Search

The first, to the best of our knowledge, mid-infrared Q-switched Ce

In high purity

Concept of a solid-state femtosecond laser system with a multigigawatt power level in the 4–5 μm range has been proposed. The system contains an ultrashort pulse seeder, a two-stage chirped pulse amplifier based on a broadband Fe2+:ZnSe active element with optical pumping by a YSGG:Cr:Er laser, and an output stage that provides additional nonlinear optical compression of an amplified pulse to approximately 30 fs in a dielectric CaF2 medium with anomalous group velocity dispersion in this spectral range.

A room-temperature laser based on a single crystal has been studied. The crystal was pumped by a nonchain electric-discharge HF laser with a light pulse FWHM of . The pump spot diameter on the crystal surface varied from 3.9 to . The slope efficiency at these values of was 37% – 39 %, respectively. The maximum laser energy was (at ) with the total efficiency with respect to the absorbed pump energy of . A further increase in the laser energy was not achieved because the crystal was destroyed at an incident pump energy and power of and , respectively. The damaged region has a form of a long narrow channel shifted from the entrance surface inside the active element.

We demonstrate a first-of-its-kind efficient chirped pulse amplification of broadband mid-IR (4-5 μm) femtosecond seed pulse (230 ps, 4μJ) generated in AgGaS2 based OPA driven by Cr:forsterite laser in multi-pass Fe2+:ZnSe amplifier optically pumped by solid-state Q-switched Cr:Yb:Ho:YSGG laser (2.85 μm, 30mJ, 5Hz, 0.6 J/cm2). The system delivers 1.2 mJ at pulse duration of 230 ps. Straightforward compression to 150 fs pulse is achievable with 70% efficiency using diffraction grating pair with peak power of about 6 GW. Further non-linear compression in a bulk CaF2 due to the SPM and anomalous GVD should provide the enhancement of peak power up to 20 GW. Possible routes to reach sub-TW and even TW power level in mid-IR are discussed.

Copper-bearing zeolite catalysts are studied to develop a catalyst free of noble metals for obtaining high-octane components of motor fuels. The activity of the catalysts prepared on the basis of ZHM, ZHS-III-895, ZHS-III-889, and ZSM-5 zeolites with the different contents of copper is tested in the conversion of a model hydrocarbon (n-hexane). It is found that the reactions of isomerization and aromatization of n-hexane can lead to the formation of high-octane hydrocarbons in nonstandard conditions of conversion of n-alkanes: without feeding a hydrogen-bearing gas into the reaction medium at atmospheric pressure on copper-bearing high-silica zeolites, while an industrial process involving platinum catalysts is carried out under increased hydrogen pressure. The use of the recommended conditions for the conversion of hydrocarbons should lead to a reduction in the cost of final products.

Continuous-wave lasing is obtained for the first time in a Cr2+:CdS crystal pumped by a thulium fibre laser at 1908 nm. The output power of the laser at 2534 nm achieved 0.81 W with the slope efficiency with respect to the absorbed pump power equal to 52.3%. The parameters of Cr2+:CdS and Cr2+:CdSe lasers are compared. A Cr2+:CdSe crystal generated 1.7 W of cw radiation at 2638 nm with the slope efficiency with respect to the absorbed power equal to 53.4%.

We report spectroscopic characteristics and laser properties of the mid-infrared active laser medium Cr2+:CdS. Temperature-dependent absorption, luminescence and lifetime measurements of the 5E exited state allow determination of peak emission cross section value of 1.35 × 10−18 cm2 in σ-polarization at room temperature. Lifetime values vary from 7.6 µs at 8 K to 0.48 µs at 320 K, corresponding to 22 % quantum yield at 285 K. Under Tm-fiber laser pumping, the continuous-wave output reached 1.8 W at 2.5 μm with 35.5 % slope efficiency. With a single CaF2 prism, the CW Cr2+:CdS laser could be tuned from 2.240 to 3.285 µm.

An investigation was made of the kinetics of formation of atomic iodine after ultraviolet photolysis of a mixture of molecular iodine and ozone diluted with various gases. It was found that the iodine dissociation process in this mixture is governed by the reactions of the oxygen atoms. Dissipation of the singlet oxygen energy was observed. A mechanism was proposed to explain this effect by quenching of singlet oxygen and of excited iodine atoms by iodine oxides formed in the mixture after photolysis.

An experimental investigation was made of the influence of molecular chlorine on the output energy of a pulsed oxygen–iodine chemical laser using CH3I and CF3I atomic iodine donors. It was found that for CF3I the addition of appreciable (0.5 Torr) quantities of chlorine to the singlet oxygen stream reduced only negligibly the output energy, whereas for CH3I the lasing was suppressed at chlorine concentrations an order of magnitude lower.

Intense luminescence was excited as a result of the interaction between a heated metal surface and a singlet oxygen stream containing a small amount of chlorine. The luminescence spectrum consisted of two regions located at 650–920 and 1070–1305 nm. A band structure with a typical interval of around 360 cm−1 was observed in each region. Dependences of the luminescence intensity on the chlorine and singlet oxygen pressures were determined.

The influence of atomic iodine donors (CH3I and CF3I) on the output energy of a pulsed oxygen-iodine laser was investigated. Their influence on the time dependence of the luminescence intensity of I (2P1/2) iodine atoms formed by laser photolysis of an RI–O2–M mixture (R = CH3, CF3, M is the buffer gas) was also studied. An analysis of the experimental data and of the results of numerical modeling, demonstrated that when CF3I was used as the iodine donor, CF3O2 quenched strongly the O2(1Δ) excited oxygen. The proposed kinetic model yielded the rate constant k = (3–5) × 10−11 cm3/s for the reaction O2 (1Δ) + CF3O2 → O2 (3∑) + CF3O2.

Singlet delta oxygen O 2 (Z 1 ' 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 10 16 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. Keywords: singlet delta oxygen, singlet oxygen yield, slab discharge, RF discharge, non-self-sustainted discharge, intracavity laser spectroscopy

Singlet delta oxygen O 2 (a 1 Δ 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 10 16 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.

Efficient lasing of Fe:ZnSe was demonstrated with a 2.94 pm Er:YAG pump laser. Output energy of 130 mJ, an absorbed energy slope efficiency of 44% and continuous tunability from 3.8 to 4.4 pm at 85 K were obtained. Laser efficiencies were determined for temperatures ranging from 85 to 253 K.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Electric properties and spectroscopy of an e-beam sustained discharge (EBSD) in oxygen and oxygen gas mixtures at gas pressures up to 100 Torr was experimentally studied in large excitation volume (~18 liter). The 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 per molecular component being higher more than order of magnitude and coming up to 6.5 kJ/(l atm). Theoretical calculations demonstrated that for the experimental conditions the singlet delta oxygen yield may reach ~20% exceeding its threshold value needed for oxygen-iodine laser operation at room temperature. The results of experiments on spectroscopy of the singlet delta and singlet sigma oxygen states in the EBSD are presented.

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.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An experimental investigation was made of intracavity second harmonic generation in a pulsed oxygen–iodine chemical laser. Lithium iodate was used as the nonlinear crystal. The efficiency of conversion of the radiation to the second harmonic was 8%. A comparison was made between the experimental results and the results of the numerical simulation. The results indicate that in a resonator with a total transmission of 1 % at the fundamental frequency the conversion efficiency may exceed 35% if the intracavity losses are low (less than 1 %).

The feasibility of developing an HgBr laser utilizing the B2∑+1/2→X2∑+1/2 transition by optical pumping of HgBr(X) radicals using the third harmonic of a neodymium laser was studied. The radicals were formed by photolysis of a mixture of HgBr2 vapor with various buffer gases using the fourth harmonic of the neodymium laser. Under these conditions the luminescence was due to the B–X transition in the HgBr radical and its intensity was three orders of magnitude lower than that calculated from the absorbed third-harmonic energy, basing due to the B→X transition in the HgBr radical could not be achieved. When the mixture was exposed to the fourth-harmonic radiation, emission of the 73S1–63P2 (λ = 546 nm) mercury line was observed and the output pulse energy increased with increasing pump energy.

The luminescence spectra (600–700 nm) were determined for active media of a chemical oxygen–iodine laser with different iodine concentrations. The red radiation observed at low iodine concentrations was attributed to the ICl molecule.

An investigation was made of the influence of the addition of polyatomic gases on the energetics of an H2–F2 laser in the case of controlled initial initiation. The results obtained indicated the presence of two mechanisms for raising the output energy of an H2–F2 laser. The first mechanism is common to all gases and involves a change in the specific heat. The second mechanism is specific to particular gases and is associated with an increased rate of the establishment of a rotational equilibrium of the HF molecules. The extent to which polyatomic gases have an effect depends strongly on the initial experimental conditions.

It is demonstrated experimentally that the early stages of photoinitiation in fluorine-hydrogen lasers may be studied using the absorption of ultraviolet radiation by FO2 radicals formed as a result of the F+O2+M→FO2+M reaction. The absorption cross section of the FO2 radical in the gas phase was determined at room temperature at the 220 nm wavelength.

A study was made of the dependence of the duration of emission from an atmospheric-pressure H2–F2 laser on the composition of the mixture and on the degree of initiation. The initiation source was a neodymium glass laser system with a harmonic generator emitting 10-nsec pulses of the third and fourth harmonics which reached energies of 5 and 2J, respectively. The duration of emission from the H2–F2 laser was 45 nsec when the initial concentration of the fluorine atoms was [F]o=3×1017cm−3 and the composition of the mixture was F2:O2:H2:He=300:30:100:320 Torr. The divergence of the radiation emitted by this chemical laser was 1.1 mrad when the specific output energy was 40J/liter; this divergence was only 1.6 times greater than the diffraction limit.

The results are presented of an experimental investigation of the energy characteristics of an H2–F2 laser with partial pressures of F2 and H2 of 3 Torr, as a function of the initial initiation α and of the pressure of the diluent gas (He or SF6). In an F2:H2:O2:He = 3:3:1.2:30 Torr gas mixture when α = 8%, a specific output energy per unit volume of ev = 4.4 J/liter was obtained for a specific output energy per unit mass of em = 330 J/g. The results obtained provided evidence of the advantage of using the chain excitation mechanism in cw HF lasers.

Stimulated emission from an oxygen–iodine laser with a photodissociation source of excited oxygen O2(1Δ), based on ultraviolet photolysis of ozone, was observed for the first time. The ozone photolysis products, particularly O(1D) atoms, had an unfavorable influence on the lasing parameters. A study was made of the possibility of using CO2, N2, and N2O gases as effective agents for quenching of O (1D). An output energy e = 0.8 mJ/cm3 and an efficiency of energy transfer from the O2(1Δ) molecules to iodine atoms amounting to η = 41% obtained for a mixture of the composition characterized by the ratio CF3I:O3:SF6:He:N2O = 0.055:0.45:11:21:6 Torr were close to the corresponding values reported for an oxygen–iodine laser with a chemical generator of O2(1Δ).

A comparison of the output parameters of an H2–F2 laser initiated alternately by photolysis and electron beam methods was used to find the energy eFe = 4.3±0.9 eV needed to form one fluorine atom by an electron beam.

Quasi-cw operation of an IF(B–X) laser was achieved as a result of filling of levels by VT relaxation. The duration of emission from the IF laser was governed by the duration of the pump pulses and it amounted to 25 μs. The output energy was 3 mJ and the quantum efficiency was 15% relative to the absorbed pump radiation. An estimate was obtained of the VT relaxation rate constant of the ground state of the IF(X) molecule interacting with helium: kVT ≈ 10− 13 cm3/s.