Self-focussing of CO2 laser radiation in SF6

Self-focussing of high-power TEA CO₂ laser pulses for a number of 10 m P-band lines is reported in SF₆ molecular gas. Application of this effect to estimating the intensity-dependent refractive index of the gas is demonstrated.     

Six-Watt mid-infrared laser using harmonic generation with Tl3AsSe3

An output of 6 W at 30 kHz was achieved using Tl₃AsSe₃ as the nonlinear second-harmonic generator. It was pumped with a CO₂ laser source at a wavelength of 9.25 m with 20 ns pulses, and the laser beam was focussed to a spot size of 150 m. The focussed spot was scanned to reduce the continuous-wave power loading, and the system could be operated for extended periods of time under these conditions.     

New FIR laser lines from CD3OD optically pumped by a CO2 waveguide laser

In this work we report new FIR laser lines from CD₃OD optically pumped by a CO₂ waveguide laser. The wide tunability of this laser (290 MHz) makes it possible to pump absorption lines with large frequency offset relative to the CO₂ laser line center, which are not possible by using conventional CO₂ lasers. As a consequence 19 new laser lines have been discovered, ranging from 38.0 m to 455.2 m in wavelength. For all lines, precise frequency offset measurements between the CO₂ line center and the center of the absorber CD₃OD line were performed using the transferred Lamb-dip technique. We also present direct Doppler-free offset measurements of infrared absorption, obtained within the FIR laser cavity itself, using optoacoustic detection.Work supported by FAPESP, CNPq, FAP-Brasil and CNR-Italy     

Study of a carbon dioxide ring laser gyroscope

We have experimentally investigated a basic ring laser gyroscope (RLG) with carbon dioxide gain, and studied the prospects of developing a practical CO₂ RLG. Rotation sensing was demonstrated on a number of transitions in the 9.4 m and 10.4 m vibration-rotation bands. Gyro response is discussed with regard to lock-in, bias, homogeneous broadening effects, and high power operation. We show that such a system may offer important advantages over standard helium-neon RLGs, including reduced quantum limit and backscattering. The prospects and possible approaches for developing a practical high power CO₂ RLG are discussed, and a method of eliminating cross-saturation at high pressure is proposed and analyzed.     

Multiple harmonic conversion of pulsed CO2 laser radiation in Tl3AsSe3

The nonlinear material Tl₃AsSe₃ is used to convert pulsed 9.6 m CO₂ laser radiation into its second, third, fourth and fifth harmonic. Internal (external) conversion efficiencies of 28, 14(6.7), 3.6(3.1), and 0.5(0.3)% from the pump fundamental are achieved in 4.8, 3.2, 2.4, and 1.9 m generation respectively.     

Detailed vibrational population distributions in a CO2 laser discharge as measured with a tunable diode laser

A tunable diode laser (TDL) operating in the 2150–2350 cm^–1 wavenumber region is used to probe a conventional cw CO₂ laser discharge. Absorption lines in more than 25 different vibrational bands are observed, enabling us to determine absolute vibrational populations inall levels of concern to the dynamics of the 10 m CO₂ laser. Levels in thev ₃ mode of CO₂ as high as 00°9 are monitored, and it is found that anharmonic effects play a significant role in the populations of such levels. Thev ₁ andv ₂ mode populations are also investigated in detail, and it is found that these modes are strongly coupled and maintain a common vibrational temperature under all discharge conditions. The use of a TDL is shown to be a powerful technique for investigating the dynamics of infrared molecular lasers.This work was supported in part by the National Science and Engineering Research Council, Canada     

Compact, high power FIR NH3 laser pumped in a three mirror CO2 laser cavity

A compact CO₂–NH₃ FIR laser system where an NH₃ laser cavity was inserted in pump, three mirror CO₂ laser cavity was designed. The total length of this system was about 1.8 m. Output energy of about 1 mJ (10 KW pea power) was obtained at the 152 m and 90 m lines in NH₃. Power conversion efficiency of 1.7 percent was obtained at the 90 m line.     

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.     

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.     

Dynamics of the CO2 lower laser levels as measured with a tunable diode laser

A tunable diode laser operating in the 4.3 m region is used to probe a conventional cw CO₂ laser discharge. Vibrational populations in the 10⁰0, 02⁰0, 02²0, and 01¹0 levels of CO₂ are measured under lasing conditions, i.e., in the presence of intense 10.4 and 9.4 m fields. The tunable diode laser is also used to monitor the energy transfer processes between the four levels after the passage of an intense 10.4 m pulse. The detailed information provided by the tunable probe laser enables us to determineseparately all the vibration-vibration (V-V) and vibration-translation (V-T) rate constants of importance in the relaxation of the lower laser levels in CO₂. The V-V rate constants are found to vary from a low value of 4.5×10⁴ s^–1 Torr^–1 for the coupling of 01¹0 to 10⁰0 to a high value of 8.0×10⁵ s^–1 Torr^–1 for the coupling of 01¹0 to 02²0.This work was supported by the National Science and Engineering Research Council of Canada and the Provincial Government of Ontario     

Infrared laser stark shift spectroscopy in ammonia

The Stark effect in ammonia has been theoretically and experimentally analyzed using lead salt tunable diode laser absorption spectroscopy and CO₂ laser absorption spectroscopy of several absorption lines around 1050 cm^–1 applied to an all-optical sensor for measuring of electric field strength. Measurements of the Stark splitting effect of theaR(5,K) ammonia lines forK=1–5 as well as for the sR(3,K) lines forK=0–3 have been made at Doppler broadening pressures and for several different electric field strengths. Theoretical electric field dependent energy levels have been evaluated by diagonalization of a 6×6 energy matrix constructed using both electric field independent and dependent terms. From the theoretical analysis the resolution can be predicted and optimized both in the Doppler broadened and in the pressure broadened regimes. The predicted resolution is 0.5% at an electric field strength of 20 kV/cm. The theoretical calculations and the experimental data recorded with the tunable diode laser system were compared with independent measurements made with a CO₂ laser system. The agreement between experimentally recorded and theoretically calculated spectra is good which indicates that the theoretical model is satisfactory for our purposes. The contribution from the normally forbidden ssR(5, 3) ammonia line to the absorption at theP(12) CO₂ laser line in the 9 m band is briefly discussed.     

Observations on the spectral dependence andT/D isotope selectivity in the CO2 laser multiple-photon dissociation of trifluoromethane

Pulsed CO₂ laser multiple-photon dissociation of CTF₃ (v ₂ mode) bathed in argon and CDF₃, CHF₃ or CCl₄ is examined as a function of laser wavelength (9.2–9.6 m) and fluence. The dependence of the dissociation profile on wavelength is analyzed and comparisons are made to prior work. The single-stepT/D enrichment factor for infrared photolysis of trifluoromethane is measured; potential practical isotope separation is discussed. Pulsed infrared laser photolysis of CTF₃ (v ₅ mode) using a 12 m NH₃ laser is also attempted.     

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.     

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.     

A new efficient far-infrared optically pumped laser gas: CH3 18OH

The¹²CH₃ ¹⁸OH molecule has been investigated for new far-infrared laser lines by optically pumping it with a cw waveguide CO₂ laser. The larger tunability (318 MHz) with respect to a conventional CO₂ laser permits the pumping of many¹²CH₃ ¹⁸OH lines. As a consequence 100 new laser lines have been discovered, ranging from 34.6 m to 653.2 m in wavelength. The infrared spectrum of¹²CH₃ ¹⁸OH has been observed and all the fundamental vibration energies measured.     

Optoacoustic Laser Stark spectroscopy and FIR laser action on CH3Br using a waveguide CO2 laser

The optoacoustic spectrum of CH₃Br around 10 m band lines of a tunable cw waveguide CO₂ laser is investigated. Several new infrared absorptions are observed and most of the correspond ing molecular transitions are assigned. Far infra red laser action is reported by pumping with the same CO₂ laser: pump offsets are given using the Transferred Lambs dip (TLD) technique. A new FIR laser emission is obtained and assigned. An optoacoustic Laser Stark spectroscopy technique is used to investigate off resonance infrared tran sitions.     

New far infrared laser lines from 13CH2F2 and frequency measurements

We report new FIR laser lines from ¹³CH₂F₂ molecules optically pumped by a waveguide CO₂ laser. The increased tunability (300 MHz) with respect to a conventional CO₂ laser allows the pumping of ¹³CH₂F₂ vibrational transitions of large offset. 34 new laser lines have been discovered, ranging from 113.1 m to 491.4 m in wavelength, thus increasing the number of known FIR laser lines from this important molecule to 99. For all the new lines and many (36) of those known previously, precise offset measurements through the transferred Lamb-dip technique were performed. The frequency of six new laser lines was also directly measured by heterodyne detection with known laser lines.     

Dopant-induced excimer laser ablation of poly(tetrafluoroethylene)

Clean ablation of poly(tetrafluoroethylene) (PTFE) at etch rates in excess of 7µm/pulse has been achieved with an excimer laser using 308nm radiation and a 25 ns pulse width. This was accomplished by doping the ultraviolet-transparent PTFE polymer with polyimide. Ablation rates were investigated as a function of fluence in the range from 1 to 12J/cm² and dopant levels up to 15% (wt/wt). Results show that at a given fluence there exists an optimum absorption coefficient _max, for which maximum ablation rates are achieved. The value of _max was found to decrease with increasing fluence. The relationship between _max and fluence was determined from existing ablation rate models and found to compare favorably with empirical results.     

Bone-ablation mechanism using CO2 lasers of different pulse duration and wavelength

Bone ablation using different pulse parameters and four emission lines of 9.3, 9.6, 10.3, and 10.6 m 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 s and a long pulse of 250 s. 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 m 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 m is lower than at 10.3 and 10.6 m. 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.     

New cw fir laser emissions from CO2 laser-pumped vinyl bromide

47 new cw far-infrared laser lines with wavelenths between 453 and 2356 m have been obtained by optically pumping vinyl bromide (C₂H₃Br) by a CO₂ laser. A significant portion of these lines has wavelengths longer than 750 m.