Nanosecond Pulse Generator Research Articles

A pulsed repetitive CO2laser pumped by a longitudinal-discharge-initiated semiconductor opening switch diode

Experimental results obtained on a pulsed repetitive CO2 laser pumped by a longitudinal discharge are reported. The laser pumping system consisting of a high-voltage nanosecond pulsed generator with a solid switching system based on a semiconductor opening switch diode and capacitive energy storage is presented. An average radiation power of 300 mW was reached at a pulse repetitive rate of 10 Hz. The radiation pulse duration at full width at half-maximum was 60 μs.

Nanosecond pulse generation in a passively Q-switched Yb-doped fiber laser by Cr/sup 4+/:YAG saturable absorber

We explored efficient nanosecond pulse generation in a passively Q-switched cladding-pumped Yb-doped fiber laser by use of an external-cavity configuration containing a Cr/sup 4+/:YAG saturable absorber crystal. By exploiting passive Q-switched regime and stimulated Brillouin scattering, pulses of durations as short as 2.7 ns, corresponding to a peak power of /spl sim/9 kW, have been achieved. The laser was tunable over 70 nm and green output power generation was obtained by external frequency doubling in a KTP crystal.

Sub Nanosecond Pulse Generation by Stimulated Brillouin Scattering using FC-75 in an Integrated Setup with Laser Energy up to 1.5 J

We have demonstrated the short pulse generation of Nd:YAG laser at the fundamental wavelength by using stimulated Brillouin scattering (SBS) in liquid FC-75 at the energy of 1.5 J with a compact single set-up consists of generator and amplifier. Minimum pulse width obtained without attenuator and with attenuator are 770 ps and 600 ps respectively. SBS Conversion efficiencies are 90% without attenuator and 55% with attenuator. The brightness of the compressed pulse was about twelve fold higher than that of incident pulse.

High-power semiconductor-based nano and subnanosecond pulse Generator with a low delay time

One of the promising designs of high-power nanosecond and subnanosecond pulse generators is based on the fast ionization dynistor (FID) stack triggered with nanosecond pulse of overvoltage. This pulse is usually formed by semiconductor opening switches. Delay time of these switches equals the sum of forward and reverse current pulse duration, i.e., several hundreds of nanoseconds. The novel opening switch, inverse recovery diode (IRD), is capable of forming a nanosecond pulse of voltage with the delay time equal to the reverse current pulse duration (15-20 ns) due to the special diode structure. High-voltage nanosecond pulse formed with IRD is used for fast triggering of the first FID from high-voltage dc-biased FID stack. The resulting fast overvoltage pulse is applied to the second FID, etc. As a result, the high-voltage FID-stack is switched for units of nanosecond. Total delay time of IRD-FID-based pulse generators is less than 30 ns.

High-energy and high-peak-power nanosecond pulse generation with beam quality control in 200-µm core highly multimode Yb-doped fiber amplifiers

We explored high-energy and high-peak-power pulse generation in large-core multimode fiber amplifiers, achieving what is to our knowledge the highest reported energies, up to 82 mJ for 500-ns pulses, 27 mJ for 50-ns pulses, and 2.4-MW peak power for 4-ns pulses at 1064 nm, using 200-microm-diameter and 0.062-N.A. core Yb-doped double-clad fiber amplifiers. The highly multimode nature of the fiber core was mitigated by use of a coiling-induced mode-filtering effect to yield a significant improvement in output-beam quality from M2 = 25 from an uncoiled fiber to M2 = 6.5 from a properly coiled fiber, with the corresponding reduction in number of propagating transverse modes from > or = 200 to < or = 20.

Modeling the plasma kinetics mechanisms of CuBr laser with neon–hydrogen additives

A mathematical model describing the discharge kinetics and lasing characteristics of copper bromide vapor laser with neon and hydrogen additives has been developed. The suggested model is based on a “zero-dimensional” model and offers simple mechanisms to explain discharge kinetics mechanisms, different physical processes and hydrogen additive effects on the copper bromide vapor laser. The model estimates the temporal evolution of discharge voltage and current, population densities, laser beam density, electron temperature and radial distribution of pressure and buffer gas temperature. The suggested mechanism assumes that the electron detachment from negative hydrogen ions does not contribute to the copper ionization process. Numerical solutions of a nonlinear rate equation system predict the generation of nanosecond pulses. The calculated maximum values of discharge voltage, current, average output laser power, electron temperature, etc. are in good agreement with other reported calculated and experimental data.

Mathematical modeling of the intracavity Q-switched Nd-glass laser

The temporal characteristics of the Q-switched Nd-glass laser have been numerically investigated. A mathematical model describing the dynamic emission and different physical processes has been adapted. This model allows the investigation of the nonlinear saturable absorber effects on the mode characteristics of the Nd-glass laser, and studying the affects of the laser input parameters on the output laser pulse characteristics. Numerical solutions of a nonlinear rate equation system predict the generation of nanosecond pulses of Q-switched Nd-glass laser. The solutions estimate the laser density and the relative population inversion of the Nd-glass laser rod and saturable absorber for different emission regimes. The estimated results of the laser output pulse characteristics are in a good agreement with the other calculated and experimental results.

Formation of High-Power Pulses of Nanosecond Duration by Generators on Reverse Switch-on Dynistors with Sharpening Circuits Based on Diode Opening Switches

The basic principles of constructing generators of nanosecond pulses on reverse switch-on dynistors with sharpening output circuits based on diode opening switches are considered. The results of an experimental study of a high-power generator incorporating such a dynistor; a step-up pulse transformer; and a high-voltage diode opening switch, which is an assembly of drift step-recovery diodes connected in series, are presented. The output voltage pulses of the generator with an amplitude of ∼45 kV, a duration of ∼50 ns, a rise time of ∼10 ns, and a repetition rate of 1 kHz are applied to a load resistance of 25 Ω.

A Megavolt Nanosecond Generator with a Semiconductor Opening Switch

A high-current nanosecond-pulse generator with a pulse power of up to 1.6 GW, an output voltage of 0.5–1 MV, pulse duration of 40–60 ns, and repetition rates of 300 Hz (in a steady-state mode) and up to 850 Hz (in a burst mode) is described. Its average output power is 30 kW at a pulse repetition rate of 500 Hz. The energy-switching system of the generator fully consists of solid-state elements: a thyristor, magnetic switches, and a semiconductor-opening switch based on SOS diodes.

Generation of monochromatic nanosecond pulses in the FIR region

We present a technique for generating short far-infrared (FIR) laser pulses, with a linewidth close to the Fourier transform limit, changing the reflectivity of an InSb crystal by the photoelectric effect. The crystal is irradiated with an optically pumped CW FIR laser and its reflectivity at an FIR frequency is changed by the ionizing radiation of a pulsed Nd-YAG laser. A reflectivity change, from 18 to 90%, has been obtained. Shorter FIR pulses can be obtained using shorter ionizing laser pulses. Finally, double pulses separated by an arbitrary time interval and of chosen amplitude are obtained.

Metal-ceramic cathodes for electron accelerators

Institute of Electrophysics, Ural Division, Russian Academy of Sciences, Komsomol’skaya ul. 34, Yekaterinburg, 620219 Russia 1. Nanosecond pulse generators with the pulse recurrence frequency as high as 1 kHz and the resource up to 1010–1011 pulses and electron accelerators with such generators [1, 2], which are of considerable promise for technological applications [3, 4], have been developed on the basis of semiconductor current switches. In connection with this, the problem of creating simple, inexpensive, and high-resource cathodes with high and stable emissivity in the course of the exploitation becomes urgent. Metal–dielectrics–metal cathodes [5], in which electrons are emitted from plasma arising at a point of contact of special electrodes with ceramics (triple points), most fully conform to these requirements. Among disadvantages of these cathodes are a complexity of the structure and limited number of emitting points. This causes the erosion of igniting electrodes and the ceramics under them, a inhomogeneity in the current distribution at the output foil of a vacuum diode, and a reasonably high impedance of the diode for small dimensions of the cathode unit.

Highly efficient second-harmonic and sum-frequency generation of nanosecond pulses in a cascaded erbium-doped fiber:periodically poled lithium niobate source

By combining erbium-doped fiber sources based on a large mode-area design and periodically poled lithium niobate, we have obtained single-pass conversion efficiencies of as much as 83% (energy efficiency) for second-harmonic generation into the near IR (768 nm) and of 34% for sum-frequency generation into the green (512 nm) for nanosecond pulses, using first-order quasi-phase matching. Pulse energies in excess of 80microJ of second harmonic have been obtained from systems pumped by a single laser diode.

Efficient broadband sum frequency based on controlled phase-modulated input fields: theory for 351-nm ultrabroadband or ultrashort-pulse generation

A new method of efficient sum-frequency generation for broadband input fields is proposed and analyzed. It involves the mixing of controlled phase-modulated waves for phase matching over a broad bandwidth. Regardless of the form of the modulation, phase matching can be maintained over the whole pulse duration, provided that the ratio of the chirp parameters of the incident waves is correctly chosen, thereby driving highly efficient sum-frequency generation. The case of 1.05-μm frequency tripling with KDP crystals is analyzed in detail and is shown to be applicable to the efficient generation of either broadband nanosecond pulses or ultrashort and intense pulses at 351 nm.

Semiconductor saturable absorber mirrors (SESAM's) for femtosecond to nanosecond pulse generation in solid-state lasers

Intracavity semiconductor saturable absorber mirrors (SESAM's) offer unique and exciting possibilities for passively pulsed solid-state laser systems, extending from Q-switched pulses in the nanosecond and picosecond regime to mode-locked pulses from 10's of picoseconds to sub-10 fs. This paper reviews the design requirements of SESAM's for stable pulse generation in both the mode-locked and Q-switched regime. The combination of device structure and material parameters for SESAM's provide sufficient design freedom to choose key parameters such as recovery time, saturation intensity, and saturation fluence, in a compact structure with low insertion loss. We have been able to demonstrate, for example, passive modelocking (with no Q-switching) using an intracavity saturable absorber in solid-state lasers with long upper state lifetimes (e.g., 1-/spl mu/m neodymium transitions), Kerr lens modelocking assisted with pulsewidths as short as 6.5 fs from a Ti:sapphire laser-the shortest pulses ever produced directly out of a laser without any external pulse compression, and passive Q-switching with pulses as short as 56 ps-the shortest pulses ever produced directly from a Q-switched solid-state laser. Diode-pumping of such lasers is leading to practical, real-world ultrafast sources, and we will review results on diode-pumped Cr:LiSAF, Nd:glass, Yb:YAG, Nd:YAG, Nd:YLF, Nd:LSB, and Nd:YVO/sub 4/.

Spatial and temporal characteristics of the radiation emitted by an array of injection lasers generating nanosecond pulses

Radiation pulses of 4 ns duration, 450 W power, and 1 kHz repetition frequency were generated by an array consisting of 150 AlGaAs/GaAs injection lasers. A comparative analysis was made of the spatial and temporal characteristics of the radiation emitted by this array when it was pumped with current pulses of 50 and 3 ns duration and with the rise times 10 and 1 ns, respectively. A reduction of the rise time of the pump pulses reduced from 3 to 0.5 ns the range of changes in the delay times of the output radiation pulses at different points in a plane perpendicular to the plane of the array.

Generation of nanosecond soft X-ray pulses as a result of interaction of the Nd: glass laser radiation with gas puff targets

A new method of generation of nanosecond soft X-ray pulses with a photon energy around 1 keV is presented. X-rays are generated in a high-temperature plasma, which is created as a result of the interaction of Nd:glass laser radiation with a gas puff target. The target was obtained by puffing a small amount of gas through the nozzle into the vacuum chamber by means of a pressure electromagnetic valve. The pulses of laser radiation, with pulse duration of 1 ns and energy up to 15 J, generated in the system of a high-power Nd:glass laser were used for the target heating. Spatial, spectral, and temporal measurements of X-ray emission have shown that the high-intensity soft X rays are generated as a result of the interaction of nanosecond pulses of Nd:glass laser radiation with the gas puff target. A high efficiency of X-ray generation is suggested to be related to the effect of condensation of the gas outflowing from the valve nozzle and, in effect, to the interaction of laser radiation with matter in a form of aerosol.

Lund high-power laser facility – systems and first results

A high-power laser facility has been established at the Lund Institute of Technology, Sweden, available to national groups and their international collaboration partners. The laboratory incorporates three major 10Hz laser systems, that can be operated individually or synchronized in combined use. Each system represents extreme optical powers in a certain sense. The main system is a terawatt laser based on chirped pulse amplification in titanium doped sapphire. It generates radiation tunable in the 760-840 nm region with a maximum power of 1.5 TW in 150 fs long pulses. A further system is set up to generate nanosecond pulses of extremely bright VUV radiation (down to 120 nm) by sum-difference four-wave mixing in krypton gas. Finally, a third system generates widely tunable radiation (200-900 nm) of a pulse duration of 10's of picoseconds. The experimental areas incorporate target chambers, spectrometers and fast electronics. The systems have been used in a number of experiments requiring high optical powers, and a brief account of the initial activities is given. Detailed studies of high-harmonic generation in inert gases are reported as well as the generation and application of hard X-rays from microplasmas. Intense whitelight generation by self-phase modulation in water has been used for biological tissue studies and for chemical pump/probe experiments. VUV radiation has been used for studies of radiative properties of excited states.

Generation of short nanosecond pulses in a YAG:Nd laser with aQswitch made of a GSGG:Cr:Nd crystal

Stable single-frequency generation of short (2 ns) radiation pulses in a YAG:Nd laser was achieved by using a passive Q switch made of a GSGG:Cr3+:Cr4+:Nd3+ crystal.

ナノ秒方形波パルス電圧印加による液体窒素の絶縁破壊進展

The electrical breakdown phenomena in liquid nitrogen under atmospheric pressure for point-to-plane electrode configuration have been investigated using a photo optical current measuring technique and a 790 nano-second rectangular high-voltage pulse generator. The waveforms of the prebreakdown current in liquid nitrogen were essentially the same as those in hydrocarbon liquids and in polyethylene. Discharge from positive point was more intense and faster than from negative point. A linear relation to formative time lag and gap spacing was observed for gap length more than some critical values, which indicates an average velocity of the discharge propagation in the most part of gap spacing. The velocities are deduced to be the range 13-18km/s for positive point and 3-12km/s for negative point under the applied voltage range 20-50kV. These values are an order higher than those in hydrocarbon liquids and are same order as those in chlorinated liquids for both point polarities.

Photoconductive nanosecond pulse generation utilizing radial transmission lines

A nanosecond, kilovolt pulse generator utilizing a radial transmission line was investigated. The device incorporates a gallium arsenide, photoconductive switch to connect the radial line to the coaxial output. Identical gridded electrodes are used on opposite sides of the switch. Switching is achieved with a 75-ps-wide pulse from a mode-locked Nd:YAG laser. In addition to the radial design, a quasi-radial structure was also investigated, in which improvements in rise time and pulsewidth were achieved at the expense of voltage gain. For the same charging voltage of 9.2 kV, the radial device delivered a 10-kV, 1.3-ns-wide pulse, while the quasi-radial device gave a 6-kV, 500-ps-wide pulse. An integrated pulser design in which the switch and the dielectric medium between conducting planes are combined into a single semi-insulating GaAs wafer is described. The potential advantages of such a device are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>