Fiber optical Sagnac interferometer is applied for absolute calibration of ultrasonic pulsed source. Method of topological phase is used for the maintenance of &pgr;/2 phase bias of the counterpropagating waves. Non-disturbing absolute measurement of the ultrasonic displacement with sensitivity of 10-1 Å within 100 kHz ÷ 30 MHz band is demonstrated which is comparable with more complicated and expensive analogs.
Ring interferometer for ultrasonic sensing with homodyne amplification of interference signal is proposed and experimentally investigated. Owing to an inherent mechanism of suppression of laser phase noise, the proposed interferometer is significantly less critical to the path imbalance between signal and reference waves than classical interferometers with homodyne amplification (Michelson and Mach-Zander). Experiment shows that actual performance of fiber optic homodyne ring interferometer is seriously corrupted by the backscattering interference noise. Backscattering noise-free, non-ring topology of time-delay homodyne interferometer with laser phase noise rejection is discussed.
Low coherence interferometric systems using multimode fiber link between reference interferometer and sample or (and) between sample and photodetector are studied. The general theory of these systems is developed, and their real world performance in industrial environments is estimated. The hybrid interferometric systems are proposed in whose the sample is illuminated via singlemode fiber, and the light from the sample is delivered to the photodetector via multimode fiber. The advantages of such systems are shown. Possible industrial applications of multimode fiber optical interferometry for in-line measurement of geometric parameters are discussed.
New low coherence interferometric technique for remote comparison of two optical path differences utilizing common path geometry is proposed and demonstrated. The differential profiling of transparent structures by new technique is considered and demonstrated experimentally. In the experiment, nanometer accuracy of differential profiling is achieved, and high noise immunity of the proposed technique is demonstrated. The "sample-etalon" version of the technique is proposed which enables measurement of optical path difference with better noise immunity, than conventional low coherence interferometry. High noise immunity of the technique allows its efficient application for in situ precision measurements of geometric parameters of micro- and nanostructures in adverse environments.
A commercial fibre optic low coherence tandem interferometer (FOLCTI) multichannel measuring system for in-line hot point gauging of float glass is described. Optical methods of in-line absolute gauging of transparent bodies are reviewed, and the advantages of FOLCTI are shown. Multimode fibre based FOLCTI gauges are considered, and their advantages and limitations are shown. Possible industrial applications of FOLCTI gauges beyond the glass industry are discussed.
The results of many electron calculations of photoionization cross section in Kr isoelectronic sequence are presented. The resonance structure associated with excitation of autoionizing 4s4p6np states has been studied with account for the dynamic many electron correlations. Double- electron excitations are shown to play a crucial role in describing of resonance shapes.
A new improved study of resonance features has been made in the photodetachment process from such strong correlated system as negative ions with np3 half-filled shells. The photodetachment cross sections from two outer shells of Si-, Ge- and Sn- negative ions have been calculated with account of many electron correlations. The formation and autodetachment of the quasi-bound 'nsnp4' states revealed themselves as a very sensitive interference structure in the cross section.
The results of theoretical analysis of quasi one-dimensional electron gas within the Hartree-Fock approximation are presented. Ground state energies of completely polarized and non-polarized states are calculated at T equals 0. A formation of spontaneously spin-polarized state at low linear concentration of electrons and its transformation into non- polarized state as concentration grows are discussed.
In this work we present the results of the theoretical calculations of a ballistic conductivity of smooth and modulated quantum wires under nonideal conditions, i.e. at nonzero temperature and finite longitudinal bias. Deviations from the Landauer-Buttiker theory are described.
In this work we have developed a simple self-consistent spherical model for the treatment of the outer shell electron structure in the fullerene C60 molecule, starting from the self-consistent solution of the Kohn-Sham equation within the local-density approximation (LDA) for the exchange-correlation functional Exc[(rho) ]. Our model is applicable for the many-body description of various collision processes involving the fullerene C60, in which only valence electrons are important. Using our model one can describe the plasmon resonance structure in the photoabsorption and electron loss spectra in the vicinity of 19 eV.
In this contribution we present the results of many-body calculation on electron photodetachment from inner subshells of Sn- negative ion. The main attention is paid to qualitative changes in the near threshold 4d cross section induced by rearrangement effects.
We present the findings of the quantized conductance in a modulated quantum wire. The energy dependence of the transmission coefficient through a smooth and modulated quantum wire is analyzed to define the role of elastic back scattering process in the formation of the conductance oscillations and the current staircase. We demonstrate the oscillations of 1D conductance plateaus as a function of drain-source voltage that are evidence of the interference effects caused by varying the energy of ballistic holes in the modulated quantum wire electrostatically created inside the silicon self-assembled quantum well. The Aharonov-Bohm (AB) rings prepared inside the silicon self-assembled quantum wells are used to study the interference of ballistic carriers tunneling through parallel quantum wires as a function of their length and modulation which are revealed by varying the external magnetic field and the drain-source voltage. The AB double-path interferometer defined by the quantum point contacts from the leads is found to exhibit the periodic oscillations in the quantized conductance that are evidence of the magnitude and phase of the transmission coefficient through the quantum wire embedded within the AB ring's arm.
In this contribution we present the results of many-body calculations on electron photodetachment from outer subshells of Sn- negative ion. The main attention is paid to the resonance feature near 5s subshell threshold related to the quasi-bound `5s5p4(4P)' state.
The recent development of the many-body theory methods when applied to the study of structure and photodetachment characteristics for a series of negative ions (He-, B-, C-, Cr-) are reported. The aim of this work is to investigate many-electron effects which are known to play significant role in photodetachment from negative ions. The main attention is paid to the resonant processes in negative ions with open subshells, where the collective phenomena happen to be most pronounced.
We present the findings of quantized conductance (QC), Coulomb staircase (CS) and local tunneling spectroscopy (LTS) techniques which reveal the single-hole confinement and charging phenomena in the smooth and modulated quantum wires created electrostatically inside self-assembly longitudinal (SLQW) and lateral (SLaQW) silicon quantum wells. The current- voltage (CV) characteristics obtained are in a good agreement with the data of the theoretical calculations taking account of quantum interference effects in the field-dependent value of the transmission coefficient through the quantum wires that exhibit the different degree of a modulation.
Method for phase nonreciprocity measurement in optical ring resonators using low coherent light sources is proposed. Two pass low coherent ring resonant interferometer is considered, in which broadband light is intended to pass through the ring resonator, first in clockwise direction, and then, after the reflection from retromirror, in counterclockwise direction. It is shown that output light power in this interferometer depends on a frequency shift between clockwise and counterclockwise resonances, due to phase nonreciprocity in the ring, as well as light frequency shift by reflection from retro-mirror. Observation of Sagnac effect in low coherent two pass ring resonant interferometer is reported.
The new Faraday mirror for compensation of parasitic optical anisotropy in two pass single mode fiber optic systems, is proposed and experimentally tested. Proposed Faraday mirror is based on ring polarization Sagnac interferometer with Faraday cell placed on the way of counterrunning waves. Unlike conventional Faraday mirrors, where precise compensation is achieved only when Faraday rotation angle is exactly equal to 45 degrees, proposed ring interferometer based Faraday mirror is not sensitive to deviations of Faraday rotation angle from 45 degrees. In the experiment, where the quality of polarization restoration by both conventional and new Faraday mirrors have been compared good compensation by new Faraday mirror has been observed in wide range of Faraday rotation angles. As the experiment shows new Faraday mirror has the better performance then conventional one even at the angles of Faraday rotation close to 45 degrees. New FM may be applied in the fiber optic interferometric sensors, where high polarization stability is needed.
The new theoretical and experimental studies of magnetochiral optical effects in anisotropic crystals in external magnetic fields and of related magneto-optical effects are reviewed. Magnetochiral effects arise when temporal and parity symmetries are simultaneously violated. The most interesting of magnetochiral effects is magneto- optical nonreciprocal linear birefringence, which is the difference of refractive indices for counterrunning eigenwaves proportional to external magnetic field. New highly sensitive methods for experimental study of nonreciprocal linear birefringence independent of optical losses in sample crystals. To measure the anisotropy of nonreceiprocal linear birefringence the two-pass optical scheme, in which the sample crystal is placed between two quarterwave plates is developed. With this scheme, the anistropy of nonreciprocal linear birefringence in LiIO3 is measured at Ar-Kr laser lines. Also, the new accurate method for measurement of Faraday effect in anisotropic crystals in proposed, which is based on spatial segregation of eigenwaves in wedge-shaped samples. In this method, parasitic effects of natural linear anisotropy do not affect the measurements.
This report presents the results of theoretical study, performed in the atomic theory group in St. Petersburg State Technical University for last years, on electronic structure of small metallic clusters and their interactions with external fields.
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