ti3C2 MXene coated D-shaped fiber SA, mode-locking was achieved at a pump power of 209.9 mW with a center wavelength of 1915.9 nm and having a repetition rate and pulse width of 12.6 MHz and 1.89 ps, respectively. The experimental results indicate that the Ti3C2 MXene based SA could generate Q-switched pulses when in the form of a thin film but can only be used as a mode-locker when the SA material is coated along the surface of the D-shaped fiber.

Ultrafast all-anomalous-dispersion Er-doped large-mode-area fiber lasers

Ultrafast Er-doped large-mode-area (LMA) fiber lasers are demonstrated in the all-anomalous-dispersion regime. With the assistance of a home-made carbon nanotube saturable absorber, stable and chirp-free solitons are always observed for output coupling ratios (OCRs) varying from 10% to 90%, leading to the simultaneous achievement of the maximum pulse energy and minimum pulse duration at the OCR of 70%. To validate the universality of the all-anomalous-dispersion mode-locking, an all-fiber saturable absorber based on nonlinear multimode interference effect is incorporated into the LMA fiber laser cavity, which can also generate chirp-free solitons. The influences of gain fiber dispersion on solitons are numerically simulated, revealing that the dispersion consistency of fibers in the laser cavity is in favor of generating stable and chirp-free solitons even at an ultrahigh OCR. This work paves the way for ultrafast Er-doped LMA fiber lasers in the all-anomalous-dispersion regime, which provides an alternative route to further improve the stability and output pulse energy of ultrafast LMA fiber lasers, i.e. ensuring the dispersion consistency and hence enlarging the OCRs.