Tunable CO2 Research Articles

Study of crystals in medium-and long-wavelength IR ranges by surface-electromagnetic-wave spectroscopy

First observation of excitation of surface electromagnetic waves (SEW) is reported in the reststrahlen region in for biaxial crystal KTiOPO4 (KTP) using a tunable CO2 laser around 10 µm, and for CaF2, BaF2, MgO (cubic crystals), and LiNbO3 (uniaxial crystal) in the far IR using ith a free-electron laser. The parameters of SEW propagation in these crystals have been obtained by the interference method of SEW phase spectroscopy, and the possibility of determining the complex dielectric permittivity of crystals from the SEW propagation parameters demonstrated in the range of SEW existence.

Analysis of isotopic CO_2 mixtures by laser photoacoustic spectroscopy

Photoacoustic spectroscopic studies on a mixture of six CO(2) isotopes ((12) C(16) O(2), (12) C(18) O(2), (13) C (16) O(2), (13) C(18) O(2), (16) O(12) C(18) O, and (16) O(13) C(18) O) in the wavelength range of 9-11 mum by use of a home-built high-pressure continuously tunable CO(2) laser with a bandwidth of 0.017 cm(-1) are discussed. The concentrations of all CO(2) isotopes present in the mixture could be determined with good accuracy. Furthermore, the previously unknown absorption cross sections of some important lines of the(12) C(18) O(2), (13) C(18) O(2), and (16)O (13) C(18) O isotopes in the 9-11-mum range are reported.

Simplified tunable single-sideband CO<sub>2</sub> laser spectrometer: absorption measurements of ozone

There is a major interest in monitoring the fate of the earth’s ozone layer. A heterodyne spectrometer for the remote sensing of the vertical, integrated stratospheric ozone number density profile has been developed. A local oscillator ~LO! based on the tunable single-sideband CO2 laser with an external modulator capable of providing a sideband tuning range of 68 to 18 GHz on either side of the laser carrier.

Visible luminescence study of the infrared multiphoton dissociation of 2-chloroethenylsilane

The infrared multiphoton dissociation of 2-chloroethenylsilane induced by a tunable CO 2 laser, under both collision-free and collisional conditions, results in an intense visible luminescence. Spectral analysis of this emission was carried out, and a broad, structureless band, centered at about 650 nm, was obtained. The intensity of this luminescence was studied in relation to multiphoton dissociation as a function of the gas pressure and the frequency and fluence of the laser beam. Lifetime measurements of the luminescence were performed for different pressures of the parent molecule, and the radiative decay time was found to be 480 ± 20 ns. The quenching rate of this emission by homogeneou collisions is (1.44 ± 0.08) × 10 −10cm 3 molecule −1 s −1. The luminescence was assigned to decay from the if 1B 1 electronic state to the 1 B 1 ground state of silylene formed within the laser pulse. The detection of silylene supports the previously postulated reaction pathways in the infrared multiphoton dissociation of 2-chloroethenylsilane. It also suggests that, at high fluence conditions, the chloroethane elimination channel dominates the dissociation reaction.

Pulsed frequency-selective tunable Q-switched CO laser excited by an electron-beam-controlled discharge

A frequency-selective tunable Q -switched CO laser was constructed. It was excited by an electron-beam-controlled discharge and it emitted short (τ0.1 ∼ 1 — 10 μs) pulses of 0.1 — 0.5 J energy at a wavelength in the range λ0=4.9— 6.5 μm. The pulse energy was sufficient to exert a force on absorbing materials. A study was made of the influence of the composition, density, and temperature of the laser mixture, of the pulse duration τ0.1, and of the spectral interval Δν of the laser radiation on the output characteristics of this laser. A special optical system was developed for investigating the influence of suppression and 'locking' inside the cavity of various parts of the laser radiation spectrum on the output energy Eout and on the efficiency η. In the single-pulse regime (τ0.1=5 μs) the efficiency was η ≈0.6% at λ0 ∼5.2 μm (near the maximum of the spectrum obtained in the free-running regime) and η ≈ 0.1% at λ0 ∼ 6.0 μm. Frequency-selective generation of a series of short pulses was the result of repeated Q switching during one pump pulse. In this case, the efficiency at the long-wavelength edge of the spectrum was η ∼ 0.6% and the total output energy was Eout ∼ 0.5 J (the number of pulses in a series was M=8, their duration was τ0.1=5 μs, and the wavelength was λ0 ∼ 5.8 μm). At some wavelengths the values of η and Eout depended weakly on the temperature of the laser mixture in the range 100 — 150 K. The fine temporal structure of the laser pulses was investigated with nanosecond resolution.

Quantitative chemical identification of four gases in remote infrared (9–11 µm) differential absorption lidar experiments

A combined experimental and computational approach utilizing tunable CO(2) lasers and chemometric analysis was employed to detect chemicals and their concentrations in the field under controlled release conditions. We collected absorption spectra for four organic gases in the laboratory by lasing 40 lines of the laser in the 9.3-10.8-mum range. The ability to predict properly the chemicals and their respective concentrations depends on the nature of the target, the atmospheric conditions, and the round-trip distance. In 39 of the 45 field experiments, the identities of the released chemicals were identified correctly without predictions of false positives or false negatives.

Efficient continuous-wave frequency doubling of a tunable CO_2 laser in AgGaSe_2

Second-harmonic output at 4.6-5.5 mum of the order of 6 mW with a 0.12% external conversion efficiency has been obtained by pumping a AgGaSe(2) crystal with a low-power cw CO(2) laser. The surface damage threshold of AgGaSe(2) for cw radiation was found to be inside the limit of 33-45 kW/cm(2) in the 9.2-10.8-mum wavelength region. Another important limitation of the pump power connected with a thermal lensing effect in crystal was determined experimentally. A comparison was made of AgGaSe(2) and ZnGeP(2) crystals as materials suitable for the efficient generation of the second harmonic of cw CO(2) laser radiation.

High power pulsed millimeter laser Raman generation in CH 3F

This work reports about the production of millimeter Raman pulsed emission obtained in CH 3F by means of a high pressure continuously tunable CO 2 laser. Some new strong lines are observed with peak power up to the kW range. The results are in agreement with the Raman scattering theory. The emissions are observed by tuning the CO 2 laser over several GHz.

Infrared multiple photon dissociation spectra of methanol-attached anions and proton-bound dimer cations

The infrared absorption spectra of several gas-phase ions solvated by a single methanol molecule have been determined indirectly by infrared multiple photon dissociation (IRMPD) spectroscopy. A modified White-type multi-pass cell was used in a Fourier transform ion cyclotron resonance mass spectrometer to record the disappearance of the parent ion as a function of the wavelength of a tunable CO 2 laser operating in the range of 920–1060 cm −1. Spectra were obtained for fluoride, chloride and methoxide anions to which either a methanol or a d-methanol molecule was attached. In addition, spectra of proton-bound methanol and d-methanol dimer cations are presented. The shifts in the IRMPD peak frequencies are compared with the respective neutral infrared spectra. A consistent and interesting splitting is observed in the case of ions to which a methanol-d 1 molecule is attached.

Photoacoustic spectroscopy on trace gases with continuously tunable CO_2 laser

A novel photoacoustic (PA) system that uses a continuously tunable high-pressure CO(2) laser as radiation source is presented. A minimum detectable absorption coefficient of 10(-6) cm(-1) that is limited mainly by the desorption of absorbing species from the cell walls and by residual electromagnetic perturbation of the microphone electronics has currently been achieved. Although a linear dependence of the PA signal on the gas concentration has been observed over 4 orders of magnitude, the dependence on energy exhibits a nonlinear behavior owing to saturation effects in excellent agreement with a theoretical model. The calibration of the laser wavelength is performed by PA measurements on low-pressure CO(2) gas, resulting in an absolute accuracy of ± 10(-2) cm(-1). PA spectra are presented for carbon dioxide (CO(2)), ammonia (NH(3)), ozone (O(3)), ethylene (C(2)H(4)), methanol (CH(3)OH), ethanol (C(2)H(5)OH), and toluene (C(7)H(8)) in large parts of the laser emission range. The expected improvement in detection selectivity compared with that of studies with line-tunable CO(2) lasers is demonstrated with the aid of multicomponent trace-gas mixtures prepared with a gas-mixing unit. Good agreement is obtained between the known concentrations and the concentrations calculated on the basis of a fit with calibration spectra. Finally, the perspectives of the system concerning air analyses are discussed.

Partly tunable mid-infrared NH3 laser

Using a continously tunable pulsed 20-atmosphere CO2 laser as a pump source, we generated pulses of mid-infrared radiation, partly tunable in frequency intervals in the range between 200 and 900 cm−1 via stimulated Raman scattering in gaseous ammonia. As a Raman cell we used a multiple pass cell. We observed for14NH3 and15NH3 laser lines at 52 different frequencies with 39 lines observed for the first time. Tuning ranges up to 150 GHz and peak powers of several MW were achieved. The quantum efficiency reached 40 %.

Nanometric Si-based oxide powders: Synthesis by laser spray pyrolysis and characterization

The versatility of the laser synthesis method has been improved during the last few years. In this paper we present the synthesis of amorphous, nanosized Si/C/O powders obtained via ultrasonic injection of aerosol droplets into the beam of a high-power tunable CO 2 laser, using (CH 3) x Si(OC 2H 5) 4− x (0 ≤ x ≤ 3) and hexamethyldisiloxane as alkoxysilane precursors. All these precursors strongly absorb the CO 2 laser emission between 9 and 11 μm. The addition of precursors containing Al or Ti in tetraethoxysilane ( x = 0) leads to Si,Al or Si,Ti oxide composite powders. The evolution of the powders (chemical composition, crystallization, morphology) during heat treatment under air, argon or nitrogen is studied by infra-red absorption, thermogravimetric analysis, transmission electron microscopy and X-ray diffraction. Silica powders with specific surface area up to 500 m 2 g −1 are obtained when heating in air.

Computer code long path method for long path differential-absorption predictions using CO2 laser lines

A computer program LPM (Long Path Method) has been developed for imitative modeling of the concentration at gases (H2O, CO2, O3, NH3, C2H4) in the atmosphere using a long-path double-wavelength laser system equipped with two tunable CO2 lasers. The model is designed for four different lasing isotopes of CO2 (12C16O2, 13C16O2, 12C18O2, 13C18O2). The program determines optimal pairs of CO2 laser wavelengths, and the gas concentration retrieval errors from sounding data caused both by detector noise and systematic inaccuracy. The program was written in MS FORTRAN and Visual Basic languages for Windows 3.1 and an IBM-compatible PC. © 1995 American Institute of Physics.

Virtual instrumentation of a resonant spectrophone

The acoustic modes of a gaseous system in a cylindrical resonant cavity were excited with a tunable CO2 laser. The experimental setup is completely controlled by a personal computer and virtualized as an application-oriented system by employing a so-called virtual instrumentation software through a GPIB interface. A detailed description of the hardware arrangement, software virtualization, and the measured resonant profile of the spectrophone is presented.

Second-harmonic and sum-frequency generation in AgGaSe2 with tunable waveguide CO2 lasers

A tunable source is described, giving extensive coverage of a spectral region around 2000 cm−1. A frequency self-calibration routine allows for the recording of Doppler-limited absorption profiles with an absolute accuracy of better than 10 MHz. The applicability of the source is demonstrated through measurements on the12C16O,12C17O, and12C18O isotopomers. Collision-broadening parameters and line strengths are determined, some of the data showing evidence of motional narrowing. Sensitivity limits are determined for linear absorption measurements as well as for photoacoustic absorption, and the feasibility of monitoring all three isotopomers with ppm sensitivity is demonstrated.

Dynamics of a CO 2 ring laser with a saturable absorber

We present numerical results of the dynamics of a bidirectional single mode (per direction) line tunable CO 2 ring laser with an intracavity saturable absorber. We employ a rate equation model which includes laser detuning, Doppler effect of the gain medium caused by gas flowing and the coupling of two counter propagating modes. A lower dynamical threshold was found in such a ring laser system comparing with a Fabry-Perot laser type. In addition to the subcritical Hopf bifurcation and inverse cascaded period double bifurcation caused by the competition of gain and absorber, we found one more inverse period double bifurcation caused by the competition of two counter propagating modes.

Laser photoacoustics for gas analysis and materials testing

The application of laser photoacoustics to two different areas is discussed. First, laser-induced spallation and interferometric detection of transient surface displacements is proposed as a powerful noncontact tool for the investigation of adhesion properties of solid surface coatings. Results for nickel and plasma-sprayed ceramic coatings are presented. Delamination processes at the interface between substrate and coating could be detected with excellent spatial and temporal resolution and adhesion strengths in the 0.2 to 2 GPa range be determined. Second, laser photoacoustic spectroscopy is applied to trace gas monitoring. An automated mobile CO₂ laser photoacoustic system is employed for <i>in situ</i> air monitoring with parts per billion sensitivity in industrial, urban, and rural environments. An improvement in detection selectivity for multicomponent gas mixtures is achieved with a continuously tunable highpressure CO₂ laser with a narrow linewidth of 0.017 cm^-1. A CO laser photoacoustic system previously used for the analysis of motor vehicle exhausts is now employed for studying dimerization phenomena in fatty acid vapors. Finally, emphasis is put on the development of widely tunable, narrow-band, mid-IR laser sources based on optical parametric oscillation or difference frequency generation employing tunable diode lasers and AgGaSe² as nonlinear material.

Saturation Spectroscopy of C2H4 Using a CO2 Laser Sideband Spectrometer

We have studied the saturation spectrum of the ν7 band of C2H4 using the tunable sideband CO2 laser technique coupled to a Fabry-Pérot cavity containing C2H4. About 40 line frequencies have been determined with a typical 100-kHz accuracy. An overall fit including all available information on the coupled ν4, ν7, and ν10 levels improves the nu7 state and the ground state parameters.

Intraline tunable CO 2 waveguide lasers and applications in high resolution spectroscopy

Although early publications on the CO 2 waveguide laser reported tuning ranges close to and exceeding 1 GHz in individual laser lines, this potential has not been widely exploited for spectroscopy. In this paper we outline the difficulties which have hampered spectroscopic applications, and we point out their theoretical background and the avenues for solution. Following this, we review the work that has been done, including fundamental as well as applied spectroscopic work.

硬組織の9μm帯巨大吸収波長の検索とその加工効果の検討

硬組織の9μm帯巨大吸収波長の検索とその加工効果の検討