We report on the investigation of narrow sub-Doppler-width resonances observed at the D2 line of Cs atoms (Fg = 4 → Fe = 3, 4, 5 hyperfine transitions), confined in thin optical cells. These cells have a thickness of L = 6λ (λ = 852 nm) and L = 700 μm, and are irradiated by two narrow-band laser radiations (one with fixed and the other with scanned frequency). We show that for zero frequency detuning of the fixed-frequency laser from the Fg = 4 → Fe = 5 hyperfine transition, its absorption spectrum in the thin cell consists of resonances, centered at the respective hyperfine transitions. The spectral widths of these resonances range from 2 to 20 MHz, and they are characterized by a good contrast and extremely small Doppler background. This spectrum is highly sensitive to the frequency offset of the fixedfrequency laser. The analysis leads to the conclusion that the spatial restriction of Cs vapor suppresses the interaction of the light with atoms with significant velocity component along the direction of the laser beam propagation.
The fluorescence and non-linear absorption spectra of Cs133 vapour in an extremely thin cell were calculated by using the perturbation theory with respect to the pumping field intensity. The problem of the atoms’ non-linear polarization was solved for arbitrary values of the total momenta of the resonance levels pumped by a linearly-polarised laser field. It was demonstrated that the spontaneous emission from the upper level affects the amplitude and sign of the lower level longitudinal alignment and results in a change of the amplitude and sign of the non-linear absorption resonance at the closed transition. The comparison of the numerical calculations with the experimental data for the D2 line of 133Cs shows a very good agreement.
In the present work we investigate the relation of the polarization moments having different ranks with the tensor components which form the observable integral CPT signal, in the presence of a stray magnetic field. A numerical experiment with parameters close to the real ones is performed, using a program based on the irreducible tensor operator formalism1. The integral fluorescent signal is calculated for the non-polarized fluorescence at different laser power excitation. Detailed analysis of the numerical solutions for all tensor components which describe population and alignment allows visualizing the dynamics of their behavior in dependence on the experimental geometry and laboratory magnetic field B′. The dependence of population f00, longitudinal f02 and transverse f22 alignment in the presence of transverse magnetic field is investigated. The shape and sign of the resonance change with laser power.
KEYWORDS: Luminescence, Polarization, Magnetism, Signal detection, Fluorescence spectroscopy, Coating, Chemical species, Rubidium, Magnesium, Magnetic sensors
In this work we investigate the magneto-optical resonance on 87Rb D1 line. In two-level degenerated system this resonance is due to the interference between the Zeeman sub-levels, created by interaction of resonance linear polarized laser beam with the atoms. The observed signal is detected by sweeping magnetic field B around its zero value. This phenomenon is also known as a Coherent Population Trapping (CPT) in Hanle-configuration. In a coated vacuum cell the fluorescence signal has a complex form, because the anti-relaxation coating preserves the created coherence, having different relaxation rates. The ground state coherence is transmitted by the laser field to the upper level; thereby polarization moments with different rank contribute to the fluorescence. The manifestation of the different polarization moments in the observed signal depends on the geometry of the experiment – direction of observation, plane of the laser polarization, polarization of the registered light. The resonances obtained in the fluorescence having different polarization are compared in order to clear up what are the contributions to the fluorescent signal from the polarization moments with different rank. The experiment is performed on the D187Rb line, F=2→ F=1 transition in a paraffin-coated cell. The magneto-optical resonances, detected in two orthogonal polarizations are measured. Numerical calculations with parameters, close to the experimental ones are performed by using a program, which is based on the irreducible tensor operator formalism. The results of the modelling are compared with the measured ones at different experimental conditions.
We report experimental and theoretical examinations of the peculiarities in Velocity Selective Optical Pumping (VSOP) resonance behavior at open and closed hyperfine transition spectra of Cs atoms (on the D2 line), confined in optical cell with thickness L = 6λ, where λ = 852 nm. For linear and circular polarizations of the irradiating light, open transitions exhibit reduced absorption (fluorescence) VSOP resonances whose contrast increases with atomic concentration and light intensity. However, in case of closed transition the situation is different, the enhanced absorption (fluorescence) VSOP resonance reverses its sign with the atomic concentration and light intensity. Theoretical analysis based on the density matrix formalism, taking into account the statistical tensors describing atomic population and longitudinal alignment, shows that the VSOP resonance sign reversal at the closed transition can be attributed to the efficiency reduction of population transfer by the spontaneous decay with atomic source temperature.
μInterest to the narrow band gap semiconductors for example Pb1-xCdxSe is connected with problem of creation of new
sources of IR radiation. Possibility of control of the properties of polycrystalline films of the lead chemical compounds
by luminescent and Raman methods is considered.
The fast development of CPT applications and the need of good magnetooptical sensors result in an increased interest in
the Coherent Population Trapping (CPT) resonances and the processes that determine their shape. In this work the shape
and width of the CPT resonances are investigated in two different paraffin-coated Rb vapor cells from point of view of
understanding the processes influencing the shape of the resonances and building of miniature and sensitive detector. The
dependence of the shape of the resonances on the laser power is measured. Narrow resonances on three hyperfine
transitions of the D1 87Rb line are registered. For explanation of the bright structure in the resonance shapes at low laser
powers analysis of the influence of different processes is made.
Coherent Population Trapping (CPT) resonance obtained with linearly polarized laser beam through magnetic field
sweep (Hanle configuration) was investigated in 87Rb D1 line. Influence of the coherence due to high-rank polarization
moment (hexadecapole moment), created in the medium, on the CPT resonance shape was calculated and experimentally
detected in fluorescence. It was observed as an inverted structure at a high power of excitation. To distinguish resonances
due to coherence between Zeeman sub-levels with ΔmF=2 from that with ΔmF=4, the Larmour frequency ωLmodulated by applying an a.c. magnetic field (a.c. MF). Resonance signal at frequency corresponding to 4ωL observed in a fluorescence, and after lock-in on the frequency corresponding to frequency difference between sub-levels
ΔmF=4.
A model for description of the shapes of the coherent population trapping (CPT) resonances at different geometries of
excitation and observation is developed. The numerical calculations, based on the irreducible tensor operator formalism,
take into account the experimental geometry, the velocity distribution of the atoms, the Gaussian distribution of the laser
beam intensity and the high rank polarization moments (HRPM). The results for different laser beam diameters, aperture
of the detection, position of the photodetector etc. are compared with the experimental data. A method for description of
the experimental shapes is proposed.
We report new results on the light enhanced teeth whitening obtained in a research collaboration financed by the Medical
Science Council of the Medical University of Sofia. The project is an extension of previous research and its basic goal is
to develop new teeth bleaching substances and procedures, in which the activators are diode lamps (LED).
Comparative studies of MO resonances and MG responses with and without resonant laser irradiation were
carried out to establish the interconnection of the effects and the influence of the self-alignment destruction on the MO
signal in positive column discharge. These studies aim to clarify the possible formation mechanisms of the neon 1 si
(2p53s) states coherences and to examine the possibility to use the galvanic resonances for estimation of the relaxation
constants of the neon 1 s5 state.
In the present work we consider theoretically the influence of an arbitrary oriented additional magnetic field on the main properties of the Coherent Population Trapping (CPT) resonances in fluorescence and/or in absorption. The exact numerical solutions are obtained for the tensor components Ρk0 (ρ = f, φ) which describe the population and the longitudinal alignment of the resonant (f) levels with quantum numbers Ff 0 and Ff =1, exited with a single frequency laser field from the ground (φ) state with Fφ=l and Fφ=2. Numerical simulations was used to obtain the width and the amplitude dependences of the resonances under different parameters and parasitic fields. The results are in qualitative agreement with resent experimental investigations.
The absorption and fluorescence spectra of a submicron Cs vapour layer under resonant excitation on the D2 line are measured. Sub-Doppler features centered at the resonance frequency of the hyperfine (hf) transitions have been observed. Substantial changes in the amplitude and width of the sub-Doppler resonances for individual hf transitions were recorded in dependence on the intensity of the incident laser radiation. In the fluorescence spectra narrow dips due to the effects of saturation have been observed. We also report about the observation of coherence resonances in Hanle configuration obtained at cell thickness of the order of the wavelength of the laser light.
In this work we discuss Hanle absorption resonances obtained in a room temperature NO2 cell, irradiated by a single mode Ar+ laser. The method used is based on measuring the changes of polarization of the transmitted laser beam crossing the NO2 cell, placed in a transverse magnetic field. The resonant changes in the measured absorption signal, that occur in the magnetic field, could be explained as destruction of the alignment of the absorbing rotational state(s), belonging to the ground state (0,0,0) X2A1. The observed signal is described as a sum, taken over all F'u and F"g values, for the chosen N",J"→N',J' transition. The numerical calculations show, that despite the contributions of terms with different signs, the total signal for all examined cases preserves its sign, the determining role being played by the most intensive hf components. Thus a confirmation of Chaika's hypothesis for creation of NO2 ground state levels (self)alignment is obtained as well an estimation of the effective life time for coherences τ(2).
The purpose of this communication is to summarize and compare the results obtained under the project "New all-optical systems and methods for magnetic and electromagnetic field measurement", financed by EC (contract G6RD-CT-2001-000642). The main aim of the project is investigation of the potential of different approaches based on the effect of Coherent Population Trapping (CPT) for magnetic field measurement. The investigated approaches are: (i) CPT prepared by coupling pairs of non-degenerate Zeeman sublevels belonging to the two ground-state hyperfine components of alkali atoms by means of polychromatic laser field; (ii) CPT prepared by coupling degenerate Zeeman sublevels belonging to a single ground-state hyperfine component of alkali atoms by means of single-frequency laser field of appropriate polarization at zero magnetic field (MF); and (iii) polychromatic laser field coupls pairs of non-degenerate Zeeman sublevels belonging to a single ground-state hyperfine level of alkali atoms.
Theoretical model describing the influence of a parasitic magnetic field on CPT-resonance in Hanle configuration in a strong laser field was proposed. The exact solution of the system of equations has been obtained for the transition between a ground state with Jφ=1 and an excited state with Jf=0 and/or 1. The solutions for the tensor components f k0, describing the population and longitudinal alignment of the upper level f, are obtained, and the dependences of the resonances on the different parameters and parasitic fields were analyzed. The results are in qualitative agreement with resent experimental investigations.
The present investigations are directed at a more detailed studying of methods for colour determination aimed at estimation of human teeth whiteness degree, sufficiently handy for common use in clinical practice. In order to be obtained unbiased results of the whitening, specific techniques for the degree of whiteness (coloration) determination had been developed on the basis of common colorimetric and spectral methods and apparatus, including a standard computer processing and accorded to the three-dimensional colour scheme Vita 3D. Comparative experimental investigations with two lasers (Ar+, CuBr) and three experimental whitening compositions for treatment of 6 different groups of samples were carried out. The results of the applied spectral and colorimetric techniques are in a good agreement with those of the standard computer processing of the corresponding digital photographs and comply with the visually estimated degree of the teeth whiteness judged according to the standard reference scale commonly used in the aesthetic dentistry.
The lower level of laser transition on 632.8 nm (2p4) has been investigated using Hanle absorption resonance method. Advantages of the approach are discussed. Radiation width and collision (pressure and discharge current broadening are determined.
A theoretical model describing magnetic resonance in a strong laser field was proposed. The exact solution of the well known system of equations was solved for the transition between a ground state with Jφ = 1 and an exited state with Jf = 0. It was shown that in the spontaneous emission intensity from the level with Jf = 0 resonant changes will be observed when the frequency ω of the altering magnetic field becomes equal to the Larmor-frequency determined by the constant magnetic field Ho.
A more detailed investigation of optogalvanic signals, induced by resonant laser excitation of Se, Ne and Ar ions in a hollow cathode discharge, is carried out in the present work. An immediate goal was to analyze and verify some hypothesis about the mechanisms, responsible for the formation of such signals, taking into account their dependence on the current characteristics, the kind and pressure of the buffer gas, as well as their radial distribution.
In the present work some results of the comparative measurements of the tooth whitening effect using a bleaching agent activated by Ar+ (emitting at 488 nm) and CuBr (emitting at 510 nm) lasers are reported. It is shown that the whitening effect is observed in both cases. Some of the peculiarities in application of CuBr laser in the field of aesthetic dentistry are discussed, as well as the possibility to replace the more expensive Ar+ laser. In order to ensure reliable results from a light-chemical treatment of the teeth, as spectroscopy method has been developed and applied. The method is based on the analysis of laser-induced fluorescence spectra of the teeth with different coloring.
A simple theoretical description is proposed aiming at a qualitative explanation of the observed in 11 dependences of the fluorescence from the resonant Rb levels excited by a single frequency diode laser on the magnetic field, when Hanle effect configuration of the experiment is used. The components of the statistical tensor for population and longitudinal alignment are calculated by iteration method up to fourth order terms. The spontaneous emission transfer influence is taken into account. A good qualitative agrement between calculated and experimentally observed resonances is obtained.
Laser induced Galvanic Signals (LIGS) were observed in a Se- buffer gas hollow cathode (HC) discharge irradiated by He- Se+ or cw dye lasers. Radial and current dependences were studied. A similarity of the radial dependences for the two buffer gases He and Ne and maximum in the current dependences are registered. The possible mechanisms which form GS responses in Se HC discharge are discussed.
We report the observation of magneto-galvanic resonances (MGR) in traditional galvanic detectors--Ne-Cu (`Narva' type) and Ne-As (Pye Unicam) hollow-cathode lamps (HCL). We carried out comparative investigations of the characteristics of the MGR and the laser-induced galvanic signals arising as a result of the irradiation of the HCL by different laser lines. We believe that the variation of the discharge conductivity is caused by the self-alignment of the 1s5 Ne metastable state. We also discuss some of the possible mechanisms that may relate the self-alignment destruction to the discharge conductivity change.
The intensity fluctuations of laser beam cross section caused by a local air turbulence have been experimentally investigated. Registration of successive saturated images of the laser spot has been provided by imaging camera using a computer for image acquisition and processing. Evaluation of the state of turbulence by estimation of the refractive index structure parameters has been carried out.
Resonances with complex shape have been obtained experimentally in the magnetic field dependence of the optogalvanic signal induced in a Cu/Ne hollow cathode discharge by 632.8 nm laser radiation. Either population trapping or transfer of coherence are considered as possible mechanisms of formation of these resonances. Both of them, however, appear insufficient to obtain full qualitative explanation of the observed dependencies.
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