Q-switched Laser Pulses Research Articles

Continuous-wave and passively Q-switched pulse Er:Yb:Ca3NbGa3Si2O14 microlasers at 1.5–1.6 μm

Compact continuous-wave and passively Q-switched pulse microlasers at 1.5–1.6 μm were developed by using a 5-mm-thick Er:Yb:Ca3NbGa3Si2O14 crystal as a gain medium. End-pumped by a 975.6 nm continuous-wave laser diode, a 1555 nm continuous-wave laser with a maximum output power of 1.05 W and a slope efficiency of 8.8% was obtained at an absorbed pump power of 14.2 W. End-pumped by a 975.6 nm pulsed laser diode with a pulse width of 0.3 ms and a pulse period of 1.0 ms, a stable 1534 nm passively Q-switched pulse laser operating at a repetition frequency of 1.0 kHz was realized by using a Co2+:MgAl2O4 crystal with an initial transmission of 95% as a saturable absorber. At a peak absorbed pump power of 23.6 W, the obtained single-pulse energy, pulse width and peak output power were 8.06 μJ, 7.9 ns, and 1.02 kW, respectively.

Te Film as a Saturable Absorber for the Mid-Infrared Er3+-Doped ZBLAN Fiber Laser

We demonstrate a Q-switched Er3+-doped ZBLAN fiber laser at 2.8 µm mid-infrared (mid-IR) region achieved by adopting Te as the saturable absorber mirror (SAM). The modulation depth and saturation intensity of the Te-SAM were measured to be ∼7.2% and 10.81 MW∕cm2, respectively. Stable Q-switched laser pulses with the maximum pulse energy of 3.05 µJ and the minimum pulse width of 0.457 µs at the launched pump power of 4.51 W were obtained. Maximum average output power of 357 mW with repetition rate of 116.98 kHz were achieved. The signal-to-noise ratio (SNR) is 52 dB, which is higher than that of most 2.8 µm mid-infrared Q-switched fiber lasers reported so far. To the best of our knowledge, this is the first demonstration from a Q-switched fiber laser at 2.8 µm based on a Te-SAM.

Passively Q-switched Tm:YAP laser based on SnS2 saturable absorber

In this paper, a passively Q-switched Tm:YAP laser with a SnS2 saturable absorber (SA) fabricated by the liquid-phase exfoliation method was demonstrated for the first time. The optical characteristics of SnS2 SA were characterized. The continuous-wave Tm:YAP laser was investigated first. An incident pump power of 7.92 W was used to generate a continuous-wave laser with a maximum average output power of 920 mW and a slope efficiency of 20.1%. By inserting SnS2 SA into the resonant cavity, a Q-switched pulsed laser operated at 2 µm with the shortest pulse width of 1.073 μs, the maximum repetition frequency of 58.79 kHz, the highest peak power of 8.15 W, and the maximum average output power of 514 mW was obtained. The corresponding slope efficiency was 14.7%. Apart from these, the beam profiles and the quality factor M2 were measured.

Laser Direct Activation of Polyimide for Selective Electroless Plating of Flexible Conductive Patterns

Flexible conductive patterns on polyimide substrates are attracting increasing research interest in the areas of wearables, biomedicals, automotives, and energy harvesters. This paper reports a laser-induced selective activation (LISA) process for electroless metallization and, therefore, the creation of complex conductive patterns on polyimide substrates. In this process, a Q-switched pulsed laser is utilized for scanning the surface and forming the catalytic layer consisting of microporous structures, which enhances the stability of electroless plated metallic structures on the polyimide surface and exhibits superior mechanical stability under repeated bending and harsh environments. The high resolution of the metallic patterning enables the demonstration of a copper microgrid pattern with a line width down to 50 μm. Moreover, flexible light-emitting diode displays and electromagnetic interference shielding films are successfully manufactured to indicate the promising capability of our LISA process.

Effect of MAX phase chromium aluminum carbide thin film thickness on Q-switched Erbium-doped fiber lasers

In recent years, chromium aluminum carbide (Cr2AlC) has gained attention because of its good performance in terms of high-temperature resistance, transparency and conductivity. Therefore, it has been widely used in solar cells, photonics and electronics. Although some related characteristics are investigated in pulse lasers, the effect of thin film thickness in generating laser pulses have not been reported. Therefore, the effect of thin film thickness on the performance of Q-switched erbium-doped fiber laser (EDFL) is explored in this work. Two films of different thicknesses were applied to generate Q-switched laser pulses. The thickness of the films were about 45 µm and 16 µm and they were prepared by a casting method with polyvinyl alcohol (PVA). The effects of two different film thicknesses on laser performance were investigated separately. The results show that the film thickness affects the modulation depth, saturation intensity and insertion loss of SA, which in turn effects the Q-switched laser pulses.

PtSe2 as a Wideband Saturable Absorber for Passively Q-Switched High-Power Mid-Infrared Fiber Laser

We report a transition metal dichalcogenides-PtSe₂ Q-switched single-mode fiber laser operating at 2783.2 nm with a nearly watt-level average output power. We made a PtSe₂ coated highly reflective gold mirror to serve as a saturable absorber mirror. The modulation depth, saturable intensity and non-saturable loss of our PtSe₂ sample were measured to be 10.2&#x0025;, 0.093 GW/cm² and 37.71&#x0025;, respectively. By incorporating the as-prepared saturable absorber mirror in a single-mode Er^3&#x002B;-doped zirconium fluoride fiber laser, stable Q-switched laser pulses were obtained with a maximum average power of 932.7 mW. The pulse duration and repetition rate were <inline-formula> <tex-math notation="LaTeX">$1.04 ~\mu \text{s}$ </tex-math></inline-formula> and 93.10 kHz, respectively. The corresponding pulse energy was <inline-formula> <tex-math notation="LaTeX">$10.02 ~\mu \text{J}$ </tex-math></inline-formula> and the slope efficiency was 18.1&#x0025;. By employing a plane ruled grating in the resonator, we also investigated the operating wavelength range of the PtSe₂-coated mirror. A continuously wavelength-tunable Q-switched laser was obtained from 2733.0 nm to 2803.0 nm. To the best of our knowledge, this is the first demonstration of PtSe₂ working as a saturable absorber for the 2.73-<inline-formula> <tex-math notation="LaTeX">$2.80 ~\mu \text{m}$ </tex-math></inline-formula> waveband, and the Q-switched laser presents threefold and twofold increase in output power and pulse energy, respectively, over previously reported values achieved from &#x007E;3-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> single-mode Q-switched fiber lasers enabled by two-dimensional materials. The results indicate that PtSe₂ is an excellent wideband optical switch for high-power broadband mid-infrared laser pulses generation.

Diode-pumped Dy[formula omitted], Tb[formula omitted]:LuLiF[formula omitted] continuous-wave and passively Q-switched yellow lasers

We report on the power-scaling continuous-wave (cw) Dy3+, Tb3+:LuLiF 4 yellow laser, which comprises a single-emitter blue laser diode (LD) that functions as a pump source. The maximum output power of the laser is evaluated to be 220 mW at 574 nm. The passively Q-switched yellow laser is generated by using Cr4＋:Y3Al5O12 (Cr:YAG) as the saturable absorber. The shortest pulse width (full width at half maximum) is less than 582 ns with a repetition rate of 5.8 kHz. Meanwhile, the pulse energy and peak power are ∼4.5 μJ and ∼7.7 W, respectively. This work reveals that Dy3+, Tb3+:LuLiF 4 crystal is a potential laser gain material that can be used to develop compact and efficient yellow lasers, which can not only be employed in cw lasers but also in passively Q-switched pulse lasers.

Investigating the Threshold Conditions of Air Breakdown with Mode-Locked Q-Switched Laser Pulses, and the Temporal Dynamics of Induced Plasma with Self-Scattering Phenomenon

A Q-switched Nd:YAG laser with mode-locked modulations is utilized to explore the laser-induced air breakdown. The various modulation depths of the mode-locking within the Q-switched pulse can be utilized to investigate the threshold conditions. With the GHz high-speed detectors to accurately measure the temporal pulse shape pulse by pulse, it is verified that the air breakdown threshold is crucially determined by the peak-power density instead of the energy density from the statistic results, especially for mode-locked Q-switched lasers. The stability of the system for laser-induced breakdown can be evaluated by threshold width through fitting the statistical result. Otherwise, by measuring the temporal characteristics of the excitation pulse and the induced plasma, it is further found that the plasma radiation displays a few-nanoseconds time delay to the excitation pulse and shows a decaying tail to be 10 times longer than the plasma build-up time. Moreover, the incident laser pulse is observed to be self-scattered by the air breakdown, and a rapidly modulated scattering rate is found with a slight delay time to the excitation mode-locked subpulse modulations.

Mxene Ti3C2Tx Langmuir–Blodgett films as saturable absorber for near-infrared Q-switched laser

MXene is a fast-growing family of 2D materials with unique light–matter interactions. Ti3C2Tx belongs to the family of MXene that show nonlinear saturable absorption characteristics and has been studied widely. However, translating the excellent performance of MXene flakes into stable thin film saturable absorbers (SA) devices has been a challenging task. Herein, we report the fabrication of a long term stable MXene Ti3C2Tx film SA deposited on a quartz plate by the Langmuir–Blodgett (LB) method for the first time, and it was used in passive Q-switched solid-state pulsed laser generation at the central wavelengths of 1.06 and 1.34 μm, respectively. LB Ti3C2Tx SAs exhibits excellent optical properties such as high modulation depth, low loss, and high linear transmittance at mid-infrared wavelengths. By inserting the LB Ti3C2Tx SAs into two Nd-doped solid-state lasers, short pulses were generated with the pulse duration of 244 ns and 311 ns in the 1.06 and 1.34 μm regimes, respectively. In addition, long-term stability was maintained in constant temperature drying. The results illustrate the potential of the MXene LB Ti3C2Tx SA films for laser applications, paving new ways for producing large-area, ultra-uniform, low-loss and stable MXene SA by the LB method.

Highly efficient mode-locked and Q-switched Er3+-doped fiber lasers using a gold nanorod saturable absorber

Mode-locked and Q-switched pulsed fiber laser sources with wavelengths of 1.55 μm are widely used in various fields. Gold nanorods (GNRs) have been applied in biomedicine and optics owing to their biocompatibility, easy fabrication, and unique optical properties. This paper presents the analysis of a saturable absorber based on a colloidal gold nanorod (GNR) thin film for dual-function passively mode-locked and Q-switched 1.55-μm fiber lasers. The colloidal GNR thin film possesses superior properties such as a wide operating wavelength range, large nonlinear absorption coefficient, and a picosecond-order recovery time. Its modulation depth and saturation intensity at 1.55 μm are 7.8% and 6.55 MW/cm2, respectively. Passive mode-locked or Q-switched laser operation is achieved by changing the number of GNR thin-film layers. The advantages of these high-quality GNRs in mode-locked and Q-switched fiber lasers with record-high slope efficiency are verified by conducting comprehensive material and laser dynamic analyses. The self-starting mode-locked fiber laser with an efficiency as high as 24.91% and passively Q-switched fiber laser with the maximum energy of 0.403 μJ are successfully demonstrated. This paper presents the novel demonstration of reconfigurable mode-locked and Q-switched all-fiber lasers by incorporating colloidal GNR thin films.

Liquid-Phase Exfoliated Graphene-MoS2 Based Saturable Absorber for Q-switched Erbium Doped Fiber Laser

Upon exfoliation from the bulk form, two-dimensional materials have shown ubiquitous properties which are suitable for Q-switched pulsed laser generation. In this research, a successful solution process of graphene-MoS2 nanocomposite saturable absorber through liquid phase exfoliation has been carried out. The method offers a low-cost route for simple and scalable production while providing a promising material quality with on-demand properties and integration flexibility. Stable Q-switched laser operation was realized with graphene-MoS2 hybrid saturable absorber. The pulse duration was measured to be 6 µs with repetition rate of 63.92 kHz corresponding to a peak power and pulse energy of 5.05 mW and 30.87 nJ, respectively.

Output characteristics regulation of Q-switched fiber laser by Fe3O4 nanoparticle-polyimide film

Fe 3 O 4 (FO) nanoparticles (NPs) - polyimide (PI) film was used as saturable absorber (SA), and achieved passive Q-switched output at 1.5 μm successfully. Based on the reverse saturable and saturable absorptions of FO NPs-PI film, the laser output characteristics can be further optimized by adjusting the ratio of FO NPs to PI. When the ratio of FO NPs to PI is 1:5 (FO NPs-PI (1:5)), the pulse duration and repetition rate are 0.669 μs and 5.51 kHz; this is the first time to realize the simultaneous compression of repetition rate and pulse duration. The single pulse energy and peak power are up to 364 nJ and 556 mW. The optical conversion efficiency can reach 855%, and it is about two orders of magnitude higher than other reports. The results show that it is helpful to construct high performance Q-switched pulse laser by introducing proper cavity loss through reverse saturable absorption. • Fe 3 O 4 (FO) nanoparticles (NPs) - polyimide (PI) film was used as saturable absorber (SA). • By introducing proper cavity loss through PI's reverse saturable absorption, so compression of pulse duration and repetition rate simultaneously. • Corresponding Q-switched pulsed laser performance are realized regulation and optimization by adjusting the ratio of FO NPs to PI.

Lanthanum hexaboride for Q-switching and mode-locking applications

In this paper, a new saturable absorber (SA) based on Lanthanum Hexaboride (LaB6) is used to produce Q-switched and mode-locked laser pulses. In constructing the SA, the prepared LaB6 powder is dispersed in polyvinyl alcohol (PVA) solution before the mixture is dried to form a thin film. A small piece of the film is placed between two fiber ferrules to form a LaB6 PVA SA and added to a laser cavity of an erbium-doped fiber laser (EDFL) to produce Q-switched and mode-locked pulses. The Q-switched laser operates at 1531 nm. The pulse width of the pulses can be varied between 4.32 to 2.46 μs with a corresponding repetition rate of 62.0 to 89.6 kHz when the pump power is increased from 45.4 to 97.6 mW. At the maximum output power of 4.31 mW, the highest pulse energy of 48.1 nJ was obtained. A passively mode locked EDFL was also successfully realized with LaB6 SA by adding 100 m long single mode fiber inside the cavity. A stable mode-locked laser operating at 1559.1 nm was achieved at the threshold pump power of 102.8 mW with a pulse rate of 1.88 MHz. The pulse energy of 5.6 nJ and output power of 10.54 mW were obtained at a maximum pump power of 144.6 mW. To the best of our knowledge, this is the first demonstration of utilizing LaB6 material as SA to produce pulses in the 1.5 μm region.

Continuous-wave and passively Q-switched pulse 1060 nm Nd:GdPO4 lasers

1060 nm continuous-wave and passively Q-switched pulse lasers were demonstrated in a 3.5-mm-thick X-cut Nd:GdPO4 crystal. At an absorbed pump power of 1.91 W, a 1060 nm continuous-wave laser with a maximum output power of 0.72 W and a slope efficiency of 42% was realized. When a Cr4+:YAG saturable absorber with an initial transmission of 85% was used, a passively Q-switched pulse laser with repetition frequency of 6.7 kHz, pulse energy of about 19 µJ, pulse duration of 58 ns, and peak power of 0.33 kW was obtained in a plano-concave cavity with a length of 95 mm and an absorbed pump power of 1.91 W. For a plano-plano cavity with a length of 9 mm and the same pump power, a pulse laser with repetition frequency of 7.2 kHz, pulse energy of about 14.1 µJ, pulse duration of 4.1 ns and peak power of 3.4 kW was obtained.

Synthesis of silver nanoparticles using chemical reduction techniques for Q-switcher at 1.5 µm region

This research investigated the generation of passively Q-switched erbium (Er)-doped fibre laser using silver nanoparticles/poly (vinyl alcohol) (Ag/PVA) as a saturable absorber (SA). The Ag nanoparticles were synthesised via the chemical reduction technique. The Ag/PVA film based SA was fabricated by blending Ag nanoparticles powder into the PVA suspension, then left to dry at ambient to develop a free-standing SA film. Next, the Ag/PVA film was sandwiched in between two FC/PC fibre ferrules and integrated into the laser cavity for Q-switched pulse generation. The result shows that the Q-switched pulsed laser achieved pulse energy and peak power of 128.04 nJ and 21.34 mW at the maximum pump power of 107.1 mW. A signal-to-noise ratio (SNR) value of 66.23 dB was obtained at a frequency of 66.23 kHz proving that it is an excellent candidate as a SA material for Q-switched generation in future large-scale manufacturing.

A Sagnac-based interferometer with optimal polarization control for Lamb wave detection

Sagnac-based interferometers are promising devices for laser ultrasound (LU) inspection with the advantages of being robust, low-cost, and easy to integrate. Compared with all-Polarization Maintaining (all-PM) method, non-Polarization Maintaining (non-PM) method is more cost-effective and has greater compatibility, making it more practical in low-frequency ultrasound detection. The initial π/2 phase bias (IPB) and high fringe visibility are crucial for realizing the interferometer's full potential. However, a specific process of obtaining the optimal polarization control for non-PM configuration is still absent, leading to the unpredictable fringe states. In this paper, a novel and specific approach to obtaining optimal interference fringes for non-PM configuration based on the polarization control is proposed. Experimentally, the initial π/2 phase bias and 43.9% fringe visibility (50% is the highest in theory) were obtained. Guided waves of low-frequency A0 mode in aluminum sheets were excited by a Q-switched pulse laser and detected by a non-PM Sagnac-based interferometer to inspect artificial defects on the surface of samples. Such a system provided a cost-effective non-contact detection scheme for out-of-plane Lamb wave which was very difficult to separate from LU signal with complex modes composition using conventional piezoceramics sensors.

Passively Q-switched semiconductor disk laser with microsecond pulse duration

A semiconductor disk laser was passively Q-switched by the use of a Cr4＋:YAG crystal and a semiconductor saturable absorb mirror, respectively, and stable Q-switched laser pulse trains with microsecond pulse duration were produced. The width and the repetition rate of the Q-switched pulses were 10 μs and 26.3 kHz when a Cr4＋:YAG crystal was inserted, while the pulse width and the repetition rate were 8 μs and 26.3 kHz when a semiconductor saturable absorb mirror was employed. Based on the time characteristics of the quantum structure in the active region of the semiconductor disk laser, and the time behaviors of the saturable absorbers, i.e., the Cr4＋:YAG crystal and the semiconductor saturable absorb mirror, the formatting mechanisms of the Q-switched pulses with width of microsecond magnitude were analyzed, and the related physical pictures of the passively Q-switched semiconductor disk laser were further disclosed.

Enhancing Q-Switched Fiber Laser Performance Based on Reverse Saturable and Saturable Absorption Properties of CuCrO2 Nanoparticle-Polyimide Films

We demonstrate CuCrO2 (CCO) nanoparticle (NP)-polyimide (PI) composite film as a saturable absorber (SA) to regulate the output characteristics of passively Q-switched fiber laser at 1.55 μm. Based on the reverse saturable and saturable absorptions of the CCO NP-PI film, the passively Q-switched fiber laser expressed two stages with the increase of pump power for substantial performance enhancement. Reverse saturation absorption is observed to introduce appropriate cavity loss, which constructs effective pathways for promoting both the modulation depth and over threshold degree, as well as reducing the photon lifetime. In particular, our results realized the pulse duration and repetition rate compressing simultaneously for the first time. The second stage output laser exhibits a peak power of 1016 mW and a single pulse energy of 183 nJ, which are about 88 and 9 times higher than those of the first stage. Furthermore, the optical-optical conversion efficiency is up to 1270%. All of these can evidently demonstrate the importance of the appropriate cavity loss design for optimizing the Q-switched pulse laser output characteristics.

LightSpeed: A Compact, High-Speed Optical-Link-Based 3D Optoacoustic Imager.

Wide-scale adoption of optoacoustic imaging in biology and medicine critically depends on availability of affordable scanners combining ease of operation with optimal imaging performance. Here we introduce LightSpeed: a low-cost real-time volumetric handheld optoacoustic imager based on a new compact software-defined ultrasound digital acquisition platform and a pulsed laser diode. It supports the simultaneous signal acquisition from up to 192 ultrasound channels and provides a hig-bandwidth direct optical link (2x 100G Ethernet) to the host-PC for ultra-high frame rate image acquisitions. We demonstrate use of the system for ultrafast (500Hz) 3D human angiography with a rapidly moving handheld probe. LightSpeed attained image quality comparable with a conventional optoacoustic imaging systems employing bulky acquisition electronics and a Q-switched pulsed laser. Our results thus pave the way towards a new generation of compact, affordable and high-performance optoacoustic scanners.

Lawsone dye material as potential saturable absorber for Q-switched erbium doped fiber laser

In this paper, lawsone (2-hydroxy-1,4-naphthoquinone), a natural dye material is proposed and demonstrated as a saturable absorber (SA) for passive Q-switching operation in Erbium-doped fiber laser (EDFL) cavity. The lawsone-based SA was fabricated using a liquid-phase exfoliation technique. A tiny piece of the lawsone film was then cut and slot-in between two fiber ferrules so that it can easily be incorporated into a laser cavity as a Q-switcher. A stable Q-switched pulse train operation was observed with the repetition rate of 80 kHz and pulse width as narrow as 1.7 µs at 1564 nm wavelength. The maximum pulse energy and average power were obtained to be 53 nJ and 4.3 mW, respectively. The results indicate that the lawsone material can be a suitable SA for Q-switched pulse laser operating at the 1.5-µm region. To the best of our knowledge, this is the first time lawsone material is utilized as a SA device for generating Q-switched pulse.