We investigate the excitation of the 5D_{5/2} level in Rb atoms using counter-propagating laser beams, which are nearly resonant to the one-photon 5S_{1/2} - 5P_{3/2} and 5P_{3/2} - 5D_{5/2} transitions, ensuring that a sum of the optical frequencies corresponds to the 5S_{1/2} - 5D_{5/2} transition. The excitation produced by two-photon and step-wise processes is detected via spontaneously emitted fluorescence at 420 nm arising from the 6P_{3/2} - 5S_{1/2} transition. The dependences of blue fluorescence intensity on atomic density and laser detuning from the intermediate 5P_{3/2} level have been investigated. The sensitivity of the frequency detuned bi-chromatic scheme for atom detection has been estimated. A novel method for sum frequency stabilization of two free-running lasers has been suggested and implemented using two-photon Doppler-free fluorescence and polarization resonances.
We propose and demonstrate a laser frequency stabilization scheme which generates a dispersion-like tunable Doppler-free dichroic lock (TDFDL) signal. This signal offers a wide tuning range for lock point (i.e. zero-crossing) without compromising on the slope of the locking signal. The method involves measurement of magnetically induced dichroism in an atomic vapour for a weak probe laser beam in presence of a counter propagating strong pump laser beam. A simple model is presented to explain the basic principles of this method to generate the TDFDL signal. The spectral shift in the locking sig…
We study modulation spectroscopy of the potassium D2 transitions at 766.7 nm. The vapour pressure, controlled by heating a commercial reference cell, is optimized using conventional saturated absorption spectroscopy. Subsequent heterodyne detection yields sub-Doppler frequency discriminants suitable for stabilizing lasers in experiments with cold atoms. Comparisons are made between spectra obtained by direct modulation of the probe beam, and those using modulation transfer from the pump via nonlinear mixing. Finally, suggestions are made for further optimization of the signals.
Collisions with background gas particles can shift the resonance frequencies of atoms in atomic clocks. The internal quantum states of atoms can also become entangled with their motional states due to the recoil imparted by a collision, which leads to a further shift of the clock frequency through the relativistic Doppler shift. It can be complicated to evaluate the Doppler and collisional frequency shifts for clock atoms in such entangled states, but estimates of these shifts are essential in order to improve the accuracy of optical atomic clocks. We present a formalism that describes collisi…
The optical manipulation of Ba$^{+}$ ions is mainly performed by a 493 nm laser for the S$_{1/2}$-P$_{1/2}$ transition and a 650 nm laser for the P$_{1/2}$-D$_{3/2}$ transition. Since the branching ratio between the 493 nm and 650 nm transitions of a single Ba$^{+}$ ion is comparable, stabilization systems of both lasers are equally important for Doppler cooling, sub-Doppler cooling, optical pumping and state detection. The stabilization system of a 493 nm laser to an absolute Te$_2$ reference has been well established. However, the stabilization of a 650 nm laser has not been presented before…
We perform detailed analysis of sub-Doppler cooling limits for various atoms by direct solving quantum kinetic equation for atom density matrix in standing-wave light field generated by counterpropagating waves. It was demonstrated that the polarization gradient cooling effects are sensitive to atom recoil parameter (the ratio of recoil energy to natural linewidth) that results to limitation of sub-Doppler cooling and allows to outline the limits of well-known sub-Doppler cooling theory. We also give a comparison the cooling limits for well-known $σ_+-σ_-$ and $lin\perp lin$ configurations.
The grating magneto-optical trap (GMOT) requires only one beam and three planar diffraction gratings to form a cloud of cold atoms above the plane of the diffractors. Despite the complicated polarization arrangement, we demonstrate sub-Doppler cooling of 87Rb atoms to a temperature of 7.6(0.6) uK through a multi-stage, far-detuned GMOT in conjunction with optical molasses. A decomposition of the electric field into polarization components for this geometry does not yield a mapping onto standard sub-Doppler laser-cooling configurations. With numerical simulations, we find that the polarization …
A new approach to the theory of atoms' interaction with chirped Raman pulses is developed. When the pulses have sufficiently close effective wave lengths, which are smaller than the atomic cloud size, equations for the family of the matrix elements of the atomic density matrix in the Wigner representation are derived. The solution, involving linear (in the pulse duration) phase corrections, is obtained for the rectangular pulse. The interferometric part of the atoms' excitation is calculated.
We propose and analyze the possibility of performing two-photon continuous-wave Doppler-cooling of hydrogen atoms using the 1S-2S transition. "Quenching" of the 2S level (by coupling with the 2P state) is used to increase the cycling frequency, and to control the equilibrium temperature. Theoretical and numerical studies of the heating effect due to Doppler-free two-photon transitions evidence an increase of the temperature by a factor of two. The equilibrium temperature decreases with the effective (quenching dependent) width of the excited state and can thus be adjusted up to values close to…
Literature mentions only incidentally a sub-Doppler contribution in the excitation spectrum of the backward fluorescence of a dense vapor. This contribution is here investigated on Cs vapor, both on the first resonance line (894 nm) and on the weaker second resonance line (459 nm). We show that in a strongly absorbing medium, the quenching of excited atoms moving towards a window irradiated under near normal incidence reduces the fluorescence on the red side of the excitation spectrum. Atoms moving slowly towards the window produce a sub- Doppler velocity-selective contribution, whose visibili…
The exact nondipole minimal-coupling Hamiltonian for an atom interacting with an explicitly time- and space-dependent laser field is transformed into the rest frame of a classical free electron in the laser field, i.e., into the Kramers-Henneberger frame. The new form of the Hamiltonian is used to study nondipole effects in the high-intensity, high-frequency regime. Fully three dimensional nondipole {\it ab initio} wavepacket calculations show that the ionization probability may decrease for increasing field strength. We identify a unique signature for the onset of this dynamical stabilization…
We report Monte Carlo wave function simulation results on cold collisions between magnesium atoms in a strong red-detuned laser field. This is the normal situation e.g. in magneto-optical traps (MOT). The Doppler limit heating rate due to radiative collisions is calculated for Mg-24 atoms in a magneto-optical trap based on the singlet S_0 - singlet P_1 atomic laser cooling transition. We find that radiative heating does not seem to affect the Doppler limit in this case. We also describe a channelling mechanism due to the missing Q branch in the excitation scheme, which could lead to a suppress…
We consider the phase stability of a local oscillator (or laser) locked to a cavity QED system comprised of atoms with an ultra-narrow optical transition. The atoms are cooled to millikelvin temperatures and then released into the optical cavity. Although the atomic motion introduces Doppler broadening, the standing wave nature of the cavity causes saturated absorption features to appear, which are much narrower than the Doppler width. These features can be used to achieve an extremely high degree of phase stabilization, competitive with the current state-of-the-art. Furthermore, the inhomogen…
The $3p^{4}$ $^{3}$P$_{J}$ - $3p^{3}4p$ $^{3}$P$_{J}$ transition in the sulphur atom is investigated in a precision two-photon excitation scheme under Doppler-free and collision-free circumstances yielding an absolute accuracy of 0.0009 cm$^{-1}$, using a narrowband pulsed laser. This verifies and improves the level separations between amply studied odd parity levels with even parity levels in S I. An improved value for the $^{3}$P$_{2}$ - $^{3}$P$_{1}$ ground state fine structure splitting is determined at $396.0564$ (7) cm$^{-1}$. A $^{34}$S - $^{32}$S atomic isotope shift was measured from …
A two-dimensional model atom is employed to study the ionization behavior of initially excited atomic states in highly-frequent intense laser pulses beyond the dipole approximation. An additional regime of ionization suppression is found at laser intensities where the stabilization effect is expected to break down. The appearance of this effect is due to a strong coupling of the initial wave function to the ground state of the cycle-averaged space-translated ionic potential, followed by a subsequent population transfer to the ground state during the laser pulse turn-off. Non-dipole effects are…
We propose and demonstrate a scheme to enable Doppler compensation within optical cavities for atom interferometry at significantly increased mode diameters. This has the potential to overcome the primary limitations in cavity enhancement for atom interferometry, circumventing the cavity linewidth limit and enabling mode filtering, power enhancement, and a large beam diameter simultaneously. This approach combines a magnified linear cavity with an intracavity Pockels cell. The Pockels cell introduces a voltage tunable birefringence allowing the cavity mode frequencies to track the Raman lasers…
We present a 3D theoretical comparison between the radiation-pressure forces exerted on an atom in an isotropic light cooling scheme and in a six-beam molasses. We demonstrate that, in the case of a background vapor where all the space directions of the atomic motion have to be considered, the mean cooling rate is equal in both configurations. Nevertheless, we also point out what mainly differentiates the two cooling techniques: the force component orthogonal to the atomic motion. If this transverse force is always null in the isotropic light case, it can exceed the radiation-pressure-force lo…
Deactivation of broad quasi-one-dimensional dibosonic molecules is analyzed. Within integrable Lieb-Liniger-McGuire (LLMG) model an exact expression does not demonstrate suppression of the deactivation at low collision energies. Solution of Faddeev equations demonstrates that when a Feshbach resonance lifts the symmetry of the LLMG model the deactivation becomes suppressed. This effect shows a way for formation of a stable gas of dibosonic Feshbach molecules.
Stabilizing important physical quantities to atom-based standards lies at the heart of modern atomic, molecular and optical physics, and is widely applied to the field of precision metrology. Of particular importance is the atom-based microwave field amplitude stabilizer, the so-called atomic candle. Previous atomic candles are realized with atoms in their ground state, and hence suffer from the lack of frequency band tunability and small stabilization bandwidth, severely limiting their development and potential applications. To tackle these limitations, we employ microwave-dressed Rydberg ato…
We study the absorptive and dispersive properties of Doppler-broadened atomic media as a function of detuning. Beginning from the exact lineshape calculated for a two-level atom, a series of approximations to the electric susceptibility are made. These simplified functions facilitate direct comparison between absorption and dispersion, and show that dispersion dominates the atom-light interaction far from resonance. The calculated absorption and dispersion are compared to experimental data, showing the validity of the approximations.
We report on Doppler-free laser spectroscopy in a Cs vapor cell using a dual-frequency laser system tuned on the Cs D$_1$ line. Using counter-propagating beams with crossed linear polarizations, an original sign-reversal of the usual saturated absorption dip and large increase in Doppler-free atomic absorption is observed. This phenomenon is explained by coherent population trapping (CPT) effects. The impact of laser intensity and light polarization on absorption profiles is reported in both single-frequency and dual-frequency regimes. In the latter, frequency stabilization of two diode lasers…
We study numerically stabilization against ionization of a fully correlated two-electron model atom in an intense laser pulse. We concentrate on two frequency regimes: very high frequency, where the photon energy exceeds both, the ionization potential of the outer {\em and} the inner electron, and an intermediate frequency where, from a ``single active electron''-point of view the outer electron is expected to stabilize but the inner one is not. Our results reveal that correlation reduces stabilization when compared to results from single active electron-calculations. However, despite this des…
We demonstrate in situ fluorescence detection of $^7$Li atoms in a 1D optical lattice with single atom precision. Even though illuminated lithium atoms tend to boil out, when the lattice is deep, molasses beams without extra cooling retain the atoms while producing sufficient fluorescent photons for detection. When the depth of the potential well at an antinode is 2.4 mK, an atom remains trapped for 30 s while scattering probe photons at the rate of $1.7 \times 10^5$ s$^{-1}$. We propose a simple model that describes the dependence of the lifetime of an atom on well depth. When the number of t…
This paper derives a general procedure for the numerical solution of the Lindblad equations that govern the coherences arising from multicoloured light interacting with a multilevel system. A systematic approach to finding the conservative and dissipative terms is derived and applied to the laser cooling of gallium. An improved numerical method is developed to solve the time-dependent master equation and results are presented for transient cooling processes. The method is significantly more robust, efficient and accurate than the standard method and can be applied to a broad range of atomic an…
We report on a simple and robust technique to generate a dispersive signal which serves as an error signal to electronically stabilize a monomode cw laser emitting around an atomic resonance. We explore nonlinear effects in the laser beam propagation through a resonant vapor by way of spatial filtering. The performance of this technique is validated by locking semiconductor lasers to the cesium and rubidiumD2 line and observing long-term reduction of the emission frequency drifts, making the laser well adapted for many atomic physics applications.
We explore the possibility of decelerating and Doppler cooling an ensemble of tree-level $Λ$-type atoms by a coherent train of short, non-overlapping laser pulses. We show that $Λ$-atoms can be Doppler cooled without additional repumping of the population from the intermediate ground state. We derive analytical expression for the scattering force in the quasi-steady-state regime and analyze its dependence on pulse train parameters. Based on this analysis we propose a method of choosing pulse train parameters to optimize the cooling process.
We report on the demonstration of Doppler-free spectroscopy of metastable Sr atoms using a hollow cathode lamp (HCL). We employed a custom Sr HCL which is filled with a mixture of 0.5-Torr Ne and 0.5-Torr Xe as a buffer gas to suppress velocity changing collisions and increase the populations in all the $(5s5p){}^3P_J(J=0,\ 1,\ 2)$ metastable states. We performed frequency-modulation spectroscopy for the $(5s5p){}^3P_0-(5s6s){}^3S_1$, $(5s5p){}^3P_1-(5s6s){}^3S_1$, $(5s5p){}^3P_2-(5s5d){}^3D_2$, and $(5s5p){}^3P_2-(5s5d){}^3D_3$ transitions with sufficient signal to noise ratios for laser freq…
We show that the Second Derivative (SD) technique of the absorption spectra of Rb atomic vapours confined in a nanocell with a thickness $\ell= λ/2=398$ nm allows to achieve close to Doppler-free spectroscopy. Narrow linewidth and linearity of the SD signal response with respect to transition probabilities allow us to study separately, in an external transverse magnetic field (0.6 to 4 kG), a big number of the atomic transitions of $^{85}$Rb and $^{87}$Rb atoms. Atomic transitions $|F_g,0\rangle \rightarrow |F_e=F_g,0'\rangle$, for which the dipole moment is null at zero magnetic field (so-cal…
We present an experimental scheme that produces Doppler-free spectra of the $5s \to 6p $ second resonance transition in atomic rubidium. The experiment uses the saturation of the cascade fluorescence that occurs when thermal rubidium atoms interact with two counterpropagating $420 $ nm laser beams of comparable intensity. Part of the excited atomic population goes through the $5p_{3/2}$ level which then decays by emission of $780$ nm photons. Narrow dips appear in this otherwise broad $780$ nm fluorescence, which allows resolution of the $6p_{3/2}$ hyperfine structure. A rate equation model is…
We present a novel and simple method of stabilizing the laser phase and frequency by polarization spectroscopy of an atomic vapor. In analogy to the Pound-Drever-Hall method, which uses a cavity as a memory of the laser phase, this method uses atomic coherence (dipole oscillations) as a phase memory of the transmitting laser field. A preliminary experiment using a distributed feedback laser diode and a rubidium vapor cell demonstrates a shot-noise-limited laser linewidth reduction (from 2 MHz to 20 kHz). This method would improve the performance of gas-cell-based optical atomic clocks and magn…
We report on the observation of sub-Doppler resonances on the back-scattered light from a random porous glass medium with rubidium vapor filling its interstices. The sub-Doppler spectral lines are the consequence of saturated absorption where the incident laser beam saturates the atomic medium and the back-scattered light probes it. Some specificities of the observed spectra reflect the transient atomic evolution under confinement inside the pores. Simplicity, robustness and potential miniaturization are appealing features of this system as a spectroscopic reference.
A crucial step towards enabling real-world applications for quantum sensing devices such as Rydberg atom electric field sensors is reducing their size, weight, power, and cost (SWaP-C) requirements without significantly reducing performance. Laser frequency stabilization is a key part of many quantum sensing devices and, when used for exciting non-ground state atomic transitions, is currently limited to techniques that require either large SWaP-C optical cavities and electronics or use significant optical power solely for frequency stabilization. Here we describe a laser frequency stabilizatio…
We study the non-linear interaction of a cold sample of strontium-88 atoms coupled to a single mode of a low finesse optical cavity in the so-called bad cavity limit and investigate the implications for applications to laser stabilization. The atoms are probed on the weak inter-combination line $\lvert 5s^{2} \, ^1 \textrm{S}_0 \rangle \,-\, \lvert 5s5p \, ^3 \textrm{P}_1 \rangle$ at 689 nm in a strongly saturated regime. Our measured observables include the atomic induced phase shift and absorption of the light field transmitted through the cavity represented by the complex cavity transmissio…
Ultracold atoms at temperatures close to the recoil limit have been achieved by extending Doppler cooling to forbidden transitions. A cloud of ^40Ca atoms has been cooled and trapped to a temperature as low as 6 μK by operating a magneto-optical trap on the spin-forbidden intercombination transition. Quenching the long-lived excited state with an additional laser enhanced the scattering rate by a factor of 15, while a high selectivity in velocity was preserved. With this method more than 10% of pre-cooled atoms from a standard magneto-optical trap have been transferred to the ultracold trap. M…
We theoretically investigate the damping and trapping forces in a three-dimensional magneto-optical trap (MOT), by numerically solving the optical Bloch equations. We focus on the case where there are dark states because the atom is driven on a "type-II" system where the angular momentum of the excited state, $F'$, is less than or equal to that of the ground state, $F$. For these systems we find that the force in a three-dimensional light field has very different behaviour to its one dimensional counterpart. This differs from the more commonly used "type-I" systems ($F'=F+1$) where the 1D and …
In this work we perform polarization spectroscopy of erbium atoms in a hollow cathode lamp (HCL) for the stabilization of a diode laser to the 401-nm transition. We review the theory behind Doppler-free polarization spectroscopy, theoretically model the expected erbium polarization spectra, and compare the numerically calculated spectra to our experimental data. We further analyze the dependence of the measured spectra on the HCL current and the peak intensities of our pump and probe lasers to determine conditions for optimal laser stabilization.
A counterintuitive scheme to produce ultracold hydrogen via fragmentation of laser cooled diatomic hydrides is presented where the final atomic H temperature is inversely proportional to the mass of the molecular parent. In addition, the critical density for formation of a Bose-Einstein Condensate (BEC) at a fixed temperature is reduced by a factor ratio hydrogen mass: parent mass raised to power 3/2 over directly cooled hydrogen atoms. The narrow Feshbach resonances between a singlet S atom and hydrogen are well suited to a tiny center of mass energy release necessary during fragmentation. Wi…
We demonstrate sub-Doppler cooling of 40K on the D_1 atomic transition. Using a gray molasses scheme, we efficiently cool a compressed cloud of 6.5x10^8 atoms from ~ 4\mK to 20uK in 8 ms. After transfer in a quadrupole magnetic trap, we measure a phase space density of ~10^-5. This technique offers a promising route for fast evaporation of fermionic 40K.
Radio frequency antennas based on Rydberg atoms can in principle reach sensitivities beyond those of any conventional wire antenna, especially at lower frequencies where very long wires are needed to accommodate the growing wavelength. This paper presents a detailed theoretical investigation of Rydberg antenna sensitivity, elucidating parameter regimes that could cumulatively lead to 2--3 orders of magnitude sensitivity increase. Of special interest are three-laser setups proposed to compensate for atom motion-induced Doppler spreading. Such setups are in indeed shown to be advantageous, but o…
We report the construction of a simple, light weight and compact atomic beam spectroscopy cell for Strontium atoms. The cell is built using glass blowing technique and includes a simple Titanium Sublimation Pump for active pumping of the residual and background gases to maintain ultra-high vacuum. Commercially available and electrically heated dispenser source is used to generate the beam of Sr atoms. We perform spectroscopy on the $5s^2\ ^1S_0\longrightarrow 5s\ 5p\ ^1P_1$ transition to obtain a well resolved Doppler free spectroscopic signal for frequency stabilization of the laser source. T…
A frequency-stabilized ultraviolet laser system, locked to the thallium resonant transition of 377.5 nm, was demonstrated using a novel bichromatic spectroscopy technique for tuning the zero-crossing laser-lock point. The atomic thallium system is a promising candidate in atomic parity violation and permanent electric dipole moment experiments, and its 377.5 nm 6P1/2->7S1/2 transition is important for thallium laser cooling and trapping experiment. The pressure shift, owing to the high pressure buffer gas of the hollow-cathode lamp, was observed using an atomic beam resonance as reference. Suc…
Dynamic stabilization of atomic hydrogen against ionization in high-frequency single- and two-color, circularly polarized laser pulses is observed by numerically solving the three-dimensional, time-dependent Schrödinger equation. The single-color case is revisited and numerically determined ionization rates are compared with both, exact and approximate high-frequency Floquet rates. The position of the peaks in the photoelectron spectra can be explained with the help of dressed initial states. In two-color laser fields of opposite circular polarization the stabilized probability density may be …
We explore the possibility of decelerating and Doppler cooling of an ensemble of two-level atoms by a coherent train of short, non-overlapping laser pulses. We develop a simple analytical model for dynamics of a two-level system driven by the resulting frequency comb field. We find that the effective scattering force mimics the underlying frequency comb structure. The force pattern depends strongly on the ratio of the atomic lifetime to the repetition time and pulse area. For example, in the limit of short lifetimes, the frequency peaks of the optical force wash out. We show that laser cooling…
The erbium atomic system is a promising candidate for an atomic Bose-Einstein condensate of atoms with a non-vanishing orbital angular momentum ($L \neq 0$) of the electronic ground state. In this paper we report on the frequency stabilization of a blue external cavity diode laser system on the 400.91 $nm$ laser cooling transition of atomic erbium. Doppler-free saturation spectroscopy is applied within a hollow cathode discharge tube to the corresponding electronic transition of several of the erbium isotopes. Using the technique of frequency modulation spectroscopy, a zero-crossing error sign…
We revisit the stabilization of ionization of atoms subjected to a superintense laser pulse using nonlinear dynamics. We provide an explanation for the lack of complete ionization at high intensity and for the decrease of the ionization probability as intensity is increased. We investigate the role of each part of the laser pulse (ramp-up, plateau, ramp-down) in this process. We emphasize the role of the choice for the ionization criterion, energy versus distance criterion.
Combination of the electromagnetically-induced-transparency (EIT) effect and Rydberg-state atoms has attracted great attention recently due to its potential application in the photon-photon interaction or qubit operation. In this work, we studied the Rydberg-EIT spectra with room-temperature $^{87}$Rb atoms. Spectroscopic data under various experimental parameters all showed that the contrast of EIT transparency as a function of the probe intensity is initially enhanced, reaches a maximum value and then decays gradually. The contrast of spectral profile at the optimum probe field intensity is …
We discuss a candidate solution for the controlled trapping and manipulation of two individual Rydberg atoms by means of a magnetic Ioffe-Pritchard trap that is superimposed by a constant electric field. In such a trap Rydberg atoms experience a permanent electric dipole moment that can be of the order of several hundred Debye. The interplay of electric dipolar repulsion and three dimensional magnetic confinement leads to a well controllable equilibrium configuration with tunable trap frequency and atomic distance. We thoroughly investigate the trapping potentials and analyze the interaction-i…
We report on the realization of sub-Doppler laser cooling of sodium atoms in gray molasses using the D1 optical transition ($3s\, ^2S_{1/2} \rightarrow 3p\, ^2P_{1/2}$) at 589.8 nm. The technique is applied to samples containing $3\times10^9$ atoms, previously cooled to 350 $μ$K in a magneto-optical trap, and it leads to temperatures as low as 9 $μ$K and phase-space densities in the range of $10^{-4}$. The capture efficiency of the gray molasses is larger than 2/3, and we observe no density-dependent heating for densities up to $10^{11}$ cm$^{-3}$.
A new possibility of laser cooling of alkaline-earth-metal and Ytterbium atoms using a two-photon transition is analyzed. We consider a $^{1}S_{0}$ - $^{1}S_{0}$ transition, with excitation in near resonance with the $^{1}P_{1}$ level. This greatly increases the two-photon transition rate, allowing an effective transfer of momentum. The experimental implementation of this technique is discussed and we show that for Calcium, for example, two-photon cooling can be used to achieve a Doppler limit of 123 microKelvin. The efficiency of this cooling scheme and the main loss mechanisms are analyzed.
We propose a novel `butterfly' level scheme to generate highly correlated photon pairs from atomic vapors. With multi-photon Doppler-free pumping, background Rayleigh scattering is dipole-forbidden and collective emission is permitted in all directions. This results in usable pairs generated simultaneously in the full $4π$ solid angle. Collecting these pairs can produce photon pairs at a rate of $\sim 10^{12}$ per second, given only moderate ensemble sizes of $\sim 10^6$ atoms.
