M P Frolov

The methods of singlet oxygen detection for DOIL program

The problem of development of a singlet delta oxygen O2(1Δg) (SDO) generators alternative to chemical one needs application of the accurate methods of measuring the SDO concentration. A chemical SDO generator providing efficient operation of a chemical oxygen-iodine laser (COIL) is proposed to be used as a reference source for absolute calibration of the system measuring the SDO concentration. The principle of the COIL operation results in the threshold and output COIL parameters make it possible to evaluate the SDO yield with a satisfactory accuracy. A convenient sparger chemical SDO generator was applied as a reference source for absolute calibration of detectors of dimole (λ=634nm) and b→X (λ=762 nm) radiations. The values of b-state concentration formed in a longitudinal electric discharge were evaluated. The intracavity laser spectroscopy (ICLS) was absolutely calibrated for measuring the SDO concentration. ICLS method has a very high sensitivity and makes it possible to monitor the absorption corresponding to the O2(1Δg)→O2(1Σg+) (λ = 1.91 μm) transition. The cross-sections of lines of the Q - branch of the vibrational 0-0 band of the a1Δg → b1Σg+ transition of molecular oxygen were measured. The method developed was applied to measure the concentration of singlet oxygen produced in the microwave discharge. He - Ne laser (λ = 633 nm) was used for absolute calibration of a system monitoring the dimole radiation. The rate constant of the process responsible for dimole emission was measured. The value obtained kd=7.34•10-23 cm3/s is in agreement with literature.

Singlet delta oxygen production in e-beam sustained discharge: theory and experiment

Singlet delta oxygen (SDO) production in a pulsed e-beam sustained discharge (EBSD) ignited in molecular oxygen with carbon monoxide stabilizing this discharge is theoretically and experimentally studied. Temporal behavior of SDO concentration and yield in the EBSD afterglow is analyzed. Experimentally measured SDO yield for oxygen mixture O2:Ar:CO=1:1:0.05 at total gas pressure 30 Torr comes up to 7% at specific input energy (SIE) of ~3.0 kJ/(1 atm(O2+CO)), whereas its theoretical value riches ~ 17.5%. The efficiency of SDO production is theoretically analyzed as function of the SIE.

Theoretical studies on kinetics of singlet oxygen in nonthermal plasma

An idea to replace singlet delta oxygen (SDO) generator working with wet chemistry by electric discharge generator has got much attention last years. Different kinds of discharge were examined for this purpose, but without a great success. The existing theoretical models are not validated by well-characterized experimental data. To describe complicated kinetics in gas discharge with oxygen one needs to know in detail processes involving numerous electronic excited oxygen molecules and atoms. To gain new knowledge about these processes experimental studies were made on electric discharge properties in gas mixture flow with independent control of inlet SDO concentration. The theoretical model extended to include minor additives like oxygen atoms, water molecules, ozone was developed. Comparison with careful experimental measurements of electric characteristics along with gas composition allows us to verify the model and make theoretical predictions more reliable. Results of numerical simulations using this model for an electron-beam sustained discharge are reported and compared with the experimental data.

Testing of Cr:ZnSe Laser with Intracavity Methane Cell in 77-300 K Temperature Range

The mid-IR cw tunable solid state two-mode Cr²⁺:ZnSe laser with intracavity methane cryocell was developed. The laser was applied for sub-Doppler spectroscopy of (υ₁+υ4) vibrational-rotational band of methane and observation of narrow resonances of saturated dispersion at λ = 2.36 μm. The new technique of low pressure methane gas cooling was used instead of liquid nitrogen “jacket” design applied in our previous work. Parameters of saturated dispersion resonances were estimated in 77-300 K temperature range. The experiments confirmed that laser with the new “dry cooled” methane cell has prospectives for reaching a short-term frequency stability at the level of 10^-15-0^-16 and can be used as a compact device.

2.94 μm Er:YAG Q-switched laser with Fe2+: ZnSe passive shutter

A passive Q-switching of 2.94-μm Er:YAG laser has been demonstrated using Fe2+:ZnSe single crystal saturable absorber. A giant pulse width ofabout 35 ns and output energy up to 30 mJ in fundamental mode were obtained.

Electron-beam sustained discharge in oxygen gas mixtures: singlet delta oxygen production for oxygen-iodine laser

Electric properties and spectroscopy of an e-beam sustained discharge (EBSD) in oxygen and oxygen gas mixtures at gas pressure up to 100 Torr were experimentally studied. The pulsed discharge in pure oxygen and its mixtures with noble gases was shown to be very unstable and characterized by low input energy. When adding small amount of carbon monoxide or hydrogen, the electric stability of the discharge increases, specific input energy (SIE) per molecular component being more than order of magnitude higher and coming up to 6.5 kJ/(l atm) for gas mixture O2:Ar:CO = 1:1:0.1. The results of experiments on spectroscopy of the singlet delta oxygen O2(a1Δg)(SDO) and O2(b1Σg+) states in the EBSD are presented. The calibration of the optical scheme for measuring the SDO absolute concentration and yield using the detection of luminescence of the SDO going from a chemical SDO generator was done. The preliminary measurement of the SDO yield demonstrated that it was ~3% for the SIE of ~1 kJ/(l atm), which is close to the results of theoretical calculations for such a SIE. Theoretical calculations demonstrated that for the SIE of 6.5 kJ/(l atm) the SDO yield may reach ~20% exceeding its threshold value needed for oxygen-iodine laser operation at room temperature, although a part of the energy loaded into the EBSD goes into the vibrational energy of the molecular admixture, (which was experimentally demonstrated by launching a CO laser operating on an oxygen-rich mixture O2:Ar:CO = 1:1:0.1 and measuring its small-signal gain).

Room-temperature operation of a Fe2+:ZnSe laser

Pulsed lasing ofthe Fe2+:ZnSe single crystal was demonstrated at room temperature. The laser action centered at 4.4 μm with pulse energies up to 1.4 mJ and an input energy slope efficiency of 11% was obtained vith a 2.94 μm Q-switched Er:YAG pump laser. Continuous tuning from 3.9 to 5.1 μm was demonstrated.

Singlet delta oxygen production in a slab discharge in oxygen

Singlet delta oxygen O2a1&Dgr;g (SDO) production in a slab discharges ignited in oxygen gas mixtures was experimentally studied. An influence of gas mixture content and input electric power on SDO yield was analyzed. In self-sustained RF slab discharge SDO yield of 10±5 % was measured by comparison luminescence intensity of SDO going from a chemical generator and SDO generated in electric discharge. SDO yield of 7.2 % was measured by intracavity laser spectroscopy method. It was demonstrated that the choice of electrodes material is very important. Experiments on SDO production in slab non-self-sustained discharge with external ionization by repeating high-voltage pulses were carried out. SDO concentration was measured by the method of intracavity laser spectroscopy. The measured concentration of SDO was about 1.5×1016 cm-3, with SDO yield of ~10.6 %. A development of electric discharge oxygen-iodine laser with SDO production in long electrodes slab discharge is discussed.

Cr2+:ZnSe laser for application to intracavity laser spectroscopy

Absorption spectra of atmospheric air in the 2.41-2.46 μm wavelength region are recorded by intracavity laser spectroscopy technique using a Cr2+:ZnSe laser. The dynamics of intracavity absorption was studied for the generation time of 0-100 μs. The experiment demonstrates that the Cr2+:ZnSe laser operating in the IR 2-3 μm spectral region can be utilized for high sensitivity intracavity laser spectroscopy measurements.

Co:MgF2 laser for intracavity laser spectroscopy

The dynamics of the intracavity absorption was studied in a cw Co:MgF2 laser. The linear growth of the intracavity absorption was observed for the generation time values form 0 to at least 4 ms which corresponds to a 1200-km effective absorption path length.