Pulsed Output Power Research Articles

All-normal dispersion fiber lasers with magneto-optical polarization controllers.

An all-normal dispersion fiber laser mode-locked by nonlinear polarization evolution is presented in this paper. A magneto-optical polarization controller is employed in a fiber laser to optimize the polarization state and mode-locking operation. In order to provide an adjustable and large enough magnetic field for magneto-optical crystals, a magnetic yoke is designed with silicon steel and copper coil. The Q-switched and continuous-wave mode-locking regime of the fiber laser are investigated experimentally. At a pumping power of 2.08 W, the laser can generate stable mode-locking pulses with an average power of 213 mW. The repetition rate and the pulse duration are 63.7 MHz and 6.2 ps, respectively, corresponding to a pulse energy of 3.34 nJ and a peak power of 539 W. The laser can operate continuously in mode-locking states over five hours with almost no variation in pulse profile, optical spectrum, and output power.

Extension of electron cyclotron heating at ASDEX Upgrade with respect to high density operation

The ASDEX Upgrade electron cyclotron resonance heating operates at 105 GHz and 140 GHz with flexible launching geometry and polarization. In 2016 four Gyrotrons with 10 sec pulse length and output power close to 1 MW per unit were available. The system is presently being extended to eight similar units in total. High heating power and high plasma density operation will be a part of the future ASDEX Upgrade experiment program. For the electron cyclotron resonance heating, an O-2 mode scheme is proposed, which is compatible with the expected high plasma densities. It may, however, suffer from incomplete single-pass absorption. The situation can be improved significantly by installing holographic mirrors on the inner column, which allow for a second pass of the unabsorbed fraction of the millimetre wave beam. Since the beam path in the plasma is subject to refraction, the beam position on the holographic mirror has to be controlled. Thermocouples built into the mirror surface are used for this purpose. As a protective measure, the tiles of the heat shield on the inner column were modified in order to increase the shielding against unabsorbed millimetre wave power.

Temperature characteristics of tilted wave lasers

We report on the temperature characteristics of edge-emitting tilted wave lasers (TWL) composed of a thin active waveguide (0.7 μm) optically coupled to a thick passive waveguide (26 μm). The active region is based on four 1040-nm InGaAs/GaAs quantum wells. The 2-mm-long and 50-μm-wide broad area lasers show characteristic temperature of 115 K and lasing up to 120°C in the continuous-wave mode. The maximal pulsed output power as high as 40 W was achieved being limited by the available current source. Vertical far-fields of the TWLs consist of two tilted narrow lobs (2.4 deg full width at half maximum each), which contain >70% of the total output power. The tilt angle of the lobes slightly increases with the temperature (by 1 deg/40°C) due to the transverse mode hopping caused by the temperature-induced changes of the waveguide refractive indices.

Wavelength-tunable dissipative pulses from Yb-doped fiber laser with Sagnac filter

We experimentally demonstrate a wavelength-tunable passively mode-locked Yb-doped all-normal-dispersion fiber laser by exploiting a high-birefringence Sagnac fiber loop as a flexible filter. The wavelength of pulses is controlled by properly rotating the polarization controllers in a Sagnac loop. The spectrum of output pulses could be shifted by up to 15 nm at a repetition rate of 18 MHz. Output power of more than 43 mW at pulse durations below 11.4 ps is achieved at the central wavelength of 1035 nm. The pulse temporal frequency and output power change slightly over the tunable range.

Picosecond green and deep ultraviolet pulses generated by a high-power 100 kHz thin-disk laser.

We report on the generation of the second (515 nm) and fourth (257.5 nm) harmonics from a 100 kHz diode-pumped solid-state laser operating at a wavelength of 1030 nm which uses one Yb:YAG thin disk in the regenerative amplifier and delivers 60 W of the average output power in pulses of 4 ps duration. Thirty-five W in green light and 6 W in deep ultraviolet (DUV) were achieved. The sensitivity of the second harmonic generation efficiency toward the lithium triborate crystal temperature is demonstrated in experiment. The overall conversion efficiency from NIR to DUV of 10% was achieved. The β-barium borate and cesium lithium borate crystals were used as green to DUV convertors and compared regarding the efficiency and spectral bandwidths. The achieved output power is unique for DUV picosecond pulses.

Optimizing the Parameters of a 12-Cavity Rising-Sun Relativistic Magnetron With Single-Stepped Cavities for $\pi $ -Mode Operation

We investigated the use of single-stepped cavities instead of typical tapered cavities in an A6 magnetron with diffraction output (MDO) and a 12-cavity MDO through particle-in-cell (PIC) simulations using MAGIC [1] and UNIPIC [2] in our earlier publications [3] – [5] . The interaction space, where the charged particles interact with the induced RF waves, was increased by replacing tapered cavities with single-stepped cavities in a 12-cavity rising-sun relativistic magnetron with diffraction output (RMDO) that the electronic efficiency of $\pi $ -mode generation in a 12-cavity rising-sun RMDO with single-stepped cavities driven by a transparent cathode [6] with gigawatt output power level can be as high as 83% for $\alpha = 12.5^{\circ }$ , 79% for $\alpha = 17.5^{\circ }$ , and 82% for $\alpha = 18.2^{\circ }$ at $\beta = 32^{\circ }$ , where $\alpha $ is the angle between the inner wall and the $z$ -axis, and $\beta $ is the angle between the outer wall and the $z$ -axis. When $\alpha $ , the angle between the inner wall and the $z$ -axis, is changed, the depth of single-stepped cavities was changed. This would lead to the coupling between deep cavities and shallow cavities in the 12-cavity rising-sun MDO changing too, and which finally results in different frequencies of magnetron operation in the $\pi $ -mode. As we know, gigawatt nanosecond output power pulse is useful for the nanoradar system, and our PIC simulations found that when a 400-kV voltage pulse of 10-ns duration is applied to a 12-cavity rising-sun MDO driven by a transparent cathode or a solid cathode, the output power of the $\pi $ -mode can be as high as 1.5 GW. Without loss of generality, for $\alpha = 12.5^{\circ }$ and $\beta = 32^{\circ }$ , the peak efficiency of $\pi $ -mode generation in a 12-cavity rising-sun MDO with single-stepped cavities design is around 82% and occurs for voltage $V\sim 400$ kV ± 50 kV. This paper describes optimizing the parameters in a 12-cavity rising-sun RMDO for the desired $\pi $ -mode operation.

Effects of Er,Cr:YSGG Laser Pulse Frequency on Microtensile Bond Strength to Enamel.

Literature regarding the influence of Er,Cr:YSGG laser pulse frequency with different output power levels on adhesion properties of adhesive resin to lased enamel is limited. Therefore, the aim of the present study was to evaluate the effects of laser pulse frequency (20, 35, and 50 Hz) at two different output power settings (3 and 6 W) of Er,Cr:YSGG on the microtensile bond strength (μTBS) of adhesive resin to enamel. Crowns of 35 intact bovine incisors were embedded into self-cure acrylic resin individually, and then flat enamel surfaces were prepared with 600-grit silicon carbide papers under water cooling. Teeth were divided randomly into seven groups. Enamel surfaces were irradiated with Er,Cr:YSGG laser operated at one of six output power-pulse frequency combinations (6 W20 Hz, 6 W-35 Hz, 6 W-50 Hz, 3 W-20 Hz, 3 W-35 Hz, and 3 W-50 Hz) in groups 1-6, respectively. Bur-treated surfaces served as a control in group 7. After surface treatments and bonding procedures, composite build-ups were done in three layers up to a height of 4 mm. Next, all bonded teeth were sectioned into the resin-enamel sticks to be tested in a μTBS testing machine. The μTBS data were analyzed with univariate analysis of variance under a general linear model with the factor 'tooth' added as a random effect to the design. Resin-enamel interfaces were evaluated with scanning electron microscopy (SEM). The μTBS to laser-irradiated enamel in group 1 (6 W-20 Hz) was significantly lower than those of bur-treated enamel (p<0.05). However, group 6 (3 W-50 Hz) showed significantly higher μTBS values than did bur-treated teeth (p<0.05). SEM evaluation revealed enormous morphological alterations of laser-irradiated specimens, such as extensive vertical and horizontal microcracks and gaps, with the exception of group 6. The bonding effectiveness of adhesive resin to laser-irradiated enamel was affected by the pulse frequency of the Er,Cr:YSGG laser. Although the parameters recommended by the manufacturer lowered μTBS, increasing the pulse rate may maintain optimum μTBS.

A generation of 2 μm Q-switched thulium-doped fibre laser based on anatase titanium(IV) oxide film saturable absorber

We demonstrate a Q-switched thulium-doped fibre laser operating at approximately 1935 nm wavelength using anatase titanium(IV) oxide (TiO2) embedded in polyvinyl alcohol as the passive newly saturable absorber (SA). The film has absorption loss of 3.5 dB and modulation depth of 33%. It is sandwiched between two fibre ferrules in a ring laser cavity to produce self-started pulse train with a repetition rate that is tuned from 30.12 to 36.96 kHz as the 1552-nm pump power is increased from 289 to 485 mW. At maximum pump power, the laser produced a Q-switching pulse train with pulse duration, output power, pulse energy and peak power of 1.91 μs, 11 mW, 0.3 μJ and 146 mW, respectively. These results show that the TiO2 is a new potential SA material for pulsed laser applications.

Simulation of a three-millimeter-band pulse travelling wave tube

The results of numerical simulation of electrodynamic characteristics of a slow-wave structure shaped as a folded waveguide and an electron–optical system of a three-millimeter-band pulse travelling wave tube with an output pulsed power of up to 50 W are presented. The matching devices, the interaction space, and the electron–optical system are calculated, which allows determination of their constructive parameters. The effect of loss caused by the roughness of the surfaces of the walls of the electrodynamic system on the output characteristics of the device is estimated.

Plate-shaped Yb:LuPO4 crystal for efficient CW and passively Q-switched microchip lasers

It is demonstrated that plate-shaped crystals of Yb:LuPO4, which are grown from spontaneous nucleation by high-temperature solution method, can be utilized to make microchip lasers operating in continuous-wave (CW) or passively Q-switched mode. Efficient operation of such a microchip laser, which is built with a 0.3 mm thick crystal plate in a 2 mm long plane-parallel cavity, is realized at room temperature. With 2.37 W of pump power absorbed, 1.45 W of CW output power is generated with a slope efficiency of 73%. When passively Q-switched with a Cr4+:YAG crystal plate as saturable absorber, the laser produces a maximum pulsed output power of 0.53 W at 1013.3 nm, at a pulse repetition rate of 23.8 kHz, the resulting pulse energy, duration, and peak power are 22.3 μJ, 4.0 ns, and 5.6 kW, respectively.

High-power gas-discharge excimer ArF, KrCl, KrF and XeCl lasers utilising two-component gas mixtures without a buffer gas∗∗Reported at the Fifth Russian-Chinese Workshop and School for Young Scientists on Laser Physics and Photonics (RCWLP&P, Novosibirsk, August 26 – 30, 2015).

Results of an experimental study of the influence of a gas mixture (laser active medium) composition on an output energy and total efficiency of gas-discharge excimer lasers on and molecules operating without a buffer gas are presented. The optimal ratios of gas components (from the viewpoint of a maximum output energy) of an active medium are found, which provide an efficient operation of laser sources. It is experimentally confirmed that for gas-discharge excimer lasers on halogenides of inert gases the presence of a buffer gas in an active medium is not a necessary condition for efficient operation. For the first time, in two-component gas mixtures of repetitively pulsed gas-discharge excimer lasers on electron transitions of excimer molecules and , the pulsed energy of laser radiation obtained under pumping by a transverse volume electric discharge in a low-pressure gas mixture without a buffer gas reached up to and a high pulsed output power (of up to ) was obtained at a FWHM duration of the KrF-laser pulse of . The maximal total efficiency obtained in the experiment with two-component gas mixtures of KrF and XeCl lasers was 0.8 %.

Microchip laser converter based on InGaN laser diode and (Zn)CdSe quantum dot heterostructure

A high-efficiency microchip violet–green laser converter based on a molecular-beam epitaxy grown green-emitting (Zn)CdSe quantum dot (QD) II–VI laser heterostructure, optically pumped by emission of a cheap violet InGaN laser diode (LD) was demonstrated. The active region of the II–VI laser heterostructure consisted of three electronically coupled (Zn)CdSe QD sheets in a single ZnSe quantum well (QW) placed asymmetrically inside a graded-index ZnMgSSe/ZnSe superlattice optical waveguide. The cavity length of the cleaved-facet II–VI laser was 130 μm which is a nearly optimal value for minimizing the excitation power. InGaN LD radiation was focused into a narrow stripe on the surface of the II–VI laser by a microlens optical system. The converter showed laser emission at 541 nm with threshold excitation power of ∼0.5 W. The maximal output pulse power and conversion efficiency of 1.5 W and ∼15%, respectively, were achieved. The device was mounted in a standard TO-18 LD package. Photograph of the operating violet–green microchip laser converter.

Q‐switched thulium‐doped fibre ring lasers operating at 1.9 μm using multi‐walled carbon nanotubes in UV‐curing resin

The passively Q-switched operation of all-fibre thulium fibre lasers using UV-curing resin doped with multi-walled carbon nanotubes as a saturable absorber is demonstrated. A single-mode thulium-doped silica fibre is pumped by a laser diode emitting at 1.63 µm through a wavelength-division multiplexing coupler. Unidirectional laser output from the fibre ring resonator is attained by using the retroreflector at the counter-directional output port. The fibre laser exhibits 1.9 µm wavelength pulsed oscillation at a repetition rate of 7.2 kHz. When the pump power is increased to 161 mW, the output pulse power is measured by 150 mW with a pulse width of 3.2 µs.

Physical and Physiological Comparison Between Indian Female College Basketball Players and Sedentary Students

The study aimed to assess and compare the physical and physiological performances of Indian female college basketball players (BB) with sedentary females (SS) of same age group. Randomly selected 20 female college students, 10 each in 2 groups, BB (19.0 ± 0.8) and SS (19.7 ± 1.3) respectively, volunteered for this study. Standing height, body weight, resting blood pressure, resting and maximum heart rate (RHR and MHR respectively), resting oxygen consumption (VO_2rest), maximal aerobic capacity (VO_2max), anaerobic power, hand grip strength (HGS) and back leg strength (BLS) were recorded. Body surface area (BSA), body mass index (BMI), maximum oxygen pulse (O₂P_max), fatigue percentage and relative peak power output (RPP) were calculated. Significant difference was observed between BB and SS in body weight (P<0.001), BSA (P<0.01), BMI (P<0.001), HGS (left; P<0.05 and right; P<0.01) and BLS (P<0.01). No significant difference was observed in height and blood pressure among the players and sedentary females, while, significantly lower RHR (P<0.01), higher MHR (P<0.01), VO_2max (P<0.001), O₂P_max (P<0.01) were noted in sportswomen compared to sedentary females. Peak anaerobic power, average anaerobic power (both P<0.01) and RPP (P<0.001) of sportswomen was also significantly higher than the sedentary group. The study revealed that female college basketball players were physiologically potent than sedentary students of similar age group. It is once again substantiated the fact that involvement in sports or games like basketball, renders a person with better physiological health and physical fitness as compared to sedentary individuals.

The nonlinear simulation, design and experiments on 0.42 THz gyrotron with gradually tapered complex cavity

Gyrotron oscillators are one of promising sources to generate high power terahertz radiation. To achieve high power at high frequency, gyrotrons have to operate at high order modes to alleviate the problem of wall heating and the miniaturization of interaction structures at these frequencies. Due to high order modes, the mode spectrum is very dense and the electron beam is likely to interact with several modes. Mode competition is a major hurdle in achieving stable and efficient operation of a gyrotron at cyclotron harmonics. The gradually tapered complex cavity could suppress mode competition by locking a pair of operating modes in two single cavities. Starting from the general transmission line equations with an electron beam, self-consistent nonlinear simulations on the second harmonic complex cavity gyrotron operating at 0.42 THz are presented. The influences of the electron beam parameters on the interaction efficiency are analyzed. The experimental results show that the designed complex cavity gyrotron is operationally stable at TE17.4 with pulse output power of 22.25 kW when the beam current is 4.8 A, beam voltage is 45 kV, and applied magnetic field is 8.185 T. The corresponding frequency and interaction efficiency are 421.60 GHz and 10.27%, respectively.

Vitamin D is associated with cardiopulmonary exercise capacity: results of two independent cohorts of healthy adults.

Vitamin D has an important role in calcium homeostasis and is known to have various health-promoting effects. Moreover, potential interactions between vitamin D and physical activity have been suggested. This study aims to investigate the relationship between 25-hydroxyvitamin D (25(OH)D) and exercise capacity quantified by cardiopulmonary exercise testing (CPET). For this, 1377 participants from the Study of Health in Pomerania (SHIP-1) and 750 participants from the independent SHIP-TREND cohort were investigated. Standardised incremental exercise tests on a cycle ergometer were performed to assess exercise capacity by VO2 at anaerobic threshold, peakVO2, O2 pulse and peak power output. Serum 25(OH)D levels were measured by an automated chemiluminescence immunoassay. In SHIP-1, 25(OH)D levels were positively associated with all considered parameters of cardiopulmonary exercise capacity. Subjects with high 25(OH)D levels (4th quartile) showed an up to 25% higher exercise capacity compared with subjects with low 25(OH)D levels (1st quartile). All associations were replicated in the independent SHIP-TREND cohort and were independent of age, sex, season and other interfering factors. In conclusion, significant positive associations between 25(OH)D and parameters of CPET were detected in two large cohorts of healthy adults.

Multichannel Systems of Resonant Microwave Pulse Compression

Different designs of multichannel resonant microwave pulse compression systems operating in $X$ - and $S$ -bands are described. The output pulsed microwave power of these systems is expected to be severalfold greater than that of compression systems with a single output channel. These compression systems can be used as compact sources of high-power nanosecond-duration microwave pulses, sources of synchronized sequences of microwave pulses, and sources for development of phased arrays of compressed microwave pulses. In particular, the authors describe the characteristics of a two-channel $S$ -band resonant microwave pulse compression system with nanosecond-duration output pulse and an output pulsed microwave power of 1 GW. The operation of a four-channel $X$ -band compression system with a possible eightfold output pulsed microwave power increase, relatively to the microwave power in the cavity, is also described. The design of an eight-channel system with a 16-fold output pulsed microwave power increase is reviewed. The parameters of an $X$ -band compression system with multichannel output unit formed as a set of interference microwave switches extracting the energy in synchronism are presented.

Operation Characteristics of a 12-Cavity Relativistic Magnetron When Considering Secondary and Backscattered Electrons’ Emission

The particle-in-cell (PIC) simulation of an A6 magnetron with diffraction output (MDO) in our earlier work shows the peak output power (especially the short power pulse with several nanoseconds duration) is lowered when electrons with high energy strike the anode block, which leads to the emission of secondary and backscattered electrons. In addition, the PIC simulation for a 12-cavity MDO also shows when secondary electron emission occurs, the boundary for neighboring modes becomes more complicated than before. Replacing tapered cavities by single-stepped cavities in a relativistic MDO increases the interaction space where the charged particles interact with the induced RF waves. The electronic efficiency of the A6 relativistic MDO as well as the 12-cavity MDO with single-stepped cavities driven by the transparent cathode can be over 70% with gigawatts output power level. And with single-stepped cavities, the distance between the cathode and the wall of relativistic MDO is increased such that the possibility for electrons with high energy striking on the wall is decreased, which results in less emission of secondary and backscattered electrons under the same applied voltage. The PIC simulation demonstrated that in the 12-cavity MDO with single-stepped cavities driven by the transparent cathode with 400-kV applied voltage, the electrons with above 500 eV from cathode under the crossed electromagnetic field can strike on the anode block of MDO, resulting in a secondary and backscattered electron current that can cause different modes to be prevalent or stop the designed mechanism from working. Especially when applied with short voltage pulse with 10-ns duration, the output power pulse is shorted with peak power lowered. The simulation results presented in this paper possibly provide references for multicavity resonator when considering mode selection or mode switching experiments.

Experimental Study of Microwave Pulse Compression Using a Five-Fold Helically Corrugated Waveguide

This paper presents the experimental study of microwave pulse compression using a five-fold helically corrugated waveguide. In the experiment, the maximum power compression ratio of 25.2 was achieved by compressing an input microwave pulse of 80-ns duration and 9.65-9.05-GHz frequency swept range into a 1.6-ns Gaussian-envelope pulse. For an average input power of 5.8 kW generated by a conventional traveling-wave tube, a peak pulse output power of 144.8 kW was measured corresponding to an energy efficiency of 66.3%.

Monolithically integrated mid-infrared sensor using narrow mode operation and temperature feedback

A method to improve the sensitivity and selectivity of a monolithically integrated mid-infrared sensor using a distributed feedback laser (DFB) is presented in this paper. The sensor is based on a quantum cascade laser/detector system built from the same epitaxial structure and with the same fabrication approach. The devices are connected via a dielectric-loaded surface plasmon polariton waveguide with a twofold function: it provides high light coupling efficiency and a strong interaction of the light with the environment (e.g., a surrounding fluid). The weakly coupled DFB quantum cascade laser emits narrow mode light with a FWHM of 2 cm−1 at 1586 cm−1. The room temperature laser threshold current density is 3 kA∕cm2 and a pulsed output power of around 200 mW was measured. With the superior laser noise performance, due to narrow mode emission and the compensation of thermal fluctuations, the lower limit of detection was expanded by one order of magnitude to the 10 ppm range.