Rb D2 Line Research Articles

Optical properties of an inhomogeneously broadened multilevel V-system in the weak and strong probe regimes

We present a theoretical model, using density matrix approach, to study the effect of weak as well as strong probe field on the optical properties of an inhomogeneously broadened multilevel V-system of the $$^{87}$$ Rb D2 line. We consider the case of stationary as well as moving atoms and perform thermal averaging at room temperature. The presence of multiple excited states results in asymmetric absorption and dispersion profiles. In the weak probe regime, we observe the partial transparency window due to the constructive interference that occurs between transition pathways at the line center. We present our results after carrying out Doppler averaging at room temperature atomic vapor and observe that the line width of transparency window is enhanced, whereas the positive slope of corresponding dispersion curve become less steep. In the presence of strong probe field, the transparency window (with normal dispersion) at line center switches to enhanced absorption (with anomalous dispersion). Here, we also present the dependence of electromagnetically induced transparency on the polarization of applied fields. In the end, we present transient behavior of our system which agrees with corresponding absorption and dispersion profiles. This study may help to understand optical switching and controllability of group velocity.

Electromagnetically induced transparency of 87Rb in a buffer gas cell with magnetic field

We have studied the phenomenon of electromagnetically induced transparency (EIT) of 87Rb vapor at room temperature in a magnetic field with an arbitrary angle to the laser propagation direction. Rather than exposing atoms to a parallelled or transverse magnetic field as usual, in our work, we apply a magnetic field (up to 45 Gauss) with an arbitrary angle to the laser propagation direction and the spectra become much more complex. More EIT dips are observed due to the Zeeman splitting on the D2 line of 87Rb in a -type configuration. With a 5 Torr N2 buffer gas in the thermal 2 cm vapor cell, the state has a very short effective lifetime, corresponding to a large energy broadening, which removes the velocity selective optical pumping effect almost completely and keeps the high resolution EIT spectrum for the energy splitting of 87Rb in magnetic fields. The shifting of the EIT resonances with the strength of the applied magnetic field coincides well with the theory based on a full matrix Hamiltonian combined with a spectral decomposition method. Our work can be extended to measure the magnetic field vector in space. The effects of the detuning of the probe and coupling beams on the spectral lines are also investigated.

Straightforward retrieval of dispersion in a dense atomic vapor helped by buffer gas-assisted radiation channeling

Strong enhancement of group refractive index in a dense buffered atomic vapor is recorded using a technique of reflection from a low-finesse Fabry–Perot cavity filled with dense atomic vapor allowing the retrieval of a dispersion curve for the hyperfine structure of Rb D2 line buffered by a high-density Cs vapor. Oscillations of the recorded signal resulting from interference of beams reflected from the front and rear windows of the cell appearing with the laser frequency scanning across the resonance allow easy reconstruction of the dispersion curve. Contribution from concomitant interconnected processes, in particular, the determinative role of radiation channeling in enhancement of the resonator Q-factor, is analyzed.

Generation of Narrow-Band Polarization-Entangled Photon Pairs at a Rubidium D1 Line

Using the process of cavity-enhanced spontaneous parametric down-conversion (SPDC), we generate a narrow-band polarization-entangled photon pair resonant on the rubidium (Rb) D1 line (795 nm). The degenerate single-mode photon pair is selected by multiple temperature controlled etalons. The linewidth of generated polarization-entangled photon pairs is 15 MHz which matches the typical atomic memory bandwidth. The measured Bell parameter for the polarization-entangled photons S=2.73+-0.04 which violates the Bell-CHSH inequality by ~18 standard deviations. The presented entangled photon pair source could be utilized in quantum communication and quantum computing based on quantum memories in atomic ensemble.

Frequency reference for atomic transitions of Rb D2-line based on the effect of selective reflection

On an example of the D2-line of the Rb atoms the work of the frequency reference of atomic transitions is demonstrated, based on the application of the spectrum of a selective reflectance (SR) from the boundary of atom vapors with the use of nano-cell (NC) with the thickness L ~ λ/2, where λ is the laser wavelength equal to 780 nm. When changing the thickness of the nano-cell near the thickness L ~ λ/2, we observe the inversion of sign of the SR slope profile which is positive when L λ/2. In the case when the incidence angle of the laser beam on the surface of the nano-cell is close to the normal, in real-time it is possible to form the derivative of the SR which represents a resonance peak with ~35 MHz spectral linewidth and located at the atomic transition. The phenomenon of oscillation of the sign of slope while changing the nano-cell thickness from L ~ λ/2 up to L ~ 3/2λ is demonstrated. The practical application of the SR is noted.

(Invited) Photonic Chip for Laser Stabilization to a Rubidium Atomic Vapor

— We report on recent progress on stabilization of an optical laser to a photonic chip based MEMS fabricated rubidium vapor cell. The interrogation light is delivered to the cell from the edge of the photonic chip via a fiber-pigtailed SiN waveguide. The light is directed into the vapor cell from the waveguide using a diffractive grating coupler. We will discuss the stability and environmental sensitivity of a laser locked to the photonic chip device. Additionally, observation of sub-Doppler features in the atomic absorption spectrum have been observed using a counter propagating pump beam generated from a partial reflector placed above the photonic chip. The development of high precision, ultraminiature, quantum based measurement devices has the potential to transform measurement science, enabling precision metrology outside the laboratory [1]. To this end, we are developing a photonic chip based platform for precision optical spectroscopy of alkali vapors. A laser stabilized to an optical transition in an alkali vapor can provide an accurate wavelength standard. The photonic chip is based on a silicon nitride/silicon dioxide on silicon structure. Fig. 1 shows an optical image and schematic of the photonic chip. Rubidium is introduced into the evacuated MEMS cell via optical heating of an alkali metal dispenser pill located inside the MEMS cell [2]. Waveguides direct probe light from the edge of the photonic chip to the Rb vapor cell. Grating output couplers direct the probe light out of the waveguide up through the Rb vapor cell and onto a silicon photodetector placed on top of the chip. The lower right panel of Fig. 1 shows an absorption spectrum of the Rb D1 line at 795nm taken using the photonic cell. We will report on the stability of a laser locked to this transition using the photonic chip. Retro-reflection of the probe beam by a partial reflector allows for the observation of sub-Doppler features. These sub-Doppler features allow for higher stability laser stabilization. Additionally, we will compare the performance of photonic chips with grating couplers that provide different output laser beam diameters. Figure 1. Top Left: Image of photonic chip. The chip contains two wells of dimension 1mm x 1mm. The left well contains a Rb alkali metal dispenser. The right well contains the photonic structures. Upper Right: Close up of photonic waveguides and grating output couplers. Lower Left: Cross section of the photonic chip describing the planar structure. PD: photodetector. Lower Right: Rubidium D1 line absorption spectrum at 795 nm. The photonic cell is heated to a temperature of 90 °C. Acknowledgment This work is a contribution of NIST and is not subject to copyright.

Selective reflection from Rb vapor in half- and quarter-wave cells: Features and possible applications

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 1 line, are studied. It is shown that, because of the behavior of the nanocell as a low-Q-factor Fabry–Perot 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.

High pressure line shapes of the Rb D1 and D2 lines for 4He and 3He collisions

Line shapes for the Rb D1 (5S1/22↔5P1/22) and D2 (5S1/22↔5P3/22) transitions with 4He and 3He collisions at pressures of 500–15,000Torr and temperatures of 333–533K have been experimentally observed and compared to predictions from the Anderson–Talman theory. The ground XΣ1/2+2 and excited AΠ1/22, AΠ3/22, and BΣ1/2+2 potential energy surfaces required for the line shape predictions have been calculated using a one-electron pseudo-potential technique. The observed collision induced shift rates for 4He are dramatically higher for the D1 line, 4.60±0.12MHz/Torr, than the D2 line, 0.20±0.14MHz/Torr. The asymmetry is somewhat larger for the D1 line and has the same sign as the shifting rate. The 3He broadening rate for the D2 line is 4% larger than the 4He rate, and 14% higher for the D1 line, reflecting the higher relative speed. The calculated broadening rates are systematically larger than the observed rates by 1.1–3.2MHz/Torr and agree within 14%. The primary focus of the current work is to characterize the high pressure line shapes, focusing on the non-Lorentzian features far from line center. In the far wing, the cross-section decreases by more than 4 orders of magnitude, with a broad, secondary maximum in the D2 line near 735nm. The potentials do not require empirical modification to provide excellent quantitative agreement with the observations. The dipole moment variation and absorption Boltzmann factor is critical to obtaining strong agreement in the wings.

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.

Frequency comb metrology with an optical parametric oscillator.

We report on the first demonstration of absolute frequency comb metrology with an optical parametric oscillator (OPO) frequency comb. The synchronously-pumped OPO operated in the 1.5-µm spectral region and was referenced to an H-maser atomic clock. Using different techniques, we thoroughly characterized the frequency noise power spectral density (PSD) of the repetition rate frep, of the carrier-envelope offset frequency fCEO, and of an optical comb line νN. The comb mode optical linewidth at 1557 nm was determined to be ~70 kHz for an observation time of 1 s from the measured frequency noise PSD, and was limited by the stability of the microwave frequency standard available for the stabilization of the comb repetition rate. We achieved a tight lock of the carrier envelope offset frequency with only ~300 mrad residual integrated phase noise, which makes its contribution to the optical linewidth negligible. The OPO comb was used to measure the absolute optical frequency of a near-infrared laser whose second-harmonic component was locked to the F = 2→3 transition of the 87Rb D2 line at 780 nm, leading to a measured transition frequency of νRb = 384,228,115,346 ± 16 kHz. We performed the same measurement with a commercial fiber-laser comb operating in the 1.5-µm region. Both the OPO comb and the commercial fiber comb achieved similar performance. The measurement accuracy was limited by interferometric noise in the fibered setup of the Rb-stabilized laser.

Resonantly enhanced Bragg-scattering spectroscopy of an atomic transition

A novel resonantly enhanced Bragg-scattering (REBS) spectroscopy from a population difference grating (PDG) is reported. The PDG is formed by a standing-wave (SW) pump field, which periodically modulates the space population distributions of two levels in the 87Rb D1 line. Then, a probe beam, having identical frequency and orthogonal polarization with the SW pump field, is Bragg-scattered by the PDG. The research achievement shows that the Bragg-scattered light is strongest at an atomic transition, and forms an REBS spectrum with a high signal-to-noise ratio and sub-natural linewidth. The observed REBS can be applied in precise frequency measurements.

On the efficiency of 1D atom localisation via EIT in a degenerate two-level atomic system

We analyse one-dimensional (1D) subwavelength atom localisation in a cold atomic medium under the action of two optical fields, the standing-wave and travelling probe fields, in the presence of a magnetic field. Optical Bloch equations are solved numerically for the hyperfine atomic transition of the 87Rb D1 line. All Zeeman sublevels are included in the calculations. This atomic scheme allows electromagnetically induced transparency (EIT) if the applied magnetic field is zero or small. The results for the position-dependent probe absorption are presented for two configurations, depending on the orientation of the magnetic field with respect to the optical fields’ polarisations. The efficiency of the atom localisation is analysed for a large range of field intensities and applied magnetic fields. The observed behaviour of the probe absorption is analysed through the effects of EIT induced by two fields of various strengths and its dependence on the applied magnetic fields.

Stray magnetic field influence on the CPT resonance in a coated Rb vacuum cell

Interaction of a resonant laser beam with an atomic absorption medium creates population redistribution and interference between atomic levels. This anisotropy of the medium is experimentally observed as coherent population trapping (CPT) or electromagnetically induced transparency (EIT). Due to the small sub-natural width of the CPT and EIT resonances, they find wide applications in metrology, quantum optics, atom cooling. A non-compensated stray magnetic field (SMF) can change the shape and sign of the resonance or destroy it completely. In this work, we present an experimental and theoretical investigation of the influence of a stray magnetic field on the CPT resonances obtained on Zeeman sublevels of the D1 line of 87Rb in a paraffin-coated vacuum cell. The role is clarified of the polarization moments with different rank in creating the integral registered fluorescent signal in the presence of a stray magnetic field. It is shown that a transverse magnetic field plays an important role in changing the shape of the signal.

Line shapes in sub-Doppler DAVLL in the 87Rb-D2 line

We present a theoretical and experimental study of the sub-Doppler dichroic atomic vapor laser lock (DAVLL) for the D2 transition line of 87Rb atoms. The experimental results of the sub-Doppler DAVLL spectra are compared with calculated results using both accurate density matrix equations and approximate rate equations. We find good agreement between the experimental and calculated results. In particular, the coherence effect must be included in the signal for the cycling transition line.

Electromagnetically induced transparency in a Zeeman-sublevels Λ-system of cold 87Rb atoms in free space**Project supported by the National Basic Research Program of China (Grant No. 2011CB921504) and the National Natural Science Foundation of China (Grant No. 91536107).

We report the experimental investigation of electromagnetically induced transparency (EIT) in a Zeeman-sublevels Λ-type system of cold 87Rb atoms in free space. We use the Zeeman substates of the hyperfine energy states 52S1/2, F = 2 and 52P3/2, F′ = 2 of 87Rb D2 line to form a Λ-type EIT scheme. The EIT signal is obtained by scanning the probe light over 1 MHz in 4 ms with an 80 MHz arbitrary waveform generator. More than 97% transparency and 100 kHz EIT window are observed. This EIT scheme is suited for an application of pulsed coherent storage atom clock (Yan B, et al. 2009 Phys. Rev. A 79 063820).

Measuring the spin polarization of alkali-metal atoms using nuclear magnetic resonance frequency shifts of noble gases

We report a novel method of measuring the spin polarization of alkali-metal atoms by detecting the NMR frequency shifts of noble gases. We calculated the profile of 87Rb D1 line absorption cross sections. We then measured the absorption profile of the sample cell, from which we calculated the 87Rb number densities at different temperatures. Then we measured the frequency shifts resulted from the spin polarization of the 87Rb atoms and calculated its polarization degrees at different temperatures. The behavior of frequency shifts versus temperature in experiment was consistent with theoretical calculation, which may be used as compensative signal for the NMRG closed-loop control system.

Study of the Rb D 2-line splitting in a strong transverse magnetic field with Doppler-free spectroscopy in a nanocell

Atomic transitions of 85Rb and 87Rb isotopes in a strong transverse magnetic field with induction of up to 7 kG have been studied experimentally. High spectral resolution is achieved owing to the application of the linear Doppler-free spectroscopy method to a nanometric thin cell with the thickness of L = λ/2 = 390 nm, where λ is the wavelength of laser emission tuned to the resonance with the Rb D 2-line (λ/2-method). It has been observed that the number of atomic transitions in the transmission spectrum of linearly polarized (π) radiation decreases from 64 down to 20 transitions as the field strength increases above B > 5 kG. Four atomic transitions (two of 85Rb and two of 87Rb), which are forbidden in the absence of magnetic field, acquire significant strength in the strong magnetic field. Experimental results are in a good agreement with theory. Several practical applications of alkali-vapor-filled nanometric thin cells have been proposed.

Two color pumping of the Rb D2 line laser (780 nm) through the photoassociation of Rb-Ar or Rb-Xe thermal pairs: Realization of a quantum efficiency above one

A two color process for optical pumping of the Rb D2 line laser (λ = 780 nm) in Rb vapor-rare gas mixtures is demonstrated to yield an overall quantum efficiency &amp;gt; 1. Combining photoexcitation of the Rb D2 line blue satellite in Rb-Xe or Rb-Ar mixtures with free ← free optical pumping of the A2Π12←X2Σ12+ transition at large internuclear separation (R &amp;gt; 5 Å) also increases the laser efficiency and pump absorption coefficient, relative to the single color, B ← X pumped system, by a factor of 1.7 and more than an order of magnitude, respectively. Simultaneous photopumping of Rb-Xe thermal collision pairs at 760 nm (D2 satellite) and 794.3 nm results in a 780 nm (D2 line) laser with a quantum efficiency of 1.008 which corresponds to the removal of ∼102 cm–1 (12.6 meV) of thermal energy per emitted photon.

Compact stabilized semiconductor laser for frequency metrology.

We report on the development of a frequency modulatable 795 nm semiconductor laser based on self-injection locking to a high-quality-factor whispering-gallery-mode microresonator. The laser is characterized by residual amplitude modulation below -80 dB and frequency noise better than 300 Hz/Hz(1/2) at offset frequencies ranging from 100 Hz to 10 MHz. The frequency modulation speed and span of the laser exceed 1 MHz and 4 GHz, respectively. Locking of the laser to the Doppler-free saturated absorption resonance of the (87)Rb D1 line is demonstrated and relative frequency stability better than 10(-12) is measured for integration time spanning from 1 s to 1 day. The architecture demonstrated in this study is suitable for the realization of frequency modulatable lasers at any wavelength.

Hanle electromagnetically induced absorption in open transitions of the 87Rb D2 line

The influence of the closed transition on the neighboring and open transitions of the 87Rb D2 line, partially resolved under Doppler broadening, is studied at different ellipticities in the Hanle configuration with longitudinal and transverse magnetic field scans. We show that a sign reversal from an electromagnetically induced transparency (EIT) resonance to an electromagnetically induced absorption (EIA) resonance occurs with an increase in ellipticity for the transition in a transverse field scan. This transformation is not observed for a longitudinal field scan. These observations are attributed to the higher amplitude of the EIA resonance for the transition in transverse field scans for elliptical polarized light. The EIA character in the Hanle transmission profile of and transitions is enhanced (weakened) when the laser beam frequency is detuned towards (away from) the transition. We show by computation that at higher ellipticities, a transformation from an EIT to an EIA resonance for the transition occurs at low frequency shifts (towards the transition) in a transverse field scan.