Dynamics of photoprocesses induced by femtosecond infrared radiation in free molecules and clusters of iron pentacarbonyl

The dynamics of photoprocesses induced by femtosecond infrared radiation in free Fe(CO)₅ molecules and their clusters owing to the resonant excitation of vibrations of CO bonds in the 5-μm range has been studied. The technique of infrared excitation and photoionization probing (λ = 400 nm) by femtosecond pulses has been used in combination with time-of-flight mass spectrometry. It has been found that an infrared pulse selectively excites vibrations of CO bonds in free molecules, which results in a decrease in the yield of the Fe(CO)₅⁺ molecular ion. Subsequent relaxation processes have been analyzed and the results have been interpreted. The time of the energy transfer from excited vibrations to other vibrations of the molecule owing to intramolecular relaxation has been measured. The dynamics of dissociation of [Fe(CO)₅]_n clusters irradiated by femtosecond infrared radiation has been studied. The time dependence of the yield of free molecules has been measured under different infrared laser excitation conditions. We have proposed a model that well describes the results of the experiment and makes it possible, in particular, to calculate the profile of variation of the temperature of clusters within the “evaporation ensemble” concept. The intramolecular and intracluster vibrational relaxation rates in [Fe(CO)₅]_n clusters have been estimated.     

A Compact Pulsed HF Laser Based on an Auto-Wave Photon-Branched Chain Reaction

Huge energy gain is detected theoretically in a pulsed chemical laser-amplifier based on a photon-branched chain reaction initiating in a gaseous disperse medium composed of H₂–F₂–O₂–He and Al particles by focused external infrared radiation. It is shown that this effect is observed due to the other optical effect of diffractive multifocal focusing of the input radiation on a certain type of bicomponent optical system coupled structurally with the input mirror of an unstable telescopic laser cavity. Such a relatively simple bicomponent diffraction system, consisting of two plane screens with circular apertures on a given optical axis, enables one to focus the input beam without using classical refraction elements such as lenses and prisms. The focusing of the input signal ensures the minimization of the initially excited volume of the laser active medium and the appropriate sharp lowering of the necessary energy of the input pulse up to 10^-6 J. This enables the laser system to reach a high value of the energy gain of 10⁹. The huge laser energy gain allows us to use a master oscillator in the form of a small microjoule laser powered by an accumulator, and consequently makes it possible to construct a completely self-contained compact pulsed chemical HF-laser.     

Monomer counterrotations and tunneling splitting in CO dimer by data of millimeter wave spectroscopy

Analysis of the rotational spectrum of the molecular dimer (CO)₂ measured in the millimeter wave range has been performed and four new rotational states are revealed. Three of these states are characterized by almost free rotations of both monomers in the dimer. These states have approximately the same first term σ in the expansion of the rotational energy in powers of the rotational angular momentum J for various values of the momentum projections on the dimer axis (K=0, 1, 2) and various rotational constants B. The intrinsic rotational angular momenta of CO dimers, j₁=j₂=1, are determined from the σ value. In addition, a state with K=2 is found which corresponds to one of the known shape isomers of (CO)₂. The values of the tunneling splitting for each of the new states are determined. The results indicate that previous data on the suppressed tunneling are determined by the asymmetry of internal rotations in the CO monomers rather than by the _K value.     

Master-oscilltor-amplifier electroionization carbon monoxide laser system and propagation of its radiation through atmosphere

Conclusion Thus, we have created an EI carbon monoxide laser systems, operating by the scheme master-oscillator-amplifier. We have experimentally studied the amplification and absorption of IR (5–6 m) by multilevel active medium of EI CO laser. Conditions of saturated amplification of EI CO laser radiation have been found. By using various methods we have performed the formation of the EI CO laser system spectrum in accordance with atmospheric transparency windows. It should be noted that EI CO laser system with selected spectral lines can be used in laser ranging, laser chemistry, and laser isotope separation.     

Tunable te-CO2 laser-pumped formaldehyde far-infrared lasers: Offsets, assignment, and superfluorescence

Sixty and three absorption transitions in D₂CO and H₂CO, respectively, have produced a number of far infrared laser lines when they are pumped by an etalon-tuned TE-CO₂ laser. Almost all the absorption transitions pumped previously by a free runing TE-CO₂ laser have been efficiently pumped by the etalon tuned CO₂ laser and found to have offset within ±500 MHz from the line-center of the relevant CO₂ pump lines. 22 (1) absorption and 63 (4) emission lines of D₂CO (H₂CO) are assigned. Some of these lines have generated superfluorescence. In paticular, the D₂CO 319-m line pumped by CO₂-9P(32) delivered an output energy of approximately one half that of the well-known D₂O 66-m. It is shown that a large electric dipole moment and an appreciable amount of fractional population in the lower level of the pump transition of this line are responsible to the superfluorescence.     

CO-laser side-band spectrometer: Sub-Doppler heterodyne frequency measurements around 5 µm

We report the realization of a tunable sub-Doppler heterodyne spectrometer with high absolute accuracy, employing side-band generation with a CO laser. The fixed-frequency CO-gas laser, working from 4.7 to 8.4µm, is made partially tunable by the use of microwave side-band generation in a CdTe Electro-Optical Modulator (EOM). This leads to tunable radiation of high spectral purity. We describe the design of the microwave EOM, adapted to the CO laser, its performance and its first application to highly accurate frequency measurements. The side-band radiation is used for sub-Doppler stabilization of the CO laser, while the carrier frequency is mixed with the frequencies of two CO₂ reference lasers. As a first result, we present measurements of OCS transitions in the 4.9µm (61 THz) region, reaching an absolute accuracy of 30 kHz (/ = 5×1O^–10). Further application of our spectrometer to calibration gases will establish a variety of InfraRed (IR) calibration standards with a new quality of accuracy. On visit from: Fachbereich Physik, Humboldt-Universität zu Berlin     

Emission brightness,photon yield,and radiation losses of ultrarelativistic electrons in oriented thick crystals

The brightness E_rad/ of -radiation produced in oriented single crystals and amorphous targets of various thicknesses by electrons with E₀=900 MeV has been measured experimentally. Comparison with theoretical calculations reveals that the radiation channeled in the axial direction in diamond has the maximum brightness. The measured angular distributions and spectral composition of the radiation have been used to determine the photon yield in the cone with angle _c=0.6 mrad and it is shown that diamond has no competitors in this respect. It is concluded that the use of targets made of single crystals with Z as small as possible (diamond and beryllium) is preferable.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 8–20, June, 1991.We wish to express our sincere gratitude to Professor E. Uggeroi for providing a perfect tungsten single crystal.     

Near-Field Diffractive Optical Pumping of a Laser Medium

A Nd:YAG rod active element placed inside a resonator was pumped by the second harmonic radiation (the wavelength =0.532 m) of a Q-switched Nd:YAG laser diffracted at a circular aperture. Various distributions of pumping intensity in the Fresnel (near-field) region along the direction of the pump beam diffraction were produced. Inversion profiles with maxima or minima at the resonator axis were formed in the active element, depending on its distance from the circular aperture. Gain-switched operation of the Nd:YAG rod laser at =1.064 m is reported at the fundamental mode and also at the TEM₀₁, TEM_01* and other higher-order modes for different positions of the active element in the near-field region. Applications of such diffractive optical pumping for the concentration of the pumping radiation into the active media and for laser beam profling are discussed. © 2004 The Optical Society of Japan     

On the origin of the acoustic signals generated in KDP by pulsed UV laser excitation

The origin of the acoustic signals that are generated in the bulk of a KDP crystal during irradiation with short UV laser pulses is determined. The generation of these signals by excitation with moderate or high optical fluences is linked to the evolution of the population of point defects that is generated in the crystal by absorption of two UV photons. These defects are bleached due to their efficient linear absorption of UV radiation, and their non-radiative relaxation is shown to be the origin of the acoustic signals. The rate constants for the different processes involved in both the linear and the non-linear interactions were determined from the experiments presented here. Characteristic values for the quantum efficiency for the generation of defects, _F = 0.95 ± 0.05, and for the quantum efficiency for bleaching of defects, _B = 0.065 ± 0.005, were obtained for 266-nm laser radiation. The model developed for the intensity of the acoustic signals reproduces the experimental facts with very good accuracy.     

New Series of Dyes for Flashlamp-Excited Lasers

A new series of laser compounds which are derivatives of 7H-benzo[4, 5]imidazo[1, 2-c]chromeno[3, 2–e]pyrimidine have been developed and their working characteristics are presented. It is shown that the new compounds fluoresce with a high quantum yield (0.83–0.97) in the green spectral region; their methanol solutions gave effective lasing upon flashlamp excitation with a pulse duration of about 2.0 sec at the level 0.5. In a nonselective cavity they emit laser radiation in the range 540–570 nm. The influence of the molecular structure of the investigated dyes on their fluorescence and laser characteristics is discussed.     

Polarization Characteristics of the He–Ne Laser Radiation Reflected from Rhododendron Leaves Subjected to Acid Treatment

Results of laboratory simulation experiments on the influence of H₂SO₄ solutions on the optical characteristics of the radiation reflected from Rhododendron smirnovii leaves illuminated at an angle of 55° by He–Ne laser radiation ( = 0.63 m) linearly polarized in the plane of incidence are presented. The coefficients of correlation between the optical characteristics of the reflected radiation, the concentration of the acid, and the pigment composition of the leaves have been calculated. It is shown that the influence of acidic stresses on the polarization characteristics of the radiation reflected from a leaf manifests itself indirectly as changes in the concentration of chlorophyll a and chlorophyll b and changes in their ratio in the leaf when observation is performed at angles of 50–60°.     

Changes in the Polarization Characteristics of He–Ne Laser Radiation Reflected From Plant Leaves

It is shown that the widest differences in the values and angular distributions of the polarization characteristics of the radiation reflected from the leaves of different kinds of plants are observed when a leaf is illuminated at an angle of 55° by He–Ne laser radiation ( = 0.63 m) linearly polarized in the plane of incidence. It has been found that the radiation reflected from a leaf becomes elliptically polarized at observation angles of 55° ± 10°. The ellipticity of the radiation reflected from a leaf depends on the thickness of the leaf plate and the position of the top or undersurface of the leaf relative to the direction of illumination.     

Polarization Characteristics of He–Ne Laser Radiation Reflected by Glass‐Reinforced Plastic

We have measured the Stokes parameters of the He–Ne laser radiation ( = 0.63 m) reflected at angles of incidence from 5 to 70° by glassreinforced plastic based on a siliconorganic polymer binder before and after its heating to 1200 K by CO₂ laser radiation. The probe radiation from the He–Ne laser is linearly polarized parallel or perpendicular to the incidence plane. It is shown that the flux reflected in the mirror direction by samples illuminated at a Brewster angle ( 56°) by He–Ne laser radiation linearly polarized in the plane of incidence contains a component with elliptical polarization.     

Spectral‐Polarization Contrasts in the Problems of Remote Sensing

The results of the investigation of the angular and spectralpolarization characteristics of 4501080nm radiation reflected from the surfaces of natural (leaves of trees, bark) and artificial (colored smooth surface, fabric) objects are discussed. Based on a study of the contrasts between these characteristics, we have determined the most informative spectralpolarization characteristics and the spectral and angular intervals the use of which in remote optical observations of objects would allow their most effective discrimination.     

Calculation of the Loss Coefficient of Amplified Luminescence in the Active Layer of a Laser Diode

A method to calculate the loss coefficient of amplified luminescence _loss ^lum in the active layer of a laser diode on the basis of radiation transfer equations and the balance between emission, amplification, and absorption of spontaneous radiation is suggested. The values of _loss ^lum and also of the density of fluxes of amplified luminescence have been determined in one- and two-dimensional approximations for laser diodes based on GaAs, GaN, and ZnSe compounds with different configurations of resonators.     

On the Neutron Yield in the Two-Beam Scheme of Laser Heating and Compression of Spherical Shell Targets with a Low‐Density Coating

At the initial stage of development of large-scale multiple-beam laser facilities for the ignition of the fusion reaction, facilities with a small number of beams is expected to be created. Such facilities are characterized by poor symmetry of irradiation of spherical targets. We have shown that with appropriate design of the target and distribution of the radiation intensity in laser beams the attainment of a neutron yield of 10¹⁵-10¹⁶ is possible even in twoside irradiation of the spherical targets.     

Direct generation of photons in\tilde v_e e-annihilation into hadrons

In the quark-parton model we obtain an expression for the effective cross section of the process of direct photon generation in the annihilation of an antineutrino and an electron into hadrons (_e + e + X). The angular and energy dependences of the photons are investigated. It is shown that for large photon energies, the contribution from hadronic radiation dominates that from leptonic radiation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 98–103, November, 1987.     

Indicatrices of the Radiation Intensity of Laser Plasma Formations in the Air

We have investigated the indicatrices of the visible and IR radiation of laser plasma formed under irradiation of cadmium, indium, and silicon in the air by radiation from a monopulsed neodymium laser with a power density at the irradiation spot of up to 12 GW/cm² on the first harmonic and up to 4 GW/cm² on the second harmonic. It is shown that the radiant intensity indicatrices have a prolate form depending on the target material, the spectral range of observation, and the power density of the acting laser radiation. The radiant intensity of laser plasma in the 0.3–4.2 m range is approximately proportional to the laser radiation power density and depends on the target material.     

Simulations of a photopumped X-ray laser using the H-like Cl−Li-like Se scheme

Calculations of the modal photon densities and gain in a photopumped Cl XVII-Se XXXII X-ray laser are presented. In this paper we undertake a realistic simulation of the generation of both Cl and Se plasmas, using a high-power optical laser, which includes radiation from both Ly-α fine-structure components of H-like Cl pumping the 2p_3/2-5d_5/2 transition in Li-like Se. The calculations are performed in two dimensions in a realistic geometry taking into account plasma gradients. This gives information about the spatial extent and time evolution of X-ray lasing gain on the 5-4 transitions in Li-like Se. We find that gain (about ) is expected only when the optical laser includes a pre-pulse. Calculations show that the absorption of pumping radiation in the pumped plasma can reduce the gain by 20%. Time-dependent calculations have shown that the gain is reduced by 30% in comparison to the steady-state calculations. The effect of the spectral profile and self-radiation of 5d_5/2-2p_3/2 transition in Li-like Se reduces the gain by about 2%.