Supersonic Laser Research Articles

Influence of operational parameters on the efficiency of overtone generation in a supersonic cw chemical HF laser

An experimental investigation was made of the influence of the mass flow rate of the fuel components and of the position of the axis of an optical cavity on the efficiency of generation of radiation representing the first overtone of the HF molecule in a supersonic cw HF laser. The length of the active medium was 70 cm and a radial-expansion nozzle array was used. An output radiation power of 2.61 kW (from one third of the nozzle array height) was generated at the wavelength ~1.3 μm in a three-mirror optical cavity. This corresponded to the overtone generation efficiency of the laser amounting to ~35% and the overtone generation efficiency of ~50% when considered from the point of view of conversion of energy of the active medium. The output radiation power could be increased to ~8 kW by the use of cavity optics capable of utilising the radiation from the whole height of the nozzle array.

Supersonic cw chemical HF laser with a three-jet nozzle array

An experimental investigation was made of the operational characteristics of a self-contained supersonic cw chemical HF laser. A three-jet nozzle array with reagent jets separated spatially by helium jets was used. This nozzle array (replacing its two-jet analogue) made it possible to increase by a factor of 1.20–1.35 the energy characteristics of the laser and by a factor of 1.4–1.7 (up to 125–150 mm) the length of the active medium, and at the same time reduce by 30% the level of optical inhomogeneities in this medium.

Cavity ringdown laser absorption spectroscopy and time-of-flight mass spectroscopy of jet-cooled gold silicides

The cavity ringdown technique has been employed for the spectroscopic characterization of the AuSi molecule, which is generated in a pulsed supersonic laser vaporization plasma reactor. Fifteen rovibronic bands have been measured between 340 nm–390 nm, 8 of which have been analyzed to yield molecular properties for the X and D 2Σ states of AuSi. This assignment is in disagreement with previous emission studies of AuSi, which had assigned the ground electronic state as a 2Π state. A time-of-flight mass spectrometer simultaneously monitors species produced in the molecular beam and has provided evidence for facile formation of polyatomic gold silicides. Comparison of AuSi with our recent results for CuSi and AgSi indicates regular bonding trends for the three coinage metal silicide diatoms.

Experimental investigation of the efficiency of overtone generation in a cw supersonic chemical HF laser

An experimental investigation was made of the feasibility of increasing the output radiation power in the generation of overtone oscillations in a cw supersonic HF laser with a radial-expansion nozzle array, which produced an active medium 70 cm long. The requirements in respect of the resonator optics were formulated. It was necessary to develop and deposit special discriminating dielectric coatings, which made it possible to achieve overtone lasing in a four-mirror cavity resonator. The output radiation power (at one-third of the nozzle array height) was about 0.5 kW at the wavelength of 1.3 μm. The corresponding overtone lasing efficiency was 6.5%. The use of resonator optics of size sufficient to collect radiation from the full height of the nozzle array should increase the output power to 1.5 kW.

Tandem time-of-flight mass spectrometer for cluster–surface scattering experiments

A new tandem time-of-flight mass spectrometer is described which is designed to study the mass-, velocity-, and angle-resolved scattering of cluster ions from solid surfaces. Clusters are produced in a supersonic jet laser desorption/vaporization source, ionized either directly in the formation step or by subsequent photoionization of neutrals, mass selected in a primary time-of-flight region, and decelerated to the impact energy (50–1000 eV) close to the target surface. Cluster–surface collisions take place in a field-free region in order to determine both velocity and angular distributions of the scattered clusters and fragments with an independently pulsed, rotatable secondary time-of-flight mass spectrometer. Several surface targets can be mounted in the UHV scattering chamber (10−10 Torr base pressure) on a five-axis manipulator which, together with the rotatable secondary TOF, allows for independent variation of incident and scattering angles. Target surfaces can be cleaned by direct current heating and sputtering with an argon-ion gun. Surface structure and composition are assessed by low-energy electron diffraction (LEED) and Auger spectroscopy with a four grid reverse view LEED/Auger system. Surface collision experiments of fullerenes (C+60, C+70, C+76, C+84, ...) and metallofullerenes (La@C+82) with highly oriented pyrolitic graphite (HOPG) surfaces are described as examples for the performance of the instrument. Effects of surface contamination in the scattering of fullerenes from HOPG are described to demonstrate the need for thorough cleaning procedures in order to obtain reproducible results. © 1995 American Institute of Physics.

Experiment and modeling of a small-scale, supersonic chemical oxygen-iodine laser

We report on detailed experiment and modeling of a small-scale, supersonic chemical oxygen-iodine laser. The laser has a 5 cm long active medium and utilizes a simple sparger-type O2(1 Δ) chemical generator and a medium-size pumping system. A grid nozzle is used for iodine injection and supersonic expansion. 25 W of cw laser emission at 1.315 µm are obtained in the present experiments. The small size and the simple structure of the laser system and its stable operation for long times make it a convenient tool for studying parameters important for high-power supersonic iodine lasers and for comparison to model calculations. The lasing power is studied as a function of the molar flow rates of the various reagents, and conditions are found for optimal operation. Good agreement is found between the experimental results and calculations based on a simple one-dimensional semi-empirical model, previously developed in our laboratory and modified in the present work. The model is used to predict optimal values for parameters affecting the laser performance that are difficult to examine in the present experimental system.

Deep penetration welding using a CO laser with an unstable resonator

An unstable resonator ( M = 2) has been applied to reduce the beam divergence of a gas-dynamically cooled supersonic CO laser operating at 105 K in a semiclosed gas cycle. A 4.7 kW laser beam with a total divergence of 2.5 mrad is obtained with an efficiency of 9.4%. The results of welding experiments are compared with those using a CO 2 laser. The weld depths obtained with the CO 2 laser are drastically reduced using argon as the assist gas, whereas the results with the CO laser are independent of the assist gas because of the lower plasma absorption coefficient for the shorter CO laser wavelength.

Parametric study of the gain in a small scale, grid nozzle, supersonic chemical oxygen-iodine laser

We report on experiments and model calculations of the small-signal gain and the gain profile in a grid nozzle supersonic chemical oxygen-iodine laser. The laser has a 5-cm long active medium and the gain is measured using a diode laser. The calculations are based on a simple one-dimensional semiempirical model previously developed in our laboratory. The gain is studied as a function of the molar flow rates of the various reagents and optimal conditions are found for maximum gain. In particular, an optimal value of the flow rate of I/sub 2/ is found in the experiment and explained by the present model. The small size and the simple structure of the laser combined with the simplicity of the model make the present system a useful tool for studying parameters important for high power supersonic iodine lasers. >

Infrared laser spectroscopy of the linear C13 carbon cluster.

The infrared absorption spectrum of a linear, 13-atom carbon cluster (C13) has been observed by using a supersonic cluster beam-diode laser spectrometer. Seventy-six rovibrational transitions were measured near 1809 wave numbers and assigned to an antisymmetric stretching fundamental in the 1 sigma g+ ground state of C13. This definitive structural characterization of a carbon cluster in the intermediate size range between C10 and C20 is in apparent conflict with theoretical calculations, which predict that clusters of this size should exist as planar monocyclic rings.

Continuous-wave supersonic first-overtone chemical HF laser

A theoretical analysis is reported of the feasibility of highly efficient utillisation of overtone vibrations in a cw supersonic HF laser with a slot nozzle array. The laser kinetics and the Navier—Stokes equations are solved simultaneously. The latter equations are considered within the framework of a 'narrow channel' model both for single nozzles and for the mixing (lasing) zone. The following energy parameters of the overtone laser are calculated for the 2–0 and 3–1 transitions: the specific output energy, the reduced power, and the distribution of radiative loads along the direction of flow. It is shown that the overtone conversion efficiency may exceed 30% of the fundamental-tone efficiency.

A small scale, supersonic chemical oxygen-iodine laser

A supersonic chemical oxygen-iodine laser of 5 cm long active medium has been operated utilizing a simple sparger-type O 2( 1Δ) chemical generator and a medium size pumping system. A grid nozzle was used for iodine injection and supersonic expansion. 9 W of cw laser emission at 1315 nm were obtained in the present experiments. The small size and the simple structure of the laser system and its stable operation for long periods make it a convenient tool for studying parameters important for high-power supersonic iodine lasers.

Transport of high-pressure O2(1Δ)

Calculations and experimental studies were made of the influence of heat evolution on the transport of high-pressure singlet oxygen used in a supersonic oxygen—iodine laser. The heat release as a result of relaxation of O2(1Δ) slowed down the motion of the gas in the singlet-oxygen generator and also in the duct along which the oxygen was transported. Moreover, the heat reduced the mass flow rate of the gas and the efficiency of the singlet-oxygen generator in the supersonic laser.

Effects of a nonhomogeneous gain saturation law on predicted performance of a high-gain and a low-gain laser systems

A modified Rigrod theory that uses a nonhomogeneous gain saturation law is used to model outcoupled, total, and intracavity power from a high-gain and a low-gain cw HF chemical laser with good accuracy. The homogeneous gain saturation law is found to have significant limitations when used to model total power data over a wide range of threshold gain values. The use of a nonhomogeneous gain saturation law indicates that a gain saturation law parameter of m = 1.2 models University of Illinois at Urbana-Champaign supersonic cw HF fundamental laser data more accurately than a homogeneous gain saturation law (m = 1). A completely inhomogeneous saturation law (m = 2) models University of Illinois at Urbana-Champaign supersonic HF overtone laser data more accurately than a completely homogeneous gain saturation law.

Atomic oxygen generators for surface studies in low Earth orbit

Two facilities for the generation of energic atomic oxygen beams have been developed to investigate the degradation of materials in low Earth orbit. An atomic oxygen generator using an ion beam method was used mainly for studying the effect of kinetic energies on surface reactions. Another generator combined pulsed supersonic valve and pulsed YAG laser systems for long-duration exposure experiments without maintenance. The velocity of atomic oxygen was measured by a retarding energy analyzer and a plasm time-of-flight analyzer

Numerical Simulation of Supersonic Flow CO Chemical Laser Solving Navier-Stokes Equations.

The flow field of a supersonic flow CO chemical laser is simulated solving two-dimensional Navier-Stokes equations, and the effects of viscosity, shock waves and the mixing process on the small signal gain coefficients are studied. The calculated flow pattern agrees very well with the chemiluminescence from the laser cavity which was observed previously. Both the calculation and the experiment show that the O2 streams and the dissociated CS2 streams collide with each other at the nozzle exits, generating oblique shock waves. It is also shown that mixing of the O2 streams and the dissociated CS2 streams is significantly slow, and the temperature and gain distributions in the mixing layer are strongly influenced by the shock waves and expansion waves. The calculated distributions of the small signal gain coefficients along the flow agree fairly well with the measured values in the region near the nozzle exits where the three-dimensional effects are relatively weak.

Halogen atom/metal trimer CW laser engineering concept overview

A halogen atom/metal vapor laser is discussed in terms of CW power and performance. Fluorine and sodium represent surrogates for the halogen and metal species; other combinations are possible. Since lasing may occur from a variety of excited electronic states, operation is expected to be broadly dispersed over the visible and near UV wavelength regions. The device is a low pressure, supersonic mixing laser that resembles the HF/DF CW laser, e.g., separate plenums are utilized for the fluorine and sodium vapors, and each plenum feeds a nozzle array. Sodium trimer formation begins in the nozzle and continues inside the laser cavity. The design of this nozzle is particularly important; the concept of controlled condensation is introduced. Downstream of the nozzle bank, the two vapor streams mix and the F-Na3 reaction pumps several electronically excited states that have gain in the blue-green region. Estimates are given for power per unit mass flow rate and power per unit nozzle bank cross-sectional area. 15 refs.

High power gasdynamically cooled carbon monoxide laser

A capacitively coupled transverse radio frequency discharge has been successfully applied to excite a gasdynamically cooled supersonic CO laser operating at 105 K in a semiclosed gas cycle. The laser head is characterized by a very compact design and a high discharge power density (160 W/cm3). At a discharge pressure of 390 mbar a maximum laser output of 6 kW is obtained with an efficiency of 12.4%.

Supersonic CO laser with rf excitation

A supersonic CO laser with a maximum output power of 990 W has been developed. The gas is excited in a dielectrically stabilized radio-frequency discharge before it is cooled to a temperature of 90 K by the adiabatic expansion in a supersonic nozzle. After extraction of laser power the gas is recompressed by a supersonic diffuser and a Roots-pump system. No liquid nitrogen is needed for the operation of the laser. At a pressure of 500 mbar the rf discharge could be operated homogeneously with a specific input power of 180 W/cm3. It could be shown that the length of the discharge region and the distance between the discharge and the supersonic nozzle should be rather short. By this the vibrational relaxation of the carbon monoxide is reduced and more laser power can be obtained. The laser power can be increased by using a folded resonator system. If the laser is operated at a low Fresnel number by inserting an aperture inside the cavity, a nearly diffraction limited beam quality can be obtained. Using a supersonic nozzle with a low Mach number enables the operation of the diffuser with a high pressure recovery. Thereby the overall system efficiency is increased.

Experimental study of continuous wave hydrogen-fluoride chemical laser overtone performance

The overtone lasing performance of the supersonic continuous wave hydrogen-fluoride chemical laser at the University of Illinois at Urbana-Champaign was optimized by the same set of flow rates that optimized the fundamental performance. When the absorption/scattering losses of the mirrors were taken into account, an overtone efficiency (the ratio of overtone power to maximum fundamental power for the same flow conditions) of 70-90% was achieved. The overtone efficiency was a strong function of medium saturation. There was no significant change in overtone power and efficiency as the mode volume increased. However, there was an increase in the number of lasing lines and a shift to higher rotational (J) lines. Overtone performance was as sensitive to cavitypressure as fundamental performance was

Combustion-driven supersonic rf-pumped CO laser

Lasing in a combustion-driven supersonic electric-discharge CO laser is reported for the first time. The output power of this laser is ∼12 W, and its electrooptic efficiency is about 0.12% (the low efficiency is due to the particular design of the cavity). The achievement of a uniform rf discharge in the supersonic flow and the achievement of lasing on the basis of combustion products demonstrate that it is possible to develop efficient, high-power carbon monoxide lasers.