Linear Flashlamps Research Articles

Design and construction of tunable solid-state dye laser pumped by flashlamp

Over the past six decades, dye laser technology has improved substantially. The usage of solid matrices containing laser dyes is becoming more and more popular as a viable substitute for the traditional liquid dye solutions. In this research, we designed and built a tunable solid dye laser device which consists of three main parts. (i) The active material producing the laser beam, which is a polymer rod [glycidyl methacrylate (GMA) polymer] doped with the laser dyes pyrromethene 597 (PM-597) or Nile blue (Nb-690). (ii) The pumping source is xenon linear flashlamp driven by a homemade power supply. (iii) Two broadband mirrors providing the optical feedback stable optical resonator. The properties of the gain medium and hence the laser emission characteristics were determined, and the results showed the efficiency of the homemade tunable solid dye laser device, that is suitable for a variety of applications.

影响高功率脉冲氙灯寿命的因素

影响高功率脉冲氙灯寿命的因素

Experimental verification of semiclassical and RPA calculations of the static conductivity in moderately nonideal plasmas.

We present an experimental verification of the semiclassical theory for static conductivity calculations in the case of moderately nonideal plasmas. Such plasmas are produced in linear flashlamps filled with pure helium and are characterized by on axis electron densities in the range 2x10(17)-1.7x10(18) cm(-3) and temperatures (2-3)x10(4) K. Precise measurements of the discharge electrical parameters have been carried out and in each case the impedance of the plasma was compared with the calculated value using the semiclassical theory, which is a simpler approximation than the quantum-mechanical theory based on the random-phase approximation.

Experimental verification of theoretical calculations of the static electrical conductivity in moderately non-ideal helium plasmas produced in flashlamps

We present an experimental verification of the semiclassical theory [1] for static conductivity calculations in the case of moderately non-ideal plasmas which has been developed as a more simple approximation than the quantuum-mechanical theory based on the RPA method [2,3]. Such plasmas are produced in linear flashlamps (inner diameter 5mm, inter-electrode length 100mm) filled with pure helium and are characterized by on axis electron densities in the range 2.10 17 -1.7.10 18 cm -3 and temperatures around (2-3)×10 4 K, giving a plasma parameter r close to 0.1. Different methods of diagnostics based on measurements of continuum intensities, neutral line intensities and opacities (taking into account the effect of the statistical ionic microfields on the atomic levels), and infrared laser interferometry (3.39μm), are applied to determine the radial profiles of particles and temperature. Profiles so deducted are relatively flat and show a good filling of the plasma inside the flashlamp. Such experimental conditions coupled with precise measurements of the disharge electrical parameters (current intensity and electrical field) allow for a reliable evaluation of the validity of this semiclassical theory. Finally, for each case, the impedance of the plasma so calculated is in good agreement with the experimental value, proving the validity of the semiclassical theory, and thereby of the RPA theory in our plasmas.

Wavelength-dependent model of Kr flash lamp emission and absorption

We present a simple model of the angular intensity distribution of linear flash lamps for laser pumping application, which also takes into account the plasma column absorption during flash pulse. The model parameters are derived by single-shot measurements of plasma emission and transmission, performed with an imaging spectrometer and a CCD detector. The model consists in a linear superposition, wavelength by wavelength, of a surface (opaque) and a volume (transparent) emitter and represents a good approximation of the time-averaged lamp emission and absorption for pulse durations from 50 mus to 2 ms. This model is a suitable tool for reflector optimization of flash-lamp-pumped solid-state lasers, allowing complete wavelength-dependent ray tracing with currently available computing power. Some sample applications are also shown and discussed, with results of ray tracing for a slab laser and evaluation of the effects of lamp blackbody emission for several laser active media and flash lamp excitation pulses.

Flash lighting instrumentation for color schlieren shock wave photography

Single-shot color schlieren photography of supersonic flow phenomena requires a technically complex flash light source. In particular, it should be of ultrashort duration to minimize motion blur, of high intensity to expose regular color film with only one flash, and should emit an almost “white” spectrum to provide the full scale of possible hues. Furthermore, matching Settles' (1970) direction indicating color dissection method the source should be of an areal geometry to uniformly illuminate a tricolor filter in the source plane. Two different types of light sources have been constructed and compared to each other: an array of five Xe-filled linear flash lamps and a module of eight closely stacked U-shaped loops of micro gliding sparks. The spark module consists of a total of 280 individual micro gliding discharges which are all arranged uniformly within an area of 40×40 mm. Connected in a series and pulsed by a modified eight-stage 15 kV Marx-surge generator they are operated in a nitrogen gas atmosphere doped with xenon by about 15% of volume at a total pressure of 1.5 bar. The emitted flash has a peak light intensity of 29 Mcd and a flash duration of 292 ns FWHM. Advantageously in comparison to flash lamps, the flash of a gliding spark module is shorter and free of oscillatory afterglow, thus providing clear and sharp schlieren photos of shock waves which, for example, are purged from preceding “phantom shock fronts”.

Spatial and angular characteristics of the radiation from high-power lasers utilizing solutions of organic compounds with active elements in the form of hollow cylinders

A study was made of the characteristic features of the output radiation pattern of a rhodamine laser with cells in the form of hollow cylinders excited from outside and from inside by linear flashlamps. Different methods of suppressing nonaxial rays were proposed and tested. It was found that when a cell in the form of a hollow cylinder was excited from the inside, the active medium acquired the properties of a negative lens and the paths of the rays in the resonator became similar to those in an unstable resonator. This made it possible to increase the radiation brightness by more than an order of magnitude and also to demonstrate the advantages of using internally excited active elements in the form of hollow cylinders in high-power low-divergence dye solution lasers.

Long-pulse dye laser pumped by linear flashlamp.

This paper describes a long-pulse and high-energy dye laser. The use of an oxygen-saturated Rhodamine 6G methanol solution pumped by an argon-filled linear flashlamp and a confocal resonator permits long-pulse operation with a pulse duration of 95 μs and an output energy of 830mJ at a conversion efficiency of 0.18%.

Recrystallisation of amorphous silicon films by rapid isothermal and transient annealing

Undoped amorphous silicon films have been produced by the implantation of 70 keV 8*1014 28Si ions cm-2 into (100) silicon wafers. These layers have been recrystallised by rapid isothermal annealing at 600 degrees C and transient thermal annealing for 400 mu s in the temperature range 800-1100 degrees C. The annealing has been carried out in an optical annealing furnace consisting of a bank of tungsten-halogen lamps below the specimen, with which the rapid isothermal anneals were performed, and a bank of linear flashlamps above the specimen for the transient annealing. After annealing, the thickness and quality of the recrystallised layers have been assessed by ellipsometry and transverse TEM. In the RIA material the average rate of recrystallisation has been calculated by carrying out constant temperature anneals for different times and measuring the remaining film thickness. Using these results in conjunction with published data on the temperature dependence of the recrystallisation rates the annealing temperature has been calculated and compared with the temperature measured by a thermocouple. This technique provides a valuable tool with which isothermal annealing temperatures may be calibrated. Measurements have been made of the total recrystallisation that occurred in the flash annealed material. This data has been compared with the temperature profiles that are predicted by a one-dimensional heat-flow simulation program that models the absorption and heat flow within the wafer during flash annealing.

Diode Laser—Pumped Solid-State Lasers

Diode laser-pumped solid-state lasers are efficient, compact, all solid-state sources of coherent optical radiation. Major advances in solid-state laser technology have historically been preceded by advances in pumping technology. The helical flash lamps used to pump early ruby lasers were superseded by the linear flash lamp and arc lamp now used to pump neodymium-doped yttrium-aluminum-garnet lasers. The latest advance in pumping technology is the diode laser. Diode laser-pumped neodymium lasers have operated at greater than 10 percent electrical to optical efficiency in a single spatial mode and with linewidths of less than 10 kilohertz. The high spectral power brightness of these lasers has allowed frequency extension by harmonic generation in nonlinear crystals, which has led to green and blue sources of coherent radiation. Diode laser pumping has also been used with ions other than neodymium to produce wavelengths from 946 to 2010 nanometers. In addition, Q-switched operation with kilowatt peak powers and mode-locked operation with 10-picosecond pulse widths have been demonstrated. Progress in diode lasers and diode laser arrays promises all solid-state lasers in which the flash lamp is replaced by diode lasers for average power levels in excess of tens of watts and at a price that is competitive with flash lamp-pumped laser systems. Power levels exceeding 1 kilowatt appear possible within the next 5 years. Potential applications of diode laser-pumped solid-state lasers include coherent radar, global sensing from satellites, medical uses, micromachining, and miniature visible sources for digital optical storage.

High-power high-energy linear flashlamp-pumped dye laser

A high-energy dye laser pumped by twelve preionized linear flashlamps is described. Output energy of 40 J in a 7-micros pulse has been obtained with rhodamine 6G at an energy conversion efficiency of 0.4% and with excellent reproducibility.

Transient arc self-inductance and simmer effects in linear flashlamps for laser pumping

The physical processes influencing lamp stability and efficiency are studied in this paper. Experimental evidence demonstrates that undesirable lamp output energy variation is believed to be caused by the random nature of the triggering process. The random effect can be decreased by the induced back emf of the transient arc self-inductance under the preferred trigger polarity and the simmer mode operation of the lamp. Simmering a lamp results in a uniform current and plasma density, hence higher optical efficiency is obtained. The best simmer action is provided by the full simmer mode; it allows the arc to grow uniformly from the axis of the lamp.

Low-pressure flashlamps: influence of the wall ablation phenomena on their output characteristic

When operating with linear low-pressure flashlamps (0.1–20 Torr) two different linear zones of the Eout/Ein characteristics are described: high-energy density zone corresponds with a wall-ablation regime having a strong influence from the material extracted from the walls; low-energy density zone corresponds with an isolated normal discharge regime. Spectroscopic measurements also demonstrate this behavior. The input energy density needed for the regime transition is constant when varying tube geometry. Pyrex and quartz tubes with 10-μsec pulses; the value of Etransition was ∼38 J/cm3 at 5-Torr air pressure.

Prediction of flash lamp explosion by stress measurements

We have precisely measured stress distributions in the quartz tubes of high-energy linear flash lamps, and determined the correlations between the measured stress and flash lamp explosion. Premature lamp explosion can be ascribed to the initial tensile stress at the outer surface of the tube, whereas normal lamp explosion can be ascribed to the accumulated tensile stress at the inner surface. The upper limits of the stresses in these two cases are given so that they can be used to prevent the lamp explosions by removing marginal tubes from use before explosion.

Spectroscopic studies of small linear flashlamps for use as solar radiation simulators

Spectroscopic studies of small linear flashlamps for use as solar radiation simulators

A reliable high power repetitive pulsed dye laser

A reliable Rhodamine 6G dye laser pumped by eight preionized linear flashlamps in a closely coupled arrangement is described. Megawatt pulses of 2.5 μs duration with a low divergence (<0.2 mrd) and a repitition rate up to 10 Hz are produced.

Performance analysis of a dye-switched ruby laser under the step function Q-switch model

The performance of a dye-switched, 15 cm × 0.95 cm ruby laser, pumped by two linear flashlamps, in a polished, double elliptical cavity is reported. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -switched output energy is examined under the step function <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -switch model. It is noted that the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -switched output energy shows a linear dependence on the flashlamp input energy, at variance with the step function <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> -switch theory, for a uniformly pumped laser. This anomaly is explained on the basis of non-uniform pumping. The energy ultilization factor using this theory is also reported.

On the proper choice of the preionization mode of linear flashlamps

By using preionization techniques the linear flashlamps can produce reliable fast discharges for the pumping of high power dye lasers. The choice between the two known preionization modes — DC simmer or prepulse technique — is determined by the bore diameter and the gas filling pressure of the lamps. The parameters for an efficient preionization are investigated for two flashlamps of 7 and 13 mm arc diameter respectively.

Comparison of coaxial- and preionized linear flashlamps as pumping sources for high power repetitive pulsed dye lasers

Prepulse preionized linear flashlamps are well suited as pumping sources of nearly diffraction limited high power dye lasers. 250 kW pulses of 800 ns duration at 10 Hz with a beam divergence of 0.4 mrd were obtained by using a conventional parallel-plane mirror system of 90 cm length. The energy conversion efficiency is 0.3%.

A large coaxial lidar for elastic and inelastic scattering studies of the stratosphere

A very powerful, fixed zenith laser radar system, based upon a liquid dye laser, is described in detail. The laser is a linear flashlamp pumped dye system capable of an average power output of 6W at a prf of 3 s−1 using rhodamine 6G dye and about 3W with the same prf using esculin monohydrate dye. The use of this laser as a transmitting source in the lidar system has permitted the detection of Stokes shifted vibration/rotation Raman back-scattered light from neutral nitrogen in the stratosphere and from these measurements, stratospheric temperature profiles have been derived. The lidar has also been used to study elastic backscattering from the stratosphere at two wavelengths and preliminary results of a new technique for studying stratospheric aerosol are presented.