COSMA: Coherent Optics Sensors for Medical Application is an European Marie Curie Project running from 2012 to March 2016, with the participation of 10 teams from Armenia, Bulgaria, India, Israel, Italy, Poland, Russia, UK, USA. The main objective was to focus theoretical and experimental research on biomagnetism phenomena, with the specific aim to develop all-optical sensors dedicated to their detection and suitable for applications in clinical diagnostics. The paper presents some of the most recent results obtained during the exchange visits of the involved scientists, after an introduction about the phenomenon which is the pillar of this kind of research and of many other new fields in laser spectroscopy, atomic physics, and quantum optics: the dark resonance.
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.
The interest in quantum dots fluorescence is connected with the problem of implementing new protective luminescence markers and labels. We studied the luminescence spectra of multi-sized quantum dots fluorescent labels and quantum dots fluorescent labels with different matrix pore size.
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.
Modulated optical reflectance (MOR) technique is employed for defectoscopy and structural analysis of La2/3Sr1/3MnO3(LSMO) ferromagnetic nanolayers. The optical reflectance is affected by the change of free charge carrier density due to
periodic photothermal modulation described by Drude effect. A dual wavelength setup of a pulsed heating laser and a
probe CW laser, whereas the laser focal spots are precisely aligned on the scanned sample surface, provides electrical
signal proportional to the variation of optical reflectance at each measurement point. The probe beam is modulated
selectively by reflection without interference by the substrate properties or external fields. It is shown theoretically and
experimentally that MOR signal is proportional to the thermal derivative of magnetoresistance. The described contactless
measurement may find important application in investigation of a range of new magnetoelectric devices.
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.
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.
KEYWORDS: Magnetism, Modulation, Rubidium, Luminescence, Polarization, Chemical species, Magnesium, Signal detection, Magnetic sensors, Telecommunications
In this communication we present an investigation of the influence of an alternative magnetic field (a.c.MF) on the
Coherent Population Trapping (CPT) resonances obtained in Hanle configuration. A.c.MF applied parallel to the
sweeping magnetic field creates side-bands of the CPT resonance
1. Their position in dependence on the a.c.MF
frequency and amplitude were investigated. This phenomenon was studied for the cases of linear and circular polarized
laser excitation. Coherent signal due to the hexadecapole momentum created was detected. At high amplitudes of the
a.c.MF alignment to orientation conversion was recorded.
The investigation of the coherent population trapping (CPT) resonance on the degenerate two-level system of the (Fg=2→Fe=1) transition of the 87Rb D1 line by means of Hanle effect configuration in an uncoated vacuum cell (Opt. Lett. 28, 1817, 2003), has shown that the measured in fluorescence resonance has a complex shape: a very narrow (about 1mG) resonance superimposed on a broader one (about few tens mG). In this work the narrow and wide CPT resonances are registered in fluorescence, transmitted light and Faraday rotation. The dependence of the CPT resonances structures width and amplitude are measured at different laser power densities when the registration was in fluorescence and transmission. While the narrow resonance width doesn't change in the limits of the accuracy of our measurements, the wide resonance width dependence is complex and it is different in fluorescence and transmission. The origin of the observed dependencies and the differences between CPT signals observed in fluorescence and transmission are discussed.
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.
A refractometric structure consisting of a side-polished single-mode optical fiber covered with a thin film of hydrogenated amorphous silicon (a-Si:H) has been studied. a-Si:H films have been deposited by plasma-enhanced chemical vapour decomposition of silane. The sensors elements working with zero and first order optical modes of the amorphous silicon waveguide have been demonstrated. A high sensitivity of 5300 nm per unit refractive index has been obtained for the low values of superstrate refractive indices in the range of 1.33-1.38 by using a-Si:H film with a thickness of about 14 nm, i.e. the interaction with TE0 mode of the PWG. Despite of the very low thickness of the a-Si:H film there is no need of any additional layer protecting the structure from the analyzed medium. The mechanical and optical stability of the film and its very good adhesion to fused silica eliminate the possibility of the film damaging and makes the structure reliable in use.
Coherent population trapping (CPT) resonances on the degenerate two-level system of the (Fg=2→Fe=1) transition of the 87Rb D1 line were investigated in an uncoated vacuum cell by means of level-crossing type experiments-sweeping a magnetic field around zero value and using a single laser beam. The two-photon resonance manifests itself as fluorescence canceling when the system of levels is degenerate (at zero point of magnetic field). The influence of weak transverse magnetic fields on the amplitude and width of the resonance was investigated. The CPT resonances were observed with linear, circular and elliptical polarized laser light. Transverse magnetic field widens the resonances obtained by linear and circular polarization but splits the resonance created by slightly elliptically polarized laser light. The dependence of this splitting on the elliptical ratio and experimental geometry were investigated. Due to its narrow width and sensitivity to low magnetic fields (< 1 G) this resonance is very promising for small magnetic field measurement.
Coherent population trapping (CPT) resonances in the degenerate two-level system of the Fg = 2 → Fe = 1) transition of the 87Rb D1 line were investigated in an uncoated vacuum cell by means of Hanle effect configuration. CPT signals with complex shape (narrow resonance approximately 2 mG superimposed on the wide one approximately 150 mG) were observed. The influence of weak transverse magnetic fields (0-1.2 G) on the amplitude and width of the two components was measured. The observed narrow resonances are interesting for application in high resolution spectroscopy and magnetometry.
In the present work we present a Fizeau wavemeter built on the base of uncoated optical flats for cw lasers. Testing of the wavemeter is made for a 1-mm thick wedge with apex angle of 3 min. The accuracy of the wavemeter is 5 X 10-6. As a second task we study the possibility to use a wedge with reflecting coatings for enhancement of the interference pattern. The main advantage of such a wedge is the substantial rise in the peak intensity of the reflected fringes (two orders of magnitude larger intensity for 50% reflectivity of the coatings compared with the case of uncoated surfaces). The main drawback of using coated surfaces is that they create asymmetric fringes with many subfringes. We show by computer simulation that detection of the interference pattern in the zero-shear plane ensures symmetric fringes and high-accuracy wavelength estimates up to 50% reflectivity of the wedge coatings.
KEYWORDS: Magnetism, Signal detection, Absorption, Signal to noise ratio, Nonlinear optics, Polarization, Shape analysis, Interference (communication), Luminescence, Correlation function
A nonlinear Hanle effect on the 23 P yields 33 D HeI transition has been investigated. The experiment was performed in way to eliminate from the signal the contribution of the population dependence on the magnetic field. The shapes and widths of the Hanle curves were analyzed for different saturation parameters. The signal arises from two nonresolved He transitions-the 23P2 yields33D2 and the 23P2 yields 33D3. Cross-correlation analysis was suggested to analyze the contribution of a low intensity optical signal to the main experimental curve.
In this work we present a theoretical estimation for VUV superluminescent laser gain employing electron-impact excitation and Super-Koster-Cronig decay in Zn vapors. The stimulated emission is produced on the 3d84s21G4 - 3d94p 3D3 130.6 nm two-electron transition of ZnIII. We use the existing information on atomic constants available in the literature to estimate the current densities that will be necessary to observe a significant gain, comparable to that observed in an experiment using x-ray excitation, produced in laser induced plasma. Our estimations show that such values of the gain are obtainable by pulsed electron excitation with time longitude greater than 1 microsecond(s) and high but possible current densities of the order of 10 kA/cm2.
We report magneto-optical rotation due to the interaction of atoms with a resonance laser beam. Our experiment is performed on the excited He states, 23P-33D transition, (lambda) equals 587,56nm. Two processes are responsible for the magneto-optical activity: the Zeeman coherences, induced in the absorbing level, and the optical pumping processes, each of them due to the laser beam excitation. The Zeeman coherence creates peaks with a width determined by the coherence relaxation rate, while the optical pumping creates a structure with a width in the order of the natural width of the transition. Due to the difference between the relaxation rates of the 2P and 3D He levels, the two parts of signal are well resolved and depend on the He pressure in different ways. The narrow coherence signal disappears at high He pressure, unless the amplitude of the optical pumping signal increases. The optical pumping signals saturates as He pressure increased and changes its sign. At high gas pressures, such that only the optical pumping signal exists, an increase of the He pressure leads to the narrowing of both the 'classical parabolic dependence' and the optical pumping signal.
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