Rb D2 Line Research Articles

Determination of the partial and total pressures of the mixed gases in atomic vapor cells by optical absorption

We study the partial and total pressures of the mixed gases in a Rb vapor cell from its absorption spectrum under the influence of natural broadening, self-broadening, pressure broadening, the pressure shift, and Doppler broadening. A comprehensive model of the absorption coefficient on the Rb D2 line is developed, which takes into account the influence of multiple gas species. The importance of light intensity selection and frequency calibration to obtain accurate experimental results are discussed. Accurate abundances are deduced from the experimentally measured absorption spectra of vacuum cells and are used to optimize the abundance parameters in our model. We fit the experimentally measured absorption spectrum of a gas-filled cell to the optimized model and obtain a root mean square error better than 0.1%. The extracted partial pressures indicate that the mixture ratio agrees well with the designed value, while the total pressure has an increment of about 17% of its nominal value. We further estimate the amount of helium leakage in a cell to be 89.1 Torr for 6 months. Moreover, using a series of absorption spectra generated by our model as benchmarks, we evaluate the effectiveness of the commonly used single and double Lorentzian fitting models and give some suggestions for using the double Lorentzian model. This study provides a reference for designing the appropriate gas mixture for comagnetometer systems.

Measurement of the temperature dependency of the linewidths and amplitudes of the sub-Doppler resonances of the 87Rb D2 line with π (π) polarized pump (probe) laser beams

Measurement of the temperature dependency of the linewidths and amplitudes of the sub-Doppler resonances of the 87Rb D2 line with π (π) polarized pump (probe) laser beams

The Variation of the Linewidths and Amplitudes of Sub-Doppler Resonances of 87Rb D2 Line with Laser Beam Intensity

The sub-Doppler resonances linewidths and amplitudes depend on the laser beam intensity. The effect of laser beam intensity on the resonance linewidths and amplitudes obtained from different energy transitions of atoms varies from resonance to resonance. The effect of laser beam intensity on resonance linewidths and amplitudes is of great importance for diode laser frequency stability applications. It needs to be determined by measuring. The effect of the laser beam intensity on the linewidths and amplitudes of sub-Doppler resonances were measured by laser heterodyne spectroscopy using the linearly polarized frequency stabilized extended cavity diode lasers. The measurements are compatible with the theory and the uncertainty of the measurements are fewer than 1.6 MHz and 0.3 mV for linewidths and amplitudes, respectively.

Effect of an Anti-Relaxation Coating in Electromagnetically Induced Transparency in D2 Line of 87rb in Presence of Magnetic Field

Effect of an Anti-Relaxation Coating in Electromagnetically Induced Transparency in D2 Line of 87rb in Presence of Magnetic Field

Geometric-phase-lens collimated vertical-cavity surface-emitting laser turned on Rb D1 line for miniature atomic magnetometers

We report on the geometric-phase-lens collimation of commercially available vertical-cavity surface-emitting laser (VCSEL), performed in the Rb D1 line spectroscopy experiments. The geometric-phase-lens (GP lens) is fabricated by the direct-write approach and employed photo-patterned liquid crystals in thin films to control the geometric phase shift. It generates the positive and negative first-order diffraction of laser beam, which are spatially separated to two focal points with one focused and the other one defocused. The Diffraction efficiency at 794.9 nm is up to 99 %. Changing the polarization state of the incident VCSEL laser continuously, the collimation and polarization conversion of divergent VCSEL laser is accomplished via GP lens. The σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and σ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> components of circularly polarized light are separated via different diffraction orders, which suppresses the light shift in atomic atoms. Then a compact atomic magnetometer is constructed based on a Rb micro-cell. High sensitivity up to 30 fT/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> is achieved in the single-beam configuration. It’s expected that directly fabricating the liquid crystal film on the surface of vapor cells can further reduce the sensor volume. This work extends integrated photonics to atomic spectroscopy and spin-based sensing and of great significance to promote the application of miniature atomic magnetometers in biomagnetic measurements.

Analysis of the hyperfine splitting spectral structure of rubidium atomic D1 and D2 lines with pressure broadening

A physical model is established to describe the broadening mechanism of rubidium atomic D1 and D2 lines, hence to improve rubidium vapor laser efficiency. Hyperfine energy level structures of rubidium D1 and D2 transitions are analyzed and plotted. Considering the effects of the isotopic frequency shift, the pressure broadening and the hyperfine energy levels splitting, contributions of every hyperfine component to the cross sections are calculated and discussed. The relationship between cross sections and the ratio of helium pressure to ethane is achieved, and the composition of the buffer gas is optimized. The broadening effects of Rb D1 line and D2 line under different buffer gas pressure are also presented. The calculation results have a good agreement with that of experiments, which shows the validity of this model. The simulations data provides a reference for the experiment to further improve the bandwidth matching between alkali atomic D2 absorption line and the diode laser pump source.

18W ultra-narrow diode laser absolutely locked to the Rb D2 line.

We described a wavelength locked and spectral narrowed high-power diode laser with a Faraday anomalous dispersion optical filter (FADOF). By an external cavity with a 85Rb FADOF, the central wavelength of the diode laser was precisely locked to the Rb resonance D2 line. The bandwidth was narrowed from the free-running 4 nm to 0.002 nm (1.2 GHz, FWHM). At 4.9 A maximal driven current, the laser produced a continuous wave (CW) output of 18 W with an external cavity efficiency of 80%, either the current or the temperature had no impact on the central wavelength of the diode laser. The Rb cell works well without any damage under a long-time running. This ultra-stable and extreme-narrowed high power diode laser would find many applications in alkali lasers pumping, metastable rare gas laser pumping, spin-exchange optical pumping, and quantum optics.

Quantum-enhanced rubidium atomic magnetometer based on Faraday rotation via 795 nm stokes operator squeezed light

With the help of Stokes operator Ŝ2 squeezed state (also called polarization squeezed state (PSS)) of 795 nm light, rubidium-87 (87Rb) atomic magnetometer based on Faraday rotation (FR) has been implemented and characterized. The PSS of Stokes operator Ŝ2 of 795 nm light has been prepared by means of coherently combining the polarization coherent state (PCS) of a linearly p-polarized bright 795 nm light beam and a linearly s-polarized squeezed vacuum state (SVS) generated by a 397.5 nm ultraviolet laser pumped sub-threshold optical parametric oscillator (OPO) with a PPKTP bulk crystal inside the OPO cavity. PSS with a squeezing level of −3.7 ± 0.3 dB has been achieved around the analysis frequency of 10 kHz. At different transitions of D1 line, various frequency detuning, and reasonable atomic vapor cell’s temperature, FR has been measured and compared. To decrease absorption (scattering) losses and the back-action from atomic spin noise to the probe beam’s polarization noise for maintaining the quantum properties of PSS of Stokes operator Ŝ2 of 795 nm light, we had to run our magnetometer with 87Rb vapor cell’s temperature below 60 °C, at which the PSS was almost destroyed. The sensitivities of magnetic field measurement were characterized via measuring signal-to-noise ratio of the alternating current calibrated magnetic field signal with a balanced polarimeter. Under the conditions of the atomic number density of ∼5.8 × 1010 cm−3 (T ∼ 40 °C) and the probe beam with a detuning of ∼−400 MHz relative to the 5S1/2 (F g = 2) − 5P1/2 (F e = 1) transition of 87Rb D1 line, a typical sensitivity of ∼19.5 pT (Hz1/2)−1 has been achieved employing PSS of Stokes operator Ŝ2 as the probe, compared with a sensitivity of ∼28.3pT (Hz1/2)−1 using PCS as the probe. We preliminarily demonstrated that the quantum-enhanced sensitivity in a Faraday-rotation-based 87Rb atomic magnetometer with the help of PSS of 795 nm light.

Laser frequency stabilization via bichromatic Doppler-free spectroscopy of an 87Rb D1 line.

We demonstrate a bichromatic Doppler-free spectroscopy of an 87RbD1 line by using a dual-frequency, counterpropagating laser field with orthogonal linear polarizations. A reversed Doppler-free resonance dip is observed in the dual-frequency scheme, and a significant improvement of frequency discrimination curve is acquired due to the coherent population trapping (CPT) effect. The influence of the static magnetic field and laser intensity on the spectroscopy is studied in both single- and dual-frequency schemes. After locking the laser frequency to the 87RbD1 line in the dual-frequency stabilization scheme, the beat note fractional frequency stability is at the level of 7×10-12 at 1 s integration time. This technique can be used in various applications, such as CPT atomic clocks, laser spectroscopy, quantum optics, and laser-cooling experiments.

Study of multi-window electromagnetically induced transparency (EIT) and related dispersive signals in V-type systems in the Zeeman sublevels of hyperfine states of 87Rb-D2 line

We have theoretically studied the multi-window electromagnetically induced transparency (EIT) and the related dispersive signals in multi-level V-type systems which are formed by the co-propagating circularly polarized pump (σ −) and probe (σ +) laser fields in the Zeeman sublevels of hyperfine states of 87Rb-D2 line. The optical Bloch equations (OBEs) are derived and numerically solved under the steady-state condition to obtain the probe absorption and dispersion spectra. We present the study of a single-window EIT for the three-level, double-window EIT for the four-level and triple-window EIT for the five-level V-type systems under both Doppler-free and Doppler-broadened conditions. The dispersive signals corresponding to the multi EIT windows for each system are also observed separately. From the knowledge of the slopes of the probe dispersion signals, we have calculated group index (n g) of the medium considering three different V-type schemes. The effect of temperature on the EIT, dispersion and group index profiles is also studied in detail. It is found that the amplitudes of EIT and dispersion signals and also the positive and negative values of n g are decreased as the temperature of the medium increases. To understand the Doppler-broadening effect on the group index profiles, we have considered three different velocity groups of atoms in the calculation of group index profiles. Moreover, the effects of probe intensity variation on the Doppler-broadened EIT and dispersive signals are studied extensively, and the conversions of EIT to EIA and dispersive positive slope to negative slope are observed under strong probe regime. Also, we have investigated the variation of dispersive slope and group index with the variation of probe intensity and probe frequency, respectively, at the multi-frequency position of the multi-window EIT. Finally, the switching between subluminal (slow light) to superluminal (fast light) propagation of light with the variation of both probe intensity and probe frequency is discussed in detail.

Features of magnetically-induced atomic transitions of the Rb D1 line studied by a Doppler-free method based on the second derivative of the absorption spectra

In this paper we show that the second derivative (SD) technique of the absorption spectra of Rb atomic vapours, confined in a nanocell with a thickness ℓ = λ/2 = 398 nm, allows us to achieve close to Doppler-free spectroscopy. The narrow linewidth and linearity of the SD signal response with respect to transition probabilities allows us to study separately, in an external transverse magnetic field (0.6 to 4 kG), a large number of the atomic transitions of 85Rb and 87Rb atoms. Atomic transitions |Fg, 0⟩ → |Fe = Fg, 0′⟩, for which the dipole moment is null in a zero magnetic field (so-called magnetically-induced transitions), show a gigantic increase in probability with an increasing magnetic field. When a magnetic field is applied to the vapour, we show the possibility of forming a dark resonance on these transitions by adding a coupling laser. We are therefore able to demonstrate a five-fold increase in the transmission of the probe radiation when the coupling laser is on. Theoretical calculations are in very good agreement with the experimental results.

Understanding asymmetry in electromagnetically induced transparency for 87Rb in strong transverse magnetic field

We present the results of our experimental investigation performed for D2 line of 87Rb. In this work, we have studied the phenomenon of electromagnetically induced transparency of 87Rb in presence of a transverse magnetic field and it is interesting to find the EIT spectrum shows signature of the closely lying hyperfine excited states in particular F′ = 1. We choose two different configurations for our study namely, Λ1 and Λ2 realised by locking probe beam at two different transition i.e. |F = 1〉 → |F′ = 2〉 and |F = 2〉 → |F′ = 2〉 respectively. We observe asymmetric features in both configurations at high magnetic field and for Λ1 configuration we find complete conversion from transmission to absorption. We explain the observations by quantitative assessment of the impurities in the dark states which arises because of the influence of the neighbouring states. We substantiate our experimental findings with density based numerical calculations.

Electromagnetically induced absorption resonances in Hanle-configuration prepared in a paraffin coated 87Rb cell

We present an experimental investigation of electromagnetically-induced absorption (EIA) at the D1 line of 87Rb contained in an anti-relaxation coated vacuum optical cell. The configuration includes a pump and a probe beam propagating in opposite directions and having mutually orthogonal linear polarizations; the probe beam absorption is registered depending on the value of a magnetic field scanned around zero and applied collinearly to the laser beams. The advantages of this scheme have been recently evidenced in vapor cells filled with a buffer gas. In the present work we studied the width and the contrast of the EIA resonances obtained in a coated cell for different values of the pump power. The results are compared with those obtained in a buffer gas cell for the same transition of 87Rb. The theoretical calculations are in good agreement with the experiment.

An efficient, tunable, and robust source of narrow-band photon pairs at the 87Rb D1 line

We present an efficient and robust source of photons at the 87Rb D1-line (795 nm) with a narrow bandwidth of δ = 226(1) MHz. The source is based on non-degenerate, cavity-enhanced spontaneous parametric down-conversion in a monolithic optical parametric oscillator far below threshold. The setup allows for efficient coupling to single mode fibers. A heralding efficiency of ηheralded = 45(5) % is achieved, and the uncorrected number of detected photon pairs is 3.8 × 103/(s mW). For pair generation rates up to 5 × 105/s, the source emits heralded single photons with a normalized, heralded, second-order correlation function g c ( 2 ) &lt; 0.01 . The source is intrinsically stable due to the monolithic configuration. Frequency drifts are on the order of δ/20 per hour without active feedback on the emission frequency. We achieved fine-tuning of the source frequency within a range of &gt;2 GHz by applying mechanical strain.

Application of Magnetically Induced Transitions of 87Rb Atoms in Coherent Optical Processes

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.

Применение магнито-индуцированных переходов в атомах -=SUP=-87-=/SUP=-Rb в когерентных оптических процессах

The prospects of using Fg = 1-Fe = 3 magnetically induced (MI) transitions of the 87Rb D2 line to form optical resonances in strong magnetic fields up to 3 kG have been experimentally demonstrated. A micrometer-thick cell filled with the Rb atomic vapor is used. A simple and convenient method for determining the magnetic induction with a micron spatial resolution is presented. In this case, there is no need for a reference frequency spectrum. The probability of the MI transition in the magnetic field range of 0.3–2 kG may exceed the probability of a “normal” atomic transition; therefore, it is reasonable to use MI transition at the frequency of “coupling” or probe lasers in Lambda- and V systems to form EIT- resonance (also called dark resonance) in the process of electromagnetically induced transparency (EIT). The formation of dark resonances in strong magnetic fields, when there is a frequency shift of the dark resonance up to ~ 10 GHz, has a number of practical applications. Note that when using “ordinary” atomic transitions in the Lambda- system for magnetic fields of &gt; 1 kG, dark resonances are practically absent.

A cold-atom beam clock based on coherent population trapping

We present results from an atomic clock that employs a beam of cold 87Rb atoms and spatially separated (Ramsey) coherent population trapping interrogation of the hyperfine clock transition at 6.834 GHz. The cold atomic beam is generated through the use of a 2D+-magneto-optical trap. The interrogation is performed on the D2 line of 87Rb, and the optical fields use a counter-propagating σ+–σ− probing scheme. The use of cold atoms allows for relatively narrow Ramsey fringes even for a small spatial separation between the two interrogation zones (4.6 cm). The resulting clock has a short-term stability of 3×10−11/τ.

Gray-Molasses Optical-Tweezer Loading: Controlling Collisions for Scaling Atom-Array Assembly

We show that with a purely blue-detuned cooling mechanism we can densely load single neutral atoms into large arrays of shallow optical tweezers. With this ability, more efficient assembly of larger ordered arrays will be possible - hence expanding the number of particles available for bottom-up quantum simulation and computation with atoms. Using Lambda-enhanced grey molasses on the D1 line of 87Rb, we achieve loading into a single 0.63 mK trap with 89% probability, and we further extend this loading to 100 atoms at 80% probability. The loading behavior agrees with a model of consecutive light-assisted collisions in repulsive molecular states. With simple rearrangement that only moves rows and columns of a 2D array, we demonstrate one example of the power of enhanced loading in large arrays.

Faraday Effect in Rubidium Atomic Layers Thinner than 100 nm

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.

Broadening and shifting of Rb D1 and D2 line in low pressure vapor cell

The absorption line of the alkali metal is unstable in the atomic vapor cell, which is usually affected by the temperature and vapor pressure of the cell. However, the line shifting and broadening of the alkali metal in the atomic vapor cell could severely essential effect to the atomic sensors. This paper has systematically measured the broadening and shifting effect of Rubidium D1 and D2 line when the pressure of buffer gas N2 is lower than 1 atm. The broadening coefficient of Rb D1 line on the N2 pressure is 35.4MHz/torr, while the D2 line on the N2 pressure is 21.2MHz/torr. When the N2 pressure is near 1 atm, the shifting coefficients are 30.4MHz/K and -45.4MHz/K for D1 and D2 line through linear fit, respectively. The method in this paper, measuring the width shifting and broadening of the alkali metal absorb line, provides a way to verify the actual inner pressure of the vapor cell.