arXiv subjects

Aram Papoyan

Publications and source records attributed to Aram Papoyan.

At least 19 recordsLinked to original sources

arXiv2026

Degenerate mirrorless lasing in thermal vapors

Theoretical predictions were made for the steady-state gain of an orthogonally polarized probe field in a degenerate two-level alkali atom system driven by a linearly polarized continuous-wave pump field in [Opt. Mem. Neural Networks 32 (Suppl 3), S443-S446 (2023)]. Employing linear response theory, we computed the probe absorption spectrum under conditions where the pump was detuned from resonance. The results revealed a sub-natural linewidth dispersive feature near the pump resonance, characterized by both gain and absorption. Furthermore, a distinct pure gain peak emerged at a sideband associated with a dressed-state transition. These phenomena are generally absent outside the ultracold regime due to inhomogeneous broadening, primarily from Doppler effects, which obscure the fine spectral structure. In this paper, it is demonstrated that the sideband gain peak is sustained in the warm vapor regime when both the pump Rabi frequency and detuning exceed the Doppler width, $Ω_P > Δ_P \gg Δ_{Dop}$. Our results can enable degenerate mirrorless lasing in thermal alkali atom vapors, offering a significant enhancement in the signal-to-noise ratio for fluoroscopic remote magnetic sensing applications. The theoretical model studied in this paper is also a complete description of atomic vapors with isolated $J = 2 \to J' = 3$ transitions, such as atomic samarium.

physics.atom-ph↗

arXiv2024

Electromagnetically induced transparency with magnetically-induced $ΔF=0, m_F=0 \rightarrow m_F=0$ probe transition

Interest in magnetically induced (MI) transitions of alkali metal atoms is caused by the fact that their intensities can exceed the intensities of regular atomic transitions in a wide range of magnetic field (200 - 4000 G). The goal of this work was to form and study, for the first time, an electromagnetically induced transparency (EIT) resonance in a strong magnetic field using a probe radiation tuned to |Fg = F; mF = 0-> Fe = F; mF = 0> MI transition, which is forbidden in zero magnetic field. Two narrow-band linearly-polarized cw diode lasers were used to form a EIT resonance on a lambda-type system of Cs atomic D2 line in a strong transverse magnetic field (up to 1000 G). The resonance was formed in Cs atomic vapor nanocell with the atomic vapor column thickness of 850 nm.

physics.atom-ph↗

arXiv2023

Mirrorless lasing: a theoretical perspective

Mirrorless lasing has been a topic of particular interest for about a decade due to promising new horizons for quantum science and applications. In this work, we review first-principles theory that describes this phenomenon, and discuss degenerate mirrorless lasing in a vapor of Rb atoms, the mechanisms of amplification of light generated in the medium with population inversion between magnetic sublevels within the $D_2$ line, and challenges associated with experimental realization.

quant-ph↗

arXiv2022

All magnetic field values cancelling $D_1$ line transitions of alkali metal atoms

In this work, $π$, $σ^+$ and $σ^-$ transitions between magnetic sublevels of the $D_1$ line of all alkali atoms are considered analytically. General block Hamiltonian matrices in presence of a magnetic field for the ground and excited states are built in order to describe all the transitions. Eigenvalues and eigenkets describing ground and excited levels are calculated, "modified" and unperturbed transfer coefficients as a function of the nuclear spin $I$, the magnetic quantum number $m$ and the magnetic field magnitude $B$ are defined. Transition cancellations are observed only for some $π$ transitions of each isotope. The main result is that we obtain one single formula which expresses the magnetic field values cancelling these transitions. These values also correspond to the case when some of other transitions intensity have their maximum. In addition, we examine the derivative of $π$ transition "modified" transfer coefficients in order to find the magnetic field values which correspond to the intensities maximum. The accuracy of the magnetic field $B$ values is only limited by the uncertainty of the involved physical quantities.

physics.atom-ph↗

arXiv2020

New standard magnetic field values determined by cancellations of ${}^{85}\text{Rb}$ and ${}^{87}\text{Rb}$ atomic vapors $5{}^2{S}_{1/2} \rightarrow 6{}^2{P}_{1/2,~3/2}$ transitions

In this article, we study the theoretical behaviour of all the possible hyperfine transitions ($π$, $σ^+$ and $σ^-$) between the $5S$ and $6P$ states of ${}^{87}\text{Rb}$ and ${}^{85}\text{Rb}$ atomic vapors under the influence of an external magnetic field $B$. We show that, for specific transitions, we obtain one or several $B$-values for which the transition intensity is cancelled. The precision of these values is limited to the uncertainty of the physical quantities that are involved in the problem, thus measuring precisely the $B$-values for the cancellations could be a way to determine these quantities more precisely. In the simplest cases involving $2\times 2$ hamiltonians, we give eigenvectors, eigenvalues and analytical formulas to determine the transition cancellation. By checking accuracy between formulas and numerical simulations, we conclude that it is possible to use the latter in order to determine all the cancellations even in the most complicated cases.

physics.atom-ph↗

arXiv2020

Observation of optical Rabi oscillations in transmission signal of atomic vapor under continuous-wave laser excitation

We have studied the temporal behavior of the atomic absorption signal under resonant excitation with a continuous-wave laser radiation. Measurements done for D2 line of 85Rb with ~ 1 ns temporal resolution have shown irregular oscillatory behavior of the transmission signal, which becomes well pronounced for high laser power, and disappears when the laser is tuned off-resonance. Application of the fast Fourier transform analysis of the transmission signal reveals power-dependent frequency peaks, which are shown to be associated with Rabi frequency. Possible linkage of the observed results with the phase-to-amplitude noise conversion caused by the the phase fluctuations of laser field is discussed.

physics.atom-ph↗

arXiv2020

Transition cancellations of $^{87}$Rb and $^{85}$Rb atoms in a magnetic field setting new standards

We have analyzed the magnetic field dependences of intensities of all the optical transitions between magnetic sublevels of hyperfine levels, excited with $σ^+$, $π$ and $σ^-$ polarized light, for the $D_1$ and $D_2$ lines of $^{87}$Rb and $^{85}$Rb atoms. Depending on the type of transition and the quantum numbers of involved levels, the Hamiltonian matrices are of $1\times 1$, $2\times 2$, $3\times 3$ or $4\times 4$ dimension. As an example, analytical expressions are presented for the case of $2\times 2$ dimension matrices for $D_1$ line of both isotopes. Eigenvalues and eigenkets are given, and the expression for the transition intensity as a function of $B$ has been determined. It is found that some $π$ transitions of $^{87}$Rb and $^{85}$Rb get completely canceled for certain, extremely precise, values of $B$. No cancellation occurs for $σ^+$ or $σ^-$ transitions of $D_1$ line. For matrices with size over $2\times 2$, analytical formulas are heavy, and we have performed numerical calculations. All the $B$ values cancelling $σ^+$, $π$ and $σ^-$ transitions of $D_1$ and $D_2$ lines of $^{87}$Rb and $^{85}$Rb are calculated, with an accuracy limited by the precision of the involved physical quantities. We believe our modeling can serve as a tool for determination of standardized values of magnetic field. The experimental implementation feasibility and its possible outcome are addressed. We believe the experimental realization will allow to increase precision of the physical quantities involved, in particular the upper state atomic levels energy.

physics.atom-ph↗

arXiv2019

Fluorescence of rubidium vapor in a transient interaction regime

We have studied modification of the fluorescence spectra of a room-temperature atomic rubidium vapor in the region of $^{85}$Rb and $^{87}$Rb D$_2$ line while changing the temporal rate of linear (triangular) scanning of laser radiation frequency. Increase of the ramping speed over certain value ($\approx$ 10$^6$ MHz/s) results in essential modification of magnitudes of individual atomic transitions, different on rising and falling slopes, which characterize transition from a steady-state interaction regime to a transient one. Our experimental results are well consistent with the developed theoretical model. The obtained results can be used for determination of atomic system parameters such as ground-state relaxation rate. Possible follow-up actions on addressed control of atomic levels population is discussed.

physics.atom-ph↗

arXiv2019

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 D$_2$ 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 neodimuim-iron-boron alloy ring magnet at different distances. The computational tasks are realized by relatively cheap electronic components: an Arduino Due board for the 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 a high measurement precision also for stronger magnetic fields ($>500~$mT), in the hyperfine Paschen-Back regime, where the evolution of the atomic transitions can be calculated with a high accuracy.

physics.atom-ph↗

arXiv2019

Resolution-enhanced quantitative spectroscopy of atomic vapor in optical nanocells based on second-derivative processing of spectra

We present a method for recovery of narrow homogeneous spectral features out of broad inhomogeneous overlapped profile based on second-derivative processing of the absorption spectra of alkali metal atomic vapor nanocells. The method is shown to preserve the frequency positions and amplitudes of spectral transitions, thus being applicable for quantitative spectroscopy. The proposed technique was successfully applied and tested for: measurements of hyperfine splitting and atomic transition probabilities; development of an atomic frequency reference; determination of isotopic abundance; study of atom-surface interaction; and determination of magnetic field-induced modification of atomic transitions frequency and probability. The obtained experimental results are fully consistent with theoretical modeling.

physics.atom-ph↗

arXiv2019

Dark resonance formation with magnetically-induced transitions: extension of spectral range and giant circular dichroism

Dark resonances were formed via electromagnetically induced transparency for the first time involving magnetically-induced $ΔF = \pm2$ atomic transitions of alkali metal atom, which are forbidden at zero magnetic field. The probability of these transitions undergoes rapid growth when $300 - 3000$~G magnetic field is applied, allowing formation of dark resonances, widely tunable in the GHz range. It is established that for $ΔF = +2$ ($ΔF =-2$) transition, the coupling laser tuned to $ΔF = +1$ ($ΔF =-1$) transition of the hyperfine $Λ$-system must be $σ^+$ ($σ^-$) polarized, manifesting anomalous circular dichroism.

physics.atom-ph↗

arXiv2018

Evidence for degenerate mirrorless lasing in alkali metal vapor: forward beam magneto-optical experiment

We report an experimental observation of degenerate mirrorless lasing in forward direction under excitation of a dilute atomic Rb vapor with a single linearly polarized cw laser light resonant with cycling Fe > Fg atomic D2 transitions. Light polarized orthogonally to the laser light is generated for the input light intensity exceeding a threshold value of about 3 mW/cm^2. Application of a transverse magnetic field directed along the input light polarization reveals a sharp about 20 mG wide magnetic resonance centered at B = 0. Increasing the incident light intensity from 3 to 300 mW/cm^2, the generated light undergoes rapid amplitude increase followed by a decline and resonance broadening. Such nonlinear behavior of the observed magnetic resonance is attributed to the population inversion on optical transitions between magnetic sublevels established under linearly polarized excitation. We present observations that indicate that a combination of nonlinear-optical effects occurs in this system, including degenerate mirrorless lasing and four-wave mixing.

physics.atom-ph↗

arXiv2017

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

We have studied the peculiarities of selective reflection from Rb vapor cell with thickness $L <$ 70 nm, which is over an order of magnitude smaller than the resonant wavelength for Rb atomic D$_1$ line $λ$ = 795 nm. A huge ($\approx$ 240 MHz) red shift and spectral broadening of reflection signal is recorded for $L =$ 40 nm caused by the atom-surface interaction. Also completely frequency resolved hyperfine Paschen-Back splitting of atomic transitions to four components for $^{87}$Rb and six components for $^{85}$Rb is recorded in strong magnetic field ($B >$ 2 kG).

physics.atom-ph↗

arXiv2017

Magnetic field--induced modification of selection rules for Rb D$_2$ line monitored by selective reflection from a vapor nanocell

Magnetic field-induced giant modification of the probabilities of five transitions of $5S_{1/2}, F_g=2 \rightarrow 5P_{3/2}, F_e=4$ of $^{85}$Rb and three transitions of $5S_{1/2}, F_g=1 \rightarrow 5P_{3/2}, F_e=3$ of $^{87}$Rb forbidden by selection rules for zero magnetic field has been observed experimentally and described theoretically for the first time. For the case of excitation with circularly-polarized ($σ^+$) laser radiation, the probability of $F_g=2, ~m_F=-2 \rightarrow F_e=4, ~m_F=-1$ transition becomes the largest among the seventeen transitions of $^{85}$Rb $F_g=2 \rightarrow F_e=1,2,3,4$ group, and the probability of $F_g=1,~m_F=-1 \rightarrow F_e=3,~m_F=0$ transition becomes the largest among the nine transitions of $^{87}$Rb $F_g=1 \rightarrow F_e=0,1,2,3$ group, in a wide range of magnetic field 200 -- 1000 G. Complete frequency separation of individual Zeeman components was obtained by implementation of derivative selective reflection technique with a 300 nm-thick nanocell filled with Rb, allowing formation of narrow optical resonances. Possible applications are addressed. The theoretical model is perfectly consistent with the experimental results.

physics.atom-ph↗

arXiv2016

Decoupling of hyperfine structure of Cs $D_1$ line in strong magnetic field studied by selective reflection from a nanocell

Decoupling of total electronic and nuclear spin moments of Cs atoms in external magnetic field for the case of atomic $D_1$ line, leading to onset of the hyperfine Paschen-Back regime has been studied theoretically and experimentally. Selective reflection of laser radiation from an interface of dielectric window and atomic vapor confined in a nanocell with 300 nm gap thickness was implemented for the experimental studies. The real time derivative of selective reflection signal with a frequency position coinciding with atomic transitions was used in measurements, providing $\sim$ 40 MHz spectral resolution and linearity of signal response in respect to transition probability. Behavior of 28 individual Zeeman transitions in a wide range of longitudinal magnetic field (0 - 6 kG) has been tracked under excitation of Cs vapor by a low-intensity $σ^+$- polarized cw laser radiation. For $B\ge 6~$kG, only 8 transitions with nearly equal probabilities and the same frequency slope remained in the spectrum, which is a manifestation of the hyperfine Paschen-Back regime. The obtained experimental results are consistent with numerical modeling. Due to small divergence of selective reflection signal, as well as sub-wavelength thickness and sub-Doppler spectral linewidth inherent to nanocell, the employed technique can be used for distant remote sensing of magnetic field with high spatial and $B$-field resolution.

physics.atom-ph↗

arXiv2014

Active narrowband filtering, line narrowing and gain using ladder electromagnetically induced transparency in an optically thick atomic vapour

Electromagnetically induced transparency (EIT) resonances using the $5\rm{S}_{1/2}\rightarrow5\rm{P}_{3/2}\rightarrow5\rm{D}_{5/2}$ ladder-system in optically thick Rb atomic vapour are studied. We observe a strong line narrowing effect and gain at the $5\rm{S}_{1/2}\rightarrow5\rm{P}_{3/2}$ transition wavelength due to an energy-pooling assisted frequency conversion with characteristics similar to four-wave mixing. As a result it is possible to observe tunable and switchable transparency resonances with amplitude close to $100\%$ and a linewidth of 15 MHz. In addition, the large line narrowing effect allows resolution of $^{85}$Rb $5\rm{D}_{5/2}$ hyperfine structure even in the presence of strong power broadening.

physics.atom-ph↗

arXiv2012

N -resonances in a buffered micrometric Rb cell: splitting in a strong magnetic field

N -resonances excited in rubidium atoms confined in micrometric-thin cells with variable thickness from 1 μm to 2 mm are studied experimentally for the cases of a pure Rb atomic vapor and of a vapor with neon buffer gas. Good contrast and narrow linewidth were obtained for thicknesses as low as 30 μm. The higher amplitude and sharper profile of N-resonances in the case of a buffered cell was exploited to study the splitting of the 85Rb D1 N-resonance in a magnetic field of up to 2200 G. The results are fully consistent with the theory. The mechanism responsible for forming N-resonances is discussed. Possible applications are addressed.

physics.atom-ph↗

arXiv2011

High contrast D$_{1}$ line electromagnetically induced transparency in nanometric-thin rubidium vapor cell

Electromagnetically induced transparency (EIT) on 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 4 orders as compared with an ordinary cm-size cell still allows to form an EIT resonance for $L= λ$ ($λ=794$ nm) with the contrast of up to 40%. Remarkable distinctions of EIT formation in nanometric-thin and ordinary cells are demonstrated. Despite the Dicke effect of strong spectral narrowing and increase of the absorption for $L=$ $λ/2$, EIT resonance is observed both in the absorption and the fluorescence spectra for relatively low intensity of the coupling laser. Well resolved splitting of the EIT resonance in moderate magnetic field for $L=$ $λ$ can be used for magnetometry with nanometric spatial resolution. The presented theoretical model well describes the observed results.

physics.atom-ph↗