Molybdenum tungsten disulphide (MoWS2) as a saturable absorber for a passively Q-switched thulium/holmium-codoped fibre laser

In this work, a passively Q-switched Thulium/Holmium-doped fibre laser (THDFL) using a molybdenum tungsten disulphide (MoWS₂) saturable absorber (SA) is proposed and demonstrated. The MoWS₂ nanosheets are prepared by hydrothermal exfoliation and then suspended in a polyvinyl alcohol (PVA) thin film host. Q-switching of the THDFL at a maximum 1550 nm pump power of 445.2 mW gives a maximum repetition rate and minimum pulse width of 36.3 kHz and 2.8 µs with a corresponding pulse energy of 86.4 nJ and peak power of 31.1 mW. The MoWS₂ based Q-switched THDFL's output has a very high signal-to-noise value of ～62.2 dB which strongly indicates that the laser is working in a stable operation. To the best of our knowledge, this is the first demonstration of MoWS₂ as a passive SA in a THDFL for operation in the 2.0 µm region. The proposed laser would have significant medical and sensing applications, particularly at the biologically active 2.0–2.1 µm regions.     

Triple-wavelength passively Q-switched ytterbium-doped fibre laser using zinc oxide nanoparticles film as a saturable absorber

We report on the generation of a triple-wavelength passively Q-switched ytterbium-doped fibre laser using a saturable absorber (SA) based on zinc oxide nanoparticles (ZnO NPs) film. The SA was fabricated by embedding ZnO NPs powder into a polyvinyl alcohol as a host polymer. By properly adjusting the pump power and the polarization state, single-, dual- and triple-wavelength Q-switching are stably generated without additional components (such as optical filter, or fibre grating). For the triple wavelength operation, the fibre laser generates a maximum pulse repetition of 87.9 kHz with the shortest pulse duration of 2.7 μs. To the best of authors’ knowledge, it’s the first demonstration of triple-wavelength passively Q-switching fibre laser using ZnO NPs as a SA. Our results suggest that ZnO is a promising SA for multi-wavelength laser operation.     

Emission Regimes of 1.06 μm Spectral Bandwidth Two-Sectional Lasers with Quantum Dot Based Active Layer

We have investigated two-sectional semiconductor lasers with an active region comprising five layers of InGaAs quantum dots, emitting in the spectral range near 1.06 μm. Regimes of passive mode-locking, passive Q-switching, and mode-locking with pulse modulated amplitude are realized. The transition conditions between generation regimes are investigated. The frequency tuning range with current increase in the Q-switched regime exceeds more than 4 times. The duration of the mode-locked pulses was 2 ps at the pulse repetition rate of 44.3 GHz.     

Diode-end-pumped passively Q-switched 1.34 μm Nd:Gd0.5Y0.5VO4 laser with Co:LMA saturable absorber

In this paper, the output performances at 1.34 μm in continuous wave operation and passive Q-switching regime of a diode-end-pumped Nd:Gd_0.5Y_0.5VO₄ laser have been investigated. The passive Q-switching regime was achieved with Co²⁺:LaMgAl₁₁O₁₉ (Co²⁺:LMA) saturable absorbers crystals. A maximum average output power of 230 mW was recorded with a Co²⁺:LMA with initial transmission of 81%. The minimum pulse duration was 116 ns, which corresponded to a repetition rate of 360 kHz, the single pulse energy of 2.1 μJ and the pulse peak power of 5.5 W.     

High-Repetition-Rate Q-Switched Diode-Pumped Nd:YAG Laser at 1.444 mum

A diode-pumped Q-switched Nd:YAG laser that operates at the eye-safe 1444 nm wavelength has been developed. When pumped by a 10-W fiber-coupled array at 808 nm, it generated 1 W in cw operation and 560 mW at 20-kHz repetition rate with active Q-switching. Design issues such as thermal lensing characterization and beam quality are discussed.     

Q-switched fiber lasers with carbon nanotubes hosted in ceramics

Q-switched fiber ring lasers operated by single-walled carbon nanotubes (SWNTs) hosted in SiO(2) matrix are demonstrated by highlighting their stable operation and dramatically improved thermal damage threshold. Employing aerosol deposition process, SWNTs are incorporated into the ceramic host at room-temperature without solubility limitation. After experiencing the intracavity optical power higher than 15.3 dBm, the hosted SWNTs survive to provide Q-switching operation. The continuous repetition rate tuning is achieved in the range of 11.1-32.2 kHz with the pulse-duration of 7.1-15.8 μs at 1558.5 nm.     

Narrow-linewidth passively Q-switched fibre laser based on microsphere resonator

We experimentally demonstrate a stable narrow-linewidth passively Q-switched fibre laser based on a microsphere resonator (MSR) and graphene saturable absorber (SA). The MSR made by the arc discharge method has the characteristics of easy fabrication, broad free spectral range (FSR) and flexibility. And it acts as a narrow band-pass filter to ensure narrow-linewidth operation. A stable passively Q-switched pulse with 0.016?nm narrow spectral linewidth is successfully achieved. The output pulse has the pulse width of 5.2 µs, repetition frequency of 28 kHz and high signal to noise ratio (SNR) of ～60?dB. The results demonstrate that our works may provide an effective way to achieve narrow-linewidth pulsed fibre lasers.     

The effect of passive Q-switching observed in an erbium-doped fiber laser at a low pumping power

The effect of passive Q-switching was observed in an erbium fiber laser at a pumping power below 100 mW. The phenomenon is explained by a cascade process of the Rayleigh light scattering and the induced Mandelshtam-Brillouin scattering in a fiber resonator of the laser. In the Q-switched mode, the laser produced giant output pulses with a duration below 15 ns, a peak power up to 200 W, and a repetition period of 300–500 μs. The proposed Q-switching mechanism is inferred from the characteristic features of the laser pulse oscillograms measured at a ∼1 ns resolution. Previously, this effect was observed only in high-power fiber lasers at a pumping power of ∼2 W.     

Beam-quality improvement of a passively Q-switched Nd:YAG laser with a core-doped rod

We present experimental results that demonstrate the great efficiency of a core-doped Nd:YAG rod (a hexagonal Nd:YAG core surrounded by undoped YAG) in producing high output power and excellent beam quality. An additional improvement in beam quality is clearly observed when the core-doped rod is used in combination with a LiF:F(2)(-) crystal, which acts as a passive Q-switching element. This improvement is quantified by beam-propagation factors as low as M(2) approximately = at a maximum average output power of 9 W. We show that transversally pumped core-doped rods with the addition of LiF:F(2)(-) crystals fulfill the requirements for high-beam-quality, scalable, compact all-solid-state lasers in passively Q-switched operation.     

Korrosion von grauem Gußeisen in konzentrierter Schwefelsäure

Corrosion of Grey Cast Iron in Concentrated Sulphuric Acid The Pauling process of regenerating spent sulphuric acid is an example of industrial application of the corrosion resistance of grey cast iron in boiling strong sulphuric acid. The corrosion behaviour of cast iron in boiling sulphuric acid depends on the corrosion potential. At a high corrosion potential, the material shows a stable passive state. In a study on the influence of the alloy components Si, Cu and Sn on the corrosion resistance of grey cast iron, the following results were derived: In the active state, cast iron containing more than 1,4-1,5% Si exhibits a corrosion maximum in 97% boiling sulphuric acid, whereas alloyed grey cast iron with low Si content displays in the active state better corrosion behaviour over the whole concentration range from 93–98% H₂SO₄. When the alloyed cast iron is in the passive state, corrosion resistance increases as the silicon content is reduced and the sulphuric acid concentration is raised.     

Nickel oxide nanoparticles thin film saturable absorber for 1-micron pulsed all-fibre lasers operation

A passive Q-switched and mode-locked ytterbium-doped fibre laser (YDFL) pulse generation using a nickel oxide thin film as a saturable absorber is reported. The nickel oxide nanoparticle thin film was fabricated by a simple processing technique, and it has a modulation depth of 39% and saturation intensity of 0.04 MW/cm². The saturable absorber was constructed by inserting a small piece of the film between two fibre ferrules. Then it was integrated in a YDFL cavity. The Q-switching operation started at a threshold pump power of 117.73 mW with an initial wavelength of 1073.5 nm. When the pump power was raised from 117.73 to 133 mW, the repetition rate grew from 9.5 to 15.8 kHz. The pulses had a maximum pulse energy of 478 nJ. Furthermore, a stable self-started mode-locked pulse was also succesfully generated at the threshold pump power of 97.3 mW. The central wavelength and repetition rate of the laser were 1037.72 nm and 23 MHz, respectively. The maximum pulse energy of 0.56 nJ and a peak power of 26.4 W were recorded at a pump power of 137.5 mW.     

Self-seeded Ti: Sapphire laser with an active feedback mirror

Abstract

A single-longitudinal mode (SLM) dual-cavity pulsed Ti:sapphire laser is presented. It is self-seeded by means of an active feedback mirror (AFM) consisting of a partially reflecting mirror and additional active medium. The use of AFM results in an increase of both the laser output energy and overall conversion efficiency by a factor of about 1.4 compared to results achieved with a passive feedback mirror, under equivalent conditions. A reliable, temporally stable SLM regime of operation is achieved in the 740–820 nm spectral range.     

Prelase stabilization of the polarization state and frequency of a Q-switched, diode-pumped, Nd:YAG laser

We present an experimental investigation of the energy statistics of the linear polarization components of pulses from a Nd:YAG laser that is repetitively Q-switched with an acousto-optic modulator. Varying the modulator-induced diffraction losses leads to changes in the pulse polarization state and the energy statistics of the polarization components. For conventional Q-switching there is no laser oscillation during the low-Q intervals, and we find that the orthogonal components of the pulses can display large relative energy fluctuations even though the total pulse energy is quite stable. In the prelase mode, a weak continuous-wave background seeds the Q-switched pulses and results in the emission of highly linearly polarized, single-longitudinal-mode pulses with small relative energy fluctuations.     

Liquid-phase epitaxy growth and characterization of Co,Si:YAG thin film saturable absorber

Thin films of Co,Si:YAG were grown on YAG and Er,Yb:YAG substrates by means of the isothermal liquid-phase epitaxy (LPE) dipping technique. X-ray diffraction analysis, optical transmission spectra measurements, and passive Q-switching experiments were performed to characterize the obtained layers. Absorption saturation measurements of Co,Si:YAG thin films were carried out at 1.54 μm. Passive Q-switching of the Er:glass laser by use of epitaxial Co,Si:YAG/YAG was observed. We demonstrated experimentally that the Co,Si:YAG layers could be used as an effective saturable absorber for the lasers operating near 1.5 μm.     

Wideband-tunable nanotube Q-switched low threshold erbium doped fiber laser

An all-fiber passively wideband-tunable nanotube Q-switched low threshold erbium doped fiber laser is presented. With a low insertion loss carbon nanotube based saturable absorber, C- and L-band tunable Q-switched lasers are achieved by tuning the transmission wavelength of one C-band tunable filter and the other L-band one, respectively. The threshold of the Q-switched operation is only 12.8 mW. The self-mode-locking effect on the Q-switching can be effectively reduced by introducing a spatial hole burning effect with two optical circulators. The tunable wavelength range of the Q-switching laser can be changed by inserting a variable optical attenuator in the laser cavity to tune the gain spectrum.     

Adaptive nanowires for switchable microchip devices

This paper demonstrates for the first time the use of adaptive functional nickel nanowires for switching on-demand operation of microfluidic devices. Controlled reversible magnetic positioning and orientation of these nanowires at the microchannel outlet offers modulation of the detection and separation processes, respectively. The former facilitates switching between active and passive detection states to allow the microchip to be periodically activated to perform a measurement and reset it to the passive ("off") state between measurements. Fine magnetic tuning of the separation process (postchannel broadening of the analyte zone) is achieved by reversibly modulating the nanowire orientation (i.e., detector alignment) at the channel outlet. The concept can be extended to other microchip functions and stimuli-responsive materials and holds great promise for regulating the operation of microfluidic devices in reaction to specific needs or unforeseen scenarios.     

Flash-lamp-pumped Ho:Tm:Cr:YAG and Ho:Tm:Er:YLF lasers: experimental results of a single, long pulse length comparison

Flash-lamp-pumped, room-temperature Ho:Tm:Cr:YAG and Ho:Tm:Er:YLF are compared for single but long pulse operation, with pulse lengths of approximately 1.0 mus. Under similar operating conditions in normal-mode operation, a slope efficiency of 0.0331 was observed for Ho:Tm:Er:YLF compared with 0.0047 for Ho:Tm:Cr:YAG. For Q-switched operation, Ho:Tm:Er:YLF yielded a slope efficiency of 0.0075. In comparison, a slope efficiency of 0.0012 was obtained for Ho:Tm:Cr:YAG. Two methods of producing long pulse lengths are compared: pulse selection of normal-mode relaxation oscillations and Q-switching in a long resonator. Theoretical models developed in a companion paper for normal-mode relaxation oscillations and Q-switching in quasi-four-level solid-state lasers are in agreement with the experimental results.     

Erbium–ytterbium microlasers: optical properties and lasing characteristics

In this paper we present a comprehensive review of the work done by our group on diode-pumped bulk erbium–ytterbium microlasers. Starting from an analysis of the optical properties of Er–Yb doped phosphate glasses, addressed to the modeling of the active material and to the design and optimization of laser cavities, different operating regimes and peculiar properties of these novel laser devices are described and discussed, including multi-longitudinal mode and single-frequency operation, frequency tuning and stabilization, intensity stabilization, Q-switching, mode-locking and frequency-modulation operation. Due to the high performance in terms of emission characteristics and potential low cost, these microlasers are attractive for a large number of applications and, in particular, for optical communications at 1530–1560 nm wavelengths, metrology, and telemetry at an eye-safe wavelength.     

Transition from random packing to stable state in a continuously avalanching granular flow

We investigate the transition evolution from the initial state with the random packing of the particles to the stable state in which successive avalanches exhibit consistent characteristics under the slumping regime. It is found that there exist three distinct stages in the transition evolution, considering the change of the volume fraction. The coordination number is almost unchanged during the transition evolution, which indicates the particle contact form is consistent in the three stages. The pause phenomena are discovered in some avalanches, and the probability of pause occurrence increases continuously in the three consecutive stages. We also explore the distribution of particles in the passive layer at the stable state. The particles in the middle region of the passive layer have the closest packing status, and the deeper the region is located, the later it reaches the stable state.     

Tri-wavelength passively Q-switched Yb3+:GdAl3(BO3)4 solid-state laser based on WS2 saturable absorber

Using the WS₂ nanosheets prepared by a facile hydrothermal reaction as saturable absorber (SA), we demonstrate a tri-wavelength passively Q-switching operation of a diode-pumped Yb:GdAl₃(BO₃)₄ (Yb:GAB) crystal laser for the first time. The single pulse energy up to 1.30 μJ with the output power of 140 mW is obtained. The corresponding pulse width and repetition frequency rate are 440 ns and 107.8 kHz, respectively. The stable pulsed laser operates at 1044.9, 1045.6 and 1048.5 nm, simultaneously. This work suggests that solvothermal synthesized WS₂ could be a promising SA to realize a simultaneously multi-wavelength laser operation.