Electromagnetically Induced Transparency and optical pumping processes formed in Cs sub-micron thin cell

Experiments in Electromagnetically Induced Transparency (EIT) have produced ultraslow light propagation [1, 2, 3, 4] with spatial compression, and have made it possible to enhance nonlinear optical processes by orders of magnitude [5,6]. Similar techniques have been utilized to store light pulses both in an ultracold atomic medium [7] and in a hot gas [8]. Small group velocities are accomplished by the large index changes near the EIT resonance, and the steepness of the dispersion function is directly related to the width of the transparency window. Therefore, in addition to achieving EIT, the spectral width of the EIT resonance is an important aspect in the study of slow light as well as precision measurements [9, 10, 11, 12]. In hot gas experiments, not like in the case of u1tracold atoms, Doppler broadening becomes crucial as it is the dominant dephasing mechanism. In this paper, we present an analytic expression of the spectral width of EIT resonance in a Doppler broadened.

Imidacloprid is a common insecticide, which can remain in water, soil, and plant parts with long-term consumption, threaten environment, and human health. Therefore, it is necessary to propose an effective method for imidacloprid detection. Here, a terahertz metamaterial based on electromagnetically induced transparency (EIT) is theoretically and experimentally demonstrated. This metamaterial displays an EIT resonance at 0.89 THz and the physical mechanism of the EIT effect is investigated by analyzing the electric fields and surface current distribution. The EIT resonance can be modulated by changing the geometric structure parameters of the metamaterial. This metamaterial can be used to detect the thickness and the refractive index of the dielectric layer based on the EIT resonance, and can achieve a refractive index sensitivity of 210 GHz/RIU. The detection of imidacloprid shows that the frequency shift and the transmittance change at peak are depend on the change of imidacloprid concentration. The minimum detectable imidacloprid concentration reaches a level of 0.01 ppm in this case. These results theoretically and experimentally prove the feasibility of terahertz metamaterial based on EIT resonance applied in the detection of imidacloprid concentration.

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 D2 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 87Rb D1 transition Fg=1Fe=1,2.

We study Λ-type Electromagnetically Induced Transparency (EIT) on the Rb D2 transition in a buffer-gas-free thermal vapor cell without anti-relaxation coating. Experimental data show well-resolved features due to velocity-selective optical pumping and one EIT resonance. The Zeeman splitting of the EIT line in magnetic fields up to 12 Gauss is investigated. One Zeeman component is free of the first-order shift and its second-order shift agrees well with theory. The full width at half maximum (FWHM) of this magnetic-field-insensitive EIT resonance is reduced due to Doppler narrowing, scales linearly in Rabi frequency over the range studied, and reaches about 100 kHz at the lowest powers. These observations agree with an analytic model for a Doppler-broadened medium developed in (Javan et al 2002 Phys. Rev. A 66 013805; Lee et al 2003 Appl. Phys. B, Lasers Opt. (Germany) B 76, 33–9; Taichenachev et al 2000 JETP Lett. 72, 119). Numerical simulation using the Lindblad equation reveals that the transverse laser intensity distribution and two Λ-EIT systems must be included to fully account for the measured line width and line shape of the signals. Ground-state decoherence, caused by effects that include residual optical frequency fluctuations, atom-wall and trace-gas collisions, is discussed.

A terahertz metamaterial structure consisting of two U-shaped split-ring resonators and a horizontal cut-line resonator is designed for realizing the electromagnetically induced transparency (EIT) effect and the Fano resonance effect. The genesis of the EIT and Fano resonance bifunctionality is illustrated by combining the near-field distribution analysis of transparent windows and transmission dips. Interestingly, the bifunctional dual-band transparency effect could transform into a single-functional single-band transparency effect when we change the position of the square metal sheet in the vertical direction of the composited terahertz metamaterial structure. In addition, based on the high-quality factor of Fano resonance response, the proposed bifunctional terahertz metamaterial device has good refractive index sensing sensitivity. These results indicate that our proposed terahertz metamaterial can provide guidance for the design of subsequent multifunctional and integrated metamaterials and optoelectronic devices.

The electromagnetically induced transparency (EIT) on the atomic D 1 line of rubidium is studied using a nanometric-thin cell with atomic vapor column length in the range of L=400–800 nm. It is shown that the reduction of the cell thickness by four orders as compared with an ordinary cm-size cell still allows to form an EIT resonance for L=λ=794 nm with the contrast of up to 40%. Further reduction of thickness to L=λ/2 leads to significant reduction of EIT contrast, verifying that the key parameter for EIT in wavelength-scale-thickness cells is not the value of L itself but L/λ ratio. Remarkable distinctions of EIT formation in nanometric-thin and ordinary cells are demonstrated. Well-resolved splitting of the EIT resonance in a magnetic field for L=λ can be used for magnetometry with nanometric spatial resolution. The presented theoretical model well describes the observed results.

EIT line shape in an open and partially closed multilevel V-type system

Standing wave pump field induced coherent non-linear resonances in rubidium vapor

As terahertz (THz) technology rapidly develops, room temperature THz detectors with high sensitivity and wide bandwidth are urgently required. Rydberg atoms are very sensitive to external electric fields, and offer a promising approach for THz detection with exceptional sensitivity. In this paper, we propose a method for measuring the THz field with the frequency of 0.17 THz using 85Rb Rydberg atoms. By analyzing the probe laser transmission spectrum and atomic population, the electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting effect are explained by the presence and splitting of the Rydberg dark states; the THz field, coupling laser and probe laser play a crucial role in the EIT signal; and the EIT spectral transmission will increase when the atomic population of the excited state decreases. Moreover, a method was demonstrated to improve the THz detection sensitivity by changing the eigenfrequencies of the Rydberg dark states with THz detuning. This work finds the relationship between EIT-AT effect and atomic population of Rydberg atoms caused by THz wave and provides what we believe to be a new method to improve the detection efficiency.

This paper presents a comprehensive analytical investigation of a photonic demultiplexer leveraging Fano and Electromagnetically Induced Transparency (EIT) resonances. The device features a ψ-shaped waveguide configuration, consisting of a single input waveguide and three output waveguides. Each output waveguide includes a pair of resonators strategically positioned relative to the input. Analytical expressions are developed to achieve selective transmission of a specific propagating mode through one output channel, while the other channels remain unaffected. The frequency selection process is governed by either Fano or EIT resonances, with the resonance characteristics, such as position and width, determined by the tailored lengths of the waveguides. The Green’s function approach is employed to calculate the transmission and reflection coefficients, offering a precise methodology for analyzing and designing the demultiplexer.

We investigate the electromagnetically induced transparency (EIT) in Rb atoms interacting with a pseudothermal probe light exhibiting a Bose–Einstein photon number distribution. The EIT spectrum in the 5S1/2−5P1/2 transition of the Λ-type system of the 87Rb atom was observed using a coupling laser and the pseudothermal probe light generated by passing the probe laser though a rotating rough disk. From the EIT spectrum with pseudothermal light, we experimentally demonstrated that the fluctuation of the number of photons was the same as the superposition of frequency noise of the probe light. The coherence time of the pseudothermal probe light was estimated from the measured EIT spectra. We confirmed that the experimental results as a function of the rotating speed of the rough disk were in good agreement with the numerically calculated results.

We study electromagnetically induced transparency (EIT) in a room-temperature cesium vapor cell using wavelength-modulated probe laser light. In the utilized cascade level scheme, the probe laser drives the lower transition 6S(F = 4) → 6P (F’ = 5), while the coupling laser drives the Rydberg transition 6P → 57S. The probe laser has a fixed average frequency and is modulated at a frequency of a few kHz, with a variable modulation amplitude in the range of tens of MHz. The probe transmission is measured as a function of the detuning of the coupling laser from the Rydberg resonance. The first-harmonic demodulated EIT signal has two peaks that are, in the case of large modulation amplitude, separated by the peak-to-peak modulation amplitude of the probe laser times a scaling factor , where and are the probe- and coupling-laser wavelengths. The scaling factor is due to Doppler shifts in the EIT geometry. Second-harmonic demodulated EIT signals, obtained with small modulation amplitudes, yield spectral lines that are much narrower than corresponding lines in the modulation-free EIT spectra. The resultant spectroscopic resolution enhancement is conducive to improved measurements of radio-frequency (RF) fields based on Rydberg-atom EIT, an approach in which the response of Rydberg atoms to RF fields is exploited to characterize RF fields. Here, we employ wavelength modulation spectroscopy to reduce the uncertainty of atom-based frequency and field measurement of an RF field in the VHF radio band.

We discuss the process of modulation transfer in a coherently prepared three-level atomic medium and its prospective application to atomic frequency offset locking (AFOL). The issue of modulation transfer through coherence is treated in the framework of temporal evolution of dressed atomic system with externally superimposed deterministic flow. This dynamical description of the atom-field system offers distinctive advantage of using a single modulation source to dither passively the coherent phenomenon as probed by an independent laser system under pump-probe configuration. Modulation transfer is demonstrated experimentally using frequency modulation spectroscopy on a subnatural linewidth electromagnetically induced transparency (EIT) and a sub-Doppler linewidth Autler-Townes (AT) resonance in Doppler broadened alkali vapor medium, and AFOL is realized by stabilizing the probe laser on the first/third derivative signals. The stability of AFOL is discussed in terms of the frequency noise power spectral density and Allan variance. Analysis of AFOL schemes is carried out at the backdrop of closed loop active frequency control in a conventional master-slave scheme to point out the contrasting behavior of AFOL schemes based on EIT and AT resonances. This work adds up to the discussion on the subtle link between dressed state spectroscopy and AFOL, which is relevant for developing a master-slave type laser system in the domain of coherent photon-atom interaction.

Electromagnetically induced transparency (EIT) is a well-known phenomenon due in part to its applicability to quantum devices such as quantum memories and quantum gates. EIT is commonly modeled with a three-level lambda system; however, this simplified model does not capture all the physics of EIT experiments with real systems. We present a theoretical study of the effect of two closely-spaced excited states on EIT and off-resonance Raman transitions. In addition to the expected broadening of the EIT resonance and reduction in EIT transparency due to multiple excited states, we find some unexpected and interesting results. A comparison with a model that does not allow for coupling of the excited states shows that the coherent interaction of the fields with two excited states whose separation is smaller than their Doppler broadened linewidth can enhance the EIT transparency under some conditions and can enhance and shift the resonance frequency of off-resonance Raman absorption. Furthermore, through a dressed state analysis of the full four-level system, we find that the underlying mechanism for the reduction in EIT transparency is a shift in the two-photon resonance due to unequal dipole moments of the transitions coupled by the control field. Complete transparency can only be recovered for systems with equal dipole moments or when the separation between the two excited states is at least of the order of the Doppler width. To support our theoretical study, we present experimental EIT measurements in the D1 lines of 85Rb and 87Rb that agree with our predictions of an enhancement or reduction of EIT transparency under specific conditions. The experimental results also verify the roles that the dipole moments and the separation between the two excited states have on recovering the EIT transparency.

A dual-band asymmetric transmission device based on the nonlinear electromagnetically induced transparency (EIT) effect is presented in this paper. The device structure is composed of two P-type branches and two split ring resonators (SRRs). Dual-band EIT effect is induced based on the destructive interferences between scattering fields of the SRRs and branches in a microstrip transmission line system. Moreover, nonlinear varactor diodes and the asymmetric absorption resistor are added to EIT structure based on microstrip line couplings, which results in the asymmetric transmission property. The 10 dB and 7.5 dB transmission light contrasts at the frequencies of 0.85 GHz and 0.95 GHz with the input power of − 3 dBm are demonstrated experimentally. Such low-loss, broadband and high-contrast asymmetric transmission device results from the EIT mechanism, which possesses narrower, sharper and higher transmittance features. Such results will be very beneficial for new nonlinear electromagnetic devices.