Detuning effects of FM mode-locking in atmospheric CO2 lasers

We describe a study of the detuning of the intracavity FM modulation of the homogeneously broadened laser applied to CO₂ systems. The analysis is done by working in the frequency domain and by describing the field in terms of discrete amplitudes and phases. The coupled mode equations are solved for modulation frequencies near the axial mode-separation frequency. The asymmetry of the mode-locking behaviour due to the dispersive behaviour of the active medium is verified experimentally. We have measured both the pulse and the phase shift of the pulse with respect to the modulation signal as a function of detuning. The experimental results show clearly the asymmetry with detuning, in agreement with theory.     

Two-Frequency waveguide CO2 laser for atmospheric pollution monitoring

The present paper suggests and discusses a method allowing one to produce a two-frequency switching mode between any two adjacent transitions of a CO₂ laser. Switching is achieved by means of simple modulation of the resonator length by a piezoelement. The use of conventional electronic circuits ensures the maintainance of a high power balance (10^–2–10^–1%) vs. switching rate) at the generation frequencies. The data of the two-frequency CO₂ laser with a waveguide resonator used for various systems, based on a differential absorption technique and designed to control the atmospheric pollutions, are presented.     

Line-dependent saturation in CO2 lasers

Line dependent saturation has been studied in a CO₂ waveguide laser, operating cw in 100 lines of the 9 m and 10 m bands. In both bands, for constant discharge conditions, the saturation intensity is found to be strictly inversely proportional to the small signal gain for lines in the range J=2 to J=48 in both the P and the R branches. For lasers operating well above threshold this implies an output power which is essentially independent of the line number. The effect is verified experimentally, and discussed theoretically.Supported by the Danish Science Research Council under grant no. 11-7777     

Waveguide CO2 lasers on sequence-band transitions

Two waveguide CO₂ lasers, a quartz waveguide and an alumina waveguide, have been studied on the 00°2–[10°l,02°1]_I,II sequence bands. The use of an intra-cavity hot CO₂ cell, which is a part of the waveguide, suppresses the regular-band transitions. The quartz waveguide laser has a total of 58 lines lasing on both the 9.4 µm and 10.4 µ,m sequence bands. The alumina waveguide laser has 36 lines lasing on the 10.4 µm sequence band and twice the output power of the quartz waveguide laser, whereas lasing on the 9.4 µm sequence band is difficult. The lasers can be operated on the selected single line without line jumping problem. The frequency tuning range of the strong lines is limited by the free spectral range of the cavity.     

High-pressure pulsed CO2 lasers

This paper presents a large body of data allowing one to determine the energy, time, and spectral characteristics of high-pressure pulsed CO₂ lasers over wide ranges of parameters. Institute of High-Current Electronics, Siberian Division of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 19–28, April, 2000.     

Multichannel optoacoustic spectroscopy of molecular gases with pulsed lasers

This paper contains a review of results of the experimental investigation of linear and nonlinear absorption of atmospheric gases using the methods of multichannel optoacoustic spectroscopy with pulsed visible and IR lasers.     

Application of the optoacoustic effect in optically pumped submillimeter lasers

The dependence of the optoacoustic signal generated in an optically pumped submillimetre laser system on gas pressure and modulation frequency has been studied experimentally and the results accounted for theoretically. With care an extracavity optoacoustic cell containing the laser gas diluted with air can be used to stablize the pump laser frequency to maximum absorption but this does not always optimise laser output.     

A two-wavelength oscillation CO2 laser for differential absorption measurements of atmospheric trace molecules

A two-wavelength oscillation C0₂ laser was constructed for the differential absorption measurement of low concentrations of atmospheric trace molecules and pollution molecules. A diffraction grating was alternately angle-modulated for the two-branch oscillation using a single C0₂ laser. The output power of the two wavelengths was balanced to be equal. With these characteristics, the phase-sensitive detection technique can be applied to give highly sensitive detection of the received power difference, which is proportional to the absorption in the optical path of the transmitted beams. A differential absorption spectrometer was used to demonstrate the usefulness of this two-wavelength laser oscillation method incorporating the output power balancing technique. The concentration of ethylene molecules was detected in a calibration cell and was also measured in real time in the exhaust of a combustion engine. From these results it has been shown that this differential absorption scheme offers a minimum detectable absorption of approximately 0.8%.     

Theoretical studies of atmospheric triatomic molecules: Ab initio characterization of Rydberg series in CO2

The ab initio Koopmans' Theorem is used to determine energy levels and orbital characteristics for the lowest members of s, p, d, f, g, h Rydberg series in CO₂. The energy levels are in good agreement with results of SCF calculations and experimental energy levels. It appears that unambiguous spectral assignments can be based upon the comparison of ab initio and observed energy levels in the case of penetrating Rydberg orbits. The energy levels associated with the higher angular momentum orbits exhibit degeneracies and separations which more closely approximate those of the hydrogen atom.     

Pulsed optoacoustic detection of multiple photon excitation in molecules

Multiple photon excitation, saturation, and linear absorption of SF₆-argon mixtures when irradiated by a high power CO₂ TEA laser is investigated using a pulsed optoacoustic technique. At low intensities the expected linear dependence of the absorption on laser intensity is observed. At intermediate intensities the absorption exhibits a square root dependence on the incident laser intensity, a dependence which is typical for saturation of an inhomogeneously broadened absorption. At even higher intensities, the absorption shows an intensity dependence typical of multiple photon excitation. The laser intensity was varied between 0.016 kW/cm² and 5 MW/cm², values lower than that needed to produce multiple photon dissociation of SF₆. Increasing the collision frequency of the absorbing molecules with an inert buffer gas is observed to quench the multiple photon excitation.     

Helium-free operations in mini-TEA CO2 lasers

Summary Large helium-free emissions are obtained in two mini-TEA CO₂ lasers, by using always a corona preionization without additives and with a maximum energy density of 900J/l in the discharge. In general, helium-free emissions are more stable, but the best condition in efficiency, energy and peak power is observed always with a small He content added to the laser mixture.

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Riassunto L'uso di una piú efficiente preionizzazione a corona ha permesso l'operazione di un laser a CO₂ senza elio a pressione atmosferica con elevate densità di energia nella scarica (900 J/l) e grande efficienza di conversione dell'energia elettrica in radiazione laser.

     

On the opto-voltaic measurements in CO and CO2 lasers

We observed and compared the opto-voltaic signals in CO and CO₂ lasers. The signals are obtained capacitively from the water cooling jacket as a low voltage source not influencing the current circuit. We observed from measurement that the output power and the so-called optovoltaic input power have a distinct relationship depending on laser current and cavity parameters. It will be shown that opto-voltaic detection is a very sensitive method especially for CO lasers.     

High-power high-pressure pulsed CO2 lasers

The results of investigations and development of high-pressureCO ₂ lasers are considered. It is shown that the high-pressure active medium allows radiation pulses to be formed with smooth tuning of frequency and duration over wide ranges. Data on small-size wide-apertureCO ₂ lasers with an output pulse energy up to 5 kJ are presented. Institute of High-Current Electronics of the Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 74–77, August, 1999.     

Applications of tunable dye lasers to air pollution detection: Measurements of atmospheric NO2 concentrations by differential absorption

Remote measurements of atmospheric NO₂ concentrations by means of a LIDAR system equipped with a tunable dye laser are reported. Using the differential absorption method, concentration values of about 0.2 ppm were detected over the city of Cologne at distances up to 4 km.     

Cutting copper sheets using CO2 lasers

In this work various problems concerning cutting copper sheets using CO₂ laser are reported. First, all copper thermophysical properties, that regulate the process dynamics, and then the weight of each parameter has been evaluated numerically, even though only approximately. The surface absorption value of copper at room temperature and near the melting point and the order of laser power that is necessary to cause a gradual raise of the workpiece temperature from room to melting have been estimated. Then, the order of the cutting speed at which a sheet of a known thickness can be cut has been calculated. The analysis of all these problems, and the process dynamics and state of the art seem to confirm the validity of the current thesis on the impossibility of cutting copper by CO₂ laser. In the second part of the work the experimental data relating to the first ever tests on 0.2–4.0 mm thick copper sheet cutting by 2 kW CO₂ laser are reported. These first interesting results have been obtained thanks to the possibility of making overlapped layers of cupric oxide CuO, mixed with a small quantity of cuprous oxide Cu₂O grown under laser beam irradiation (CuO and Cu₂O, together, allow the laser cutting to be carried out). This has been confirmed by the analyses of the cutting edges with a computerized X-ray diffractometer. We have also seen that the per cent absorption of laser radiation at 10.6 micron does not increase in the presence of just cuprous oxide while, when the experimental conditions allow it, the growth of cupric oxide increases the absorption value to around 52–58 per cent, giving rise to the loop process with three variable quantities (temperature-oxide-absorption) that has been the winning clue of cutting process. The behaviour of the critical cutting speedV, the cutting widthsb and the productV·b versus the thickness for 2 kW CO₂ laser using a 4″ ZnSe and 3.5″ KCl focusing lens have been tested. Moreover, the influence of different gases and flows on the cutting process have been experimented. The work-speed turned out to be significant and various micrographic sections, performed on the workpieces have shown that the laser cutting quality is quite good. A first analysis of the results has shown that laser cutting is not comparable to the one of steel, so much so that the mathematical formalism developed for steels has proved to be unsuitable for copper. This paper was done under research contract with Italian Governmental Agency ISMEZR-INTERVENTO STRAORDINARIO NEL MEZZOGIORNO, which is supporter and financing organization within the project P.S. 35-105 IND. The first, the second and the third paper on this topic has been published on:-Review LA MECCANICA ITALIANA, n. 190, 1985, 45–47, ITALY (all rights reserved)-Review LASERS & APPLICATIONS, n. 3, Vol. 5, 1986, 59–64, High Tech. Publications Inc., Torrance, CA-USA (all rights reserved)-Proceedings of ECOOSA'86-European Conference on Optics, Optical Systems and Applications, Sept. 30–Oct. 3, 1986, Florence, ITALY (all rights reserved)     

Study on transient processes during modulation of resonator lengths in CO and CO2 lasers

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 4, pp. 588–593, April, 1991.