Optical isolator using an atomic vapor in the hyperfine Paschen-Back regime

Using FADOF to eliminate the background light influence in ghost imaging

The high solar background during the day adversely affects the long distance daytime operations of ghost imaging. It is extremely hard to distinguish the signal light from the background noise light after they are both converted to voltage or current signals by the bucket detector, so spectral filtering before the detector is quite important. In this work, a Faraday anomalous dispersion optical filter (FADOF) is used in eliminating the background light influence in ghost imaging. Results of lab experiment show that the background light noise tolerance of the ghost imaging with FADOF is at least 18 times bigger than that with a 10 nm optical filter. The method has simple structure, great performance and great algorithms compatibility.

Wide range linear magnetometer based on a sub-microsized K vapor cell

³⁹K atoms have the smallest ground state (²S_1/2) hyperfine splitting of all the most naturally abundant alkali isotopes and, consequently, the smallest characteristic magnetic field value B₀=A_²S1/2/μ_B≈170G, where A_²S1/2 is the ground state's magnetic dipole interaction constant. In the hyperfine Paschen-Back regime (B≫B₀, where B is the magnitude of the external magnetic field applied on the atoms), only eight Zeeman transitions are visible in the absorption spectrum of the D₁ line of ³⁹K, while the probabilities of the remaining 16 Zeeman transitions tend to zero. In the case of ³⁹K, this behavior is reached already at relatively low magnetic field B>B₀. For each circular polarization (σ^-,σ⁺), four spectrally resolved atomic transitions having sub-Doppler widths are recorded using a sub-microsized vapor cell of thickness L=120-390nm. We present a method that allows to measure the magnetic field in the range of 0.1-10kG with micrometer spatial resolution, which is relevant in particular for the determination of magnetic fields with large gradients (up to 3 G/µm). The theoretical model describes well the experimental results.

Tunable homogeneous kG magnetic field production using permanent magnets

We present a permanent ring magnet arrangement that can achieve a tunable axial magnetic field from 1.80(5) to 2.67(9) kG. The apparatus has been designed to accommodate a cylindrical atomic vapor cell of length 25 mm and diameter 25 mm to lie within the bore of the ring magnets, providing an alternative route for imaging through atomic vapors in large magnetic fields. The measured axial magnetic field has an rms variation of less than 4% over the length of vapor cell, while the calculated field inhomogeneity is less than 5% radially and 12% longitudinally across a cylindrical volume with diameter 20 mm and length 25 mm. The instrument consists of layered concentric off-the-shelf N42 neodymium-iron-boron axially magnetized ring magnets. The magnets are organized into four cylindrical brass holders, whose relative separation can be manipulated to achieve the desired magnetic field strength. We present magnetic field computations and Marquardt-Levenberg fits to experimental data and demonstrate excellent agreement between theory and experiment.

Structural and Magneto-Optical Characterization of La, Nd: Y2O3 Powders Obtained via a Modified EDTA Sol-Gel Process and HIP-Treated Ceramics

In this study, pure Y2O3, La0.1Y1.9O3 and La0.1Nd0.12Y1.78O3 nanosized powders were successfully synthesized by a modified sol-gel method. Pure and rare-earth ions doped yttria powders were characterized by X-ray diffraction, scanning electron microscopy and Brunauer-Emmett-Teller methods. The powders were sintered by the hot isostatic pressing process. The highest in-line transmittance of 56% was obtained at 800 nm and increased in the IR region. The influence of the lanthanum and neodymium ions on the physicochemical properties of yttria were discussed. The La-Nd-doped material exhibited a Verdet constant over 4000 deg/T·m at 400 nm and low thermal dependence. An interesting evolution of the Verdet constant across the absorption band with high resolution was studied. A study of the optical and magneto-optical properties of yttria doped with Nd3+ and La3+ is discussed in this paper.

Proof of the feasibility of a nanocell-based wide-range optical magnetometer

We present an experimental scheme performing scalar magnetometry based on the fitting of Rb $ {{\rm D}_2} $D₂ line spectra recorded by derivative selective reflection spectroscopy from an optical nanometric-thick cell. To demonstrate its efficiency, the magnetometer is used to measure the inhomogeneous magnetic field produced by a permanent neodymium--iron-boron alloy ring magnet at different distances. The computational tasks are realized by relatively cheap electronic components: an Arduino Due board for external control of the laser and acquisition of spectra, and a Raspberry Pi computer for the fitting. The coefficient of variation of the measurements remains under 5% in the magnetic field range of 40-200 mT, limited only by the size of the oven and translation stage used in our experiment. The proposed scheme is expected to operate with high measurement precision also for stronger magnetic fields ($ {\gt} {500}\;{\rm mT}$>500mT) in the hyperfine Paschen-Back regime, where the evolution of atomic transitions can be calculated with high accuracy.

Chip-scale atomic diffractive optical elements

The efficient light–matter interaction and discrete level structure of atomic vapors made possible numerous seminal scientific achievements including time-keeping, extreme non-linear interactions, and strong coupling to electric and magnetic fields in quantum sensors. As such, atomic systems can be regarded as a highly resourceful quantum material platform. Recently, the field of thin optical elements with miniscule features has been extensively studied demonstrating an unprecedented ability to control photonic degrees of freedom. Hybridization of atoms with such thin optical devices may offer a material system enhancing the functionality of traditional vapor cells. Here, we demonstrate chip-scale, quantum diffractive optical elements which map atomic states to the spatial distribution of diffracted light. Two foundational diffractive elements, lamellar gratings and Fresnel lenses, are hybridized with atomic vapors demonstrating exceptionally strong frequency-dependent, non-linear and magneto-optic behaviors. Providing the design tools for chip-scale atomic diffractive optical elements develops a path for compact thin quantum-optical elements.

Quantum coherence and the nonlinear properties of atoms are highly useful in optical devices. Here the authors show quantum-optic hybrid platforms in fully integrated chip-scale atomic diffractive optical elements by embedding hot atomic Rb vapor in microfabricated structures in silicon.

Isotope 87Rb Faraday filter with a single transmission peak resonant with atomic transition at 780 nm

We demonstrate an isotope ⁸⁷Rb Faraday anomalous dispersion optical filter (FADOF) with a single transmission peak resonant with the 5S_1/2, F = 2 → 5P_3/2, F' = 1, 2, 3 transitions at 780 nm with an enriched ⁸⁷Rb isotope at low temperature. The isotope ⁸⁷Rb FADOF achieves a single peak transmission of 74.8% with a bandwidth of 0.96 GHz. Compared with most of FADOFs operated at frequencies far from absorption, the isotope ⁸⁷Rb FADOF that we have achieved can provide a transmission band exactly covering atomic transitions for many practical applications.

Atomic optical stimulated amplifier with optical filtering of ultra-narrow bandwidth

Taking advantages of ultra-narrow bandwidth and high noise rejection performance of the Faraday anomalous dispersion optical filter (FADOF), simultaneously with the coherent amplification of atomic stimulated emission, we propose a stimulated amplified Faraday anomalous dispersion optical filter (SAFADOF) at cesium 1470 nm. The SAFADOF is able to significantly amplify very weak laser signals and reject noise in order to obtain clean signals in strong background. We show that for a weak signal of 50 pW, the gain factor can be larger than 25000 (44 dB) within a bandwidth as narrow as 13 MHz. Having the ability to amplify weak signals with low background contribution, the SAFADOF finds outstanding potential applications in weak signal detections.

Optimized ultra-narrow atomic bandpass filters via magneto-optic rotation in an unconstrained geometry

Atomic bandpass filters are widely used in a variety of applications, owing to their high peak transmission and narrow bandwidths. Much of the previous literature has used the Faraday effect to realize these filters, where an axial magnetic field is applied across the atomic medium. Here we show that by using a non-axial magnetic field, the performance of these filters can be improved in comparison to the Faraday geometry. We optimize the performance of these filters using a numerical model and verify their performance by direct quantitative comparison with experimental data. We find excellent agreement between experiment and theory. These optimized filters could find use in many of the areas where Faraday filters are currently used, with little modification to the optical setup, allowing for improved performance with relatively little change.

Magnetically Controlled Atomic-Plasmonic Fano Resonances

Following the efforts of size reduction and the integration of light and vapor systems, great promise is held in the integration of vapor and confined electromagnetic waves. By confining light to nanoscale dimensions, fundamental properties of light-vapor interactions may vary significantly. For example, the state of polarization may be modified as compared with weakly focused beams. Specifically, in transverse magnetic modes, the existence of a longitudinal field component, which is in quadrature to the transverse field, generates a "circular-like" polarized light. Here, by taking advantage of this very property, we study the interaction of confined light and vapor in a coupled system of plasmons and atomic vapors in the presence of magnetic fields. Our results show that the spectroscopic nature and Fano resonances of the hybrid plasmonic-atomic system are greatly altered. In parallel, we also exploit the existence of the atoms in proximity to the plasmonic mode to probe the polarization state of the electromagnetic field and reveal the longitudinal-to-transverse ratio between the plasmonic modes components in the near field. Interestingly, our system maps the amplitude and phase information of the electromagnetic modes to the spectral domain. As such, combining magnetic fields with the coupled plasmonic-atomic system has the potential for future applications in high spatial resolution magnetometry, near-field vectorial imaging, and magnetically induced switching and tuning.

Tunable and polarization-controlled high-contrast bright and dark coherent resonances in potassium

We demonstrate high-contrast electromagnetically induced absorption (EIA) bright resonances on the D₁ line of K39 with characteristics comparable to those of the electromagnetically induced transparency (EIT) dark resonances observed in the same conditions. EIA is produced by the interaction of a weak probe beam with the atomic ground state driven in a degenerate coherent superposition by either a co- or counter-propagating pump beam. We have obtained an order of magnitude increase of the EIA's contrast with respect to previous similar experiments, performed with other alkalis, without compromising its linewidth. Furthermore, we show that the magneto-optic resonances can be continuously tuned from EIT to EIA by changing the relative handedness of circular polarizations of pump and probe beams, or depending on whether they co- or counter-propagate. This opens new perspectives in the use of EIA in a broad range of physical domains and in a large wealth of potential applications in optics and photonics.

Selective reflection from an Rb layer with a thickness below λ/12 and applications

We have studied the peculiarities of selective reflection from an Rb vapor cell with a thickness L<70  nm, which is smaller than the length scale of evanescent fields λ/2π and more than an order of magnitude smaller than the optical wavelength. A 240 MHz redshift due to the atom-surface interaction is observed for a cell thickness of L=40  nm. In addition, complete frequency-resolved hyperfine Paschen-Back splitting of atomic transitions to four components for Rb87 and six components for Rb87 is recorded in a strong magnetic field (B>2  kG).

Dynamic Control over the Optical Transmission of Nanoscale Dielectric Metasurface by Alkali Vapors

In recent years, dielectric and metallic nanoscale metasurfaces are attracting growing attention and are being used for variety of applications. Resulting from the ability to introduce abrupt changes in optical properties at nanoscale dimensions, metasurfaces enable unprecedented control over light's different degrees of freedom, in an essentially two-dimensional configuration. Yet, the dynamic control over metasurface properties still remains one of the ultimate goals of this field. Here, we demonstrate the optical resonant interaction between a form birefringent dielectric metasurface made of silicon and alkali atomic vapor to control and effectively tune the optical transmission pattern initially generated by the nanoscale dielectric metasurface. By doing so, we present a controllable metasurface system, the output of which may be altered by applying magnetic fields, changing input polarization, or shifting the optical frequency. Furthermore, we also demonstrate the nonlinear behavior of our system taking advantage of the saturation effect of atomic transition. The demonstrated approach paves the way for using metasurfaces in applications where dynamic tunability of the metasurface is in need, for example, for scanning systems, tunable focusing, real time displays, and more.

Low-frequency shift Raman spectroscopy using atomic filters

A Faraday anomalous dispersion optical filter (FADOF) and an atomic resonant absorption filter are used in tandem to demonstrate a low-frequency shift Raman measurement down to few cm^-1. The FADOF, with an ultralow bandwidth of 0.08  cm^-1 at 780 nm, serves as a bandpass filter, while the rubidium atomic cell acts as a notch filter which has a bandwidth of 0.3  cm^-1. A proof-of-concept study to measure a Raman signal generated from a silica optical fiber is performed, demonstrating a low-frequency measurement of both the Stokes and the anti-Stokes shift down to 3  cm^-1 at an equivalent signal level. These results indicate the prospect for gigahertz-terahertz low-energy Raman spectroscopy based on atomic filters.

Hollow cathode lamp based Faraday anomalous dispersion optical filter

The Faraday anomalous dispersion optical filter (FADOF), which has acquired wide applications, is mainly limited to some gaseous elements and low melting-point metals before, for the restriction of the attainable atomic density. In conventional FADOF systems a high atomic density is usually achieved by thermal equilibrium at the saturated vapor pressure, hence for elements with high melting-points a high temperature is required. To avoid this restriction, we propose a scheme of FADOF based on the hollow cathode lamp (HCL), instead of atomic vapor cells. Experimental results in strontium atoms verified this scheme, where a transmission peak corresponding to the (88)Sr (5s(2))(1)S0 - (5s5p)(1)P1 transition (461 nm) is obtained, with a maximum transmittance of 62.5% and a bandwith of 1.19 GHz. The dependence of transmission on magnetic field and HCL discharge current is also studied. Since the state-of-art commercial HCLs cover about 70 elements, this scheme can greatly expand the applications of FADOFs, and the abundant atomic transitions they provide bring the HCL based FADOFs potential applications for frequency stabilization.

Far off-resonance laser frequency stabilization using multipass cells in Faraday rotation spectroscopy

We propose a far off-resonance laser frequency stabilization method by using multipass cells in Rb Faraday rotation spectroscopy. Based on the detuning equation, if multipass cells with several meters optical path length are used in the conventional Faraday spectroscopy, the detuning of the lock point can be extended much further from the alkali metal resonance. A plate beam splitter was used to generate two different Faraday signals at the same time. The transmitted optical path length was L=50  mm and the reflected optical path length was 2L=100  mm. When the optical path length doubled, the detuning of the lock points moved further away from the atomic resonance. The temperature dependence of the detuning of the lock point was also analyzed. A temperature-insensitive lock point was found near resonance when the cell temperature was between 110°C and 130°C. We achieved an rms fluctuation of 0.9 MHz/23 h at a detuning of 0.5 GHz. A frequency drift of 16 MHz/h at a detuning of -5.6  GHz and 4 MHz/h at a detuning of -5.2  GHz were also obtained for the transmitted and reflected light Faraday signal.

Controlling the interactions of space-variant polarization beams with rubidium vapor using external magnetic fields

Space variant beams are of great importance for a variety of applications that have emerged in recent years. As such, manipulation of their degrees of freedom is highly desired. Here, we study the general interaction of space variant beams with a magnetically influenced Rb medium exploiting the atoms versatile properties in terms of frequency and intensity dependent circular dichroism and circular birefringence. We present the particular cases of radially polarized and hybrid polarized beams where the control of the polarization states is demonstrated experimentally. Moreover, we show that such an atomic system can be used as a tunable analyzer for space variant beams. Finally, exploiting the non-linear properties of Rb vapor, we show that we can control the circular birefringence all optically, and thus modulate the polarization of the radial polarized beam.

Broadband optical isolator based on helical metamaterials

Based on helical metamaterials, a new broadband optical isolator with a triple-helix structure is proposed in this paper. The right-handed circularly polarized light can transmit through the isolator with its polarization unchanged. The reverse propagating light, which is caused by the reflection of the latter optical devices, is converted into left-handed circularly polarized light that is suppressed by the proposed isolator because of absorption. Our design has some unprecedented advantages such as broad frequency ranges and a compact structure; moreover, neither polarizers nor adscititious magnetic fields are required. Properties of the isolator are investigated using the finite-difference time-domain method, and this phenomenon is studied by the mechanism of helical antenna theory.

Atomic Faraday filter with equivalent noise bandwidth less than 1 GHz

We demonstrate an atomic bandpass optical filter with an equivalent noise bandwidth less than 1 GHz using the D1 line in a cesium vapor. We use the ElecSus computer program to find optimal experimental parameters and find that, for important quantities, the cesium D1 line clearly outperforms other alkali metals on either D-lines. The filter simultaneously achieves a peak transmission of 77%, a passband of 310 MHz, and an equivalent noise bandwidth of 0.96 GHz, for a magnetic field of 45.3 G and a temperature of 68.0°C. Experimentally, the prediction from the model is verified. The experiment and theoretical predictions show excellent agreement.

Optical response of gas-phase atoms at less than λ/80 from a dielectric surface

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 -C(α)/r(α) 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.

Saturated-absorption spectroscopy revisited: atomic transitions in strong magnetic fields (>20 mT) with a micrometer-thin cell

The existence of crossover resonances makes saturated-absorption (SA) spectra very complicated when external magnetic field B is applied. It is demonstrated for the first time, to the best of our knowledge, that the use of micrometric-thin cells (MTCs, L≈40  μm) allows application of SA for quantitative studies of frequency splitting and shifts of the Rb atomic transitions in a wide range of external magnetic fields, from 0.2 up to 6 kG (20-600 mT). We compare the SA spectra obtained with the MTC with those obtained with other techniques and present applications for optical magnetometry with micrometer spatial resolution and a broadly tunable optical frequency lock.

Broadband Faraday isolator

Driving on an analogy with the technique of composite pulses in quantum physics, we theoretically propose a broadband Faraday rotator and thus a broadband optical isolator, which is composed of sequences of ordinary Faraday rotators and achromatic quarter-wave plates rotated at the predetermined angles.