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The "mixing" of magnetic sublevels of the ground and excited levels of an atomic transition with magnetic sublevels of a nearby transition (in the hyperfine structure of atoms of alkali metals) is responsible for a strong modification of its probability. A dramatic manifestation of this mixing effect is a huge increase in the probability of the atomic transition in magnetic fields that is forbidden by selection rules in zero magnetic field B = 0; the latter is called a magnetically induced (MI) transition. Two MI transitions with different dependences on B have been studied. Another dramatic manifestation of the mixing effect is that there are atomic transitions whose frequency is practically fixed in a wide range of magnetic fields, i.e., the slope S [MHz/G] of the frequency shifts as a function of B is practically zero, with the transition probability being significant. We call these transitions "unmoved" transitions (UTs). We have studied the UTs of 87Rb atoms, the D2 line, |1, +1〉 → |1', +1'〉 and Cs atoms, the D2 line, |3, –3〉 → |5', –4'〉, where the quantum numbers F and mF of the excited and ground levels are marked with and without primes, respectively. We show that in the range B = 180–705 G for 87Rb, the D2 line, |S| ≤ 0.03 MHz/G; for comparison, S ≈ 3.6 MHz/G for 87Rb in the same B range for the MI transition |1, +1〉 → |3', +2'〉 is greater by a factor of 120. A second laser was used to control the UT amplitude. Our theoretical model describes well the experiment. [ABSTRACT FROM AUTHOR]

Four different types of spectroscopic cells that cover all possible existing versions of sealed-off cells (containing alkali atomic vapor) characterized by drastically different relaxation rates γ are used to study the electromagnetically induced transparency spectra of two Λ-systems in the D line of Rb in the presence of transverse magnetic field. Two cw narrowband diode-lasers are used to form the coupling laser radiation (with a fixed frequency) and the probe radiation with a tunable frequency. Two strongly contrasting Λ-systems are found: the first shows resonances that are transformed from dark resonances to bright resonances in all cases apart from nanocells, whereas the second shows four dark resonances in all four different types of cell. The theoretical simulations are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The phenomenon of electromagnetically induced transparency (EIT) is investigated in a Λ-system of the Rb D line in an external transverse magnetic field. Two spectroscopic cells having strongly different values of the relaxation rates γ are used: an Rb cell with antirelaxation coating ( L ~ 1 cm) and an Rb nanometric- thin cell (nanocell) with a thickness of the atomic vapor column L = 795 nm. For the EIT in the nanocell, we have the usual EIT resonances characterized by a reduction in the absorption (dark resonance (DR)), whereas for the EIT in the Rb cell with an antirelaxation coating, the resonances demonstrate an increase in the absorption (bright resonances (BR)). We suppose that such an unusual behavior of the EIT resonances (i.e., the reversal of the sign from DR to BR) is caused by the influence of an alignment process. The influence of alignment strongly depends on the configuration of the coupling and probe frequencies as well as on the configuration of the magnetic field. [ABSTRACT FROM AUTHOR]

It is shown that high-contrast resonance of electromagnetically induced transparency (EIT) in a ladder Ξ-system of 5 S-5 P-5 D levels can be formed in optical cells containing a column of rubidium vapor with thickness L in an interval of 100 nm ≤ L ≤ 780 nm. Using bichromatic laser radiation with certain parameters, an 83% contrast of the EIT resonance (or dark resonance, DR) has been achieved for a vapor column thickness of L = 780 nm. An important condition for the formation of high-contrast DR is that the frequency of the coupling laser radiation must be resonant with the frequency of the corresponding 5 P-5 D transition (for the probe radiation frequency scanned over the 5 S-5 P transition). It is also shown that a DR can be formed at a record small vapor column thickness of L ≈ 100 nm. Expressions that can be used to estimate the expected DR width at small L values are presented. [ABSTRACT FROM AUTHOR]

The effect of electromagnetically induced transparency (EIT) in a Λ-system formed by rubidium atoms contained in thin (10-60 μm) and extremely thin (0.3-5 μm) cells was studied experimentally. It was found that parameters of the EIT resonance degrade slowly in the case where the frequency of the coupling laser is in resonance with the D transition of rubidium, which enabled the registration of the EIT resonance in a record thin cell with a thickness of L = 390 nm. The specific features of EIT in extremely thin cells reveal themselves when the coupling laser has a frequency detuning Δ from the atomic transition. In this case, the width of the EIT resonance rapidly increases upon an increase in Δ at fixed L (an opposite effect takes place in centimeter-scale cells). It is shown that the width of the EIT resonance is inversely proportional to L in the case of fixed large detuning Δ. The nearly tenfold broadening of the EIT resonance for large values of detuning Δ is caused by the influence of atomic collisions with cell windows on dephasing rate of coherence. The expressions that allow the estimation of the EIT-resonance width for various values of detuning Δ and small values of thickness L are found. [ABSTRACT FROM AUTHOR]

It has been experimentally demonstrated that the use of the effect of significant narrowing of the fluorescence spectrum from a nanocell that contains a column of atomic Rb vapor with a thickness of L = 0.5λ (where λ = 794 nm is the wavelength of laser radiation, whose frequency is resonant with the atomic transition of the D1 line of Rb) and the application of narrowband diode lasers allow the spectral separation and investigation of changes in probabilities of optical atomic transitions between levels of the hyperfine structure of the D1 line of 87Rb and 85Rb atoms in external magnetic fields of 10–2500 Gs (for example, for one of transitions, the probability increases ∼17 times). Small column thicknesses (∼390 nm) allow the application of permanent magnets, which facilitates significantly the creation of strong magnetic fields. Experimental results are in a good agreement with the theoretical values. The advantages of this method over other existing methods are noted. The results obtained show that a magnetometer with a local spatial resolution of ∼390 nm can be created based on a nanocell with the column thickness L = 0.5λ. This result is important for mapping strongly inhomogeneous magnetic fields. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we are presenting the visible absorption spectrum of both rubidium and cesium vapor in the 570–870K temperature range. We used a classical absorption spectroscopy experimental scheme with several new features. The first concerns the use of modern, compact, computer operated spectrometer (Ocean Optics HR4000CG-UV-NIR), which allowed us to record spectra instantaneously resulting in higher signal-to-noise ratio. The second improvement is connected with the use of the all-sapphire cells (ASC) enabling work with a high density of alkali atoms within precisely defined vapor column. In the superheated regime (above 700K) thermal destruction of dimer molecules clearly distinguishes triplet from singlet transitions. [Copyright &y& Elsevier]

The peculiarities of intra-Doppler structures that are observed in the atomic absorption spectrum of alkali metals with the help of two independent lasers have been studied. These structures accompany ultranarrow coherent resonances of electromagnetically induced transparency and absorption. With the D 2 line of rubidium taken as an example, it is shown that, in the scheme of unidirectional waves, the maximum number of satellite resonances caused by optical pumping selective with respect to the atomic velocity is equal to seven, while only six resonances are observed in the traditional scheme of saturated absorption with counterpropagating waves of the same frequency. The spectral position of the resonances and their polarity depend on the frequency of the saturating radiation, while their number and relative amplitude depend also on the experimental geometry. These features are of general character and should show themselves in the absorption spectrum on the D 2 lines of all alkali metals. An explanation of these features is given. The calculated spectral separations between the resonances are compared to the experimental ones, and their possible application is discussed. [ABSTRACT FROM AUTHOR]

We describe the implementation of a cylindrical T-shaped alkali-vapor cell for laser spectroscopy in the presence of a longitudinal electric field. The two windows are used as two electrodes of the high-voltage assembly, which is made possible by a metallic coating which entirely covers the inner and outer sides of the windows except for a central area to let the laser beams in and out of the cell. This allows very efficient application of the electric field, up to 2 kV/cm in a rather dense superheated vapor, even when significant photoemission takes place at the windows during pulsed laser irradiation. The body of the cell is made of sapphire or alumina ceramic to prevent large currents resulting from surface conduction observed in cesiated glass cells. The technique used to attach the monocrystalline sapphire windows to the cell body causes minimal stress birefringence in the windows. In addition, reflection losses at the windows can be made very small. The vapor cell operates with no buffer gas and has no magnetic part. The use of this kind of cell has resulted in an improvement of the signal-to-noise ratio in the measurement of parity violation in cesium vapor underway at ENS, Paris. The technique can be applied to other situations where a brazed assembly would give rise to unacceptably large birefringence in the windows. [ABSTRACT FROM AUTHOR]

An extremely thin cell with a wedge gap was developed that makes it possible to form a column of Rb atom vapor with thickness in the range from 100 to 600 nm. It is experimentally shown that the use of this cell, along with commercially available diode lasers, allows one to spectrally resolve individual transitions between the Zeeman sublevels of the hyperfine structure of the [sup 87]RbD[sub 1] line (transitions F[sub g] = 1, 2→F[sub e] = 1, 2) in the resonance fluorescence spectrum in the presence of an external magnetic field (B≈200 G). This makes it possible to realize systems consisting of nondegenerate atomic levels. For comparison, it is shown that transitions between the Zeeman sublevels in the fluorescence spectrum obtained with the aid of a conventional cell (1–10 cm long) in an external magnetic field with B∼200 G remain completely masked by the Doppler-broadened profile. The results obtained can be used for the creation of a simple magnetometer based on an extremely thin cell with Rb vapor for the measurement of magnetic fields with a submicron local spatial resolution. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

An extremely thin cell (ETC) with the thickness of a Rb atomic vapor layer in the range of 100-300 nm was fabricated. It is demonstrated that a simple laser-diode technique with a single resonant light beam is sufficient to observe separately all of the atomic hyperfine transitions of the D[SUB2] line of Rb 780 nm and also allows us to measure the relative transition probabilities of the hyperfine transitions. The onset of collisional self-broadening of the hyperfine transitions as the number density of atoms increases was studied. The detrimental role of the atoms with slow longitudinal velocity in the sub-Doppler response of the Rb ETC is demonstrated by studies in which the cell is tilted from normal incidence of the laser beam. It is also shown that using an ETC allows us to resolve in a moderate external magnetic field the Zeeman splitting of the hyperfine transitions of the [SUP87] Rb D[SUB1] transition F[SUBg] = 1 → F[SUBe] = 1, 2. [ABSTRACT FROM AUTHOR]

Abstract. cw Raman lasing of Na[sub 2] molecules generated in a heated, sealed-off, all-sapphire cell is demonstrated. Being not damaged by highly corrosive alkaline vapours, this type of cell enables operation without buffer gas in contrast to the normal heatpipe operation of these lasers. This allows us to study Raman lasers in alkaline vapours in new regimes and under ideal conditions. With an argon ion pump laser at 488 nm, Raman laser operation at 525 nm with more than 10% efficiency and thresholds below 0.2 mW for a cell without buffer gas (length 9 cm) have been obtained so far. The low thresholds, being a factor of 10 less than tot comparable heatpipe operation, gives us the chance to use low-power diode lasers as pump sources and to realize compact reliable Raman laser systems. [ABSTRACT FROM AUTHOR]

Magnetically induced (MI) transitions of 85Rb atoms, D2-lines 5S1/2 → 5P3/2, Fg = 3 → Fe = 1 with circular polarization σ–, the intensities of which are zero in a zero magnetic field, have been studied experimentally and theoretically. However, their intensities increase significantly in magnetic fields of 0.5–1 kG. The MI transition Fg = 3 → Fe = 1 was used for the first time at the probe radiation frequency to implement the process of electromagnetically induced transparency (EIT). The frequency of the coupling radiation was resonant with the Fg = 2 → Fe = 1 transition. The generated EIT resonance was located on the low-frequency tail of the spectrum. It was shown that EIT resonance was formed only when the probe and coupling radiations had the same circular polarization σ–. This was true for MI transitions Fe – Fg = ΔF = –2. [ABSTRACT FROM AUTHOR]

The effect of the dielectric surface on the 39K D1 line (Fg = 1, 2 → Fe = 1, 2 transitions) at nanometer distances has been experimentally studied for the first time. A nanocell that is filled with atomic potassium and has a wedge gap has been used to study the effect of atoms at distances of 50–800 nm from the technical sapphire window surface. At distances L < 100 nm from the sapphire surface, the van der Waals interaction strongly broadens atomic transitions and their frequencies are redshifted. The second derivative method applied to the absorption spectra of the nanocell has allowed the first measurement of the van der Waals interaction coefficient C3 = (1.2 ± 0.3) kHz μm3 for the 39K D1 line. It has been shown that the dipole–dipole interaction between 39K atoms results in the additional redshift at an increase in the density of atoms for the nanocell thickness L < 70 nm. The results obtained are important for the development of submicron devices containing free atoms. [ABSTRACT FROM AUTHOR]

A cell with a submicron thickness was used to measure the broadening and shift of the D1 and D2 lines of Rb atoms by neon. The resolution of hypefine components is achieved by a combination of two techniques. First, the Rb vapor column thickness in the direction of propagation of the laser radiation was chosen equal to half of its wavelength λ under conditions of resonance with the atomic transition frequency. For rubidium atoms λ/2 ~ 400 nm. At a nanocell thickness L ~ λ/2, in the transmission spectrum A(ν), the spectral lines of atomic transitions are narrowed due to the exclusion of Doppler broadening. Second, further narrowing of the detected signals was achieved by the double differentiation of the transmission spectrum, A''(ν). The transmission spectra of pure rubidium vapor and rubidium vapor with the addition of neon have been measured at different pressures. The measured values of the shift coefficients of the D1 and D2 lines of rubidium in the presence of Ne were –1.1 ± 0.2 MHz/Torr and –2.1 ± 0.2 MHz/Torr, respectively. The broadening coefficients of the D1 and D2 lines coincide and are equal to 10 ± 1 MHz/Torr. Due to its high spectral resolution, this technique allows separate measurements for each individual transition. [ABSTRACT FROM AUTHOR]

Magnetically induced Fg = 2 → Fe = 4 transitions corresponding to the 85Rb D2 line in the case of the σ+ circularly polarized radiation have been used for the first time to form optical dark resonances in strong magnetic fields up to 1 kG under electromagnetically induced transparency conditions. A 1.5-μm-thick cell filled with Rb atomic vapor has been used. The probabilities of two of five magnetically induced transitions, which are efficiently formed only with the σ+-polarized radiation, in the magnetic field range of 0.2–1 kG exceed the probabilities of "ordinary" atomic transitions. For this reason, it is appropriate to use them in Λ systems for the formation of the dark resonance. The following rule has been established: for the formation of the dark resonance in a Λ system with the use of the σ+-polarized probe radiation at the frequencies of magnetically induced transitions, the radiation of the coupling laser should also be σ+ polarized; the dark resonance is not formed if the radiation of the coupling laser is σ– polarized, which is confirmed by the calculated theoretical curve. A significant advantage of magnetically induced resonances for electromagnetically induced transparency compared to ordinary atomic transitions corresponding to the 85Rb D2 line has been demonstrated. The formation of dark resonances in strong magnetic fields, when their frequency is shifted by several gigahertzs, can be applied in practice. [ABSTRACT FROM AUTHOR]

Atomic transitions in alkali metals that have zero probability in the absence of a magnetic field but have large probabilities in the presence of a magnetic field are called magnetically induced (MI). They are of interest because of their large probabilities, which exceed the probabilities of usual transitions in a wide magnetic field range. Magnetically induced transitions are classified as type-1 (MI1) and type-2 (MI2) and their total number is about 100. In this work, MI2 transitions are examined between ground Fg and excited levels Fe of the hyperfine structure satisfying the condition , which are forbidden in zero magnetic field but have large probabilities in the presence of a magnetic field. The probabilities of the MI2 transitions with and the MI transitions with are maximal in the case of optical radiation with the σ+ and σ– polarizations, respectively. This difference is called type-1 magnetically induced circular dichroism (MICD1). It has been shown for the first time that the probability of the strongest MI2 transition in the 85Rb atom corresponding to the D2 line in magnetic fields >100 G in the case of radiation is larger than the probability of the strongest MI2 transition in the case of σ– radiation by a factor of 2.5. This difference is called type-2 magnetically induced circular dichroism (MICD2). It has been shown how to determine the strongest MI transition for any alkali metal atom, which is important for its application in magneto-optical processes. Theoretical curves reproduce well experimental results. [ABSTRACT FROM AUTHOR]

The coherent Dicke narrowing (CDN) of the absorption spectrum in an Rb, Cs, K, or Na atomic vapor column of thickness L = (2n + 1)λ/2 (when n is an integer) and its collapse (absence of narrowing), which occurs at an atomic vapor column thickness L = nλ (where λ is the wavelength of the laser radiation in resonance with an atomic transition), are experimentally and theoretically studied. The application of second-derivative (SD) processing is shown give additional important information about CDN and its collapse. Optical nanocells with a wedge gap thickness of 30—3000 nm between the windows inner surfaces are used in experiments. At thicknesses λ/2, 1.5λ, and 2.5λ, all atomic transitions, which are even masked by a large Doppler broadening of 1000–1500 MHz, are fully spectrally resolved in SD spectra, and the frequency spacings (30–50 MHz) between the atomic transitions of a hyperfine structure and the relative probabilities of the atomic transitions are correctly displayed. CDN is shown to be applied in practice. Additional narrow velocity selective optical pumping (VSOP) resonances appear in the SD spectra of the resonance fluorescence of the Rb vapors. A developed theoretical model well describes the experimental results. [ABSTRACT FROM AUTHOR]

The influence of interaction of Cs atoms with a dielectric surface on position and shape of the hyperfine components of the D2 line in the case of nanometer-scale distance between the atom and the surface is investigated. Using a wedged nanocell enabled investigating the dependence of shift of all hyperfine components of the D2 line corresponding to Fg = 3 → Fe = 2, 3, 4 and Fg = 4 → Fe = 3, 4, 5 transitions on distance L between the atoms and the surface of a sapphire window in the interval from 50 to 400 nm. At L smaller than 100 nm, atomic transitions experience strong broadening due to van der Waals interaction and shift to lower frequencies (the red shift). Calculation of the second derivative (SD) of the absorption spectra of vapors in a nanocell allows spectrally resolving the hyperfine components of an atomic transition down to L ~ 50 nm and determining the van der Waals interaction coefficient C3. It is demonstrated that the spectrum experiences an additional red shift with increase in the density of atoms at L < 100 nm. In contrast, a blue shift occurs with increase in the density of atoms at relatively large distances between the atoms and the surface (L ~ 400 nm). The above results are important for development of miniature submicron-size devices containing alkali metals. [ABSTRACT FROM AUTHOR]

We experimentally demonstrated that magnetically induced (MI) Fg = 1 → Fe = 3 transitions of the D2-line of 87Rb are promising for the generation of optical resonances in strong magnetic fields of up to 3 kG. A cell of micron-scale thickness filled with Rb vapors was used. A simple and convenient method of determining magnetic induction that exhibits micron-scale spatial resolution is described. In the process, it becomes unnecessary using a reference spectrum. The probability of an MI transition in the interval of magnetic fields from 0.3 to 2 kG can exceed the probability of an ordinary atomic transition, which makes using it as a coupling or probe transition in Λ- or V-systems advantageous for formation of dark resonances in processes of electromagnetically induced transparency (EIT). Dark resonances shifted in strong magnetic fields by as much as 10 GHz may find a number of practical applications. Note that dark resonances are nearly absent in Λ-systems based on ordinary atomic transitions in magnetic fields exceeding 1 kG. [ABSTRACT FROM AUTHOR]

The interaction of rubidium atoms with sapphire cell windows at an interwindow distance L = 40–100 nm is studied. For studies, we used the Faraday rotation (FR) effect (rotation of the plane of radiation polarization in a magnetic field) in a thin rubidium atom vapor column for D1, 2 lines. When L decreases from 100 to 40 nm, a red shift of the FR signal frequency is detected: it increases from 10 to 250 MHz, and the broadening of the low-frequency wing increases to ~1 GHz. The atomic transition Fg = 3 → Fe = 2 for the D1 line of 85Rb is shown to be convenient for such investigations, since it can be spectrally separated from other strongly broadened atomic transitions. Coefficients C3, which characterize the atom–surface interaction for the D1 and D2 lines of Rb, are determined. An additional red frequency shift takes place at a nanocell thickness L < 100 nm when the Rb atom density increases, and this shift is absent at large L. A practical application of an FR signal for measuring strong magnetic fields of several kilogausses is described. [ABSTRACT FROM AUTHOR]

Electromagnetically induced transparency (EIT) resonances are investigated with the Rb D line (795 nm) in strong magnetic fields (up to 2 kG) with three different types of spectroscopic vapor cells: the nano-cell with a thickness along the direction of laser light L ≈ 795 nm, the micro-cell with L = 30 μm with the addition of a neon buffer gas, and the centimeter-long glass cell. These cells allowed us to observe systematic changes of the EIT spectra when the increasing magnetic field systematically decoupled the total atomic electron and nuclear angular moments (the Paschen-Back/Back-Goudsmit effects). The observations agree well with a theoretical model. The advantages and disadvantages of a particular type of cell are discussed along with the possible practical applications. [ABSTRACT FROM AUTHOR]

It is shown that the use of spectroscopic cells of micron thickness ( L = 10-50 μm) allows one to effectively study the behavior of individual levels of the Cs D line in strong magnetic fields up to 9 kG. In particular, the absorption spectrum of Cs excited by circularly polarized light in fields above 8 kG consists of two fully separated groups, each containing eight atomic transitions. The intensities of atomic transitions and their frequency slopes (vs. magnetic field) in each group are almost the same. The physical explanation for the observed features is given; in particular, it is shown that one of the 54 possible atomic transitions in moderate magnetic fields (denoted F = 4, m = 4 → F = 5, m = 5) has unique characteristics that make it possible to predict the intensities and frequency slopes of seven atomic transitions in the same group. Practical applications of devices based on micrometric-thin cells in strong magnetic fields are considered. [ABSTRACT FROM AUTHOR]

The process of electromagnetically induced transparency (EIT) is studied using an extremely thin cell with thickness of a vapor column of rubidium atoms L = 794 nm. Wavelengths of resonant laser beams λ ≈ 794 nm. Results of the study of behavior of the EIT resonance (which is also called the 'dark' resonance) formed in the Л system of the D line of Rb atoms in strong magnetic fields up to 1700 G (0.17 T) are reported for the first time. Three dark resonances are recorded in magnetic fields with induction B < 300 G, two resonances are recorded at B > 650 G, and only one dark resonance is retained at B > 1200 G. A method of the formation of a dark resonance at a given frequency is demonstrated that will allow, under the corresponding conditions, the formation of a dark resonance also at B > 0.2 T. The experimental results are well described by the known theoretical models. Practical applications of these results are indicated. [ABSTRACT FROM AUTHOR]

Electromagnetically induced transparency (EIT) resonance in strong magnetic fields of up to 1.7 kG has been investigated with the use of a 30-μm cell filled with an atomic rubidium vapor and neon as a buffer gas. The EIT resonance in the Λ system of the D line of Rb atoms has been formed with the use of two narrowband (∼1 MHz) 795-nm diode lasers. The EIT resonance in a longitudinal magnetic field is split into five components. It has been demonstrated that the frequencies of the five EIT components are either blue- or red-shifted with an increase in the magnetic field, depending on the frequency ν of the probe laser. In has been shown that in both cases the Rb atoms enter the hyperfine Paschen-Back regime in magnetic fields of >1 kG. The hyperfine Paschen-Back regime is manifested by the frequency slopes of all five EIT components asymptotically approaching the same fixed value. The experiment agrees well with the theory. [ABSTRACT FROM AUTHOR]

The narrow-band N-resonance formed in a Λ system of D-line rubidium atoms is studied in the presence of a buffer gas (neon) and the radiations of two continuous narrow-band diode lasers. Special-purpose cells are used to investigate the dependence of the process on vapor column thickness L in millimeter, micrometer, and nanometer ranges. A comparison of the dependences of the N-resonance and the electromagnetically induced transparency (EIT) resonance on L demonstrates that the minimum (record) thickness at which the N-resonance can be detected is L = 50 μm and that a high-contrast EIT resonance can easily be formed even at L ≈ 800 nm. The N-resonance in a magnetic field for Rb atoms is shown to split into five or six components depending on the magnetic field and laser radiation directions. The results obtained indicate that levels F = 2, 3 are initial and final in the N-resonance formation. The dependence of the N-resonance on the angle between the laser beams is analyzed, and practical applications are noted. [ABSTRACT FROM AUTHOR]

Experimental results of the study of processes of electromagnetically induced transparency (EIT) and two-photon absorption (TPA) are presented for the ladder Ξ-system obtained using the 5 S-5 P- nD, mS system of levels of the Rb and Rb atoms with n = 5, 26, and 27 and m = 39 and 48. To perform these studies, a high-temperature optical cell was designed with several regions with the following thicknesses L: 2 mm, 0.7 mm, and the region of 2-6 μm. The advantages of using thin cells over ordinary cells several centimeters thick are demonstrated. It is shown that the EIT resonance parameters for n = 5, 26, and 27 deteriorate insignificantly for thickness down to 700 μm. The TPA is recorded with the cell thickness decreasing down to L = 6 μm. It is shown that using the EIT and TPA processes makes it possible to measure the hyperfine and fine structures of highlying atomic levels. The influence of the cell walls is appreciable in recording the EIT resonances in the system 5 S-5 P-39 S with L = 0.7 mm and in the system 5 S-5 P-48 S with L = 2 mm. Possible applications of the processes studied are indicated. [ABSTRACT FROM AUTHOR]

The selective reflection (SR) spectrum of laser light from the boundary of the surface of the dielectric window of a spectroscopic nanocell with pairs of rubidium atoms is used to measure a magnetic field applied to the nanocell. A method is proposed for calculating the magnetic induction B in the range of 0.1–6.0 kG based on the ratio of the frequency intervals between atomic transitions, which simplifies the determination of B; in particular, there is no need for a reference spectrum at B = 0. A 300-nm column of Rb atom vapor is used to implement the SR process; atomic processes with a sub-Doppler spectral width of 80–90 MHz take place. This leads to frequency separation of transitions in the SR spectrum. The SR spectrum can be analyzed with the aid of a specially created computer program that speeds up the data processing. The small thickness of the vapor column makes it possible to attain high spatial resolution, which is important in the case of inhomogeneous magnetic fields. [ABSTRACT FROM AUTHOR]

The sub-Doppler absorption and fluorescence spectra at the frequencies of D1- and D2-line transitions in Cs atomic vapor, enclosed in a nanocell (NC) with a thickness L ~ 400 nm, have been investigated experimentally at a near-room temperature. It is shown that a decrease in the NC temperature to 35°C causes narrowing of the absorption lines to values smaller than the Doppler width by a factor of 6, due to which the strong spectral broadening induced by laser field can be measured. The high intensity threshold for optical pumping (which limits the fluorescence intensity in centimeter-length cells) made it possible to record fluorescence spectra (using laser power of several milliwatts) at a temperature of 20°C; thus, a frequency marker of transitions in the range of D1,2 lines can be developed based on a room-temperature NC. A comparison with a widely used marker based on saturated absorption is performed. [ABSTRACT FROM AUTHOR]

Two types of magnetically induced (MI) transitions in cesium atoms were studied experimentally and theoretically. The MI transitions are forbidden in the absence of magnetic field. Probabilities of MI transitions rapidly grow with increase in magnetic field and can exceed those of transitions allowed in the absence of magnetic field. Asymptotic behavior of probabilities of MI transitions in strong magnetic fields is different. In the case of magnetically induced transitions of the first type (MI1), transition probabilities experience giant increase with increase in the applied magnetic field, and with a further increase of the magnetic field, the probabilities of these transitions tend to asymptotic large value. Probabilities of magnetically induced transitions of the second type (MI2) also experience giant increase with increase in the applied magnetic field. However, probabilities of such transitions tend to zero again with further increase in the magnetic field. It is demonstrated that measurement of the second derivative (SD) of absorption spectra of Cs vapor contained in a nanocell with thickness L = 426 nm corresponding to half the wavelength of the D2 line of cesium (λ = 852 nm) enables conducting Doppler-free spectroscopy. Narrow width of atomic lines and linear relation between the SD signal amplitudes and transition probabilities allows studying individual atomic transitions in an external transverse magnetic field with induction varying from 0.5 to 5.3 kG. In particular, four MI transitions were studied: two MI1 and two MI2 ones. Theoretical calculations agree well with the experimental results. [ABSTRACT FROM AUTHOR]

The effect of electromagnetically induced transparency (EIT) in a three-level ladder system 5S1/2‒5P3/2 –5D5/2 of Rb atoms is investigated. The effect of spectral narrowing of a dark resonance (DR) as a function of atomic vapor density and thickness L of a spectroscopic cell containing Rb vapor is demonstrated. Thickness L was varied in the range of 390 nm to 4 mm, while atomic density N was increased up to ~1016 cm–3; in the process, high-intensity coupling radiation and weak probe radiation were used. The strongest effect, namely, a 22-fold spectral narrowing of the DR, was achieved in a cell of thickness L = 4 mm. The effect of spectral narrowing was decreasing with decrease in thickness L: a 2.4-fold spectral narrowing of the DR was observed at L = 2 μm. Spectral narrowing was nearly absent at L = 0.8 μm, and spectral broadening of the DR was observed with further decrease in the cell thickness down to L = 0.4 μm. A close to 100% DR contrast was achieved in nearly all cases at moderate atomic densities and high intensities of the coupling radiation. An interpretation of the effect of spectral narrowing and broadening of the DR is proposed. [ABSTRACT FROM AUTHOR]

We demonstrate that a method using the derivative of the selective reflection (SR) signal from a nanocell is a convenient and robust tool for atomic laser spectroscopy, achieving a nearly Doppler-free spectral resolution. The recorded linewidth of the signal from a potassium-filled cell, whose thickness ℓ lies in the range 350–500 nm, is 18 times smaller than the Doppler linewidth (∼900 MHz full width at half maximum) of potassium atoms. We also show experimentally a sign oscillation of the reflected signal's derivative with a periodicity of λ/2 when ℓ varies from 190 to 1200 nm confirming the theoretical prediction. We report the first measurement of the van der Waals atom-surface interaction coefficient C3 = 1.9 ± 0.3 kHz × μm3 of potassium transitions with the nanocell's sapphire windows, demonstrating the usefulness and convenience of the derivative of SR technique for cell thicknesses in the range 60–120 nm. [ABSTRACT FROM AUTHOR]

Magnetically induced (MI) transitions of the D2 line of 39K atom in an external magnetic field of 10–600 G have been experimentally and theoretically investigated for the first time using circularly polarized σ+ and σ− radiations. According to the selection rules, the transitions between the sublevels of the ground and excited levels of a hyperfine structure with Fe – Fg = ΔF = ±2 are forbidden in the zero magnetic field, whereas their probabilities increase radically in a magnetic field. For the Fg = 1 → Fe = 3 (ΔF = +2) and Fg = 2 → Fe = 0 MI transitions, the highest probabilities are achieved using the σ+ and σ– radiations, respectively. The atomic transitions have been spectrally resolved using selective reflection of laser radiation from a nanocell filled with potassium atomic vapor, which makes it possible to investigate the behavior of the MI transitions. The experimental and theoretical data are shown to be in good agreement. [ABSTRACT FROM AUTHOR]

A nanocell filled with atomic vapors of rubidium and potassium was used to develop a modified method of Faraday rotation. The formed lines are characterized by a spectral width that is a factor of 1.5‒2 smaller than those obtained by traditional method of Faraday rotation in nanocells. The new method allows obtaining the spectral width of atomic line that is 8 times smaller than the Doppler broadening in the case of the D2 line of rubidium and 15 time smaller than the Doppler broadening in the case of the D1,2 lines of potassium. In magnetic fields B = 100−1200 G, all atomic lines of Rb and K atoms are spectrally resolved and identified. In the case of the D2 line of Rb, it is demonstrated that the probabilities of magneto-induced transitions (87Rb, Fg = 1 → Fe = 3 and 85Rb, Fg = 2 → Fe = 4) can exceed the probabilities of the allowed transitions. Convenience and efficiency of the modified method of Faraday rotation for high-resolution spectroscopy is demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: The circular dichroism effect has been investigated for atomic transitions of the Rb D1 line in magnetic fields of up to 3 kG using circularly polarized σ+ and σ− radiation. The process of selective reflection from a 350-nm-thick nanocell has been used, which makes it possible to form narrow atomic lines and observe separately the behavior of individual transitions. Two groups consisting of six (85Rb atoms) and four (87Rb atoms) transitions are formed in magnetic fields B > 0.5 kG upon σ+ and σ− laser excitation. All transitions have been identified. It is shown that the strongest transitions for 87Rb and 85Rb atoms in magnetic fields of up to several kG are formed under σ− irradiation. A further increase in the magnetic field makes it possible to attain the Paschen-Back regime on a hyperfine structure, for which the probabilities of transitions upon σ+ and σ− excitation become identical. The theoretical model and experiment are in good agreement. [ABSTRACT FROM AUTHOR]

The selective reflection of laser radiation from the interface between a dielectric window and the atomic vapors confined in a nanocell of thickness L ≈ 350 nm is used to develop effective Doppler-broadening- free spectroscopy of potassium atoms. A small atomic line width and a relation between the signal intensity and the transition probability allowed us to resolve four lines of atomic transitions responsible for the D1 lines of the 39K and 41K isotopes. Two groups containing four atomic transitions form in an applied magnetic field upon pumping by radiation with circular polarization σ+ or σ-. Different intensities (probabilities) of transitions for the σ+ and σ- excitations are detected in magnetic field B0 ≈ Ahfs/μB ≈ 165 G (Ahfs is the magnetic dipole constant for the ground state and μB is the Bohr magneton). A substantially different situation is observed at B ≫ B0, since high symmetry appears for the two groups formed by radiation with circular polarization σ+ or σ-. Each group is the mirror image of the other group with respect to the frequency of the 42S1/2-42P1/2 transition, which additionally proves the occurrence of the complete Paschen-Back regime of the hyperfine structure at B ≈ 2.5 kG. A developed theoretical model well reproduces the experimental results. Possible practical applications are described. The results obtained can also be applied to the D1 lines of 87Rb and 23Na. [ABSTRACT FROM AUTHOR]

Transitions Fe − Fg = ΔF = ±2 between the excited and ground levels of the hyperfine structure of the Cs D2 atomic line in an external magnetic field of 300–3000 G have been studied for the first time with the use of σ+ and σ− circularly polarized radiation. Selection rules forbid these transitions in zero magnetic field. At the same time, the probabilities of these transitions in a magnetic field increase significantly; for this reason, we refer to these transitions as magnetically induced transitions. The following rule has been found for the intensities of 24 magnetically induced Fg = 3 → Fe = 5 and Fg = 4 → Fe = 2 transitions: the intensities of magnetically induced transitions with ΔF = +2 are maximal (the number of such magnetically induced transitions is also maximal) in the case of σ+ polarized radiation, whereas the intensities of magnetically induced transitions with ΔF = −2 are maximal (the number of such transitions is also maximal) in the case of σ− σ+ and σ− polarized radiation can reach several orders of magnitude; i.e., anomalous circular dichroism is observed. For an experimental test, absorption spectra of a Cs-filled nanocell with the thickness equal to half the wavelength of resonant laser radiation = 852 nm have been analyzed in order to separately detect magnetically induced transitions. The experiment is in good agreement with the theory. Possible applications have been discussed. [ABSTRACT FROM AUTHOR]

We studied selective reflection (SR) of laser radiation from a window of a nanocell with thickness L ~ λ /2 filled with Rb and Cs atoms, where λ = 780 nm and λ = 852 nm are the wavelengths resonant with the D laser lines for Rb and Cs, respectively. It is demonstrated that the negative derivative of the SR signal profile for L > λ/2 changes to the positive one for L < λ/2. It is shown that the real-time formation of the SR signal profile derivative (SRD) with the spectral width 30-40 MHz and located at the atomic transition is, in particular, a convenient frequency marker of D transitions in Rb and Cs. The amplitudes of SRD signals are proportional to the atomic transition probabilities. A comparison with the known saturated absorption (SA) method demonstrated a number of advantages, such as the absence of cross-over resonances in the SRD spectrum, the simplicity of realization, a low required power, etc. An SRD frequency marker also operates in the presence of the Ne buffer gas at a pressure of 6 Torr, which allowed us to determine the Ne-Rb collisional broadening, whereas the SA method is already inapplicable at buffer gas pressures above 0.1 Torr. The realization simplicity makes the SRD method a convenient tool for atomic spectroscopy. Our theoretical model well describes the SRD signal. [ABSTRACT FROM AUTHOR]

The effect of electromagnetically induced transparency (EIT) has been experimentally implemented for the first time for the (4 S -4 P -4 S ) Λ-system of potassium atom levels in a nanocell with a 770-nm-thick column of atomic vapor. It is shown that, at such a small thickness of the vapor column, the EIT resonance can be observed only when the coupling-laser frequency is in exact resonance with the frequency of the corresponding atomic transition. The EIT resonance disappears even if the coupling-laser frequency differs slightly (by ~50 MHz) from that of the corresponding atomic transition, which is due to the high thermal velocity of K atoms. The EIT resonance and related velocity selective optical pumping resonances caused by optical pumping (formed by the coupling) can be simultaneously recorded because of the small (~462 MHz) hyperfine splitting of the lower 4 S level. [ABSTRACT FROM AUTHOR]

A new device is designed: it consists of a nanocell (NC) filled with Rb atom vapors and placed in a vacuum chamber. When the pressure in the chamber changes in the range 0-1 atm, the NC thickness is smoothly varied in the range L = 140-1700 nm, which is caused by the pressure-induced deformation of thin garnet windows in the chamber. The pressure dependence has excellent reproducibility even after many hundreds of cycles of letting in of air and its complete pumping out from the chamber. The accuracy of setting required thickness L is much better than in the wedge-gap NCs to be moved mechanically that were used earlier. The processes of Faraday rotation (FR) of a polarization plane, resonance absorption, and fluorescence are studied using the D -line narrow-band continuous laser radiation when the thickness changes from L = λ/2 (398 nm) to L = 2λ (1590 nm) at a step λ/2. The FR signal is shown to be maximal at L = λ/2 and 3λ/2 and to have the minimum spectral width (≈60 MHz). At L = λ and 2λ, the FR signal is minimal and has the maximum spectral width (≈200 MHz). The resonance absorption demonstrates the same oscillating behavior; however, the effect in the case of FR is much more pronounced. The oscillating effect is absent for resonance fluorescence: its spectral width and amplitude increase monotonically with L. The detected effects are explained and possible applications are noted. [ABSTRACT FROM AUTHOR]

Atomic transitions of the K potassium isotope in strong (up to 1 kG) longitudinal and transverse magnetic fields have been studied with a high spectral resolution. It has been shown that crossover resonances are almost absent in the saturated absorption spectrum of potassium vapors in a 30-μm-thick microcell. This, together with the small spectral width of atomic transitions (~30 MHz), allows one to use the saturated absorption spectrum for determining frequencies and probabilities of individual transitions. Among the alkali metals, potassium atoms have the smallest magnitude of the hyperfine splitting of the lower level. This allows one to observe the break of the coupling between the electronic and nuclear angular momentums at comparatively low magnetic fields B > 500 G, i.e., to implement the hyperfine Paschen-Back regime (HPB). In the HPB regime, four equidistantly positioned transitions with the same amplitude are detected in circularly polarized light (σ). In linearly polarized light (π) at the transverse orientation of the magnetic field, the spectrum consists of eight lines which are grouped in two groups each of which consists of four lines. Each group has a special distinguished G-transition and the transition that is forbidden in the zero magnetic field. In the HPB regime, the probabilities of transitions in a group and derivatives of their frequency shifts with respect to the magnetic field asymptotically tend to magnitudes that are typical for the aforesaid distinguished G-transition. Some practical applications for the used microcell are mentioned. [ABSTRACT FROM AUTHOR]

The rotation of the radiation polarization plane in a longitudinal magnetic field (Faraday effect) on the D line in atomic Rb vapor has been studied with the use of a nanocell with the thickness L varying in the range of 100-900 nm. It has been shown that an important parameter is the ratio L/λ, where λ = 795 nm is the wavelength of laser radiation resonant with the D line. The best parameters of the signal of rotation of the radiation polarization plane have been obtained at the thickness L = λ/2 = 397.5 nm. The fabricated nanocell had a large region with such a thickness. The spectral width of the signal reached at the thickness L = 397.5 nm is approximately 30 MHz, which is much smaller than the spectral width (≈ 500 MHz) reached with ordinary cells with a thickness in the range of 1-100 mm. The parameters of the Faraday rotation signal have been studied as functions of the temperature of the nanocell, the laser power, and the magnetic field strength. The signal has been reliably detected at the laser power P ≥ 1 μW, magnetic field strength B ≥ 0.5 G, and the temperature of the nanocell T ≥ 100°C. It has been shown that the maximum rotation angle of the polarization plane in the longitudinal magnetic field is reached on the F = 3 → F = 2 transition of the Rb atom. The spectral profile of the Faraday rotation signal has a specific shape with a sharp peak, which promotes its applications. In particular, Rb atomic transitions in high magnetic fields about 1000 G are split into a large number of components, which are completely spectrally resolved and allow the study of the behavior of an individual transition. [ABSTRACT FROM AUTHOR]

The features of the effect of selective reflection from rubidium vapor in a nanocell with the thickness L ≈ λ/2 and L ≈ λ/4, where λ = 795 nm is the wavelength of laser radiation resonant with the Rb D line, are studied. It is shown that, because of the behavior of the nanocell as a low- Q-factor Fabry-Pérot etalon, the sign of the derivative of the selective reflection spectra changes near L ≈ λ/2 from negative at L > λ/2 to positive at L < λ/2. The simplicity of the experimental implementation, large amplitude, and sub-Doppler width (40MHz) of a detected signal at an atomic transition frequency are appropriate for applications in metrology and magnetometry. In particular, selective reflection from the nanocell is a convenient frequency marker of atomic transitions; in this case, the amplitudes of peaks are proportional to the transition probabilities. The remote optical monitoring of a magnetic field with a spatial resolution L = λ/4 ≈ 199 of nm is possible on the basis of the splitting of selective reflection peaks in a strong magnetic field (up to 3 kG). A theoretical model describes well the experimental results. [ABSTRACT FROM AUTHOR]

Features of electromagnetically induced transparency (EIT) in potassium vapors at the D line of the K isotope are studied. EIT resonances with a subnatural width of 3.5 MHz have been recorded upon excitation by two independent narrow-band diode lasers in a 1-cm-long cell filled with a natural mixture of potassium isotopes and buffer gas. The splitting of EIT resonances in potassium vapors in longitudinal and transverse magnetic fields has been studied for the first time. The splitted components also have a subnatural width. The smallness of the coupling factor of the hyperfine structure in K atoms leads to a transition to the Paschen-Back regime at relatively weaker magnetic fields than in the case of Cs, Rb, and Na atoms. Practical applications of the phenomena under study are noted. The theoretical model well explains the experiment. [ABSTRACT FROM AUTHOR]

Features of the effect of Faraday rotation (the rotation of the radiation polarization plane) in a magnetic field of the D line in Cs atomic vapor in a nanocell with the thickness L varying in the range of 80-900 nm have been analyzed. The key parameter is the ratio L/λ, where λ = 895 nm is the wavelength of laser radiation resonant with the D line. The comparison of the parameters for two selected thicknesses L = λ and λ/2 has revealed an unusual behavior of the Faraday rotation signal: the spectrum of the Faraday rotation signal at L = λ/2 = 448 nm is several times narrower than the spectrum of the signal at L = λ, whereas its amplitude is larger by a factor of about 3. These differences become more dramatic with an increase in the power of the laser: the amplitude of the Faraday rotation signal at L = λ/2 increases, whereas the amplitude of the signal at L = λ almost vanishes. Such dependences on L are absent in centimeter-length cells. They are inherent only in nanocells. In spite of a small thickness, L = 448 nm, the Faraday rotation signal is certainly detected at magnetic fields ≥0.4 G, which ensures its application. At thicknesses L < 150 nm, the Faraday rotation signal exhibits 'redshift,' which is manifestation of the van der Waals effect. The developed theoretical model describes the experiment well. [ABSTRACT FROM AUTHOR]

In this paper we present a device for measuring the magnetic field and its gradient with a spatial resolution of several hundred nanometres. This device is based on caesium metal vapour confined to an extremely thin cell (ETC). To measure magnetic signals, we use absorption and very low laser powers, which might be appealing for modern fabrication techniques. A portable, fully automated device was constructed. [ABSTRACT FROM AUTHOR]

It has been shown that the D line of atomic vapors of alkali metals excited by π-polarized radiation in a strong transverse magnetic field includes specific 'guiding' (indicating) atomic transitions between the magnetic sublevels of the hyperfine structure. The dependence of the frequency shift of the guiding transitions on the magnetic field, as well as on their dipole moments, is asymptotic for all other transitions. An experiment with a nanocell with Rb vapor with a thickness of half the wavelength (λ/2 method) for ensuring a sub-Doppler spectral resolution has completely confirmed the presence of guiding transitions. Two groups of six transitions for Rb and two groups of four transitions for Rb have been detected in the absorption spectra in magnetic fields above 4 kG. A guiding transition has been identified in each of four groups. Four transitions forbidden at B = 0 have been also detected; with an increase in the magnetic field, their probabilities also approach the probabilities of the guiding transitions. [ABSTRACT FROM AUTHOR]

An efficient λ /2-method ( λ is the resonant wavelength of laser radiation) based on nanometric-thickness cell filled with rubidium is implemented to study the splitting of hyperfine transitions of 85 Rb and 87 Rb D 2 lines in an external magnetic field in the range of B =3–7 kG. It is experimentally demonstrated that at B > 3 kG from 38 (22) Zeeman transitions allowed at low B -field in 85 Rb ( 87 Rb) spectra in the case of σ + polarized laser radiation there remain only 12 (8) which is caused by decoupling of the total electronic momentum J and the nuclear spin momentum I (hyperfine Paschen–Back regime). Note that at B > 4.5 kG these 20 atomic transitions are regrouped into two completely separate groups of 10 atomic transitions each. Their frequency positions and fixed (within each group) frequency slopes, as well as the probability characteristics, are determined. A unique behavior of two atomic transitions is stressed: one transition belongs to 85 Rb, the other to 87 Rb and for low magnetic fields they could be presented as transitions F g = 3 , m F =+ 3 → F e = 4 , m F =+ 4 and F g = 2 , m F =+ 2 → F e = 3 , m F =+ 3 , correspondingly. The experimental results of the atomic transition frequency shifts and the modification of their probabilities agree well with the theory. A comparison of the behavior of the D 1 and D 2 atomic transitions is presented. Possible applications are described. [ABSTRACT FROM AUTHOR]

We present experimental observations of atom-light interactions within tens of nanometers (down to 11 nm) of a sapphire surface. Using photon counting we detect the fluorescence from of order one thousand Rb or Cs atoms, confined in a vapor with thickness much less than the optical excitation wavelength. The asymmetry in the spectral line shape provides a direct readout of the atom-surface potential. A numerical fit indicates a power law -Cα/rα with α = 3.02±0.06 confirming that the van der Waals interaction dominates over other effects. The extreme sensitivity of our photon-counting technique may allow the search for atom-surface bound states. [ABSTRACT FROM AUTHOR]