Effect of delay in the operation of helium-free TEA CO2 lasers with sequential and parallel spark preionisers

The operation of a helium-free TEA CO₂ laser is found to depend more sensitively on the delay between the pre and main discharges as against its conventional operation. Results pertaining to the optimum delay and the temporal shape of the emission are presented for the operation of the helium-free laser with both sequential and parallel spark-type preionisers.     

Switch-less operation of a TEA CO2 laser with extended electrodes

We report here the reliable and efficient operation of a mini-TEA CO₂ laser utilizing uniform field electrodes wherein the parallel spark channels of the preioniser, an integral part of the laser, functioned as a switch as well as a source of UV photons. The operation of the laser has been realized up to a maximum energy loading of ∼197 J/l atm under widely varying gas composition including helium lean as well as helium-free gas mixtures. Under most optimized conditions the laser operated with an efficiency of ∼7.1%. The spatially symmetric nature of the emission from the laser in spite of the one sided preionisation points to the effectiveness of the excitation circuit employed here to energise the laser.     

Surface modification of the Cr-based coatings by the pulsed TEA CO2 laser

The interaction of a transversely excited atmospheric (TEA) CO₂ laser with chromium oxynitride (CrON) coating deposited on a AISI 304 steel substrate was considered. The results have shown that CrON was surface-modified by the laser beam of 45 J/cm² energy density. The energy absorbed from the TEA CO₂ laser beam was partially converted into thermal energy, which has generated a series of effects such as melting, vaporization of the molten material, and shock waves in the vapor and in the solid. Morphological manifestations on the CrON coating surface can be summarized as follows: non-uniform features with ablation and appearance of crater-like form (central zone of interaction); appearance of three damaged areas and presence of hydrodynamic effects with resolidified droplets (periphery zone of interaction). In case of applied energy density the interaction of laser radiation with CrON has been always followed by plasma creation in front of the coating. PACS 79.20.Ds; 61.80.Ba     

Synchronisation effects in broadband FIR raman scattering in NH3

By using a short pulse broad band (2 GHz) CO₂ laser around a single well detuned line (15 GHz), it is possible to analyse, with sub-ns resolution, the dynamics of a broadband FIR Raman scattering. When the Raman gain is large, well modulated ns emissions are detected also for resonant lines. Generally the pseudo cavity effects, are always present. They have important effects on the gain, in particular an aligned input window has a large positive effect on the Raman gain and on the generation of mode-locked FIR forward emissions     

Hard tissue ablation with a free running Er:YAG and a Q-switched CO2 laser: a comparative study

The Er:YAG and the CO₂ laser are competitors in the field of hard tissue ablation. The use of Er:YAG lasers (2.94 μm, pulse length _L of 100 to 200 μs) show smaller areas of thermal defects then ‘‘superpulsed’’ CO₂ lasers with pulse lengths of approximately 100 μs. Only the development of a Q-switched CO₂ laser (9.6 μm, τ_L=250 ns) allowed for similar results. In this paper new results for the Er:YAG and the Q-switched CO₂ laser under the influence of water spray will be presented. Several parameters are of special interest for these investigations: the specific ablation energy, which shows a minimum for the CO₂ laser at an energy density of 9 J/cm ² and a broad shallow minimum in the range of 10 to 70 J/cm² for the Er:YAG laser, and comparison of the cut-shape and depth. Surface effects and cutting velocity are discussed based on SEM pictures. Received: 19 July 2000 / Revised version: 1 November 2000 / Published online: 30 November 2000     

Infrared and far-infrared laser emissions from a TE CO2 laser pumped NH3 gas

In this paper, infrared (IR) and far-infrared (FIR) laser emissions from a TE CO₂ laser pumped NH₃ gas are reported. 8 IR laser emissions near the wavelength of 12 μm were observed by using 4 different CO₂ laser lines for the pumping. 3 IR laser emissions in P-branch of vibrational-rotational band (ν₂ → G) oscillated simultaneously in two pumping cases, i.e. pumping with the R(30) or R(16) line of 9.4 μm band from the CO₂ laser. 26 FIR laser emissions (26.45 μm ～ 281.0 μm) were observed by using 12 different CO₂ laser lines, and the 10 FIR emissions of them may be new laser emissions as far as we know.     

A 300 Hz TEA CO<Subscript>2</Subscript> Laser

We present a design and construction of a high pulse repetition rate (PRR) transversely excited atmospheric (TEA) CO₂ laser with ultraviolet preionization. We use a new combination of spark and corona preionizations. Under semi-sealed off condition, we obtained 220 W at 300 Hz with 7.7% efficiency in a 735 mJ/pulse. The best results we have obtained in different experiments are a 1.07 J/pulse, 320 Hz PRR, 11 MW peak power, and 10.6% efficiency.     

The effect of sliding spark,corona and semiconductor pre-ionisers on the operation and output of a tea CO2 laser

Sliding spark array, corona and Ge semiconductor preionisers were compared in a small TEA CO₂ laser by looking at their effect on the output energy of the laser. The corona and semiconductor preionisers provided good pulse-to-pulse repeatability (≈5%) with a clear discharge whilst the spark array was less repeatable (≈12%) and caused a dark deposit to appear on the electrodes. The semiconductor system was the least efficient and the sliding spark the most efficient system, with the corona providing a good compromise between the two. Of the three types tested, the corona preioniser was prefered overall.     

Wavelengths for new CH3OH laser lines

Using a grating-tuned CO₂-TEA laser to pump CH₃OH in a metallic-wave-guide resonator, submillimeter laser emissions have been produced by pumping with 36 lines in the 9.4m CO₂ band and with 23 lines in the 10.6m band. Several dozen new SMM laser lines were observed. Wavelengths accurate to within 0.1% are given for 12 previously unmeasured lines between 34m and 225m.     

Surface modifications of TiN coating by pulsed TEA CO2 and XeCl lasers

Interactions of a transversely excited atmospheric (TEA) CO₂ laser and an excimer XeCl laser, pulse durations ∼2 μs (initial spike FWHM ∼100 ns) and ∼20 ns (FWHM), respectively, with polycrystalline titanium nitride (TiN) coating deposited on high quality steel AISI 316, were studied. Titanium nitride was surface modified by the laser beams, with an energy density of 20.0 J/cm² (TEA CO₂ laser) and 2.4 J/cm² (XeCl laser), respectively. The energy absorbed from the CO₂ laser beam is partially converted to thermal energy, which generates a series of effects such as melting, vaporization of the molten material, shock waves, etc. The energy from the excimer XeCl laser primarily leads to fast and intense target evaporation. The calculated maximum temperatures on the target surface were 3770 and 6300 K for the TEA CO₂ and XeCl lasers, respectively. It is assumed that the TEA CO₂ laser affects the target deeper, for a longer time than the XeCl laser. The effects of the XeCl laser are confined to a localized area, near target surface, within a short time period.Morphological modifications of the titanium nitride surface can be summarized as follows: (i) both lasers produced ablation of the TiN coating in the central zone of the irradiated area and creation of grainy structure with near homogeneous distribution; (ii) a hydrodynamic feature, like resolidified droplets of the material, appeared in the surrounding peripheral zone; (iii) the process of irradiation, in both cases, was accompanied by appearance of plasma in front of the target.Target color modifications upon laser irradiation indicate possible chemical changes, possibly oxidation.     

Dynamics and correlated performance of a photo-triggered discharge-pumped HF laser using SF6 with hydrogen or ethane

3 , has been performed in Ne/SF₆/H₂ and Ne/SF₆/C₂H₆ mixtures. Parameters involved have been the storage line capacitance and the circuit inductance, the capacitors charging voltage, the RH-molecule type and partial pressure, and the X-ray dose for the preionization. High laser performance has been achieved with C₂H₆: an output energy up to 3 J corresponding to a specific energy of 9.6 J/l at an efficiency of 4.7%, which strengthens the advantage of the photo-triggering technique to energize high-power HF lasers. However the optimum performance achieved with H₂, 5.75 J/l and 3.5%, are lower. It is shown, through a time-resolved study of the electrical discharge and spatial dynamics correlated to laser power and energy measurements, that discharge instabilities are responsible for the poor laser performance of the mixture with H₂. These instabilities, which lead to arc development, are characteristics of the discharge in Ne/SF₆. It is demonstrated for the first time that addition of a heavy hydrocarbon, such as C₂H₆, to that mixture induces the discharge stabilization so that the laser emission arises in a homogeneous active medium. This effect allows us to achieve better laser performance than with H₂. Received: 17 March 1998/Revised version: 13 July 1998     

New CW FIR laser lines obtained in ammonia pumped by a CO2 laser, using the Stark tuning method

We report fifty seven CW FIR emissions observed in NH₃, by resonant pumping with a CO₂ laser. Exact coincidences between IR absorption lines of the gas and emission lines of the CO₂ laser have been carried out by Stark tuning. IR frequency shifts, up to 30 GHz, have allowed the pumping of forty three NH₃ transitions.These FIR emissions correspond to thirty one different wavelengths in the 50–400 m range; eighteen ones of them are new emitted wavelengths by pumping with the CO₂ laser.     

Performance study of the KrCl discharge laser with liquid chlorine donors

The effects of liquid chlorine donors (BCl₃ and CCl₄) on the output energy and the efficiency of a KrCl laser (222 nm) are investigated. Maximum laser energies of 230 mJ (3.3 J/l) in pulses of 16 ns duration were obtained from a 0.035% BCl₃/10.1% Kr/89.8% Ne mixture at a total pressure of 2600 Torr, and at a specific power loading of about 24 MW/cm³, a power conversion efficiency of 0.86% was obtained. These figures are reduced by a factor of two when He is used as buffer gas. Much weaker laser emissions were obtained when CCl₄ was used as a chlorine donor.     

Simulation of parametric oscillation in the submillimeter range at pumping of the ZnGeP2 crystal by a train of 100-ps high-power pulses

Analysis is given for a possibility of singly resonant parametric oscillation in the submillimeter range at synchronous pumping of the ZnGeP₂ crystal by a train of 100-ps second-harmonic pulses from the CO₂ laser with the radiation energy 1.0 J. The calculation shows that using the ZnGeP₂ crystal and the second harmonic of the CO₂ laser with the energy density 1.8 J cm⁻², one can get the peak submillimeter radiation power from 3.6 to 12 MW in the range from 95 to 300 μm (1.0–3.3 THz). The expected peak power values are larger than the experimental ones obtained by other nonlinear optics methods.     

Novel long-pulse TE CO2 laser excited by pulser–sustainer discharge

A novel long-pulse TE CO₂ laser with UV-preionization is presented. With an active volume of 1.17 l and gas pressure of 30 kPa, the laser can discharge stably with low pulser energy and high sustainer energy. Various long-pulse discharges such as 12, 20 or 25 μs are demonstrated. At discharge pulse width of 23.9 μs, maximum output laser energy of 6.8 J is obtained at an efficiency of 9.0%.     

A low debris laser plasma soft X-ray source

Low debris laser plasma soft X-ray source is of great importance to micro-lithography and microscopy. In this paper, a 1.06 μm YAG laser with 2 J energy, 10 ns duration is employed to irradiate a CO₂ cryogenic target. Soft X-ray spectra from the CO₂ cryogenic target are obtained. Experimental results of debris measurement from both CO₂ cryogenic and Cu targets demonstrate that the light source based on the CO₂ cryogenic target shows great improvement over conventional metal targets in debris reduction.     

Two color oscillations of TE-CO2 laser and applications to two photon process of optically pumped FIR laser

We have developed the resonance system which is able to operate a TE-CO₂ discharge tube in two color emission source. The two color source is excellent in pumping efficiency, spacial overlap and time synchronization of the two emission CO₂ lines.We indicate that the competitive operation of the two emissions is well explained by a simple model.When a TE-CO₂ laser operates at the total pressure of below half atmospheric pressure, we make clear in this work that the operation of a TE-CO₂ laser forms depression like hole burning, with regards to the J of the upper laser level by J-J collisional relaxation during the laser emission.As an example of the two-photon source, two-photon pumping of NH₃ and FIR emissions are given in this paper.     

Assignment of Fir Laser Lines of Fully Deuterated Dichloromethane

We have recently reported 16 new far-infrared laser emissions of CD₂Cl₂. While the overwhelming majority of the previously known FIR laser emissions of this molecule were polarized parallel to the polarization of the pump CO₂ line, 13 of our 16 new lines are polarized perpendicularly to the exciting CO₂ radiation. In principle, the presence of perpendicular/parallel emission pairs is extremely important for the assignment of laser transitions. In the present work we discuss the possible assignments of 16 far-infrared (FIR) laser emission pairs of CD₂Cl₂.     

Repetitive operation of a helium-free mini TEA CO2 laser

A helium-free mini TEA CO₂ laser has been operated at a repetition rate of 100 Hz wherein the gas re-circulatory loop consisting of heat exchanger and catalytic converter, mandatory for conventional repetitive operation of such lasers, have been totally dispensed with. The laser utilized inexpensive molecular gases alone that were simply flown out transversely through the inter-electrode region by an open gas flow system. The active medium was energized by making use of a spiker-sustainer excitation scheme. At this repetition rate, the laser produced an average power of 3.50 W.