Formation of a periodic wave structure on the dry surface of a solid by TEA-CO2-laser pulses

The formation of periodic wave patterns on surfaces of insulators and metals by means of TEA-CO₂-laser pulses was observed. The wavelength of the patterns equals that of the laser radiation. The phenomenon is illustrated by samples of quartz glass and copper.     

Formation of a periodic wave structure on the dry surface of a solid by TEA-CO2-laser pulses

The formation of periodic wave patterns on surfaces of insulators and metals by means of TEA-CO₂-laser pulses was observed. The wavelength of the patterns equals that of the laser radiation. The phenomenon is illustrated by samples of quartz glass and copper.     

Study of the compounds formed on damaged ZnSe windows by multi-pulse microsecond pulsed TEA-CO2 laser irradiation in air

We report on experimental data of chemical compounds formed in the damaged area at the surface of certain optical ZnSe windows subjected to multi-pulse microsecond pulsed TEA-CO₂ laser irradiation in air. The results are analysed from the viewpoint of implication of the oxidation process activated under the action of CO₂-laser power in plasma initiation and evolution of surface damage process.     

Side on interferometry at 10.6 μm of Theta pinch plasmas

An experiment for measuring electron density spatially resolved with high time resolution is described. The experiment was performed side on on a Theta pinch plasma. The light source (TEA-CO₂ laser), the window problem, the area detector for the interferogram are discussed. The sensitivity of the technique is 1–2×10¹⁵ electrons/cm². Some examples of measured density profiles show that the method may be used effectively on toroidal plasma machines.     

Spectroscopic observation of the plasma produced by a CO2 laser beam interacting with titanium target under helium and/or argon atmosphere

In many laser applications such as drilling, welding and cutting, the role of the plasma in the transfer of energy between the laser beam and the metal surface appears to be rather important. It depends on several parameters such as laser wavelength, irradiation time and deposited energy but especially on the buffer gas nature. In this work the plasma is initiated by a TEA-CO₂ laser beam perpendicularly focussed onto a Ti target (100 MW/cm²), in a cell containing He, Ar or a He-Ar mixture as buffer gas. The plasma is studied by time and space resolved spectroscopic diagnostics. The results show that helium allows target erosion whereas a highly absorbing breakdown plasma develops in argon shielding the target from the subsequent laser heating. With only 20% Ar in He, a strong quenching of the He plasma by Ar occurs, and the Ar plasma effect is dominant.     

Fir laser emissions from population inversion transition by TEA-CO2 laser pumping

In this paper, the numerical analysis is given which is applicable for a TEA-CO₂ laser pumping in search of effective pumping method.The analysis also can estimate the optimum pressure for a given molecule and a given pulse laser.Also we report in this work many FIR laser emissions from population inversion transition which have never observed before using a TEA-CO₂ laser.     

Optical free induction decay (OFID) 10 μm co2 laser systems

This paper describes new unproved and reliable optical free induction decay (OFID) picosecond-pulse CO₂-10 μm laser systems, differing mainly in the pump laser and in the peak power of the generated pulses. In this context a single-mode TEA-CO₂-10 μm laser preionized by a novel surfacecorona discharge was developed. Our improved plasma shutters operate as optical switches at variable gas pressures. They are triggered either by a laser-produced surface plasma or by an electrical high voltage discharge. With respect to the first trigger scheme we found new target materials for the surface plasma generation, i.e. metallized graphites. In the second scheme the electrical discharge is initiated by the TEA-laser pulse via a new laser-triggered spark gap. Single-mode TEA-CO₂-10 μm laser, plasma shutter plus a spectral filter form the OFID laser system, which generates the picosecond pulses. An electronic control completes the system as reliable working tool. Each of the OFID laser systems developed is capable to produce 10 μm pulses with a duration of 30–300 ps.Numerical calculations are performed to estimate the influence of various parameters on pulse shape and duration. Since a direct measurement of the time variation of the short pulses by fast IR detectors is not possible, we measure the picosecond pulses by means of an optical autocorrelation method with optical second harmonic generation. For the first time this is performed with polycrystalline material, e.g. GaAs or ZnSe, instead of a single crystal, e.g. GaAs or Te.     

EUV radiation characteristics of a CO2 laser produced Xe plasma

A CO₂ laser-driven Xe liquid jet plasma has been studied with respect to its usability as a EUV lithography light source. A short-pulse TEA-CO₂ master oscillator power amplifier system (MOPA) and a pre-pulse Nd:YAG laser were used for the plasma generation. The dependence of EUV plasma parameters, e.g., conversion efficiency, plasma image, in-band and out-of-band spectra, on the delay time between the pre-pulse and the main pulse laser was investigated. A maximum conversion efficiency of 0.6% was obtained at a delay time of about 200 ns. In addition, characteristics of fast ions were measured by the time-of-flight method. The peak energy of the fast ion energy distribution decreased significantly at delay times longer than 200 ns. This result is very promising with respect to a collector mirror lifetime extension by magnetic field mitigation. PACS 52.50.Jm     

Fracture mechanisms of Hg0.8Cd0.2Te induced by pulsed TEA-CO2 laser

The fracture mechanisms of Hg_0.8Cd_0.2Te induced by pulsed TEA-CO₂ laser have been investigated theoretically and experimentally in this paper. The Hg_0.8Cd_0.2Te target was irradiated by a TEA-CO₂ laser with wavelength of 10.6 μm and spike width of 240 ns in an ambient atmosphere. The evident cracks can be found on the surface of the target from the scanning electron microscopy (SEM) photos, indicating that the severe breaks happened during the experiment. Theoretical analysis has also been carried out and the results show that the fracture of Hg_0.8Cd_0.2Te is mainly induced by thermal stresses, although there are three forces (thermal stress, evaporation wave and laser-supported detonation (LSD) wave) exerted on the target surface during the process.     

Injection mode-locking of a 200 joule TEA-CO2 laser

A 200 joule TEA-CO₂ laser has been mode-locked by injection of a nanosecond pulse into a regenerative amplifier operating in an above threshold regime. 25 gigawatt pulses have been obtained.     

Study on the Spectrum of Miniature Optically Pumped NH3 Submillimeter-Wave Laser

By means of an iteration method and taking into account the broadening of the infrared pumping laser, the spectrum of a miniature, optically pumped, superradiant NH₃ submillimeter-wave(SMMW) gas laser pumped by CO₂-10R(8) has been calculated and studied by solving density matrix equations. Experimentally, the interferogram of miniature SMMW laser pumped by a TEA-CO₂ laser with 10R(8) line is measured. This is the first time that the theoretical spectrum has been in good agreement with experimental results.     

Effect of acoustic waves on the repetition frequency of high repetition rate TEA-CO2 lasers and calculating optimization condition

The gas channel of a pulse periodic TEA-CO₂ laser is considered as an acoustic resonator. In this paper, a three-dimensional mathematical modeling has been considered for describe of laser action. By calculating of the equations obtained from this model, the effects of cavity dimensions, Mach number and repetition frequency of laser on the acoustic wave spectrum have been investigated. At last optimum conditions for performance of laser operation has been arrived.     

Electron-microscopy investigations of the damage of aluminium mirrors as a result of repeated powerful microsecond pulsed TEA-CO2 laser irradiation in air

Progressive damage of aluminium mirrors subjected to microsecond pulsed TEA-CO₂ laser irradiation in air, at incident intensity levels lower than the thresholds for melting induction and air breakdown ignition, was evidenced by electron microscopy investigations. A simple model was developed accounting for the results of our experimental studies.     

Selectivity enhancement in tritium isotope separation by multiple frequency multiple photon dissociation of the CTF3/CHF3 System

Isotope separation of tritium by multiple photon dissociation process in multiple frequency fields of a TEA-CO₂ laser is reported for the first time. A ten-fold improvement in the bulk selectivity was obtained in 8.5 Torr CTF₃/CHF₃ in the presence of buffer gas at room temperature using 9R(8) to 9R(14) CO₂ laser lines compared to single frequency excitation. Investigations of various process parameters such as exciting laser frequencies, pulse energy, sample and buffer gas pressure indicate that this is a promising technique for the separation of tritium.     

Operating parameter optimization of optically pumped CH3OH far-infrared laser

By solving the density matrix equations of a quantum system, the output power intensity of an optically pumped CH₃OH FIR laser (CH₃OH-OPFIRL) was calculated by means of iteration method, and the spectral characteristics were got. Base on the calculation, optimization of operating parameters including operating gas pressure, pumped power and output coupling coefficient of the CH₃OH cavity laser were systematically studied. Experimental, a series of FIR emissions of the CH₃OH cavity laser pumped by TEA-CO₂ laser with 9P(16) line were measured. The experimental results were in good agreement with theoretical calculations. The project was supported by the Special Research Foundation of Doctorate Station in University of P.R.C.     

Experimental study on miniature pulsed CH3OH far-infrared laser

Using a grating tuned TEA-CO₂ laser with 9P(16) line to pump a 10cm or 20cm long miniature Fabry-Perot cavity CH₃OH laser, pulsed far infrared(FIR) lines of 570.6um and 918um wavelengths were observed, the latter is a new line. Operation performance and spectral characteristics of the miniature CH₃OH laser were studied. The project was supported by the Special Research Foundation of Doctorate Station in University of P.R.C.     

The tuning characteristics of optically pumped fir cavity laser

Based on the quantum mechanics theory of density matrix and the principle of multiple-beam interference, the tuning characteristics of optically pumped NH₃ FIR lasers were studied. A series of metallic mesh Fabry-Perot cavity lasers with sample tubes of 10cm, 20cm and 100cm in length were constructed and operated successfully, and the FIR laser spectra of the NH₃ cavity lasers pumped by a TEA-CO₂ laser were measured. Supported by the Natural Sciences Foundation of Guangdong Province, PRC     

Effect of rotational relaxation on the yield of the multiphoton dissociation of CF3Cl and CF3Br under TEA-CO2 laser pulses

The yield of the multiphoton dissociation of CF₃Cl and CF₃Br induced by TEA-CO₂ laser pulses has been studied in the pressure range between 0.25 and 8 Torr, the laser wavelength being chosen so as to excite preferentially the minor isotopic components¹³CF₃Cl and¹³CF₃Br. For both compounds the dissociation probability is found either to increase almost linearly or to decrease monotonously with gas pressure, according as the laser beam is focused or unfocused, respectively. This behaviour is explained by rotational relaxation effects, and a value of 22ns·Torr for the rotational self-relaxation time of CF₃Cl is obtained.     

Longitudinal mode rejection in TEA-CO2 oscillators

A short-cavity single-longitudinal-mode mini TEA-CO₂ laser is described and an experimental study of the effect of cavity length tuning on the mode intensity rejection is presented. A simple model based on longitudinal mode competition adequately explains the observations.     

Direct observation of the differences between Raman scatering and population inversion transition for their emission frequencies and pulse waveforms

In FIR laser emissions optically by a CO₂ laser, it has been reported that there are two different process namely induced Raman scattering and population inversion transition.In this paper, we show that the two different process have clearly different characteristics in emission frequensies and pulse waveforms in the case of a TEA-CO₂ laser excitation.We used in this work an intra-cavity etalon for the study of the emission frequensies and also we used a MOM point contact diode for the detection of the wavaformes.Especially, we show that the FIR pulse waveformes are able to analyze numerically on the concept of rate equations.In conclusion, we indicate that molecules would be classified into two categories with regard to optically pumping by a TEA-CO₂ laser. One of them produce mainly Raman scattered emissions, and other produce only the FIR emissions from population inversion transition in spite of high power intensity excitation.