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Alkali metal vapors enable access to single electron systems, suitable for demonstrating fundamental light-matter interactions and promising for quantum logic operations, storage and sensing. However, progress is hampered by the need for robust and repeatable control over the atomic vapor density and over the associated optical depth. Until now, a moderate improvement of the optical depth was attainable through bulk heating or laser desorption – both time-consuming techniques. Here, we use plasmonic nanoparticles to convert light into localized thermal energy and to achieve optical depths in warm vapors, corresponding to a ~16 times increase in vapor pressure in less than 20 ms, with possible reload times much shorter than an hour. Our results enable robust and compact light-matter devices, such as efficient quantum memories and photon-photon logic gates, in which strong optical nonlinearities are crucial., Robust and fast control of the atomic vapor pressure in alkali vapor cells would greatly extend their use for many quantum technologies. Here, the authors exploit plasmonic absorption in a cell coating containing gold nanoparticles to control the vapor pressure with milliseconds response time.

A high contrast (∼48%) Velocity Selective Optical Pumping (VSOP) resonance at the closed transition Fg=4→Fe=5 of Cs-D2 line is obtained in the fluorescence signal under co-propagating pump-probe configuration. We use a 5.2 μm cell operating at reduced temperature (∼55 °C) and the intensity of the pump-laser is kept lower than that of the probe-laser. The observed sharp narrow structure is suitable for side-arms frequency-locking of the cooling- (i.e. probe-) laser in a cold atom experiment, with possibility for “−Γ” to “−4Γ” red-detuning and “+Γ” to “+10Γ” blue-detuning using the standard properties of the commercially available electronics. We have developed a theoretical model corresponding to the thin cell, incorporating the atomic time-of-flight dependent optical pumping decay rate to describe the dimensional anisotropy of the thin cell. The model shows good qualitative agreement with the observation and simulates as well the cases of cells with smaller thickness. It also describes correctly the temperature dependence of the line broadening and shows the potential for further optimization and red-shift detuning above “−4Γ”. It may be of interest for further development of miniaturized modules, like the recently developed portable small magneto-optical traps.

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.

We present high resolution laser spectroscopy of Cs vapours confined in a unique optical cell of sub-micrometric and micrometric thickness, where a strong spatial anisotropy is pres- ent for the time of interaction between the atoms and laser radi- ation. Similarly to the spectra of selective specular reflection, the Doppler-free spectra of absorption and fluorescence are observed, not revealing cross-over resonances that will be useful for frequency stabilisation, provided the cell is cheap and com- pact. A new resonance in the fluorescence of closed transition is studied, demonstrating its high sensitivity to elastic atom - atom and atom - dielectric surface collisions. The theoretical model- ling performed is in agreement with the experimental observa- tions.

Two self-sustained unstable modes for operation of a hollow cathode discharge (HCD) are observed under some i-V operating points of both positive and negative dynamic resistance. The instabilities manifest themselves either as oscillations or pulsations. Their frequency depends on the operating i-V point. The instabilities are found to correlate with the HCD space structure.

We present a detail analysis of the line shape of electromagnetically induced transparency (EIT) in a Doppler broadened five level atomic system based on density matrix formalism. It has been shown that the velocity averaged EIT line shape in a multilevel system is very sharp. The effect of the ground state decay rates on the EIT peak has also been investigated. The linear and non-linear variations of the EIT line width (FWHM) for different pump and probe power ratios are shown. Considering the D 2 transition of 85 Rb atom the dependence of EIT width and height on pump power has been experimentally measured. Simulated spectra are compared with the experimentally obtained one. The effect of buffer gas on the EIT peak has also been observed experimentally as well as theoretically.

In this paper we report the first experimental observation of coherent population trapping (CPT) in thermal potassium vapor in a three levels lambda scheme. We demonstrate that K presents the advantage of a reduced modulation frequency with a large resonance contrast (up to 40%), in comparison to similar approaches with other alkalis. We report also the first evidence of electromagnetically induced transparency (EIT) resonances in K in the so called Hanle configuration. We tested different kinds of cells, demonstrating strong enhancement of the resonance contrast and amplitude for antirelaxation coated and buffered cells containing K vapor: resonance contrast up to 90% (for coated cells) and 65% (for buffered cells) is achieved with a linewidth of about 13 mG, while under similar conditions, the EIT resonance contrast in Cs vapor buffered by Ar gas is about 1%. Such relevant improvement is due to the reduced optical pumping in K, because of the overlapping of the hyperfine levels Doppler profiles, which does not occur in the case of Rb and Cs vapor. For this reason, K can be considered very promising for further CPT and EIT applications, especially for those where optical pumping losses represent a major limiting factor, such as light slowing and magnetometry.

The coherent population trapping (CPT) [1] and related electromagnetically induced transparency (EIT) phenomena have found a large number of applications in science and technology. The degenerate two-level systems provide many possibilities for investigation of CPT. Zeeman optical pumping destroyed by magnetic field (MF) allows the observation of EIT [2], as well as electromagnetically induced absorption (EIA) [3] in the atomic medium. CPT resonances prepared in the Hanle configuration have been investigated for atoms irradiated by monochromatic laser field in a way that different polarization components couple the Zeeman sublevels of single hyperfine (hf) ground level to a common excited state and introduce coherence between ground magnetic sublevels at zero value of a scanned around it magnetic field B, orthogonal to the orientation/alignment of atoms. As shown in [3], in absence of depolarizing collisions of the excited state, and depending on the ratio of the degeneracies of the two hf levels involved in the optical hf transition, EIT and EIA sub-natural width resonances can be observed for degenerate two-level systems. EIT is realized when the conditions Fg → Fe = Fg − 1, Fg are met, while EIA is observed for Fg → Fe = Fg+1. Here, Fg and Fe are the hf quan∗corresponding author; e-mail: stefka-c@ie.bas.bg

Magnetic field and its gradient measurements based on coherent population trapping resonances at the D1 line of Rb are performed by means of coupling two ground-state Zeeman sublevels belonging to different hyperfine levels to a common excited state. Two coherent laser fields with frequency difference of 6.8 GHz are used. They are produced by direct current modulation of a diode laser. The resonance splitting and broadening caused by the applied magnetic field is measured by scanning the laser modulation frequency around the ground-state hyperfine frequency.

The pump-probe spectra in a cell of micrometric thickness containing cesium vapor are reported. The line shape and nonlinear features observed in the case of fluorescence in the direction parallel to the cell windows and the transmission spectra observed along the propagation direction of the probe beam show considerable differences in the spectral profiles. We observed Electromagnetically Induced Transparency (EIT) and enhanced Velocity Selective Optical Pumping (VSOP) signals. Atoms moving nearly parallel to the windows and perpendicular to the collinear pump and probe beams will see much lower Doppler shift of incident frequencies and hence will lead to considerable narrowing of the Doppler background in the fluorescence spectra. The coherence decay rate is also low for such atoms as they do not meet with the cell walls. A theoretical model based on five level optical Bloch equations is used to simulate the spectra. The Doppler convolution includes all possible orientation of atomic velocities with respect to the laser beam direction. The simulated curves reproduce the observed sharp EIT peaks and enhanced broad VSOP signals for the closed probe transition in the fluorescence and absorption spectra. The observed effect of the light intensity and temperature change on the non-linear features is reproduced by the simulation.

We report new experimental evidence of a magneto-galvanic (MG) effect in commercial hollow cathode lamps (HCL). The goal of our investigation is to clarify the role of the neon 2p 5 3s configuration in the formation of the MG signals. Our results eloquently relate the origin of the MG signal in the HCL discharge with the self-alignment of the 1s 5 metastable state. The observed destruction of the narrow resonance could be explained analogously to the optical depletion ("pumping-off") of the 1s 5 metastable state.

We present a novel scheme for reducing the AC Stark effect in optical-microwave double-resonance spectroscopy and its application for efficient suppression of the light-shift-related instabilities in laser-pumped gas-cell atomic clocks. The method uses a multi-frequency pump light field that can be easily produced by frequency modulation of the single-frequency pump laser. We show theoretically that variations of the light shift with both laser frequency and light intensity can be strongly suppressed with properly chosen pump light spectra. Suitable modulation parameters can be found for both the case of pure frequency modulation as well as for pump light spectra showing amplitude-modulation contributions, as usually found for current modulation of diode lasers. We experimentally demonstrate the method for a Rb atomic clock using a frequency-modulated distributed Bragg-reflector laser diode as pump light source.

The results of a comparative study (theoretical and experimental) of two original approaches for spectral control of two-wavelength pulsed Ti:sapphire (Ti:S) lasers and the most popular conventional methods are presented. Single line operation as a particular case is considered. We compare our own methods: (i) combined dual pulse pumping–passive self-injection locking (DPP–PSIL) and (ii) coupled cavity dye laser injection locking (CCLIL) with the conventional methods: (i) intracavity selection (IS), (ii) PSIL and (iii) traditional injection locking using an external dye laser. The most important criteria—laser efficiency, emission line width, tuning range, spectral purity and buildup time are compared under optimized conditions. The comparison is made using the same pump source with constant output energy in each case. The results serve as a basis for choosing correctly the most suitable spectral control technique for a particular Ti:S laser application. It is shown that the DPP–PSIL method guarantees a remarkable improvement of the Ti:S laser performance (nearly doubling the laser efficiency with the same line width and comparable laser tuning range as IS, combined with a protection of the selectors). The CCLIL approach assures a maximum laser efficiency in narrow line emission in addition to a minimal and reproducible buildup time. The IS method provides a maximal tuning range.

In this work a cavity design for double-pulse generation in Q-switched mode from a single laser is proposed, based on the construction of a second laser channel using a FTIR (frustrated total internal reflection) Q-modulator. A time interval between the two pulses from 500 ns to 120 μs is obtained in a Nd:YAG laser. A comparison with other methods and cavity designs for double-pulse generation is presented. The case when this technique is applied on a tunable laser with metastable upper laser level (Cr:LiCAF, Cr:LiSAF, Alexandrite, Co:MgF2 or other) is also considered. Even though the method presented in the paper does not rely only on the cavity configuration proposed, some advantages can be obtained – both polarization and wavelength-independent tuning without polarization and wavelength restrictions in combination with the possibility of different wavelengths and polarizations in each pulse. Moreover, by using an active medium generating wavelengths around and up to 3 μm, the Pockels-cell-Q-switch optical transmission problems can be avoided.

Spatial and spectral control of a ring laser with a homogeneously broadened active medium has been achieved using a bi-directional injection scheme. Such a type of injection provides a new technique to obtain a controlled pulsed laser emission spectrally locked to a selected atomic absorption line. The proposed technique makes use of the strong competition between counterpropagating waves in the ring cavity. The output control relies on the unbalance between the two injected beam intensities produced by the absorption. When the injected light is scanned around the absorption line, an unidirectional light generation occurs only at the wavelength of the desired absorption line. Due to the non-linear character of the process, the emitted spectrum can be an order of magnitude narrower than the absorption line. Both computer simulation and experimental study of the phenomena are reported for a pulsed dye laser pumped with the second harmonic of a Q-switched Nd:YAG laser.

An improved passive self-injection locking (PSIL) method for the spectral control of dye and Ti:Al2O3 lasers using two-step pulse laser pumping is reported (theoretically, experimentally). By this pump technique, the typical unwanted free lasing which occurs in the non-selective cavity at high pump level is reduced by a few orders of magnitude compared with the standard PSIL application. This combined approach ensures high purity tunable emission at laser efficiency nearly equal to the maximum obtained in an optimized non-selective cavity and avoids optical damage problems. This makes the PSIL method competitive or preferable to other frequently used spectrally selective methods. Analysis and experimental check for two-wavelength lasers are included.

We describe a technique to optically characterize superparamagnetism. Faraday rotation measurements are performed on a superparamagnetic nanocomposite using small alternating current magnetic fields. The superparamagnetism of the iron oxide nanoparticles causes signals at the uneven harmonics of the magnetic field frequency. These signals provide information on the magnetic moment of the superparamagnetic nanoparticles. Dia- and paramagnetism do not cause signals at higher harmonics, resulting in a high sensitivity to superparamagnetism, even in samples with large dia- or paramagnetic contributions. This technique provides a rapid, economical method to characterize superparamagnetism in composite samples not easily accessible by other techniques. ispartof: Applied Physics Letters vol:102 issue:16 pages:161903-161903 status: published

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.

We demonstrate a bi-chromatic pump-probe spectroscopy comparison between conventional cm-size Cs-filled cell and cells with thickness miniaturized down to 5.2 μm and 700 μm. In the 5.2 μm cell very-good-contrast enhancedtransparency- resonances were obtained that can be efficiently suppressed (controlled) with small about 31 MHz detuning of the pump laser frequency. The resonances do not move their spectral position with the pump frequency detuning like it is in the classical cm-size cells. Miniaturization down to 700 μm does not compromise the enhanced-transparencyresonances. In addition, at that level of miniaturization, the probe beam transmission spectra show as narrow features as in classical cm-size cells. Comparison of the obtained coherent resonances in 700 μm cell with that in 2.5 cm shows no broadening and both have resonance width limited by the emission linewidth of the used pump and probe lasers.

We present here the behavior of Electromagnetically Induced Transparency (EIT), Velocity Selective Optical Pumping (VSOP) resonances and Velocity Selective Excitation (VSE) resonances observed in Cs vapor confined in а micrometric optical cell (MC) with thickness L = 6λ, λ = 852nm. For comparison of behavior of VSE resonance another conventional optical cell with thickness L=2.5 cm is used. Cells are irradiated in orthogonal to their windows directions by probe beam scanned on the Fg = 4 → Fe= 3, 4, 5 set of transitions and pump beam fixed at the Fg = 3 → Fe = 4 transition, on the D2 line of Cs. The enhanced absorption (fluorescence) narrow VSOP resonance at the closed transition transforms into reduced absorption (fluorescence) one with small increase of atomic concentration or light intensity. A striking difference appears between the VSE resonance broadening in L = 6λ and conventional L = 2.5cm cells.

Second harmonic generation microscopy has recently become an important tool for studying materials. In this article, we use a recently developed analytical method, for second-harmonic generation microscopy, to determine the point group symmetry of micro crystals of enantiomerically pure 1,1’-bi-2-naphtol. ispartof: pages:87701- ispartof: 17TH INTERNATIONAL SCHOOL ON QUANTUM ELECTRONICS: LASER PHYSICS AND APPLICATIONS vol:8770 pages:87701- ispartof: 17th International School on Quantum Electronics - Laser Physics and Applications (ISQE) location:Nessebar: BULGARIA date:24 Sep - 28 Sep 2012 status: published

High resolution laser spectroscopy of alkali vapor contained in conventional thermal optical cells with centimeter dimensions is widely used for various applications: among them wavelength references, atomic clocks, precise optical magnetometers, slow and stored light etc. For all these photonic sensors, the reduction of their dimensions is of significant importance. One of the main concerns is to keep the parameters of the photonic sensor when reducing its size. In this chapter are presented the obtained by authors experimental and theoretical results concerning high-resolution spectroscopy of Cs vapor layer with nanometric thickness. The thickness of the vapor layer varies from 100 nm to about 5000 nm. The practical importance of this study is accompanied by numerous new peculiarities of atomic spectra of 1 D confined atoms, when the nanometric dimension approaches the wavelength of the irradiating light. These peculiarities in the absorption and fluorescence spectra represent a basic importance as well.

The Electromagnetically Induced Transparency (EIT) effect in a Λ -system formed by Cs atoms (6 S 1/2 − 6 P 3/2 − 6 S 1/2 ) confined in an extremely thin cell (ETC) (atomic column thickness L varies in the range of 800 nm –3 µm is studied both experimentally and theoretically. It is demonstrated that when the coupling laser frequency is in exact resonance with the corresponding atomic transition, the EIT resonance parameters weakly depend on L , which allows us to detect the effect at L = λ = 852 nm. EIT process reveals a striking peculiarity in case of the coupling laser detuned by Δ from the atomic transition, namely the width of the EIT resonance rapidly increases upon an increase in Δ (an opposite effect is observed in centimeter-scale cells). The strong broadening of the EIT resonance for large values of detunings Δ is caused by the influence of atom-wall collisions on dephasing rate of coherence. The influence of the coupling laser on the velocity selective optical pumping/saturation resonances formed in ETC has been also studied. The theoretical model well describes the observed results.

We report on a novel behavior of the electromagnetically induced absorption (EIA) resonance observed on theD2line of Cs for atoms confined in cells with micrometric thickness. With the enhancement of light intensity, the EIA resonance amplitude suffers from fast reduction, and even at very low intensity (W 2), resonance sign reversal takes place and electromagnetically induced transparency (EIT) resonance is observed. Similar EIA resonance transformation to EIT one is not observed in conventional cm-size cells. A theoretical model is proposed to analyze the physical processes behind the EIA resonance sign reversal with light intensity. The model involves elastic interactions between Cs atoms as well as elastic interaction of atom micrometric-cell windows, both resulting in depolarization of excited state which can lead to the new observations. The effect of excited state depolarization is confirmed also by the fluorescence (absorption) spectra measurement in micrometric cells with different thicknesses.

We present the results of an experimental study of Coherent Population Trapping (CPT) in potassium, obtained by means of modulation of laser light amplitude with kHz frequency. The radiation from an external cavity diode laser, matching the D1 line of K, is modulated by an acousto-optical modulator. In the cell containing buffer gas, the CPT resonance width is reduced more than three orders of magnitude as compared to the cell containing pure potassium vapor. In K this resonance narrowing occurs with high resonance contrast; such behavior is not observed in buffered cells containing Rb or Cs, where the optical pumping to the non-interacting with the light ground level is very effective and depletes the population of the working ground Zeeman sublevels. The narrow CPT resonance of reduced fluorescence transforms to the one of enhanced fluorescence with the cell temperature rising. The transformed resonance exhibits higher contrast and lower width than those of the reduced fluorescence resonance. Hence, beside its scientific importance the resonance sign reversal can be used for the improvement of the CPT resonance parameters.

Laser spectroscopy experiments are reported on rubidium atoms by using two or three external cavity diode lasers to study multiple resonance transitions in Λ- and V-type systems as well as on (Λ+V)-type system. Electromagnetically induced transparency (EIT) peaks having sub-natural line-widths are found on the Doppler broadened transmission backgrounds with velocity selective enhanced absorption dips. In the presence of a pump laser, probe spectrum shows enhancement of EIT signal by tuning the control laser frequency when the Λ- and V-type EIT signals are made to overlap. Theoretical analysis is carried out by solving the optical Bloch equations for five-level atomic model under Λ configuration. With the numerically simulated spectra, variation of EIT transmission peak with ground state decay rate and excited state spontaneous decay rate are investigated. Effect of pump Rabi frequency on the transmission peak is also shown.

In this communication we report the first observation of a narrow, reduced fluorescence dip in the profile of the completely closed transition on the D 2 line of 133 Cs vapor, confined in Extremely Thin Cell with nanometric thickness. The theoretical modeling of the fluorescence based on the Optical Bloch Equation for two-level atomic system, shows that the narrow dip in the fluorescence could be attributed to a very small loss in the excitation process of the examined degenerate transition. While the population in the atomic syst em remains constant, the depolarization of the excited level can lead to some loss in the efficiency of the optical transition excitation. Under the conditions of our experiment, no dip in the fluorescence is registered for th e cell thickness where a well pronounced Di cke peak in the absorption takes place. For the cells with nanometric thickness, the previous investig ations demonstrate that the fluorescence profiles of optical transitions differ significantly from the absorption profiles. However, our experiment shows that some traces of the coherent Dicke process contributing to the absorption line still remain in the fluorescence, which is result of non-coherent processes. Keywords: extremely thin cell, nanometric vapor layers, laser spectroscopy

We present the Hanle EIT resonances obtained from the various segments of the Gaussian laser beam cross-section, selected by moving the small aperture (placed in front of the detector) radially along the laser beam. Significant differences in the Hanle lineshapes are observed depending on whether the central or outer parts of the Gaussian laser beam are detected. The line narrowing and two counter-sign peaks occur at outer, less intense parts of the beam. The theoretical model suggests that the EIT lineshapes in the laser wings are result of the interference of the laser light and coherently prepared atoms coming from the central part of the beam. By blocking the central part of the laser beam in front of the detector, narrower, and for high laser intensities, even more contrasted Hanle resonances are obtained.

We present the observation of coherent population trapping resonances on the second resonance line of potassium: 4s2S1/2 -> 5p2P3/2 with wavelength of 404.4 nm. Moreover, a transfer of the coherent population trapping resonance occurs to the excited 4p2P1/2 and 4p2P3/2 states of the first resonance line due to cascade transitions. This transfer is evidenced by the observation of narrow resonances at the infrared 4s2S1/2 -> 4p2P1/2 and 4s2S1/2 -> 4p2P3/2 transitions when alkali excitation is performed at the 404.4 nm violet line.

We present the first experimental observation of Coherent Population Trapping (CPT) in Potassium, obtained with kHz-frequency modulation of the laser light amplitude. It is performed by acousto-optical amplitude modulation of the radiation from an external cavity diode laser, matching the D1 line of K. The CPT resonances are detected both through K absorption and fluorescence. The resonances are studied in three kinds of K cells: i) pure-evacuated, ii) polydimethylsiloxane (PDMS)-coated-evacuated and iii) Ne-gas buffered. In all cases CPT-resonance narrowing with cell temperature is observed. In the pure-evacuated cell we registered the lowest contrast and the highest width of the resonance, while in buffered/coated cells a strong enhancement of the CPT resonance contrast up to 15% is observed. This behavior is the opposite to the one exhibited by Cs and Rb. The observed contrast enhancement in K is accompanied by more than two orders of magnitude reduction of the resonance width. The results here presented prove the advantage of using Potassium in CPT-based applications. © 2008 SPIE.

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.

Absorption and fluorescent spectra are obtained in saturation regime of a single beam laser spectroscopy of Cesium D 2 line, in a vapor layer with thickness close to the light wavelength. We compare experimentally and theoretically obtained spectra distinguishing between open and closed, in terms of optical pumping, hyperfine transitions. In absorption, we observe a persisting difference between open and closed transitions, in terms of Dicke narrowing, when increasing laser light intensity. In fluorescence, for open transitions we note saturation dips which do not change significantly when increasing intensity. In case of closed transition, a small feature at the fluorescence line center appears for relatively high light intensity.

Nonlinear magneto-optical rotation (NMOR) of linearly polarized light, resonant to the Fg = 2 → Fe = 1 atomic transition of D1 line of 87 Rb is investigated experimentally, by applying spatially separated laser fields in the Rb vacuum cell. In our experiment, the probe laser beam propagates through the center of the pump laser beam, which has the shape of a hollow cylinder. We have measured the rotation of the probe laser beam polarization with respect to the incident polarization, as a function of the external magnetic field, parallel to the laser beam propagation. We show substantial narrowing of the resonance if the pump beam, with the same linear polarization, is present. The opposite direction of the probe rotation was obtained when the pump laser beam polarization is orthogonal to the probe laser beam polarization. The D1 line consists of four transitions between various hyperfine sublevels: Fg = 1; 2 → Fe = 1; 2 for 87 Rb. The maximum polarization rotation is observed for the Fg = 2 → Fe = 1 transition. In this case all transitions between the Zeeman sublevels contribute to the creation of the ground-state coherence, forming three Λ links. For the Fg = 2 → Fe = 2 and the Fg = 1 → Fe = 1 transitions both Λ and V interaction schemes are equally probable; since coherent population trapping (CPT) is created only in a Λ system, the effectiveness of the optical pumping to a dark state for these transitions is lower. Finally, enhanced absorption is observed for the Fg = 1 → Fe = 2 transition. Ramsey's method of separated fields for the observation of narrow radio frequency (rf) resonances is well known from atomic and molecular beam experiments. These Ramsey fringes are induced by the use of two spatially separated rf fields 5 . We consider here modified Ramsey method, where two light fields at optical frequencies couple two lower levels via Raman resonance. Hence, this method is often called Raman-Ramsey method. Most of the papers consider nonlinear magneto optical effects (NMOE) in the case of linearly polarized light propagating along the magnetic field known as nonlinear Faraday rotation 3,6-12 . The first observation of Ramsey fringes obtained using nonlinear Faraday rotation spectroscopy in a thermal Rb atomic beam with spatially separated pumping and probing regions, was presented in experimental and theoretical work 11 . Similar Ramsey effects were observed by Kanorsky et al. in Cs vapor cells with anti-relaxation wall coating, and explained in terms of multiple wall-collision induced Ramsey resonances

Experimental and theoretical studies are presented related to the ground-state magneto-optical resonance prepared in Cesium vapour confined in an Extremely Thin Cell (ETC, with thickness equal to the wavelength of the irradiating light). It is shown that the utilization of the ETC allows one to examine the formation of a magneto-optical resonance on the individual hyperfine transitions, thus distinguishing processes resulting in dark (reduced absorption) or bright (enhanced absorption) resonance formation. We report on an experimental evidence of the bright magneto-optical resonance sign reversal in Cs atoms confined in the ETC. A theoretical model is proposed based on the optical Bloch equations that involves the elastic interaction processes of atoms in the ETC with its walls resulting in depolarization of the Cs excited state which is polarized by the exciting radiation. This depolarization leads to the sign reversal of the bright resonance. Using the proposed model, the magneto-optical resonance amplitude and width as a function of laser power are calculated and compared with the experimental ones. The numerical results are in good agreement with the experiment.

In this communication we present our results related to examination of Coherent Population Trapping resonance profile on the D1 line of 87Rb when coupling two ground-state Zeeman sublevels belonging to different hyperfine ground-state levels to a common excited-state one. For this, two coherent laser fields with frequency difference of about 6.8 GHz are used. The resonance is observed as a narrow dip in the fluorescence in dependence on the modulation frequency (fm) of the laser light, centered at 2fm = Δv hf , where Δv hf is the frequency difference between the ground-state hyperfine levels of Rb. The resonance observation and its splitting in 7 components have been demonstrated under influence of nonshielded laboratory magnetic field (MF). It has been shown that different components are with different sensitivity to the MF gradients that is in agreement with the performed estimations.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Comparative studies of MO resonances and MG responses with and without resonant laser irradiation were carried out to establish th e interconnection of the effects and the influence of the self-alignment destru ction on the MO signal in positive column discharge. These studies aim to clarify the possible formation mechanisms of the neon 1s i (2p 5 3s) states coherences and to examine the possibility to use the galvanic resonanc es for estimation of the relaxation constants of the neon 1s 5 state. Keywords: glow discharge, self-alignment, galv anic resonances, magneto-optical effect, metastable 1. INTRODUCTION For a long time the polarisation laser spectroscopy has been considered as one of the most effective methods for investigation of gas media and in particular of glow discharges. When the investigation of the resonant and the metastable states through fluorescence response is difficult, the magneto-optical (MO) methods apply successfully. These are based on the detection of polarisation changes of the absorbed or forward scattered light when a magnetic field is applied to the medium. Depending on the geometry of th e experiment one speaks of Faraday and Voigt effects and the corresponding detection is of circular-magnetic (linear dichroism) and/or birefringence. In plasma the optical activity (dichroism and birefringence) is manifested in the interaction of the resonant radiation with atoms, aligned in the discharge. The self-alignment of the neon 2p

Coherent Population Trapping resonances on the D2 line of Cs are examined under the influence of continuous and alternating magnetic fields. It is shown that alternating fields as low as a fraction of μT modifies significantly the shape of the resonances, which can be used for oscillating magnetic field measurement.

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.

We have characterized teh spectral properties and wavelength tuning behaviour of different types of diode lasers in order to evaluate their potential for applications in atomic spectroscopy and precision instruments. Here we report on studies of recently developed distributed feedback (DFB) and Fabry-Perot laser diodes, emitting around 780 and 795 nm, in solitary operation as well as in an extended-cavity configuration. In solitary operation both types of laser studied show continuous tuning ranges beyond 40 GHz and single-mode emission linewidths around 6 MHz, which makes them interesting candidates for use in high-precision instruments based on atomic spectroscopy such as atomic frequency standards and atomic magnetometers.

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.

We present a systematic quantitative comparison of the performance parameters of two Extended Cavity Diode Lasers (ECDL), stabilized to Doppler and sub-Doppler profiles. The experimental study is carried out on Rb atomic vapour cells. The frequency shift of the resonance under investigation with respect to a reference resonance is measured and analyzed, in dependence on the modulation amplitude, cell temperature, laser power, applied magnetic field and misalignment of the pump-probe beams angle. The Allan variance is measured for both locking methods. It shows that the stabilization to the Doppler profile results in about one order of magnitude lower stability than the one to SA resonances for the short-term measurement. However, the stability achieved using both methods is sufficient for many applications and for some of them the simplicity of the Doppler locking method can be advantageous.

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 availability of frequency stabilised laser sources is essential for the realisation of laser-pumped atomic clocks and other applications. Here we present a comparison of two simple spectroscopic schemes for laser stabilisation to the Rb D2 line transitions, based on linear (Doppler-broadened) and non-linear (saturated absorption) spectroscopy in thermal vapour cells, covering time scales up to 105 seconds. We measured short-term stabilities of 2.10-11 τ-1/2 and 2.10-12 τ-1/2 up to 1.10-10 seconds and long-term stabilities at one day around 1.10-10 and 2.10-12 for the Doppler and sub-Doppler scheme, respectively. From a drift analysis of different experimental parameters we find the frequency stability beyond 104 seconds to be limited essentially by variations of the reference cell temperature for both schemes, and estimate limits around 9.10-12 and 2.10-12 for improved experimental realisations. The performance and simplicity of both stabilisation schemes studied makes them interesting for applications in compact atomic clocks and other precision instruments.

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.

The lower level of laser transition on 632.8 nm (2p 4 ) 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.