Efficient ablation of organic polymers polyether sulphone and polyether ether ketone by a TEA CO2 laser with high perforation ability

Organic polymer (PES: PolyEther Sulphone and PEEK: PolyEther Ether Ketone) ablation with oscillation-line selected TEA CO₂ lasers is successfully demonstrated. With different irradiation conditions the ablative etch-rate slopes were varied, which means that the ablation process is dependent on the ablation conditions such as incident laser intensity and ambient gas. In perforation processing of the PEEK film, the TEA CO₂ laser had a higher etch rate of 42 m/pulse at a fluence of 70 J/cm² in vacuum than the XeCl laser.     

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.     

Fine frequency tuning of high power TEA CO2 lasers

A new technique is proposed to fine tune a TEA CO₂ laser within the bandwidth of a single ro-vibrational emission line. A tuning range of ±2 GHz off line center is obtained with an emission bandwidth of about 250 MHz and with a total energy output exceeding 1 joule at line center for the P20 (00°1–10°0) line. This technique can be used for single longitudinal mode operation and has the advantage of being directly scalable to higher power lasers.     

13C-separation by a continuous discharge CO2 laser q-switched at 10 kHz

Compared to atmospheric pressure pulsed CO₂ (TEA) lasers, continuous-discharge CO₂ lasers can deliver photons at much lower costs. By a Q-switched version of such a laser we demonstrated by multiphoton dissociation of CHClF₂ the production of 1 g of C₂F₄ enriched to 50% ¹³C. This is a larger quantity of high enrichment than has been produced so far using TEA lasers. The process is already automated to a large extent. Scaling up seems feasible. These results have been achieved, although the process turned out to be much more nonlinear for our pulses (length 200 ns) than for TEA laser pulses. This difference is attributed to intensity effects, caused by direct multiphoton transitions in the excitation ladder. To avoid that selectivity breaks down, the gas has to be exchanged more than once per pulse. The required speed is much less, if ~250 mbar of Ar are added to the working gas.     

Studies of a TEA CO2 laser with a cylindrical mirror unstable resonator

We describe the results of a study of a TEA CO₂ laser using a strip cylindrical unstable resonator which produces an output beam with suitable characteristics for producing a high quality line focus. Using this technique an irradiance of ?10⁹W cm^-2 over a 5 cm long line focus has been achieved.     

Heterodyne frequency measurements on N2O between 1257 and 1340 cm−1

Frequency measurements are given for the 00⁰1-00⁰0 and 01¹1-01¹0 bands of N₂O from 1257 to 1340 cm^?1. The measurements utilize heterodyne techniques by measuring small frequency differences between a tunable diode laser locked to the center of an N₂O absorption line and harmonic combinations of frequencies of radiation from two CO₂ Lamb-dip-stabilized lasers. The measurements are facilitated by the use of the CO laser as a transfer laser whose frequency is also measured. These measurements have been combined with other data to provide new band constants and frequency calibration tables for several band systems of N₂O in the following regions; 1215 to 1340, 1816 to 1930, and 2135 to 2268 cm^?1. A correction factor is also provided for existing calibration tables near 590 cm^?1.     

Tea CO2 laser beam absorption in polyethylene

The absorption coefficient of polyethylene sheets has been measured for two wavelengths (0.6328 μm, He-Ne laser; 10.6 μm, CO₂ laser). For TEA CO₂ laser power densities up to 10⁴ W cm⁻², the absorption coefficient was found to be 35.36 cm⁻¹. The measured absorption coefficient shows that polyethylene sheets are good and simple attenuators for CO₂ laser radiation.     

Space discharge and gas lasers

The main processes in TE lasers are analyzed. Significant attention is given to models for the formation of a homogeneous plasma column and space charge. The reasons for channel growth at the stage of increasing voltage are demonstrated. A method to increase the energy input to the gas using a cathode with high emission properties is proposed. It is demonstrated that, in TEA CO₂ lasers, the limiting deposited and radiated energy densities may amount to 1.35 and 0.085 J/cm³, respectively. Experimental results show that the duration of radiation can be increased using a variation in the composition and pressure of the active medium, the sectionalization of the active medium and the sequential excitation of the sections, and the excitation of the medium with a pulse train at a small (about 10⁷ s) pulse duration and an interpulse interval of about 10⁻⁵ s. Original Text ? Astro, Ltd., 2006.     

Electromagnetically induced transparency in a molecular gas

The dynamic Stark effect on the as Q(5,4) transition of the 0 → 1 vibrational band of the ν₂ mode of ammonia ¹⁵NH₃ was studied by the method of copropagating waves of radiation of two ¹³CO₂ lasers operating at the R(18)_I line. For waves with mutually orthogonal polarizations, which propagated in a waveguide cell, the intensity of the saturating radiation reached 225 W/cm², and the absorption line of the probing radiation had the form of a two-hump curve with a splitting that was consistent with the Rabi frequency for the ammonia transition being investigated. At the maximum intensity of the saturating radiation, complete transparency was observed at the center of the absorption line of ¹⁵NH₃. When identically polarized saturating and probing waves propagating in a cell at a small angle with respect to each other were used, the splitting was more weakly manifested. The effect of a spatial inhomogeneity of the optical fields on the shape of the line of saturated absorption is discussed.     

High-order stokes emission from a pulsed spin-flip raman laser at 5 μm

Pulsed spin-flip Raman laser action, up to 3rd Stokes, at 5.3 μm has been observed in n-type InSb using the harmonically doubled output from a compact 50 cm long TEA CO₂ laser as the pump. In addition magnetic field thresholds as low as 350 G have been used for first Stokes output. Spin-flip radiation line widths of 0.02 cm^-1 (full width at half height) were obtained.     

Studies of vibrational relaxation in CDF3 following intense laser excitation

The V-T/R relaxation time of CDF₃ was measured studying the laser-induced infrared fluorescence emitted by vibrationally excited CDF₃. Following excitation by the 10R(12) line of a TEA CO₂ laser infrared fluorescence has been detected without spectral resolution in the 1100–700 cm^–1 range. A decay rate of 28.8 ms^–1 Torr^–1 was obtained for pure CDF₃ when it is excited with a fluence of 390 mJ/cm². Measurements have also been made in the presence of different bath gases (He, Ne, Ar, Xe, and CHF₃).     

Rapidly tuning miniature TEA CO2 laser – rotating mirror and grating mechanism

In this research, directed toward using differential absorption lidar (DIAL) for measuring concentrations of pollutant gases, a device for rapidly tuning a transversely excited atmospheric-pressure (TEA) CO₂ laser is presented. It is shown that it is possible to utilize a rotating six-sided scanning mirror and a fixed diffraction grating to rapidly switch wavelength over randomly selected lasing transitions in the 9–11 μm region of the spectrum. The scanning mirror and an optical encoder are driven by a hysteresis synchronous motor at a speed of 1500 rpm. A surface-wire-corona preionization was utilized in a cavity. The laser system is highly automated with microprocessor-controlled laser line selection. Single-branch emission at two wavelengths with time interval ⩽10 ms has been obtained from a single cavity TEA CO₂ laser. An accurate line selection has been demonstrated in over 40 transitions at a pulse repetition frequency of up to 100 Hz. The laser energy at first-order couple output was up to 20 mJ per pulse and the pulse width is about 60 ns in an active volume of 36 cm³.     

Laser isotope separation of carbon by multiple IR photon and subsequent UV excitation of CF3I molecules

A new approach to laser isotope separation is considered. It is based on collisionless multiple photon ir laser excitation and subsequent uv laser dissociation of vibrationally excited molecules. TEA CO₂ and excimer XeF, XeCl lasers are used for ir excitation and uv dissociation, respectively. The products of photolysis (C₂F₆) are enriched with¹²C.     

Performance characteristics of a TEM00 mode TEA CO2 oscillator-amplifier system

The performances of a TEA CO₂ oscillator-amplifier system consisting of a helical laser and a one-meter Lamberton-Pearson-type double-discharge laser are reported. Time and spatial profiles for the input and output of the amplifier have been studied. A small-signal gain coefficient of 0.031 cm^-1 and a saturation energy of 0.35 J/cm² are measured for a pulse of 100 nsec duration with a low-power tail of 1 μsec.     

Optically pumped 15.90 μm SF6 laser

Optically pumped vibrational transition lasing has been achieved for the first time in a nonlinear molecule. Laser radiation at 628.74 ± 0.02 cm^?1 was generated from SF₆ using CO₂ TEA laser excitation. The SF₆ pumping is shown to be via absorption of two photons.     

A miniature tunable TEA CO<Subscript>2</Subscript> laser using isotope <Superscript>13</Superscript>C<Superscript>16</Superscript>O<Subscript>2</Subscript> and <Superscript>12</Superscript>C<Superscript>16</Superscript>O<Subscript>2</Subscript>

A miniature tunable TEA CO₂ laser using isotope ¹³C¹⁶O₂ as the active medium is developed to extend the spectral range of CO₂ lasers for further application. The optimization of the energy parameters of the tunable TEA ¹³C¹⁶O₂ laser and the same laser using ¹²C¹⁶O₂ are studied. When a gas mixture (¹³C¹⁶O₂: N₂: He = 1: 1: 3) at a total pressure of 6.4 × 10⁴ Pa is used, the TEA ¹³C¹⁶O₂ laser of a 45-cm³ active volume obtains 51 emission lines in the [00⁰1–10⁰0] and [00⁰1–02⁰0] bands. The maximum pulse energy of the TEA ¹³C¹⁶O₂ laser is about 357 mJ. The same laser using the conventional gas mixture (¹²C¹⁶O₂: N₂: He = 1: 1: 3) at a pressure of 6.66 × 10⁴ Pa is measured to obtain 69 laser emission lines and the maximum pulse energy of laser radiation is about 409 mJ.     

High resolution polarization spectroscopy and laser induced fluorescence of CO<Subscript>2</Subscript> around 2μm

High resolution Infrared Polarisation Spectroscopy (IRPS) and Infrared Laser Induced Fluorescence (IRLIF) techniques were used to probe CO₂/N₂ binary gas mixture at atmospheric pressure and ambient temperature. The probed CO₂ molecules were prepared by laser excitation to an overtone and combination ro-vibrational state (12⁰1, J=15) of CO₂, centred at 4988.6612 cm^-1. IRPS and IRLIF line profiles were recorded for several CO₂/N₂ binary mixtures. The observed IRLIF line shapes have the expected Lorentzian form while the observed IRPS line shapes are narrower by a factor of two than those recorded with the IRLIF and appear to have a Lorentzian-cubed profile. The recorded line profiles provide measurements of the pressure-broadening coefficient directly at atmospheric pressure. The Full-Width-Half-Maxima (FWHM) pressure broadening coefficients are measured, based on IRLIF, to be 0.2174±0.0092 cm^-1atm^-1 and 0.1327 ±0.0077 cm^-1atm^-1 for self- and N₂ collision broadening, respectively. The broadening coefficients obtained based on IRPS were measured to be ~8% larger than those obtained with IRLIF.     

Multi-harmonic measurements of line shape under low absorption conditions

We propose a method that employs the ratios of the 2nd and 4th harmonics at the line center to measure line shape under low absorption conditions. To verify this method, the transition of CO₂ at 6,982.0678 cm^?1 is selected to measure line shape by using the proposed method and direct absorption spectroscopy in laboratory conditions. The results from both methods have a high degree of consistency. This satisfactory agreement indicates the validity of the proposed method.     

Coherent tunable far infrared radiation

Tunable, cw, far infrared (FIR) radiation has been generated by nonlinear mixing of radiation from two CO₂ lasers in a metal-insulator-metal, (MIM) diode. The FIR difference-frequency power was radiated from the MIM diode antenna to a calibrated indium antimonide bolometer. Two-tenths of a microwatt of FIR power was generated by 250 mW from each of the CO₂ lasers. Using the combination of lines from a waveguide CO₂ laser, with its larger tuning range, with lines from CO₂, N₂O, and CO₂ isotope lasers promises complete coverage of the entire far infrared band from 100 to 5000 GHz (3–200 cm^–1) with stepwise-tunable cw radiation.Contribution of the National Bureau of Standards, not subject to copyright     

TEA CO2 laser ablation of coronary artery

Summary One of the prerequisites for successful laser angioplasty is the ablation of the atherosclerotic lesions, without thermal or shock-wave damage of the healthy tissue. In this study was evaluated the effectiveness of a TEA CO₂ laser, emitting pulses of the lower TEM mode, 100 ns duration, at a repetition rate of 2.4 Hz, for the ablation of cardiovascular tissue. Normal and atherosclerotic human arteries (post mortem) were irradiated for a range of fluences up to 10J pulse⁻¹ cm⁻². After irradiation, the samples were prepared for histologic examination. The results showed that controlled ablation of normal and atherosclerotic coronary artery can be accomplished with the TEA CO₂ laser, with minimal thermal damage.