Cesium Magneto-optical Trap Research Articles

Measurements of cesium PJ-series quantum defect with the microwave spectroscopy

High-precision microwave spectroscopy has been used to measure the transition frequency of nS1/2 → nPJ (n is the principle quantum number) and further the quantum defect of nPJ states in a standard cesium magneto-optical trap. A microwave field with 30-μs duration coupling the nS1/2 → nP1/2,3/2 transition yields a narrow linewidth microwave spectroscopy with the linewidth approaching the Fourier limit. After carefully compensating the stray electric and magnetic field and using the diluted atomic gas, we extract improved quantum defects of nPJ state, δ0(nP1/2) = 3.59159091(19), δ2(nP1/2) = 0.36092(35) and δ0(nP3/2) = 3.55907153(25), δ2(nP3/2) = 0.37344(47).

Pump–probe and Four-wave Mixing Spectra Arising from Recoil-induced Resonance in an Operating Cesium Magneto-Optical Trap

We present experimental observation of recoil-induced resonance (RIR) in an operating cesium magneto-optical trap (MOT) by both pump–probe absorption and four-wave mixing spectra simultaneously. We investigate the dependence of amplitudes of these two spectra on pump beam intensity and frequency. The measurement results agree well with the recoil-induced theory with modifications of Raman transition effect and atomic number. The systematical study on RIR spectra is meaningful for the diagnostic measurement of cold atoms in an operating MOT.

Two-color cesium magneto-optical trap with 6S1/2-6P3/2-7S1/2 (852 nm?+?1470 nm) ladder-type system

A 1470 nm+852 nm two-color (TC) cesium (Cs) magneto-optical trap (MOT) with a 6S1/2-6P3/2-7S1/2 ladder-type system is proposed and experimentally investigated. To the best of our knowledge, it is the first report about the 1470 nm+852 nm Cs TC-MOT. One of the three pairs of the 852 nm cooling and trapping beams (CTBs) in a conventional Cs MOT is replaced with a pair of the 1470 nm CTBs. Thus, the TC-MOT partially employs the optical radiation forces from photon scattering of the 6P3/2 (F′=5) −7S1/2 (F′′=4) excited-state transition (1470 nm). This TC-MOT can cool and trap Cs atoms on both the red- and blue-detuning sides of the two-photon resonance. This work may have applications in cooling and trapping of atoms using inconvenient wavelengths and background-free detection of cold and trapped Cs atoms.

Radiation-Pressure Effects in Cold-Atom Absorption Spectroscopy and Electromagnetically Induced Transparency

Radiation pressure due to the interaction between a probe light and cold atoms is investigated in a standard cesium magneto-optical trap. The radiation pressure alters the absorption spectroscopy of cold atoms, leading to line shapes and linewidths after resonant interaction that are different for positive and negative probe chirps. The difference is attributed to the radiation pressure of the probe laser, due to which atoms become accelerated at the resonance. The effect of the radiation pressure is also seen in electromagnetically induced transparency (EIT) involving an excited Rydberg level. The density matrix equation accounting for the radiation pressure is used to simulate the experiments. The simulations agree well with the measurements both for absorption and EIT spectra. We find that the effect of the radiation pressure is reduced at low probe intensities, and can be neglected when the probe intensity is smaller than Isat/2 .

Off-resonant double-resonance optical-pumping spectra and their application in a multiphoton cesium magneto-optical trap

We present an investigation of double-resonance optical pumping (DROP) spectra under the condition of single-photon frequency detuning based on a cesium 6S1/2–6P3/2–8S1/2 ladder-type system with a room-temperature vapor cell. Two DROP peaks are found, and their origins are explored. One peak has a narrow linewidth due to the atomic coherence for a counterpropagating configuration; the other peak has a broad linewidth, owing to the spontaneous decay for a copropagating configuration. This kind of off-resonant DROP spectrum can be used to control and offset-lock a laser frequency to a transition between excited states. We apply this technique to a multiphoton cesium magneto-optical trap, which can efficiently trap atoms on both red and blue sides of the two-photon resonance.

An experimental investigation of the trap-dynamics of a cesium magneto-optical trap at high laser intensities

We have developed Pakistan’s first magneto optical trap (MOT) in which we were able to capture as many as 2.8 × 109 Cs atoms and attain densities as high as 2 × 1011 atoms/cm3. The trap performance was optimized by varying the laser intensity from 50 mW/cm2 to 500 mW/cm2 as well as the magnetic field gradient from 5 G/cm to 20 G/cm. We have fully investigated the dynamics of the cesium vapor cell magneto-optical trap (VCMOT) by determining the capture rate L (atoms s−1), background collisional loss rate γ (s−1) and intra-trap excited-state collisional loss parameter β (cm3 s−1) of the cesium atoms in the trap. Also, the cloud expansion and compression with trap laser intensity and magnetic field gradient was observed. The MOT dynamics at high intensities is characterized by high capture rate (4 × 109 atoms/s), high densities, enhanced collisional losses (β ∼ 10−11 cm3 s−1) and cloud expansion due to radiation trapping. The intensities used in this study are the highest ever reported with the cesium MOT.

Measurements of Relative Transition Oscillator Strengths of Rydberg States in Cesium Magneto-Optical Trap

The oscillator strengths of 6 P 3/2 → n S / n D transitions are measured by fitting ultracold Cs Rydberg atom field-ionized spectra. The oscillator strength ratios η( n ) = f D 5/2 ( n )/ f D 3/2 ( n ) and ρ( n ) = f S 1/2 ( n + 2)/ f D 3/2 ( n ), which agree with the calculations based on the wave functions obtained by Numerov's method, are determined. The obtained results indicate that the ratios are almost independent of the principal quantum number n .

Alternative laser system for cesium magneto-optical trap via optical injection locking to sideband of a 9-GHz current-modulated diode laser

By optical injection of an 852-nm extended-cavity diode laser (master laser) to lock the + 1-order sideband of a ~9-GHz-current-modulated diode laser (slave laser), we generate a pair of phase-locked lasers with a frequency difference up to ~9-GHz for a cesium (Cs) magneto-optical trap (MOT) with convenient tuning capability. For a cesium MOT, the master laser acts as repumping laser, locked to the Cs 6S₁/₂ (F = 3) - 6P₃/₂ (F' = 4) transition. When the + 1-order sideband of the 8.9536-GHz-current-modulated slave laser is optically injection-locked, the carrier operates on the Cs 6S₁/₂ (F = 4) - 6P₃/₂ (F' = 5) cooling cycle transition with -12 MHz detuning and acts as cooling/trapping laser. When carrying a 9.1926-GHz modulation signal, this phase-locked laser system can be applied in the fields of coherent population trapping and coherent manipulation of Cs atomic ground states.

Collisional loss of cesium Rydberg atoms in a magneto-optical trap

The collisional loss rates of 63${S}_{1/2}$ Rydberg atoms in cesium magneto-optical trap are measured by using the state-selective pulse field ionization technique and used to investigate the interaction between Rydberg atoms. The collisional loss rate coefficients due to collisions with Rydberg atoms and ground-state atoms are obtained by fitting the experimental data. The results indicate that the large collisional loss mainly comes from the strong long-range interaction between ultracold Rydberg atoms, and the loss rate is significantly increased under a weak electric field.

Measurement of quantum defects of nS and nD states using field ionization spectroscopy in ultracold cesium atoms

This paper reports that ultracold atoms are populated into different nS and nD Rydberg states (n = 25∼52) by two-photon excitation. The ionization spectrum of an ultracold Rydberg atom is acquired in a cesium magneto-optical trap by using the method of pulse field ionization. This denotes nS and nD states in the ionization spectrum and fits the data of energy levels of different Rydberg states to obtain quantum defects of nS and nD states.

Loading and cooling of cesium atoms in 3D optical lattice

A four-beam 3D near-resonant optical lattice system is implemented and cold atoms are loaded into the optical lattice based on cesium magneto-optical trap and optical molasses. The dependence of the final temperature due to the Sisyphus cooling on the intensity and the frequency detuning of optical lattice are experiemently investigated，and the lifetime of the cold atoms in optical lattice are measured via the short-distance time_of_flight absorption spectra.

Enhancement in the number of trapped atoms in a cesium magneto-optical trap by a near-resonant control laser

We demonstrate enhancement in the number of trapped cesium atoms in a magneto-optical trap (MOT) using a control laser that illuminates only a small faction of the capture region of the trap without interacting with the cold cloud of atoms. The enhancement is maximized when the laser is slightly blue detuned with respect to the cooling transition. Trap loading curves point to approximately a twofold increase in the capture rate, which as a consequence results in the increase in the steady state number of trapped atoms. Enhanced loading is confirmed by MOT loading and decay curves taken under the modulation of the control laser beam. Optical pumping of the inaccessible Zeeman states into the stretched states is suggested as a possible mechanism.

Temperature measurement of cold atoms in a cesium magneto-optical trap by means of short-distance time-of-flight absorption spectrum

We report the basic idea and experimental demonstration of measuring the temperature of cold cesium atomic cloud confined in a magneto-optical trap (MOT) by analyzing absorption spectrum observed in the short-distance time-of-flight (TOF) method. Compared with the conventional TOF scheme, we measure the temperature of cold atomic cloud in MOT by short-distance TOF method for our small vapor cell. If the cold atomic cloud is released, it will fall and expand due to gravity and its initial velocity distribution. Utilizing a cylindrical resonant probe beam positioned several millimeters beneath the MOT (in this paper, we analyzed the cases for 3mm, 5mm, and 8mm of center-to-center distance between the MOT region and the probe beam, respectively), we can record the short-distance TOF absorption spectrum with a photodiode when cold atoms go through the probe region. Analysis of the short-distance TOF absorption spectrum yields the effective temperature of the cold cloud in MOT.

Optical dipole trap inside a laser resonator.

We report the first realization, to our knowledge, of an optical dipole trap inside the active resonator of a laser. The concept, which is demonstrated with a CO2 laser (lambda = 10.6 microm), combines the advantages of optical power enhancement (up to 1.3-kW peak power) with the intrinsic stability of laser intensity as a result of the feedback of the active laser medium. Two kinds of trapping geometries are presented: a Gaussian trap in a transverse TEM00 mode and a boxlike transverse confinement in a superposition of transverse modes. In addition, longitudinal superlattices are created by two-frequency operation of the laser. Transfer efficiencies of up to 50% from a cesium magneto-optical trap are achieved. Storage times (7 = 0.3 s) are mainly limited by the background gas pressure. Possible sources of additional loss of atoms are discussed.

Flux enhancement model for cold cesium fine-structure changing collisions

The measurements of fine-structure changing collisions in a cesium magneto-optical trap, reported in a previous work [A. Fioretti et al., Phys. Rev. A 55, R3999 (1997)], are reanalyzed within a model based on the flux enhancement effect, which takes place in cold atomic collisions. In the present analysis, we consider the cooperative effect of the long-range and the shorter-range excitation by the strong trap laser. We evidence also the important role of the hyperfine structure of the Cs2 molecular levels asymptotically connected to the ground-state and excited-state dissociation limits.

Photoionization cross sections for excited laser-cooled cesium atoms

Losses from a cesium magneto-optical trap induced by an additional laser ionizing the atoms in the ${6P}_{3/2}$ state have been measured as a function of the intensity and frequency of the ionizing laser. The absolute cross section for ionization of the ${6P}_{3/2}$ state has been derived as a function of the wavelength of the ionizing laser. Our values are compared with previous ones and available theoretical predictions. A simple model describing the photoionization processes has been developed.

A cesium magneto-optical trap for cold collisions studies

A cesium magneto-optical trap operating at a large atomic density in multiple scattering regime has been investigated. The trap operates with a large Rabi frequency for trapping lasers. The atomic number, the dimension of the atomic cloud, the atomic density, and the atomic temperature have been measured as a function of trap parameters. At different trap conditions, the product of the atomic number and of the atomic density, which determines the occurrence of collisional processes, has been also examined. Our results are interpreted on the basis of laser cooling processes.

Phase-space density in the magneto-optical trap.

We present an investigation of the cesium magneto-optical trap, with particular regard to the best combination of atomic density and temperature that can be produced. Conditions in the trap depend on four independent parameters: the detuning and intensity of the light, the gradient of the magnetic field, and the number of atoms trapped. We have varied all these parameters and measured the temperature and density distribution of the trapped cloud. Both the nonlinear variation with position of the restoring force and the reabsorption of photons scattered in the cloud limit the maximum density, and we present an empirical model that takes this into account. This in turn limits the density in phase space \ensuremath{\rho} (defined as the number of atoms in a box with sides of one thermal de Broglie wavelength). We have observed a maximum \ensuremath{\rho}=(1.5\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$, with a spatial density of about 2\ifmmode\times\else\texttimes\fi{}${10}^{11}$ atoms/${\mathrm{cm}}^{3}$.

Investigation of sub-Doppler cooling effects in a cesium magneto-optical trap

We present an investigation of sub-Doppler effects in a cesium magneto-optical trap. First, a simple one-dimensional theoretical model of the trap is developed for aJ g = 1 →J e = 2 transition. This model predicts the size of the trapped atom cloud and temperature as a function of laser intensity and detuning. In the limit of small magnetic field gradients, the trap temperature is found to be equal to the molasses temperature and a minimum size for the trap is calculated. We then describe several experiments performed in a three-dimensional cesium trap to measure the trap parameters, spring constant, friction coefficient, temperature and density. Whilst the temperature of the trapped atoms is found to be equal to the molasses temperature, in agreement with theory, the trap spring constant is found to be two orders of magnitude smaller than the one-dimensional prediction, a value close to that predicted by Doppler models. The maximum density is found to be on the order of 1012 atoms/cm3 or one atom per optical wavelength on average. When the number of trapped atoms becomes large, the temperature begins to increase dramatically. This excess temperature depends in a very simple way on the atom number, laser intensity and detuning, suggesting that its origin lies in multiple photon scattering within the trap.