Passive Q-switching Research Articles

Passively Q-switched 2.3 μm Tm:YVO4 laser using a Cr:ZnS saturable absorber.

A diode-pumped wavelength switchable passively Q-switched 2.3 μm Tm:YVO4 laser was demonstrated in this work. A Cr:ZnS saturable absorber was introduced into the cavity for initiating passive Q-switching. With the increase of the absorbed pump power, the passively Q-switched laser could be switched from the single wavelength of 2366 nm to the dual wavelength of 2290 and 2360 nm. The pulse duration and pulse repetition frequency could be tuned in the ranges of 0.745-1.782 μs and 2.9-43.4 kHz, respectively. The pulse energy and peak power were estimated to be 7.5 μJ and 10 W, respectively, at an absorbed pump power of 12 W.

Q-switched Er-doped fiber laser using an aqueous solution of gold nanorods and polyvinyl alcohol

Authors reported the generation of Q - Switched pulses in an erbium-ytterbium co-doped fiber laser using an aqueous solution of colloidal gold nanorods (GNRs) and Polyvinyl Alcohol (PVA) as a saturable absorber (SA). The effect of the GNRs and PVA concentrations on the pulses has been explored. Passive Q-Switching is achieved at 1.1 W (1.8 A). Pulses with a minimum width of 9.6 µs having a repetition rate of 21.5 kHz and a maximum energy of 0.15 µJ at 1.56 μm are obtained for a pump current of 2.195 W (3.12 A).

All-fiberized amorphous carbon nitride (a-CNx) based passive Q-switcher

This research presents the first-ever demonstration of a passively Q-switched fiber laser in the 1.5 μm wavelength region using amorphous carbon nitride (a-CNx) as a saturable absorber (SA) in an all-fiber configuration. The a-CNx thin film was prepared using plasma-enhanced chemical vapor deposition. The laser operation showed remarkable stability, achieving a repetition rate of 57.99 kHz and a pulse duration of 1.36 μs at maximum input pump power. The peak power and pulse energy reached 100.56 mW and 136.77 nJ, respectively. The utilization of a-CNx as an SA offers potential benefits such as a simpler and more flexible cavity design, making it an attractive candidate for various applications, including material processing and medical laser equipment. This work contributes to the advancement of fiber lasers and expands the possibilities for utilizing carbon nitride-based SAs in practical laser systems.

Pulse Laser Generation at 2.0 µm Region based on Polyvinyl Alcohol Doped Graphene Nanoplatelets Saturable Absorber

A passive Q-switcher based on graphene nanoplatelets (GnP) doped with polyvinyl alcohol (PVA) is proposed for pulse laser generation at 2.0 µm region. An optimized solution casting approach is adopted in the customized preparation of a 12.04 wt.% weight ratio of GnP to PVA. The fabricated saturable absorber (SA) is characterized using field emission scanning electron microscope (FESEM), which confirmed the embedment of GnP in PVA composite. A 5 m long thulium doped fiber (TDF) is used as a gain medium in the laser cavity measurement. Our characterization demonstrates dual-wavelength Q-switched pulse generation at 1904.0 nm and 1904.9 nm for input power ranging from 644 mW to 698 mW, respectively. The repetition rate is tunable from 69 kHz to 98 kHz with the shortest pulse width of 1.4 µs. The calculated output peak power, pulse energy and signal-to-noise ratio are recorded at 143 mW, 0.21 µJ and 35 dB, respectively. Notably, the present work is the first-ever work of a Q-switcher based on GnP doped with PVA host at 2.0 µm region.

Enhancement of mid-infrared saturable absorption of graphene by compositing with PbSe for ultra-short pulse lasers in the ∼ 2.8 to ∼ 4 μm band

The suitably large modulation depth of the saturable absorber (SA) is crucial to obtaining short pulse lasers via passive Q-switching or mode-locking techniques. Graphene could theoretically be used as a mid-infrared (mid-IR) SA due to its zero band-gap. However, the low modulation depth of graphene in the mid-IR region limits its applications. In this work, to improve the mid-IR modulation depth of graphene, a strategy of functionalizing graphene with narrow-band gap semiconductors was adopted. Graphene/PbSe (G/PbSe) composite was synthesized by a facile hydrothermal process and the reflective G/PbSe SA was prepared by spin-coating method. The saturation absorption properties were investigated by the open aperture Z-scan technique. The results indicated that the saturation absorption properties of G/PbSe SA were largely enhanced, and the modulation depth was increased from 3.02 % to 5.4 % at ∼ 2.8 μm and from 2.5 % to 6.4 % at ∼ 4 μm compared with pure graphene. Moreover, with the as-prepared reflective G/PbSe SA, passively Q-switched Er:YAP laser operation at ∼ 2.8 µm was realized. At the pump power of 6.78 W, the pulse train with pulse width of 326 ns and repetition rate of 107 kHz was obtained, and the average output power was 498 mW. This study presents a way for preparing graphene-based mid-IR SAs for short pulse mid-IR lasers.

VTe2: Broadband Saturable Absorber for Passively Q-Switched Lasers in the Near- and Mid-Infrared Regions.

In this study, we demonstrate the fabrication of a novel 2D transition metal dichalcogenide, VTe2, into a saturable absorber (SA) by using the liquid phase exfoliation method. Furthermore, the first-principles calculations were conducted to elucidate the electronic band structures and absorption spectrum. The nonlinear optical absorption properties of VTe2 at 1.0, 2.0, and 3.0 μm were measured using open-aperture Z-scan and P-scan methods, which showed saturation intensities and modulation depths of 95.57 GW/cm2 and 9.24%, 3.11 GW/cm2 and 7.26%, and 15.8 MW/cm2 and 17.1%, respectively. Furthermore, in the realm of practical implementation, the achievement of stable passively Q-switched (PQS) lasers employing SA composed of few-layered VTe2 nanosheets has manifested itself with broadband operating wavelengths from 1.0 to ∼3.0 μm. Specifically, PQS laser operations from near-infrared to mid-infrared with pulse durations of 195 and 563 ns for 1.0 and 2.0 μm solid-state lasers, respectively, and 749 ns for an Er3+-doped fluoride fiber laser at 3.0 μm were obtained. Our experimental results demonstrate that VTe2 is a potential broadband SA device for achieving PQS lasers. To the best of our knowledge, this is the first demonstration of using VTe2 as an SA in PQS lasers in the near- and mid-infrared regions, which highlights the potential of VTe2 for future research and applications in optoelectronic devices.

Rate Equations Model to Simulate the Dual Generation of Nd+3: YAG Passive Q-Switched Laser Pulses

Rate Equations Model to Simulate the Dual Generation of Nd+3: YAG Passive Q-Switched Laser Pulses

Two-dimensional tin diselenide as the saturable absorber for passively Q-switched Er:YAP 3 μm solid-state laser

A passively Q-switched (PQS) Er:YAP laser at ∼3 μm with the two-dimensional saturable absorber (SA) tin diselenide (SnSe2) nanosheet as SA was successfully demonstrated for the first time. Under the maximum absorbed pump power of 4.0 W, the obtained continuous-wave maximum output power of Er:YAP laser was 258 mW with a corresponding slop efficiency of 7.18%. In the PQS experiment, laser pulses with the shortest pulse duration of 198 ns were yielded with a repetition rate of 317 kHz under the maximum absorbed pump power of 4.0 W, and the corresponding single pulse energy and pulse peak power were 0.66 µJ and 3.3 W, respectively. The investigation indicates that SnSe2 has the potential to be an outstanding laser modulator for PQS solid-state laser at 3 μm wavelength.

High repetition rate π-polarized 1084 nm passively Q-switched Nd:MgO:LiNbO3 laser based on 888 nm thermally boosted pumping

We report a high-repetition-rate π-polarized 1084 nm passively Q-switched (PQS) Nd:MgO:LiNbO3 (Nd:MgO:LN) laser under 888 nm thermally boosted pumping. The 888 nm pumping is selected based on Nd:MgO:LN crystal absorption and energy level properties. Under 813 nm pumping, the continuous wave (CW) 1084 nm average output power (AOP) increased to 2.85 W. After that, 1084 nm is suppressed and gradually disappears as the pump power increases. At the same time, the 1093 nm AOP increases, and 4.4 W of 1093 nm laser is obtained. In contrast, under 888 nm pumping, the CW 1084 nm laser AOP of 5.16 W is obtained. The thermally boosted pumping can eliminate quantum defects caused by conventional 813 nm pumping non-radiative transitions and suppress unmatched σ-polarized 1093 nm output. Moreover, the Cr4+: YAG is replaced into the resonant cavity as the output mirror to obtain 1084 nm pulsed laser output. AOP with different initial transmission (T0) on laser output characteristics is measured under the compact resonant cavity structure. Finally, an AOP of 3.52 W pulsed laser with a repetition rate of 24.43 kHz and the highest peak power of 5.26 kW is obtained when T0 = 87 %, and the absorbed pump power is 20.87 W. The optical conversion efficiency is 16.87 %, and the slope efficiency is about 29.38 %.

Liquid crystal resonator as a nonlinear reflector for passive Q-switching and mode locking

We carry out a theoretical study of a Fabry–Perot resonator with a central layer of nematic liquid crystal as a nonlinear polarization rotation (NPR) device for passive Q-switching and mode locking. We develop a self-consistent procedure for calculating the device dynamical response as a function of the input light intensity and polarization. We show how a positive feedback effect for the optical reorientation of the liquid crystal director makes the resonator abruptly switch to high-reflectivity state. We demonstrate that the time-delay between the pulse initiation and the resonator switch can be avoided by tilted liquid crystal molequles at the resonator boundaries. We show that such a NPR optical device is suitable for Q-switching operation with μs pulses and hundreds of kHz repetition rates. Further decrease of pulse duration and increase of the pulse repetition rate is possible by either increasing the pulse power or by increasing the Fabry–Perot resonator finesse. Finally, we show that the same Fabry–Perot resonator can be used for Q-switching and mode locking at tens of MHz repetition rates and ns pulse durations by using an electro-optic uniaxial–biaxial transition as an alternative to NPR in order to reduce pulse duration and increase repetition rate.

Passive Q-Switching of a Cladding Pumped Erbium–Ytterbium Co-Doped Fiber Laser Induced by the Kerr Effect

Passive Q-Switching of a Cladding Pumped Erbium–Ytterbium Co-Doped Fiber Laser Induced by the Kerr Effect

High Peak Power Ultrashort Pulsed Passively Q-Switched Mode-Locked Bragg Laser Diode

We demonstrate a Bragg waveguide laser diode with an unbiased saturable absorber exhibiting passive Q-switched mode-locking with two AlInGaAs quantum wells. The widths of the observed passively mode-locked pulses ranged from 250 fs to 1640 fs under a Q-switching envelope. The frequency response showed the fundamental peak and smallest linewidths, for Q-switched operation, to range from 0.35 GHz to 1.15 GHz and 1.4 MHz to 9.1 MHz respectively. At 25 °C the devices demonstrated the highest peak power of ~10.1 W @ ~791 nm and highest peak to average power ratio of ~2800.

An infrared passively Q-switched laser based on graphene/BN heterojunction

Passively Q-switched solid-state lasers (PQSL) can obtain output lasers with narrow pulse widths and high peak powers, where play a vital role in the information society. Saturable absorbers (SA) are an essential part of passively Q-switched solid-state lasers. In this paper, we demonstrated 2 μm passively Q-switched (PQS) solid-state laser based on a graphene/BN heterojunction saturable absorber. In the experiments, we used two output mirrors with transmittance of 1.5 %/2.5 % for comparative study. We also used monolayer graphene as saturable absorber for experiment to compared with graphene/BN saturable absorber. The experimental results showed that the best passively Q-switched operation was achieved with the graphene/BN heterojunction saturable absorber at output mirror transmittance of 1.5 %. When the maximum absorption pump power was 1.49 W, the maximum average output power was 38 mW, corresponding with a slope efficiency of 5.4 %. At this point, the minimum pulse width was 1.56 μs, corresponding with a repetition frequency of 52 kHz. The single pulse energy and the peak power were calculated to be 730.36 nJ and 466.96 mW, respectively. The center wavelength of the PQS laser was 2066.8 nm. The experimental results showed that graphene/BN heterojunction was a promise saturable absorber in the field of 2 μm passively Q-switched solid-state lasers.

Zinc Oxide Nanoparticles-Poly(vinyl) Alcohol Thin Film for Generation Q-Switched Erbium-Doped Fiber Laser

The nonlinear optical property of Zinc oxide (ZnO) nanoparticles thin film synthesized by the solution casting method was investigated from the continuous wave to the Q-switching using an erbium-doped fiber laser cavity. Our laser experiment shows that ZnO nanoparticles embedded with polyvinyl alcohol (PVA) allow for the generation of a stable Q-switching laser pulse, centered at 1560.08nm with a 3-dB spectral bandwidth of 0.941 nm, a pulse duration of 3.53 µs and a high pulse energy of 171 nJ. Our finding suggests that ZnO nanoparticles thin film can be a useful nonlinear optical material for laser photonics devices such as passive q-switching for applications involving high energy.

Long-time stable Q-switched bulk laser at 1.34 and 1.94 μm based on antimonene saturable absorber

The low stability of laser pulse production induced by the deterioration of saturable absorber (SA) under long-time laser excitation is a common shortage of passive Q-switched bulk lasers that strongly impedes their general applications. The 2D mono-elemental nanomaterial antimonene has been recently verified as a promising SA for realizing high-stability pulsed fiber laser benefiting from its stable semimetallic bonding and superior thermal conductivity. However, its performance in enhancing the stability of pulsed bulk laser has less been investigated. Here we demonstrated the successful application of multi-layer antimonene for stable passive Q-switching operations in Tm:YAP laser at 1.94 μm and Nd:GdVO4 laser at 1.34 μm. The multi-layer antimonene was characterized to have broadband SA properties with a modulation depth of 3.2 % (12.2 %) and a saturable intensity of 0.19 GW/cm2 (0.17 GW/cm2) at 1.94 μm (1.34 μm). Stable Q-switched pulses were obtained with pulse duration of 238 ns at 1.94 μm and 324 ns at 1.34 μm. The long-time pulse duration instability was only 9.6 % at 1.94 μm and 6.9 % at 1.34 μm within 180-minute measurement. Our work indicates the exceptional potential of antimonene SA in infrared pulsed bulk laser, which may arouse great interest for developing antimonene-based optics and optoelectronics applications with enhanced stability.

Graphdiyne-Based All-Solid-State Passively Q-Switched Tm:YAP Laser at 2 μm.

All-solid-state Tm lasers have a wider wavelength range and higher output power compared to other types of lasers. In this work, we demonstrate an all-solid-state, high repetition, Tm:YAP laser Q-switched by a graphdiyne (GDY) saturable absorber. The high-quality optical nonlinear material GDY, synthesized by a cross-coupling method, exhibits a strong nonlinear optical response. The application of GDY as a saturable absorber in the passively Q-switched (PQS) Tm:YAP of an all-solid-state laser has been realized with the shortest pulse duration of ~785 ns and repetition frequency of ~199.6 kHz at a central wavelength of 1985.8 nm. This represents the shortest pulse duration and the highest repetition frequency achieved from GDY in a solid-state Tm laser to date. Our work demonstrates the remarkable nonlinear optical properties of GDY, which holds promising potential in the field of optoelectronics.

LED-pumped eye-safe pulse laser with an extracavity optical parametric oscillator.

An LED-side-pumped Nd:YAG/Cr4+:YAG passively Q-switched (PQS) laser containing an extracavity optical parametric oscillator (EOPO) is demonstrated. As far as we know, it is the first LED-pumped eye-safe laser. The Nd:YAG pump module is optimized to increase the PQS pulse energy to 24 mJ at 1064 nm. By using a single-pass EOPO design, the output energy of the signal pulse at 1573 nm is 7.44 mJ with a pulse width of 16 ns, the peak power is 434 kW, and the pump-to-signal conversion efficiency is 31%. For double-pass EOPO operation, the pump-to-signal conversion efficiency increases to 45.8%, the output energy of signal pulse is up to 10.98 mJ with a pulse width of 23.5 ns, and the peak power is 459 kW.

Comprehensive excited state carrier dynamics of 2D selenium: One-photon and multi-photon absorption regimes

Semiconductors play a critical role in optoelectronic applications, and recent research has identified group-VI 2D semiconductors as promising materials for this purpose. Here, we report the comprehensive excited state carrier dynamics of bilayer, two-dimensional (2D) selenium (Se) in one-photon and multi-photon absorption regimes using transient reflection (TR) spectroscopy. Carrier lifetime obtained from TR measurement is used to theoretically predict the photo-responsivity for 2D Se photo-detectors operating in the one-photon-absorption regime. We also calculate a giant two-photon absorption cross section of 2.9×105 GM at 750 nm hinting possible application of 2D Se as a sub-bandgap photo-detector. The carrier recombination process is dominated by surface and sub-surface defect states in one- and multi-photon absorption regimes, respectively, resulting nearly one order increased carrier lifetime in a three-photon-absorption regime (1700 ps) compared to a one-photon-absorption regime (103 ps). Femtosecond Z-scan measurement shows saturation behavior for above bandgap excitation, further indicating the possibility of 2D Se as a saturable absorber material for passive Q-switching. Our study provides comprehensive insight into the excited state carrier dynamics of bilayer 2D Se and highlights its potential as a versatile material for various linear and non-linear optoelectronic applications.

Operation of a passively Q‐switched Tm:YAP laser with Ta2NiS5 as a saturable absorber

AbstractIn this study, the operation of compact diode‐pumped continuous wave and passively Q‐switched (PQS) Tm:YAlO3 (Tm:YAP) solid‐state lasers (SSLs) on the 3F4–3H6 transition is demonstrated. The first PQS operation of a mid‐infrared (mid‐IR) Tm:YAP laser at 1986.64 nm is realized with a Ta2NiS5‐based saturable absorber (SA). Under PQS mode, the Tm:YAP laser generated a maximum output power of 1.278/1.393 W with an optical‐to‐optical conversion efficiency of 8.81%/9.61%, corresponding to a narrowest pulse duration of 787/914 ns and a high repetition frequency of 187.932/151.115 kHz for 1.5%/2.5% transmittance of output coupler. The experimental results show that Ta2NiS5‐based SA is an excellent optical switch for diode‐pumped PQS mid‐IR SSL emitting around 2.0 μm.

Passively Q-switched Nd:GdVO4 lasers with core–shell ZIF-8@ZIF-67 saturable absorber at 1 and 1.34 µm

In the current paper, the polyhedral ZIF-8@ZIF-67 nanomaterials were successfully synthesized, and the nonlinear optical features were measured through the open-aperture (OA) Z-scan technique. By employing the ZIF-8@ZIF-67 as a saturable absorber (SA), the passively Q-switched (PQS) Nd:GdVO4 lasers were demonstrated at 1064 and 1340 nm for the first time. From the 1 µm Q-switching operation, we achieved the shortest stable pulse of 85 ns under the incident excitation of 7.15 W, while the pulse repetition rate was 975 kHz. In the PQS laser at 1340 nm, the pulse width was measured as short as 79 ns with a pump level of 9.98 W, and the pulse repetition rate was 767 kHz. These results imply that the ZIF-8@ZIF-67 SA has huge advantages in the PQS laser with stable short pulse generation under the high excitations in the near-infrared (NIR) region.