Splitting of the electromagnetically induced transparency resonance on 85Rb atoms in strong magnetic fields up to the Paschen-Back regime

Electromagnetically induced transparency (EIT) resonance in strong magnetic fields of up to 1.7 kG has been investigated with the use of a 30-??m cell filled with an atomic rubidium vapor and neon as a buffer gas. The EIT resonance in the ?? system of the D₁ line of ⁸⁵Rb 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 ??_P of the probe laser. In has been shown that in both cases the ⁸⁵Rb 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.     

Spectral anomalies of the light-induced drift of rubidium atoms caused by the velocity dependence of transport collision frequencies

The spectral features of the light-induced drift (LID) velocity for rubidium atoms (⁸⁵Rb and ⁸⁷Rb) in an argon buffer medium and in binary buffer mixtures of noble gases (Ne + Ar, Ne + Kr, Ne + Xe, He + Ar, He + Kr, and He + Xe) have been investigated theoretically. A strong temperature dependence of the spectral shape of the LID signal for Rb atoms in an Ar atmosphere is predicted in the temperature range 450 K < T < 800 K. It is shown that the anomalous LID of Rb atoms in binary buffer mixtures of noble gases can be observed at almost any temperature (including the room one) depending on the fractions of neon or helium in these mixtures. The results obtained enable a highly accurate testing of the interatomic interaction potentials used to calculate the drift velocity for anomalous LID in LID experiments.     

Observation of polarized atoms of rubidium isotopes in experiments on optical orientation in a He–Rb mixture under conditions of a pulsed gas discharge

We are the first to have observed magnetic resonance signals from atoms of ⁸⁵Rb and ⁸⁷Rb isotopes when using the indirect optical orientation in conditions of helium–rubidium gas discharge plasma. An anomalously small ratio of magnetic resonance signals from isotopes of rubidium and metastable helium upon optical orientation of ⁴Не atoms has been detected. The experimental results have been considered theoretically, and an explanation of the observed anomaly in the signals is presented.Z     

Narrow-band N-resonance formed in thin rubidium atomic layers

The narrow-band N-resonance formed in a ?? system of D ₁-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 ??m and that a high-contrast EIT resonance can easily be formed even at L ?? 800 nm. The N-resonance in a magnetic field for ⁸⁵Rb 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 _g = 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.     

Multimode-diode-pumped gas (alkali-vapor) laser

We report what we believe to be the first demonstration of a multimode-diode-pumped gas laser: Rb vapor operating on the 795 nm D1 resonance transition. Peak output of approximately 1 W was obtained using a volume-Bragg-grating stabilized pump diode array. The laser's output radiance exceeded the pump radiance by a factor greater than 2000. Power scaling (by pumping with larger diode arrays) is therefore possible.     

Rb atomic absorption line reference for single Sr+ laser cooling systems

85 Rb, 5s²S_1/2(F”=2)→6p²P_1/2(F’=2,3) absorption resonance with the ⁸⁸Sr⁺, 5s²S_1/2→5p²P_1/2 transition is exploited to provide a simple, effective frequency reference for a laser cooling/fluorescence excitation source applied to single Sr⁺ ions. A modulation-free frequency stabilization system has been designed which uses the differential signal from two frequency-displaced beams traversing a Rb cell and which probe the Doppler-broadened Rb S–P lineshape at microwatt power levels. The method is applied to frequency lock a 422-nm frequency-doubled diode laser system that is used for excitation of a single ⁸⁸Sr⁺ ion. Stable, long-term laser cooling and fluorescence are achieved using the frequency-stabilized 422-nm source resulting in observed ion confinement times without adjustment of over 8 h, together with an improvement in single-ion loading efficiency. Received: 12 February 1998     

EIT resonance features in strong magnetic fields in rubidium atomic columns with length varying by 4 orders

Electromagnetically induced transparency (EIT) resonances are investigated with the ⁸⁵Rb D₁ 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.     

Dependence of the ^85Rb coherent population trapping resonance characteristic on the pressure of N2 buffer gas

In order to exploit its potential applications, we experimentally study the dependence of ^85 Rb-based coherent population trapping （CPTi resonance on N2 buffer gas with 6 vapor cells filled with natural rubidium and N2. The experiments are carried out at different pressures and temperatures, and the results reveal that higher cell temperature makes the resonance more sensitive to N2 pressure. Thus, it is importmlt to choose a proper buffer gas pressure at a given cell temperature. This work provides valuable data for the application of 85Rb CPT resonance with a buffer gas of N2.     

Coherent spectroscopy of the 87RbFg=1→ Fe=0 closed transition

This paper has observed linewidth narrowing of dark states in rubidium cell by using the Hanle configuration. The reduction of the coherent resonance width under the transition of ^87Rb Fg = 1 → Fe = 0 is observed and the qualitative explanation about its mechanism is presented. Multiple subnatural width dips are obtained with a linearly polarized laser beam for the transitions of ^87Rb Fg = 1→Fe = 0, 1, 2. The feature of negative and positive slope, namely dispersionlike feature, is observed in the transmitted light.     

Alkali lasers for magnetic resonance imaging

Spin-polarized nuclei of such gases as ³He and ¹²⁹Xe are successfully used for magnetic resonance imaging of lungs and other organs of human body. To produce large numbers of spin-polarized nuclei required for this medical application, a high power narrowband tunable laser source is required. Diode pumped alkali lasers, developed during last several years can be an ideal source for this application. In this paper we present our latest achievements in diode pumped alkali lasers development. We describe optically pumped Cs laser tunable in the range of 14 GHz and operating in single transverse mode with a linewidth less than 3 MHz. We also present continuous wave diode pumped Rb and Cs lasers with output power 17 W and 20 W.     

Temperature dependence of Rb 5P fine-structure transfer induced by 4He collisions

Employing ultrafast laser excitation and time-correlated single-photon counting, we have measured the fine-structure transfer between Rb 5P states induced by collisions with 4He buffer gas at temperatures up to 150 °C. The temperature dependence of the binary cross section agrees with earlier measurements. Our data show that the temperature dependence of the three-body rate is about the same as that of the binary rate. The three-body rate can be described as arising from the reduction of the rubidium fine-structure splitting due to nearby helium atoms.     

High contrast electromagnetically induced transparency in a nitrogen filled Rb vapour cell

We observe the electromagnetically induced transparency (EIT) spectra inside a nitrogen filled Rb vapour cell (Rb-N₂) in a five-level Λ-type system of D₂ transition of Rb atom. The high contrast EIT resonance in buffer gas filled Rb cell is obtained under our experimental conditions. The effect of velocity changing coherence preserving collisions to obtain the contrast resonance in buffer gas cell has been discussed. We measured the dependence of EIT width and height on pump intensity and find that the EIT width (FWHM) and peak height have a linear dependence on pump intensity. Our experimental results show that the presence of N2 buffer gas reduces the power broadening of the observed resonances.     

Hydrocarbon-free resonance transition 795-nm rubidium laser

For what we believe to be the first time, an optical resonance transition rubidium laser (5(2)P(1/2)-->5(2)S(1/2)) has been demonstrated with a hydrocarbon-free buffer gas. Prior demonstrations of alkali resonance transition lasers have used ethane as either the buffer gas or a buffer gas component to promote rapid fine-structure mixing. However, our experience suggests that the alkali vapor reacts with the ethane producing carbon as one of the reaction products. This degrades long term laser reliability. Our recent experimental results with a "clean" helium-only buffer gas system demonstrate all the advantages of the original alkali laser system, but without the reliability issues associated with the use of ethane.     

Pressure broadening and collisional shift of the Rb D2 absorption line by CH4, C2H6, C3H8, n-C4H10, and He

The pressure broadening and shift rates of the rubidium D2 absorption line 5²S_1/2→5²P_3/2 (780.24 nm) with CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and He were measured for pressures ≤80 Torr using high-resolution laser spectroscopy. The broadening rates γ_B for CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and He are 28.0, 28.1, 30.5, 31.3, and 20.3 (MHz/Torr), respectively. The corresponding shift rates γ_S are −8.4, −8.8, −9.7, −10.0, and 0.39 (MHz/Torr), respectively. The measured rates of Rb for the hydrocarbon buffer gas series of this study are also compared to the theoretically calculated rates of a purely attractive van der Waals difference potential. Good agreement is found to exist between measured and theoretical rates.     

Magneto-optical resonances in the field of counterpropagating waves

The resonance of the intersection of sublevels in a probe laser field resonant to the cyclic transition corresponding to the D ₂ ⁸⁷Rb line has been investigated in a zero magnetic field. The strong effect of an additional laser field acting on the adjacent transition has been revealed. In a cell without the buffer gas and antirelaxation coating, the amplitude of the probe-field absorption resonance can increase by more than an order of magnitude in the presence of a counterpropagating wave. The effect is observed at the laser frequency tuned to the cross resonance, when the counterpropagating waves simultaneously act on moving atoms at the cyclic and open transitions with the common lower level. The theoretical analysis of the effect of the additional field on the electromagnetically induced absorption resonance is in agreement with the experimental data.     

Quasi-point incoherent ArF<Superscript>∗</Superscript> excimer emission source at 193 nm using a laser-produced plasma

We have demonstrated proof-of-principle of an incoherent ArF^∗ emission source with a quasi-point emission geometry using a laser-produced plasma in an Ar/F₂/He/Ne mixed gas. The VUV emission characteristics, such as the emission size, were dependent on those of the plasma-initiating laser. The average emission power was 10 μW at a repetition rate of 10 Hz at 193 nm. The average power conversion efficiency of the 193-nm emission from the plasma-initiating Nd:YAG laser was 6.3×10⁻⁶. The average emission power at 193 nm was proportional to that of the plasma-initiating laser, indicating the scaling of the emission source.     

Performance study of the KrCl discharge laser with liquid chlorine donors

The effects of liquid chlorine donors (BCl₃ and CCl₄) on the output energy and the efficiency of a KrCl laser (222 nm) are investigated. Maximum laser energies of 230 mJ (3.3 J/l) in pulses of 16 ns duration were obtained from a 0.035% BCl₃/10.1% Kr/89.8% Ne mixture at a total pressure of 2600 Torr, and at a specific power loading of about 24 MW/cm³, a power conversion efficiency of 0.86% was obtained. These figures are reduced by a factor of two when He is used as buffer gas. Much weaker laser emissions were obtained when CCl₄ was used as a chlorine donor.     

Orientational frequency shifts of microwave 0-0 superfine resonance in 87Rb vapor with selective optical pumping

The orientational frequency shift of the UHF radio-optical resonance in the ⁸⁷Rb vapor with a selective optical pumping by laser and lamp sources is studied experimentally and theoretically. A leading role of the tensor component of the light shift is noticed for both excitation modes, and a modulation technique of the resonance frequency orientation shift suppression is demonstrated. We show that it is necessary to ensure a constancy of the angle between the pump light direction and the external magnetic field vector when using a rubidium quantum discriminator based on moving and rotating carriers.     

Rb$\mathsf{_{2}}$ diffuse band emission excited by diode lasers

We investigated collisional processes involved in the population of the Rb₂ diffuse band through resonant excitation of Rb atoms. Near-infrared (780 nm) and violet (420 nm) diode lasers were used for the Rb first ( 5 ²S_1/2? 5 ²P_3/2\rm 5 ^{2}S_{1/2}\to 5 ^{2}P_{3/2} ) and second ( 5 ²S_1/2? 6 ²P_3/2\rm 5 ^{2}S_{1/2}\to 6 ^{2}P_{3/2} ) resonant doublet excitations. Laser induced fluorescence spectra were detected and investigated at different rubidium densities, buffer gas pressures and excitation wavelengths.     

Line-shape of dark line and maser emission profile in CPT

The paper is concerned with the line shapes of resonance phenomena observed in Coherent Population Trapping (CPT) applied to alkali atoms in a cell containing a buffer gas. Significant asymmetries and departures from a Lorentzian shape have been observed in connection with the measurement of dark lines and CPT maser emission profiles. Measurements are reported as a function of the power and frequency tuning of the laser used to create the CPT phenomenon. The paper reports on different experimental conditions and a comparison between theory and experiments is made for the cases of cesium and rubidium in a buffer gas. Received 3 March 2000 and Received in final form 10 April 2000