Tunable High-pressure CO2 Laser Research Articles

Photoacoustic gas sensing employing fundamental and frequency-doubled radiation of a continuously tunable high-pressure CO 2 laser

We present the first photoacoustic spectrometer for gas sensing employing both the fundamental and the frequency-doubled radiation of a continuously tunable high-pressure CO2 laser with room temperature operation. A quasi-phase-matched diffusion-bonded GaAs crystal is used in the system for second-harmonic generation. A pulsed photoacoustic detection scheme with a non-resonant cell, equipped with an 80-microphone array, is employed. The wide continuous tuning range in the fundamental (9.2–10.7 μm) and the frequency-doubled (4.6–5.35 μm) regimes, together with the narrow linewidth of 540 MHz (0.018 cm-1) for the 10-μm region and of 1050 MHz (0.0315 cm-1) for the 5-μm region, allow the measurement of gas mixtures, individual species and isotope discrimination. This is illustrated with measurements on NO and CO2. The measured isotope ratio 15NO/14NO=(3.58±0.55)×10-3 agrees well with the literature (3.700×10-3) and demonstrates the good selectivity of the system.

Laser photoacoustic spectrometry for trace gas monitoring

Spectroscopic methods offer important features with respect to atmospheric trace gas monitoring. Some relevant techniques are briefly discussed. Emphasis is put on various aspects of photoacoustic spectrometry. Its basic principles and important experimental characteristics are outlined. Depending on molecular absorption cross-sections, a detection limit in the low ppbv concentration range is typically achieved without the use of any preconcentration device. In multi-component mixtures this limit may be increased owing to absorption interferences. Two photoacoustic (PA) systems have been developed and some specific applications are presented. A CO-laser PA system operating in the 5–6.5 µm wavelength range was applied to the analysis of motor vehicle exhausts. Apart from nitrogen oxides, CO2 and water vapour, ten different volatile organic compounds (VOCs) including o-, m- and p-xylene were selectively detected at parts per million by volume (ppmv) concentrations. As a second instrument, an automated CO2 laser PA system was implemented in a trailer for in situ measurements. It was applied to the detection of stack gases at a pharmaceutical plant and to air monitoring in urban and rural environments. As an example, ethene, ammonia and ozone were detected at ppbv concentrations in rural air. Finally, new aspects are discussed, in particular the introduction of CO2 isotopes as the laser medium, the design of PA Stark cells and the development of a continuously tunable high-pressure CO2 laser and of a widely tunable mid-infrared laser based on frequency mixing in a non-linear crystal. Although PA spectrometry already represents a valuable alternative to more established spectroscopic and non-spectroscopic schemes, these novel developments should further enhance its potential and versatility.

Efficient generation of FIR radiation by optical pumping of D2 18O

In this paper we show that D2 18O vapour, optically pumped with a continuously tunable high pressure CO2 laser, is an excellent source for far infrared radiation. Both high photon conversion coefficients and broad Raman gain regions were found for a large number of new laser transitions spread over the frequency range from 25 cm−1 to 240 cm−1. We demonstrate that these Raman gain regions can be used to generate far infrared laser pulses with high intensity and durations of about 100 ps.

New far-infrared laser lines from CH3Cl and CH3Br optically pumped with a continuously tunable high pressure CO2 laser

In this paper we report on the detection of new far-infrared laser lines from CH3Cl and CH3Br optically pumped with a continuously tunable high pressure CO2 laser. We found 80 new lines for CH3Cl and 9 new lines for CH3Br in the frequency region between 16 cm−1 and 41 cm−1, all due to stimulated Raman scattering. For the Raman gain regions bandwidths up to about 700 MHz were found. We also observed high intensity short far-infrared laser pulses of durations in the nanosecond regime.

Generation of widely tunable intense far-infrared radiation pulses by stimulated Raman transitions in methylfluoride gas

We report on the generation of widely tunable intense far-infrared radiation pulses by stimulated Raman transitions in methylfluoride gas. Using a tunable high-pressure CO2 laser we achieved, by P-branch tuning of stimulated Raman transitions in 12CH3F and 13CH3F gases, tunable generation of radiation in a series of intervals in the spectral range from 37 to 72 cm−1 covering 20% of this range. Possibilities of further extension of the tuning regions are also discussed.

Collisional broadening of theP20 line of the 0001–1000 transition in CO2measured with the aid of a tunable CO2laser

The profile of the P20 absorption line of the 0001-1000 transition in CO2 was recorded using a tunable high-pressure CO2 laser. The pressure dependence of the broadening of this profile was determined directly. The collisional broadening constant was found to be 7.56 MHz/mm Hg. The experimental profile was in good agreement with the theoretical Voigt form.

Continuously tunable high-pressure CO2 laser with uv photopreionization

The operation of a uv photoinitiated tranverse-discharge CO2 laser has been investigated at pressures up to 15 atm. Preliminary studies of a device having an active volume of [inverted lazy s] 13 cm3 have yielded a maximum output of [inverted lazy s] 1 J in 30 nsec, while the use of a grating-tuned resonator has resulted in continuously tunable operation over frequency intervals of [inverted lazy s] 20 cm−1.