Atomic Beam Apparatus Research Articles

Measurement of Photoionization Cross-Section for the Excited States of Atoms: A Review

A review of experimental studies of the measurement of the photoionization cross-section for the excited states of the alkali atoms, alkaline earth atoms, and rare-gas atoms is presented, with emphasis on using multi-step laser excitation, ionization, and the saturation technique. The dependence of the photoionization cross-section from different intermediate states populated in the first step and ionized in the second step are discussed, including results on the photoionization cross-sections measured above the first ionization threshold. Results based on different polarizations of the exciting and the ionizing dye lasers are also discussed. Examples are provided, illustrating the photoionization cross-sections measured using thermionic diode ion detector, atomic beam apparatus in conjunction with a time-of-flight mass spectrometer and DC/RF glow discharge cell as an optogalvanic detection.

Cryogenic atomic hydrogen beam apparatus with velocity characterization.

Precision spectroscopy of hydrogen often relies on effusive thermal atomic beams, and the uncertainty in the velocity distribution of these beams can introduce systematic errors and complicate lineshape models. Here, we present an apparatus capable of high signal-to-noise studies of these velocity distributions at cryogenic temperatures for both ground state (1S) and metastable (2S) hydrogen using a simple time-of-flight technique. We also investigate how the cryogenic nozzle geometry affects these results.

Saturation technique for the measurement of photoionization cross-section of atomic excited states—A review

A review on the saturation technique is presented which has made utilized extensively for the absolute measurements of the photoionization cross section of the atomic excited states. This technique employed two step photoionization, in first step the state whose photoionization cross section to be measured is excited and in second step the excited state is photoionized. The energy of the exciting laser kept fixed and that of the ionizing laser is varied until the photo-ion signal gets saturated. Least square fitting of the photo-ion signals verses the ionizing laser energy density yields the photoionization cross section. Different experimental methodologies in combination with saturation technique have been employed for the measurement of photoionization cross section. These include heat cell with capacitive electrodes, atomic beam apparatus, thermionic diode ion detector, magneto optical traps (MOT), atomic beam-time of flight (TOF) mass spectrometer and DC/RF glow discharge cell. Thermionic diode ion detector and DC discharge cell offer an additional advantage of the measurement of photo absorption cross section (oscillator strength) of the atomic excited states. In addition, the availability of intense tunable dye laser made it possible to probe different region of continuum i.e. to search the regions of copper minima.

Efficient ionization of atomic tin assisted by N-type multiphoton Raman resonances

Abstract We report on the experimental results for laser ionization spectroscopy of atomic tin using a four-color three-step laser ionization scheme in conjunction with an atomic beam apparatus. Typically, the laser ionization efficiency is remarkably limited for certain elements whose thermal population is distributed over its higher lying components of the fine structure at high temperature (e.g. about 2000 K). We demonstrate that the laser ionization efficiency can be increased by simultaneous excitation from the 3 P 0 and 3 P 1 fine-structure components of the 5s25p2 ground-state of atomic tin. This was achieved using two lasers, operating at 283 nm and 301 nm. Furthermore, four-level N-type mutiphoton Raman resonances in this four-color ionization scheme can be utilized to enhance the ionization efficiency allowing an additional ionization process from the third ground state 5 s 2 5 p 2 3 P 2 .

Towards improved measurements of parity violation in atomic ytterbium

We report on progress towards performing precision measurements of parity violation in Yb, in which the theoretical prediction for a strong weak-interaction-induced effect in the 6s^{2} ^{1}S_{0} \rightarrow 5d6s ^{3}D_{1} optical transition at 408 nm has already been confirmed, with a measurement of the effect at the \approx 10 % level of accuracy. With a new atomic-beam apparatus offering enhanced sensitivity, we are aiming at precisely determining the parity violation observable in Yb, which will allow us to probe the distributions of neutrons in different isotopes, investigate physics beyond the Standard Model, as well as to study intra-nucleus weak interactions, through an observation of the anapole moment of Yb nuclei with nonzero spin. We present the experimental principle employed to probe atomic parity violation, describe our new apparatus, and discuss the attained experimental sensitivity as well as the methods for characterizing systematics in these measurements.

Laser induced isotopic studies using time of flight mass spectrometer

The isotopic compositions in lithium and magnesium have been studied using a home built atomic beam- time of flight (TOF) mass spectrometer in conjunction with an atomic beam apparatus and a pulsed Nd:YAG laser. The linearity of the detector for non-selective ionization source has been determined from the measurements of the isotopic compositions in accordance to their natural abundance. In addition, we present two step selective excitation/photoionization of the lithium isotopes via the 3s 2S1/2 excited which reveals the concentration of Li6 enhanced up to 63% as the exciting laser is tuned to the 3s 2S1/2 excited state of Li6.

Direct loading of a large Yb MOT on the transition

We report a robust technique for laser frequency stabilisation that enables the reproducible loading of in excess of 109 Yb atoms from a Zeeman slower directly into a magneto-optical trap (MOT) operating on the transition, without the need for a first stage MOT on the transition. We use a simple atomic beam apparatus to generate narrow fluorescence signals on both the 399 nm transition used for the Zeeman slower and the 556 nm transition. We present in detail the methods for obtaining spectra with a high signal-to-noise ratio and demonstrate error signals suitable for robust frequency stabilisation. Finally we demonstrate the stability and precision of our technique through sensitive measurements of the gravitational sag of the Yb MOT as a function of the intensity of the laser cooling beams, which are in good agreement with theory. These results will be important for efficient loading of the atoms into an optical dipole trap.

Spectroscopic investigation of the 3d 2D → nf 2F transitions in lithium

We report term energies and effective quantum numbers of the odd parity 3d 2D→nf 2F series of lithium using multi-step and multi-photon laser excitation schemes. The experiments were performed using three dye lasers simultaneously pumped by the second harmonic (532nm) of a Q-switched Nd:YAG laser in conjunction with an atomic beam apparatus and thermionic diode ion detector. The first ionization potential of lithium has been determined as 43,487.13±0.02cm−1 from the much extended 3d 2D→nf 2F (17≤n≤70) series. In addition, the oscillator strengths of the 3d 2D→nf 2F (15≤n≤48) transitions have been determined, showing a decreasing trend with the increase in principal quantum number n.

Laser Ablation Atomic Beam Apparatus with Time-Sliced Velocity Map Imaging for Studying State-to-State Metal Reaction Dynamics

We report a newly constructed laser ablation crossed molecular beam apparatus, equipped with time-sliced velocity map imaging technique, to study state-to-state metal atom reaction dynamics. Supersonic metal atomic beam is generated by laser vaporization of metal rod, and free expansion design without gas flow channel has been employed to obtain a good quality of metal atomic beam. We have chosen the crossed-beam reaction Al+O2 to test the performance of the new apparatus. Two-rotational-states selected AlO(X2∑+, v=0, N and N+14) products can be imaged via P(N) and R(N+14) branches of the Δv=1 band at the same wavelength, during (1+1) resonance-enhanced multi-photon ionization through the AlO(D2∑+) intermediate state. In our experiment at 244.145 nm for simultaneous transitions of P(15) and R(29) branch, two rings in slice image were clearly distinguishable, corresponding to the AlO(v=0, N=15) and AlO(v=0, N=29) states respectively. The energy difference between the two rotational levels is 403 cm−1. The success of two states resolved in our apparatus suggests a better collisional energy resolution compared with the recent research study [J. Chem. Phys. 140, 214304 (2014)].

Measurement of the scalar polarizability within the 5P1/2-6S1/2410-nm transition in atomic indium

We have completed a measurement of the Stark shift in ${}^{115}$In within the 410-nm $5{P}_{1/2}$-$6{S}_{1/2}$ transition. We measure the Stark shift constant to be ${k}_{S}=\ensuremath{-}122.92(33)$ kHz/(kV/cm)${}^{2}$, corresponding to a difference in the $6{S}_{1/2}$- and $5{P}_{1/2}$-state polarizabilities, $\ensuremath{\Delta}{\ensuremath{\alpha}}_{0}$ (in atomic units), of $1000.2\ifmmode\pm\else\textpm\fi{}2.7\phantom{\rule{0.16em}{0ex}}{a}_{0}^{3}$. This result is a factor of 30 more precise than previous measurements and is in excellent agreement with a new theoretical value based on an ab initio calculation of the wave functions in this three-valence-electron system. The measurement was performed in an indium atomic-beam apparatus, used a GaN laser diode system, and exploited a FM spectroscopy technique to extract laser transmission spectra under conditions where our interaction region optical depth was typically less than 10${}^{\ensuremath{-}3}$.

Cascaded two-photon spectroscopy of Yb atoms with a transportable effusive atomic beam apparatus

We present a transportable effusive atomic beam apparatus for cascaded two-photon spectroscopy of the dipole-forbidden transition (6s(2)(1)S0↔ 6s7s (1)S0) of Yb atoms. An ohmic-heating effusive oven is designed to have a reservoir volume of 1.6 cm(3) and a high degree of atomic beam collimation angle of 30 mrad. The new atomic beam apparatus allows us to detect the spontaneously cascaded two-photons from the 6s7s(1)S0 state via the intercombination 6s6p(3)P1 state with a high signal-to-noise ratio even at the temperature of 340 °C. This is made possible in our apparatus because of the enhanced atomic beam flux and superior detection solid angle.

Prospects of laser cooling in atomic thallium

One of the most precisely determined upper limits for the electron electric dipole moment (EDM) is set by the thallium (Tl) atomic beam experiment. One way to enhance the sensitivity of the atomic beam setup is to laser cool the Tl atoms to reduce the EDM-like phase caused by the E$\ifmmode\times\else\texttimes\fi{}$v effect. In this report, a cooling scheme based on the $6{P}_{3/2}(F=2)\ensuremath{\leftrightarrow}6{D}_{5/2}({F}^{\ensuremath{'}}=3)$ transition in Tl is proposed. The absolute frequency measurement of this nearly closed-cycle transition was performed in an atomic beam apparatus. Two Ti:sapphire lasers were frequency-doubled using enhancement cavities in X-type configurations to provide the needed 377- and 352-nm light sources for the optical pumping and cooling transitions, respectively. The absolute frequency of this cooling transition is determined to be 851 634 646(56) MHz.

Determination of the Fine Structure Constant Using Helium Fine Structure

We measure 31,908,131.25(30) kHz for the 2(3)}P J=0 to 2 fine structure interval in helium. The difference between this and theory to order mα7 (20 Hz numerical uncertainty) implies 0.22(30) kHz for uncalculated terms. The measurement is performed by using atomic beam and electro-optic laser techniques. Various checks include a 3He 2{3}S hyperfine measurement. We can obtain an independent value for the fine structure constant α with a 5 ppb experimental uncertainty. However, dominant mα8 terms (potentially 1.2 kHz) limit the overall uncertainty to a less competitive 20 ppb in α.

Interaction of the6p2S10broad resonance with5dndJ=0autoionizing resonances in barium

We present even-parity autoionizing resonances in barium using two-step laser excitation via $5d6p$ ${^{1}P}_{1}$ intermediate level covering the energy region from the first ionization threshold to the $5d$ ${^{2}D}_{5/2}$ limit. The data are achieved using an atomic beam apparatus in conjunction with a time-of-flight mass spectrometer and a Nd:YAG pumped dye laser system. True line shape of the $6{p}^{2}$ ${^{1}S}_{0}$ autoionizing resonance at $44\text{ }850\ifmmode\pm\else\textpm\fi{}50\text{ }{\text{cm}}^{\ensuremath{-}1}$, its width $(980\ifmmode\pm\else\textpm\fi{}50\text{ }{\text{cm}}^{\ensuremath{-}1})$, and the absolute value of photoionization cross section $(185\ifmmode\pm\else\textpm\fi{}35\text{ }\text{Mb})$ are reported. A combination of parallel and perpendicular polarization vectors of the exciting and the ionizing dye lasers reveals unambiguous $J$-value assignments of the excited states. The interactions between the $6{p}^{2}$ ${^{1}S}_{0}$ broad feature with the $5{d}_{5/2}nd$ $J=0$ Rydberg series have been simulated using the phase-shifted multichannel quantum defect theory.

Optical spectroscopy of rubidium Rydberg atoms with a 297 nm frequency-doubled dye laser

We demonstrate Doppler-free, purely optical detection of laser-excited rubidium Rydberg atoms in a room-temperature gas cell. The Rydberg atoms are excited with a frequency-doubled dye laser at 297 nm in a single-excitation step from the ground state; the detection is performed with a 780 nm diode laser in a scheme similar to electron shelving. Laser spectroscopy of Rydberg transitions is demonstrated, and a frequency-doubled dye is stabilized to one Rydberg transition in the UV. The performance of this stabilization is measured with an atomic-beam apparatus and a time of flight experiment.

Absolute frequency measurement of the magnesium intercombination transitionS01→P13

We report on a frequency measurement of the $(3{s}^{2})^{1}S_{0}\ensuremath{\rightarrow}(3s3p)^{3}P_{1}$ clock transition of $^{24}\mathrm{Mg}$ on a thermal atomic beam. The intercombination transition has been referenced to a portable primary Cs frequency standard with the help of a femtosecond fiber laser frequency comb. The achieved uncertainty is $2.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$, which corresponds to an increase in accuracy of six orders of magnitude compared to previous results. The measured frequency value permits the calculation of several other optical transitions from $^{1}S_{0}$ to the $^{3}P_{J}$-level system for $^{24}\mathrm{Mg}$, $^{25}\mathrm{Mg}$, and $^{26}\mathrm{Mg}$. We describe in detail the components of our optical frequency standard such as the stabilized spectroscopy laser, the atomic beam apparatus used for Ramsey-Bord\'e interferometry, and the frequency comb generator and discuss the uncertainty contributions to our measurement including the first- and second-order Doppler effect. An upper limit of $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ in $1\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ for the short-term instability of our optical frequency standard was determined by comparison with a quartz oscillator disciplined to the signal received from the global positioning system (GPS).

Alternate technique for simultaneous measurement of photoionization cross-section of isotopes by TOF mass spectrometer

New measurements of photoionization cross-sections of the lithium isotopes are reported employing a Time of Flight (TOF) mass spectrometer in conjunction with an atomic beam apparatus. Using a two-step selective photoionization and saturation technique, we have simultaneously measured the photoionization cross-section of the 2p excited state of both the isotopes Li6 and Li7 as 15±2.5 Mb and 18 ±2.5 Mb where as the corresponding number densities have been determined as N0≈5.3×1010 atoms/cm3 and N0≈6.2×1011 atoms/cm3 respectively.

Measurements of photoionization cross sections from the 5s5p 1P1 and 5s6s 1S0 excited states of strontium

We present new measurements of the photoionization cross section from the 5s5p 1P1 state employing two-step excitation and from the 5s6s 1S0 state using two-photon excitation and then a second laser for subsequent ionization in each case. The two dye lasers, pumped by a common Nd:YAG laser, have been used in conjunction with a thermionic diode ion detector in one set of experiments and an atomic beam apparatus in the second experiment. The photoionization cross sections have been measured at six different wavelengths between 355 nm and 410 nm. The absolute value of the cross section at the peak of the (4d2+5p2) 1D2 autoionizing resonance is determined as 5450 (18%) Mb. The photoionization cross section from the 5s6s 1S0 state is estimated as 0.41 (16%) Mb.

Three-step laser excitation of the 6p3/2ns, nd, ng autoionizing Rydberg levels via the 6p5f 1/2[5/2]2 level of lead

Odd parity autoionizing Rydberg levels of atomic lead in the energy region above the 6p1/2 ionization threshold have been investigated using three-step laser excitation in conjunction with an atomic beam apparatus. The 6p3/2ns (J = 1, 2), 6p3/2nd (J = 1, 2, 3) and 6p3/2ng (J = 2, 3) levels have been observed from the 6p5f 1/2[5/2]2 intermediate level. Energy values and FWHM of forty levels belonging to the 6p3/2ns, 6p3/2nd and 6p3/2ng configurations are presented. Six levels based on the 6p3/2ng (5, 13 ≤n ≤15) configurations and three levels attached to the 6p3/28d configuration are reported for the first time. The present study of the low-lying autoionizing levels attached to the 6p3/25g (J = 2, 3) configuration completes the series adjacent to the 6p1/2 limit.

Novel rubidium atomic beam with an alkali dispenser source

We describe a novel atomic beam apparatus with a resistively heated alkali dispenser source and a cold-pumped intermediate chamber. Using laser fluorescence spectroscopy we have measured the atomic density to be 3×1011atoms∕m3 and the total flux to be 5×108atoms∕s in a 0.3cm diameter beam. We have also characterized the velocity distribution of the source based on the Doppler-shifted fluorescence spectrum. The compact geometry, flexibility, and simplicity of the beam may make it useful as an optical frequency reference or for experiments on atom-cooling.