Generation of terahertz radiation by the optical breakdown induced by a bichromatic laser pulse

Experimental results are presented on generation of terahertz radiation by the air breakdown induced by a high-intensity laser pulse having not only a fundamental component, but also a second-harmonic one. A theoretical explanation of the experimental data is proposed, based on a model of field ionization of a gas by a bichromatic laser.     

Coherent approach to analysis of modulated optical radiation

A method is proposed for determining the modulation parameters of optical radiation that does not require wide-band photodetectors for modulation at high and microwave frequencies. The method is based on measurement of the time coherence of optical radiation containing a modulation signal.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 25–28, April, 1930.     

Intensity modulated silver coated glass optical fiber refractive index sensor

Miniature optical fiber sensors with thin films as sensitive elements could open new fields for optical fiber sensor applications. Thin films work as sensitive elements and a transducer to get response and feedback from environments, in which optical fibers act as a signal carrier. A novel Ag coated intensity modulated optical fiber sensor based on refractive index changes using IR and UV-Vis(UV-visible) light sources is proposed. The sensor with an IR light source has higher sensitivity compared to a UV-Vis source. When the refractive index is enhanced to 1.38, the normalized intensity of IR and UV-Vis light diminishes to 0.2 and 0.8, respectively.     

Relaxation experiments with synchrotron radiation

Relaxation phenomena show up in standard energy domain Mössbauer spectra via line broadening. The evaluation of such spectra is in most cases done by adopting the stochastic theory mainly developed in the 60s and 70s. Due to the time structure and the polarization of the synchrotron radiation nuclear resonance forward scattering in the time domain gives valuable information on relaxation mechanisms. We report here mainly on Nuclear Forward Scattering (NFS) experiments investigating the paramagnetic relaxation of the Fe³⁺ ion in (NH)₄Al_0.95 ⁵⁷Fe_0.05(SO₄)₂·12H₂O and briefly on recent investigations on charge fluctuations in Eu₃S₄.     

Relaxation experiments with synchrotron radiation

Hyperfine Interactions - Relaxation phenomena show up in standard energy-domain Mössbauer spectra via line broadening. The evaluation of such spectra is in most cases done by applying the...     

Mid-infrared radiation transmission through fluoride glass multimode optical fibers

Measurement of the transmission laser radiation from Q-switched and free-running Er:YAG lasers operating at 2.94 μm through fluoride glass multimode optical fibers of 448, 465 and 620 μm core diameter were performed. Attenuation measurements were obtained as a function of the laser energy input, of the bending angle and of the radius of curvature. The fibers exhibited low attenuation under straight and bent conditions. The output beam quality was also studied using the appropriate beam profiler. The output beam profiles showed a central multi-spiked energy distribution.     

Collinear interaction of bichromatic radiation with one acoustic wave in biaxial crystals

The regime of collinear interaction of bichromatic optical radiation in biaxial crystals is considered. It is shown that the possibility of the realization of such an interaction is due to dispersion of the optical axes in a biaxial crystal. Zh. Tekh. Fiz. 69, 131–132 (January 1999)     

Experimental studies of polarization of laser radiation in a rotating optical glass

The results of experiments on observation of rotation of the plane of polarization of coherent laser radiation with wavelength λ = 0.632991 μm after propagation through a rotating optical disk made of TF3 glass with refractive index n = 1.71250 are analyzed. The experiments were conducted at angle of ray incidence on the flat disk surface ?₀ = 60°, and the rotational speed of the disk was varied from 0 to 200 Hz in both directions. The results indicate that rotation of optically transparent, homogeneous, and isotropic dielectric causes rotation of linear polarization of the monochromatic electromagnetic plane wave by several tens of degrees. At a rotational speed of 3 Hz, the rotation of polarization reached Δφ = 70° for the vertical component of laser output polarization. The dependences of the angle of rotation of polarization and the degree of polarization of the rays on rotational speed are nonlinear and are attributed to the appearance of substantial anisotropic properties in a rotating dielectric.     

Relaxation in the multiparameter model of the glass transition

The standard theory of the glass transition involves a set of one o r more ordering parameters which become frozen in the glassy state. Both thermodynamic relationships and structural relaxation experiments point to the need for a multiparameter model. In this paper the multiparameter theory is examined in a linear approximation, in which the first order extensive thermodynamic functions vary linearly with changes in temperature, pressure, and the ordering parameters.     

外调制光发射机双调制补偿的理论分析

在对外调制光发射机的原理及其非线性补偿技术进行阐述的基础上,重点阐述了MZ调制器的双调制补偿方案的原理和系统结构,并对这一方案的关键技术进行了详细的理论分析。通过分析和计算机仿真验证了这种方案的可行性。     

Dressed-atom model for optical pumping with modulated light

The interaction of an atomic system with the light modulated at the ground-state Zeeman frequency is analysed by the dressed atom method. The analogy between the magnetic resonance and optical pumping with modulated light is emphasized. The dependence of the effects expected in light absorption on the geometry of the experimental arrangement and light polarization is given.     

Neural stimulation with optical radiation

This paper reviews the existing research on infrared neural stimulation, a means of artificially stimulating neurons that has been proposed as an alternative to electrical stimulation. Infrared neural stimulation (INS) is defined as the direct induction of an evoked potential in response to a transient targeted deposition of optical energy. The foremost advantage of using optical radiation for neural stimulation is its spatial resolution. Exogenously applied or trans‐genetically synthesized fluorophores are not used to achieve stimulation. Here, current work on INS is presented for motor nerves, sensory nerves, central nervous system, and in vitro preparations. A discussion follows addressing the mechanism of INS and its potential use in neuroprostheses. A brief review of neural depolarization involving other optical methods is also presented. Topics covered include optical stimulation concurrent with electrical stimulation, optical stimulation using exogenous fluorophores, and optical stimulation by transgenic induction of light‐gated ion channels.     

Transport behaviour of a Bose Einstein condensate in a bichromatic optical lattice

We investigate the Bloch and dipole oscillations of a Bose Einstein condensate (BEC) in an optical superlattice. We show that, as the effective mass increases in an optical superlattice, the BEC is localized in accordance with recent experimental observations [J.E. Lye et. al. Phys. Rev. A 75, 061603 (2007)]. In addition, we find that the secondary optical lattice is a useful additional tool to manipulate the dynamics of the atoms.      

Relaxation times and low-temperature specific heat of the quadrupolar glass

Computer simulations of a simplified model for molecular orientational order in certain solids provide results consistent with glass-like linear specific heat c_v at low temperatures. The temperature dependence of the quadrupolar relaxation time is found to be well described by the expression 1/τ～exp [-A/(T?T₀)], with T₀ well below the onset of the linear c_v regime. The relationship to experiments on solid hydrogen is discussed.     

Experimental preparation of pure superposition states of atoms via elliptically polarized bichromatic radiation

We propose a simple and effective way of creating pure dark superposition states. The generation of pure states is carried out by using bichromatic radiation with controllable polarization ellipticity. We experimentally confirm analytic formulas for polarization ellipticity to obtain m-m pure dark states in the system of Zeeman sublevels of alkali atoms. For 87Rb we experimentally accumulated 60% of the atoms in the 0-0 dark state and 50% into the (+/-1) - (+/-1) dark states.     

Excitation of a hydrogen atom by bichromatic radiation with the frequency ratio 1:2 in the presence of electric field

In the framework of perturbation theory, a probability of excitation of a hydrogen atom from the ground to the first excited state under bichromatic laser radiation with the frequency ratio 1:2 in the presence of electric field is calculated, taking into account quantum interference of two process channels. In the case under study, a coherent superposition of the 2s-and 2p-states, necessary for quantum interference to occur, is formed under the action of the external electric field. The excitation probability is analyzed depending on the relative phase of monochromatic radiation components (the coherent phase control) for two extreme cases: for a strong electric field, where the Stark splitting of an upper level essentially exceeds the spin-orbit one, and for the contrary limit of a weak field. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 20–28, August, 2006.     

The effect of phase noise of bichromatic radiation upon resonances of coherent population trapping

We consider the effect of the noise difference phase of a bichromatic field upon coherent population trapping resonances in the simplest three-level system in Λ configuration. The quasi-stationary solution of Bloch optical equations, which was found with some assumptions, shows that the presence of exciting short-correlated fluctuations of the phase of radiation reduces the contrast of the resonance line without affecting its spectral width. For the Gaussian phase noise the contrast suppression factor is χ = exp[?? _rms ² ], where ? _rms ² is phase dispersion. The experimental results obtained earlier by our group are analyzed.