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The focused beam of a pulsed CO/sub 2/ TEA laser was used to photodissociate ethylene gas at total pressures of 100 to 300 torr. The laser pulse induces molecular hydrogen elimination to yield primarily C/sub 2/H/sub 2/ and H/sub 2/ in a large excess of helium to eliminate heating. An investigation was made of the dependence of product yield on wavelength, inert gas pressure, ethylene pressure and intensity. Photochemical yield was followed over a 10,000 fold range. Its dependence was investigated employing alternate methods of focusing the laser beam, one of which results in a constant volume geometry. A photometric method of characterizing this focal zone is described. A ''structureless'' computer model of the laser pumping process involving coupled rate equations and phenomenological absorption and stimulated emission coefficients is described. The model assumes rapid intramolecular energy transfer between the various vibrational modes throughout the entire vibrational manifold, and rapid equilibration of rotational states. The model includes stimulated emission and deactivating collisions, and predicts a product yield versus intensity dependence that does not exhibit threshold behavior in agreement with experiment. Calculated dependences of product yield on laser power for various parameters are given in order to relate the model to variousmore » photolysis experiments.« less

The investigation results of TEA – Xe laser operating at pulse repetition rates up to 2 kHz are presented. The influence of macro- and microinhomogeneities of the volume discharge plasma and gas-dynamic processes in the near-electrode layers on the ignition frequency of the volume discharge and the average radiation power level was determined. In TEA-Xe laser with an active volume of V A = 42×1,8×0.5 cm3 at a pulse repetition rate of 1.2 kHz the maximum value of the average radiation power of 2.8 W was reached.

In this paper different stage of pulse charging circuit (Blumlein circuit) was design. The laser system consist of different dimension printed board act as capacitor, fast spark gap switch and two parallel electrode made of Brass. TEA Nitrogen laser produce UV radiation with 337.1nm. the basic design contain two capacitor with one spark gap while, fourth design consist of four spark gap with five capacitor. As the number of stage rise the overvoltage required for breakdown increase so we can obtain gas discharge and excitation of Nitrogen molecules at lower voltage. The maximum energy obtained for OSBC was 1.02 mJ at 25 KV with laser pulse width around 8 ns. The last design with four stage blumlein circuit the energy raised to higher value more than for last design, the maximum energy was 19.01mJ at 25 kv with pulse width around 4.6 ns.

Ge15Se77Sb8 chalcogenide thin films having thickness 300 nm were grown on glass/Si wafer by vacuum evaporation technique and induced by Transverse Electrical Excitation (TEA) laser for 10, 20 and 30 min. The synthesized Ge15Se77Sb8 chalcogenide exhibited the glassy as well as amorphous nature, as evidenced in differential scanning calorimetry measurements. TEA laser irradiation on Ge15Se77Sb8 thin films showed the polycrystalline nature while the as-prepared thin films were in amorphous nature. The optical band gap of as-prepared and laser irradiated films were determined by measuring the optical absorbance with photon energy. An increase in absorption coefficient and extinction coefficient was observed while the decrease in optical band gaps with laser irradiation time was demonstrated.

George Stout investigated radiation ablation as a means of erasing white paint stripes (applied to facilitate realignment) from Philae Temple sandstone blocks after their reassembly on the island of Agilkia. Forty-two years ago state-of-the-art laser technology offered very few options in terms of diversity in wavelengths and pulse lengths. Laser divestment in art conservation had only been demonstrated for black sulfate encrustations on white calcareous stones. However, a CO2 IR (10.6 µm) TEA laser from an inertial-confinement thermonuclear fusion program was available and had been employed to ablate white tufa deposits from brown Cyprian pottery shards. Consequently, Stout adapted the heat-transfer analytical modeling of a concurrent laser divestment project in Venice to white paint upon brown sandstone, characterizing the Philae situation to guide TEA-laser divestment tests on the white-striped Isis stones. In contrast to results obtained with radiation from Nd:YAG, Nd:glass, and ruby lasers, the mid-i...

The design, development and operational characteristics of a compact corona pre-ionized helium-free TEA CO2 laser is discussed. Remarkably high efficiency of about 19% was obtained in this laser, which is attributed to the optimum concentration of CO2 and N2 gas, reduction in energy dissipation in the pre-ionization loop and the switch, minimizing the diffraction losses and finally optimization of the output coupler reflectivity. The helium-free TEA CO2 laser has also been analysed using a comprehensive theoretical model, developed based on the Boltzmann transport equations and the discharge excitation circuit equations. The voltage and current waveforms of the pulsed discharge were simulated and used as input to the laser rate equations to estimate the laser pulse energies and the pulse shapes. The theoretical estimations of the laser pulse energy agree fairly well with the experimental results. The accuracy of our theoretical model becomes evident from the numerically evaluated laser pulse shapes, which show remarkable resemblance with the experimentally measured pulse shapes. A detailed comparison with the helium-rich case is included to highlight the key aspects of a suitably designed helium-free TEA laser.

The ablation of coatings (paint, varnish, oxides, etc.) using a pulsed laser beam is a process that has a number of major benefits compared with conventional cleaning techniques (mechanical and chemical), the main advantage being the possibility of removing the surface layer without any risk of damaging the substrate. Another benefit, and certainly not the least, is the non-use of toxic solvents or chemical products that are difficult to eliminate and, in any case, will be banned from use in the near future. However, it must be stressed that, notwithstanding the above benefits, laser ablation of painted surfaces can only give good quality results if the process is properly controlled. The procedure discussed in this paper has two aims: the first involves establishing a thermal model of the interaction, applied to the ablation of paint from metal surfaces by infra-red laser. The second involves proposing an optimised paint removal process validated by experimental measurements. This second objective will be based on an analysis method of the acoustic signal transmitted by the ablation plasma beam.

Laser Ultrasonic Testing (UT) is an important technique for the non-destructive inspection of composite parts in the aerospace industry. In laser UT a high power, short pulse probe laser is scanned across the material surface, generating ultrasound waves which can be detected by a second low power laser system and are used to draw a defect map of the part. We report on the design and testing of a transversely excited atmospheric pressure (TEA) CO 2 laser system specifically optimised for laser UT. The laser is excited by a novel solid-state switched pulsing system and utilises either spark or corona preionisation. It provides short output pulses of less than 100 ns at repetition rates of up to 1 kHz, optimised for efficient ultrasonic wave generation. The system has been designed for highly reliable operation under industrial conditions and a long term test with total pulse counts in excess of 5 billion laser pulses is reported.

We constructed a TEA laser which consists of spark gap, pulse type high voltage power supply, Blumlein transmission line circuit, laser tube with Ernst electrode. We observed the self-preionization with an optical fiber in the spark gap and laser tube. The higher voltage power supplied to the Blumlein transmission line circuit, the better preionization was. An U-type transformer yielded better stability and output power than an I-type transformer. The discharge time after triggering a spark gap for the U-type transformer was also short. We obtained the stability of and output power of when the optimum conditions of the laser operation were spark gap distance of 6.0 mm, electrode distance in laser tube of 5.0 mm, gas flow rate in spark gap of 1500 cc/min, gas flow rate in laser tube of 4 /min, output window reflectivity of and repetition rate of 10 Hz.

A reliable procedure for remote high-accuracy laser detection of N 2 O as one of the principal destroyers of the protective ozone layer of the Earth has been developed. The procedure is based on using a CO 2 -laser system emitting efficiently in the ∼4.5 μm range. In this case lasing from isotopic modification 12 C 18 O 2 of carbon dioxide with its subsequent frequency doubling by a nonlinear crystal is used. With the object of reducing the price the composition of the active medium (both for TEA laser and low-pressure longitudinal-discharge-excitation laser) has been optimized. New high-efficiency intracavity frequency doubling schemes based on nonlinear AgGaSe 2 crystals have been developed for CO 2 -lasers of both types. Low concentrations of N 2 O and concentrations of the principal background gases CO and H 2 O have been measured under real atmosphere conditions with the aid of the lidar complex built around these lasers.

The experimental results on the laser-supported directed-energy "air spike" (DEAS) in hypersonic flow are presented. A CO 2 TEA laser has been used in conjunction with the IEAv 0.3-m Hypersonic Shock Tunnel to demonstratethe laser-supported DEAS concept. A single laser pulse generated during the tunnel useful test time was focused through a NaCI lens ahead of an aluminum hemisphere-cylinder model fitted with a piezoelectric pressure transducer at the stagnation point. In the more recent experiments, a double Apollo disk model fitted with seven piezoelectric pressure transducers substituted the simple hemisphere-cylinder model. The objective of the present research is to corroborate the past results as well as to obtain additional pressure distribution information.

Laser induced breakdown spectroscopy (LIBS) was used for the analysis of Ca in a soil depth profile of Patagonia (Argentina), using a CO 2 TEA Laser and solid pellets of the soil in a BaCl 2 matrix. The experimental set-up allowed for the simultaneous observation of the emission lines in the range 390–420 nm, corresponding to Ca(II) and Ba(II), so that the intensity ratio I (Ca)/ I (Ba) could be measured to obtain a calibration curve, rather than I (Ca) alone. The results of the ablation could be interpreted with an evaporation model and non-stoichiometric conditions. The experimental variables such as laser energy, number of pulses averaged, and Ca concentration in the pellet were evaluated in order to find the best conditions for the analysis. The samples were obtained at variable depths (from 0 to 18 m) and analyzed to measure the total Ca and the acid soluble Ca. These results were compared with those obtained with the standard techniques.

This paper describes numerical and analytical studies on the optimization of the ultra-broadband infrared (IR) source, a novel high average-power device. The main objective of current studies was the reduction of weight, size, and cost of the system by devising a scheme to generate the two closely spaced radiation lines with a single laser driver instead of the two CO/sub 2/ transversely excited atmospheric pressure (TEA) lasers envisioned in the initial work. By inducing the modulation instability in nonlinear media, we have obtained as good or better results as in our previous studies but with one of the TEA lasers replaced by a very low-power driver that provides the seed radiation for the excitation of the instability. Even more importantly, we have demonstrated that the second high peak-power TEA laser can be replaced by a compact, light weight, low peak-power driver by focusing the radiation to a tighter spot. The average power of the source is maintained at the previous level by operating at higher duty factor. In the new low-peak-power operating regime, the output spectrum is very similar to that of the high-power regime, provided that the ratio of the peak power to the nonlinear length that scales proportionally to the area of the laser spot remains fixed.

The pulsed laser deposition (PLD) technique is frequently applied to synthesize carbon nitride coatings having a general formula CNx. In previous experiments, the polycrystalline CNx films were deposited with the use of a CO2 TEA laser in a remote nitrogen atmosphere [1] . The x value was found to be approximately 0.6 and the grains, observed with SEM, were typically of a few hundreds of nanometers of size. This phenomenon was tentatively explained by the abundance of vapors generated by the action of the laser. It can be, in turn, related to the thermal fields in the graphite target. The numerical code ‘Fusion-2D’, describing laser/target interaction, was applied to model the temperature in two dimensions. The optical absorption data were taken for the wavelengths that corresponded to the typical lasers used in PLD processes, i.e. excimer, YAG and CO2. The evolutions in the graphite target temperature at the pulses generated by these lasers were then calculated for a given power density. The differences in these evolutions were related to the volume of produced vapors and helped to explain the morphology of the synthesized films.

Quasi-simultaneous laser action in the UV (0.337 μm ) and the IR (10.6 μm ) was observed from a pulsed laser with a sliding discharge plasma cathode. The laser operates at atmospheric pressure, with a gas mixture of CO2/N2/He, at a 0.26/0.50/4.0 l min −1 flow rate. Output energies of 30 mJ in the IR and 0.35 mJ in the UV were obtained, from a laser discharge volume of 38.0×1.0×2.8 cm 3 . The optimum gas mixtures have been determined and the temporal behavior of the discharge parameters, the performance characteristics of the laser and the beam spatial distributions were investigated.

The operation characteristics of a two-stage Blumlein circuit (TSBC), which can increase the output energy of a TEA- laser by 100% without embarking on spark-gap miniaturization, are investigated using a discharge-coupled circuit model. This circuit model predicts that a TSBC can produce a laser-channel breakdown voltage of up to , as compared with computed for a one-stage Blumlein circuit (OSBC), where is the charging voltage. Although the gain in the breakdown voltage is only 25%, it significantly increases the laser-channel current and input power which, when compared with computed values for an OSBC, are enhanced by 2.3 and 2.6 times respectively. The computed input power, as a function of , is correlated to that of the measured laser output.

X-ray photoelectron spectrometry (XPS) has been used to observe the changes in surface chemistry during the removal of paint from a zinc coated steel substrate by means of TEA-CO2 laser ablation. Laser ablation at both plasma and sub-plasma fluences is investigated and their relative merits are discussed. The laser is shown to be an effective tool for removal of the bulk of the paint layer and is not impaired by evidence of ageing in the paint. Evidence for a very thin layer of organic compounds present on the surface after cleaning at sub-plasma fluences has been found, although these can be removed at plasma fluences.

For the removal of material with pulsed laser radiation the distance travelled by the shock or blast wave and the amount of energy released in the plasma state due to the absorption of laser radiation are determined experimentally and theoretically. The distance travelled by the blast wave is detected by schlieren photography, the released energy by monitoring the transmitted laser radiation during the removal process. The theoretical evaluation is performed by numerical simulation using a model incorporating the laser-induced vaporization process and the dynamics of the plasma state. The results obtained from the experiments and the model are compared with that of the Sedov - Taylor scaling. The removal of the oxide layer from austenitic steel is investigated with laser radiation produced by a TEA and a high-power laser device. For the TEA laser with fluences of 5 and 10 J 50 - 80% of the pulse energy is released into the plasma state and the Sedov - Taylor scaling describes the distance travelled by the blast wave in agreement with data from the experiments and the simulation. For the high-power laser with a fluence of 50 J , 6% of the pulse energy is released into the plasma state and the Sedov - Taylor scaling does not describe the data of the simulation. The process of removal of copper and aluminium material is simulated for excimer laser radiation with fluences of 15 and 30 J . For copper 15 - 30% of the pulse energy is released into the plasma state and the Sedov - Taylor scaling is applicable. For aluminium, less than 2% of the pulse energy is released into the plasma state and the Sedov - Taylor scaling is only applicable for the higher fluence.

Simultaneous laser action from HF and N/sub 2/ is obtained, from a plasma cathode TEA laser, for the first time. The sliding discharge along the surface of a dielectric is used as a plasma cathode, for the main volumetric discharge. The laser operates at atmospheric pressure, with a gas mixture of SF/sub 6/:C/sub 3/H/sub 8/:N/sub 2/:He. For a typical flow rate ratio of 0.27:0.024:0.2:19.8 1 min/sup -1/, it produces simultaneously 160 mJ HF and 0.6 mJ N/sub 2/ laser outputs at 0.43% and 1.4/spl times/10/sup -3/% efficiencies respectively, at the moderate charging voltage of 28.5 kV. These output characteristics are obtained from a small active discharge volume and length of 10/sup 6/ cm/sup 3/ and 38 cm respectively. These values extend the performance, recently reported in the literature, of a sliding discharge HF/N/sub 2/ laser with corresponding simultaneous energy outputs of 12 mJ HF and 1.1 mJ N/sub 2/, to a higher energy output level, thus making the device suitable for a broader range of applications. This novel dual wavelength HF/N/sub 2/ laser system presented, can be particularly convenient for medical experiments, where the IR beam can be used for tissue ablation, while the UV beam can be used as the excitation source for fluorescence spectroscopic measurements, for the evaluation of the ablation process. Details are presented on the dependence of the laser performance parameters, such as output energy, discharge voltage and current and structure of the laser output pulses on the mixture composition and the circuit parameters.

We report an experimental investigation of the absorption and ablation characteristics of the high-temperature polymer Upilex polyimide, using a line-tunable TEA laser. It is demonstrated that excellent quality through-holes (vias) can be produced in thin films of Upilex when the laser is tuned to a strongly absorbed wavelength as a result of thermal decomposition produced by laser heating of the bulk polymer. For weakly absorbed wavelengths, transmission and probe beam deflection measurements reveal an incubation effect in the ablation which is thought to be related to particulate contamination in the film.

Construction of powerful and efficient laser sources, lasing in various IR ranges, is of importance for further development of a number of trends, e.g., spectroscopy, laser chemistry, sounding of the atmosphere, and metrology. The most natural way to solve this problem is to use unconventional (nontraditional) transitions to produce lasing in commonly used CO2 lasers. The spectral range of CO 2 lasers is greatly increased in lasing on transitions of the so-called "hot" band 0111-1110, whose P-branch is in the range of 10.9-11.3 µm. Thorough investigations of gain, vibrational temperatures (T1, T2, T3), and output parameters on lines of the hot band made it possible to achieve efficient lasing both for pulse TEA and for cw longitudinal-discharge CO2 lasers. In studying the lasing spectrum of hot transitions in TEA CO2 lasers some lines not belonging to the 0111-1110 band. We suggested, that these lasing lines belong to higher level transitions, e.g., 1001-2000 (0400), which were called "doubly hot," i.e., transitions in which compared to hot transitions two deformation quanta or one symmetric quantum rather than one deformation quantum is added both to the upper and to the lower energy level. In the present work lasing in both a TEA laser and a low-pressure laser with longitudinal discharge on some transitions of the CO2 molecule in the range of 11.0-11.6 µm is reported. The rather high resolution of the spectral equipment used and calculation of transition frequencies on the basis of recent spectroscopic constants made it possible to identify definitively the lasing lines obtained as belonging to the doubly hot bands 0221-1220 and 100l-2000 and the sequence hot band 0112-1111. To find optimum conditions for lasing on the aforementioned bands experimental studies of vibrational temperatures in active media of a TEA CO2 laser and a low-pressure laser with long itudinal discharge were carried out. Earlier the lasing on the 0200(1000)-0110 band of the CO 2 molecule has been obtained in the specific systems at cryogenic temperatures under the lowest efficiency. The optimization of the active medium and its electrical discharge pumping conditions based on the original technique of the temperature model allowed to obtain in the simple TE CO2 laser with UV preionization the powerful lasing on the 0200-0110 band at room temperature. The dependencies of the output and spectral performances of the 16 (14) micrometers lasing vs. a content of the active medium, pumping parameters and cavity characteristics have been carried out. To increase the power performances of the 16 (14) microns CO2 laser the possibility of lasing on the 0201(1001)-0111 band have been experimentally and theoretically investigated under the combined (electrical + optical) excitation of the active medium. The conditions for

HfO2 and Y2O3 films for optical applications are prepared by excimer laser ablation and CO2 TEA laser evaporation, respectively. The growing films are bombarded with oxygen ions of 150 to 550 eV energy and several 10 to 250 μA/cm2 ion current density. Films of both materials deposited at relatively low ion bombardment possess high refractive indexes approaching those of the corresponding bulk. These films are of amorphous structure and have a high packing density with low porosity. Increasing ion bombardment, i.e. increasing ion energy and current density, leads to a marked decrease in refractive index and hence in the packing density due to increasing crystallization within the films. In the case of hafnia, for example, the refractive index at 600 nm wavelength decreases from 2.15 down to 1.80. Using appropriate deposition parameters hafnia and yttria films, with both high and low refractive index, showing low absorption and high laser damage thresholds at 1.06 μm wavelength can be prepared.

Stable and repetitive single-longitudinal-mode output from a pulsed TEA carbon dioxide laser has been achieved using a time-gated gain cell. The gain cell is operated as an oscillator for the time periods between the laser pulses. Before the TEA laser is triggered, the gain cell is rapidly switched below threshold to avoid saturation of the gain-switched spike in the TEA laser pulse. Standard dither-stabilization techniques can be used during the CW operation of the gain cell to position the output coupler for single-mode operation. This method for obtaining single-mode output from a pulsed TEA laser is completely automatic and very straightforward to implement.

Using controlled feedback and coincident far infrared absorption, we have shown that the superradiant emission process in NH 3 pumped by the 9R16 line of a CO 2 TEA laser has a marked effect on the absorption of laser energy and vibrational heating of the gas. Since many polyatomic molecules pumped by IR laser are efficient superradiant far infrared sources, the effect is important for laser induced fluorescence studies in these polyatomics.

Quadrupole mass analyzers (QMAs) are receiving increasing attention for applications in time-of-flight (TOF) studies of laser-induced desorption, ablation and surface reactions in order to extend the information attainable from these experiments. With such a complicated detection device, however, it is easily possible to inadvertantly manipulate the real time-of-flight distribution, for example by missing fast or slow particles. In this work a systematic investigation of the influence of the different QMA parameters on the signal and their interplay was undertaken in laser-induced desorption experiments. The particle pulses were generated by resonant vibrational excitation of condensed benzene films with a TEA CO2 laser. Our investigations give the optimized configuratioin and setting of potentials for the instrument studied, in terms of sensitivity and energy resolution, and an accurate procedure to determine the drift time of ions in the quadrupole. This makes it possible to detect undistorted time-of-flight distributions with a time resolution of about 5 μs for a range of incident kinetic energies of at least 0–3 eV.

A theoretical analysis of the N 2 Blumlein laser circuit based on the distributed parameter model is carried out. Some typical parametric dependences are presented and compared with the well known lumped parameter model. The results indicate the validity of the distributed parameter model over a wider range of parametric studies. The analysis is quite general and can be easily extended to study other fast discharge laser systems such as TEA CO 2 , excimer and metal vapour lasers.

A simple method for the generation of short, single-mode CO2 laser pulses produced by applying two voltage gates (of amplitude 3Uλ/4 and Uλ/4) to an electro-optic Q-switch placed in a three-mirror cavity is proposed. Single, single-mode, well-synchronizable pulses of 3 ns duration and of 3 mJ energy have been experimentally achieved from a TEA CO2 laser with an intracavity Pockels cell with 3 ns switching time. Using a numerical simulation it is shown that with shorter switching time (≈1 ns) the method enables one to obtain, from such a laser, a single, megawatt pulse of 1 ns duration.

A four-channel nanosecond transversely excited atmospheric (TEA) N2 laser controlled by a simple and cost effective multistage spark gap which offers a high flexibility in varying the time sequence of the laser pulses from over 100 ns to as low as 5 ns is described. The delays between these laser pulses depend mainly on two important spark gap breakdown parameters: the charging voltage and their respective gap separations. The jitters between these laser pulses are observed to be independent of the initial ignition of the multistage spark gap-hence a precision and very fast triggering technique that is usually crucial for such work can be dispensed with.

The long-term operation of a 1 kHz, 500 W transversely excited atmospheric CO2 laser has been realized by using an all-solid-state exciter. The laser system consisted of a fast-gas-flow tunnel containing a discharge head, a pulsed power supply made of an all-solid-state exciter, and a gas regenerator with a gas analyser. The energy transfer efficiency of the exciter was 65% and an overall laser efficiency of 5.2% was obtained. Continuous operation of more than 107 shots has been achieved for sealed-off conditions.

Bone ablation using different pulse parameters and four emission lines of 9.3, 9.6, 10.3, and 10.6 μm of the CO2 laser exhibits effects which are caused by the thermal properties and the absorption spectrum of bone material. The ablation mechanism was investigated with light- and electron-microscopy at short laser-pulse durations of 0.9 and 1.8 μs and a long pulse of 250 μs. It is shown that different processes are responsible for the ablation mechanism either using the short or the long pulse durations. In the case of short pulse durations it is shown that, although the mineral components are the main absorber for CO2 radiation, water is the driving force for the ablation process. The destruction of material is based on explosive evaporation of water with an ablation energy of 1.3 kJ/cm3. Histological examination revealed a minimal zone of 10–15 μm of thermally altered material at the bottom of the laser drilled hole. Within the investigated spectral range we found that the ablation threshold at 9.3 and 9.6 μm is lower than at 10.3 and 10.6 μm. In comparison the ablation with a long pulse duration is determined by two processes. On the one side, the heat lost by heat conduction leads to carbonization of a surface layer, and the absorption of the CO2 radiation in this carbonized layer is the driving force of the ablation process. On the other side, it is shown that up to 60% of the pulse energy is absorbed in the ablation plume. Therefore, a long pulse duration results in an eight-times higher specific ablation energy of 10 kJ/cm3.

The practical application of the narrow-band transversely excited atmosphere CO(2) laser, which uses a double-grating cavity, is demonstrated by pumping spectrally pure farinfrared lines in a CH(2)OH laser.

We communicate results of the stable operation of a TEA CO(2) oscillator-amplifiers system, producing pulses of 10(14) W/cm(2) at best focus, furnished with a simple provision for retropulse isolation.

Trifluoromethyl iodide, CF(3)I, has been shown to be an efficient optical filter for TEA CO(2) laser pumped several mid IR molecular lasers. Its absorption characteristics and effectiveness of filtering capacity were examined using a pump TEA CO(2) laser and a 12.08-microm NH(3) laser.

Photochemical processes have been investigated in a TEA CO/sub 2/ laser using propanol seeding gases. (AIP)

A compact laser rangefinder has been developed, which incorporates a sealed-off pulsed CO(2) TEA laser and uses direct (i.e., nonheterodyne) detection. This device is essentially eye safe and benefits from the superior atmospheric transmission at 10.6-microm wavelength. Design parameters are presented and illustrated, and system performance is discussed.

Laser propulsion research progress has traditionally been hindered by the scarcity of photon sources with desirable characteristics, as well as integrated specialized flow facilities in a dedicated laboratory environment. For TEA CO2 lasers, the minimal requirements are time‐average powers of >100 W), and pulse energies of >10 J pulses with short duration (e.g., 0.1 to 1 μs); furthermore, for the advanced pulsejet engines of interest here, the laser system must simulate pulse repetition frequencies of 1–10 kilohertz or more, at least for two (carefully sequenced) pulses. A well‐equipped laser propulsion laboratory should have an arsenal of sensor and diagnostics tools (such as load cells, thrust stands, moment balances, pressure and heat transfer gages), Tesla‐level electromagnet and permanent magnets, flow simulation facilities, and high‐speed visualization systems, in addition to other related equipment, such as optics and gas supply systems. In this paper we introduce a cutting‐edge Laser Propulsion La...

The paper deals with an one-dimensional model of short pulse laser irradiation of the Al2O3 target and with simulation of the temperature distribution induced by it. In the model the temperature-dependent specific heat was considered. Also the latent heats of melting and evaporation were involved. The influence of energy density and absorption coefficient on the effect of overheating was examined. Experimental results on the ablation rate of the Al2O3 target by pulsed CO2 TEA laser in the evaporation regime and the threshold energy agreed well with the model.

A compact capacitor-transfer TEA CO 2 laser of 180 mJ output energy and 50 ns pulse duration in half width was designed and constructed for field use. This laser is suitable for laser microprobe spectrochemical analysis on geological and mining samples. Experiments show that the use of helium as a surrounding gas suppresses the continuous emission spectrum of the plasma, thus increasing the S/N ratio. Using glass as standard samples, the minimum detectable concentrations are estimated with Zn neutral line and F ionic line to be 60 ppm and 500 ppm, respectively.

This paper describes the resonator configuration of a double-pulse TEA CO2 laser, and discusses how to obtain single-mode operation in that configuration.

The plasma characteristics and excitation process of laser-induced plasma with the use of a TEA CO2 laser of 750 mJ pulse energy and 100 ns pulse width are studied in different surrounding gases at reduced pressures. From the time-resolved spatial distribution, it is clear that in helium and argon atmospheres, two different excitation processes take place in forming the plasma. The first excitation process is due to the blast wave, while the second process is due to the metastable state of the noble gases. It is believed that this second process transfers metastable energy to the vaporized atoms of the target for emission, even long after the laser bombardment ends, thus giving total emission intensity that is higher in the noble gases than in air. The displacement of the front of the emission line under different atmospheres is also presented.

13C isotope separation by multiphoton dissociation of CHClF2 was studied by a continuous-discharge CO2 laserQ-switched at 8 kHz. This laser can easily emit two or more wavelengths with good spatial and temporal overlap. The best irradiation results were obtained by the line pair 9P16 + 9P28. After optimizing also the pressures of CHClF2 and of buffer gases (He and Ar), the energy density and the gas speed, the process is now much less nonlinear than in previous experiments with a single wavelength. Differences to the TEA laser induced process were observed, and generally the pressure influence on yield and selectivity showed a variety of phenomena. They were interpreted in terms of collisional changes of spectra during the laser pulse.

A small photoswitched TEA CO2 laser has been developed. This small aperture, low repetition rate laser can produce 69 mJ optical pulses from a discharge volume of 12.5cm3, with an energy efficiency of 11.1%. This energy efficiency is the highest so far reported with such lasers. Corona UV sources driven by a simple inexpensive solid state exciter are used to trigger the discharge. Also demonstrated is the wider input energy loading and enhanced discharge stability provided by overvolting the laser head.

A novel multipass grating interferometer is presented that is capable of operating as an efficient, very-narrow-band output coupler for high-power, large-bandwidth lasers. Its application for tunable (up to 3.5 GHz), single-mode operation of a TEA CO(2) laser is discussed.

Sparks in the form of long, thin filaments having quasi-periodic longitudinal light and dark regions (striations) in time-integrated images have been observed in various gases using a CO(2) TEA laser. Typically, a 50-mJ pulse will produce a filament 1 cm long and 130 microm in diameter, with more than 150 striations spaced 50 microm apart in atmospheric air. Each striation is associated with the formation of a plasma region by one pulse in a train of pulses from the mode-locked laser, and the filament results from the formation of successive (nearly identical) regions, each displaced from the previous one toward the laser. The possible use of these sparks as a light source in diagnostics is noted.

Fifteen new, Raman far-infrared (FIR) laser emission lines in CH(3)F have been excited by optically pumping up to 24 GHz off resonance with high-intensity CO(2) TEA laser radiation (up to 20 MW/cm(2)). Most of these new lines are produced with high quantum efficiency in a waveguide laser system. High-intensity laser pumping could also be applied to other gases to produce many new, efficient lines. The present results suggest that a nearly continuously tunable source of FIR radiation in the 175-500-microm range could be obtained through Raman laser emission in CH(3)F using a tunable, multiatmospheric CO(2) pump laser.

Laser emission on the sequence bands of CO2 has been achieved in a TEA amplifier using either a hot-CO 2 cell or a Michelson interferometer to prevent oscillation of the regular bands. It has been found that the insertion losses of the hot-CO2 filter severely limit the energy extraction efficiency on the sequence bands. With the Michelson arrangement, output energies of 140 mJ on the sequence P(17) have been produced in a 33-cm-long TEA amplifier. The relatively low efficiencies obtained suggest that generation of high-intensity laser beams at the sequence band frequencies would require the use of oscillator-amplifier combinations.

Large-scale silicon isotope separation based on the IRMPD of natural Si2F6 has been carried out using a commercially available high power CO2 TEA laser and a flow reaction system. The decomposition product SiF4 containing 19–33% of 30Si was obtained at a production rate of 1.5×10−2−2.6×10−2 mol·h−1, depending on experimental parameters such as laser wavelength, laser fluence, pressure, and flow rate. SiF4 containing 12% of 29Si was obtained under slightly different conditions, i.e., at a shorter wavelength than that for 30Si. When 39% of Si2F6 was decomposed at a slow flow rate, residual Si2F6 was found to have 99.7% of 28Si. The production rate was 4.2×10−2 mol·h−1.