Doppler-free spectroscopy using magnetically induced dichroism of atomic vapor: a new scheme for laser frequency locking

We demonstrate a Doppler-free spectroscopic method that we test on ⁸⁷Rb and ⁸⁵Rb vapor. By using a magnetic field to induce a dichroism on the sample, we generate a dispersive signal with low background, which allows us to lock a diode laser even on small spectroscopic features. We elaborate the advantages of this simple and easy method by comparing it to other methods. Received 15 October 2002 Published online 17 December 2002     

Optical detection system for laser cooling and precision laser spectroscopy of relativistic highly charged ions at the CSRe

Laser cooling and precision laser spectroscopy experiments of relativistic highly charged ions are being prepared at the heavy-ion experimental cooler storage ring (CSRe). Optical detection of fluorescence photons, emitted from the laser-excited ions, is extremely important for both powerful methods. In this paper, we briefly report on the current status of the existing optical detectors and also on their performance during laser cooling of relativistic Li-like ¹⁶O⁵⁺ ion beams at the CSRe. In addition, we introduce the designs for our new optical detection systems, which have much higher photon detection efficiencies and can cover a much broader wavelength range. These detector systems will be used for the upcoming laser spectroscopy experiment of Li-like ¹⁶O⁵⁺ ions, as well as for future laser spectroscopy experiments with other highly charged ions.     

Vacuum ultraviolet resonance line radiation source from rare gas atoms and ions for UHV photoelectron spectroscopy

A source and differential pumping system for producing high intensity resonance line radiation from rare gas atoms and ions for ultrahigh vacuum (UHV) photoelectron spectroscopy has been developed. Photoelectron count rates from a gold sample, as measured with a double-pass cylindrical mirror analyzer at pass energy 15 eV and 0.10 eV resolution, are ～ 300,000 c s^?1 for the He(I) (21.22 eV) line and ～30000 c s^?1 for the He(II) (40.81 eV) line. The source design is based on the principle of the electrostatic charged particle oscillator and is capable of sustaining discharges over the pressure range 1 to ～ 10^?6 torr. The discharge segment consists of a cylindrical cold cathode surrounding two tungsten rod anodes which are held at high positive potential. Three stages of differential pumping are employed in order that the vacuum in the main spectrometer chamber can be maintained at 2 × 10^?10 torr during operation. The calculated helium flow reaching the main chamber under these conditions is < 101 s^?1. Details of the construction and operating characteristics of the source are presented.     

Half-open Penning trap with efficient light collection for precision laser spectroscopy of highly charged ions

We have conceived, built and operated a ’half-open’ cylindrical Penning trap for the confinement and laser spectroscopy of highly charged ions. This trap allows fluorescence detection employing a solid angle which is about one order of magnitude larger than in conventional cylindrical Penning traps. At the same time, the desired electrostatic and magnetostatic properties of a closed-endcap cylindrical Penning trap are preserved in this configuration. We give a detailed account on the design and confinement properties, a characterization of the trap and show first results of light collection with in-trap produced highly charged ions.     

A scheme for the generation of two-mode atomic laser

The quantum dynamic behavior of the system composed of V-type three-level atomic Bose-Einstein con-densate (BEC) interacting with two-mode coherent light field has been studied. The results show that the atoms of V-type three-level atomic BEC, which are excited to higher-level states under the action of light field, still keep their properties of coherent states. It demonstrates theoretically that two-mode atomic laser may be prepared by V-type three-level atomic BEC.     

Precise measurement of the line width of the photoassociation spectra of ultracold molecules by a frequency shifter

We propose a technique to precisely measure the line width of the photoassociation spectra of the excited cesium molecule by using a frequency shifter to generate two laser beams with a precise frequency difference. A series of photoassociation spectra are recorded with two laser beams induced molecular lines, whose peak separation serves as an accurate frequency ruler to measure the line width of the photoassociation (PA) spectra. The full width half maximum line width was studied as a function of PA laser intensity. The extrapolated value at zero laser intensity is (34.84 ± 0.22) MHz. By analyzing other broadening mechanisms, a value of (32.02 ± 0.70) MHz was deduced. It is shown that this scheme is inexpensive, simple, robust, and is promising for applications in a variety of other atomic species.     

High-power Ti:sapphire lasers for spectroscopy of antiprotonic atoms and radioactive ions

The ASACUSA collaboration has developed injection-seeded Ti:sapphire lasers of linewidth Γ_pl ～ 6 MHz, pulse energy 50–100 mJ, and output wavelength λ?=?726–941?nm. They are being used in two-photon spectroscopy experiments of antiprotonic helium atoms at the Antiproton Decelerator (AD) of CERN. Ti:sapphire lasers of larger linewidth Γ_pl ～ 100 MHz but more robust design will also be used in collinear resonance ionization spectroscopy (CRIS) experiments of neutron-deficient francium ions at the ISOLDE facility.     

Precise measurement of the line width of the photoassociation spectra of ultracold molecules by using a frequency shifter

We propose a technique to precisely measure the line width of the photoassociation spectra of the excited cesium molecule by using a frequency shifter to generate two laser beams with a precise frequency difference. A series of photoassociation (PA) spectra are recorded with two laser beam induced molecular lines, whose peak separation serves as an accurate frequency ruler to measure the line width of the PA spectra. The full width half maximum line width was studied as a function of PA laser intensity. The extrapolated value at zero laser intensity is (34.84 ± 0.22) MHz. By analyzing other broadening mechanisms, a value of (32.02 ± 0.70) MHz was deduced. It is shown that this scheme is inexpensive, simple, robust, and is promising for applications in a variety of other atomic species.     

High resolution laser spectroscopy of metallic atoms and molecules: Storage of singly and doubly charged ions transferred from externally generated laser plasmas

A radio-frequency (RF) ion trap has been constructed for high resolution laser spectroscopy of metallic ions. Ions in externally generated laser plasma have been directly introduced into the RF ion trap. An Nd:YAG laser is used to vaporize and ionize sample metals placed behind a ring electrode. Both hyperbolic and cylindrical electrodes are successfully used for confinement of the ions. Trapped ions are detected either with a quadrupole mass spectrometer or with a photomultiplier for the measurement of laser-induced fluorescence. Metallic ions such as Ca⁺, Ba⁺, La⁺, Nd⁺, Tm⁺, Lu⁺, and Ta⁺ have been confined for the time range of several to 20 minutes in the presence of He buffer gas, and a doubly charged ion Ba²⁺ for several seconds. Some ions like Nd⁺, Lu⁺, Hf⁺, and Ta⁺ are found to be highly reactive with background gaseous molecules.     

About a possibility of a decrease in the radiative width of excited levels of atoms and nuclei

The radiative width of quasi-energy states of a system, interacting with an external monochromatic field, is found in the present work. It is shown that a new physical effect — the formation of states with anomalous large life times — is possible in such systems.     

Study of a line width estimation model for laser micro material processing using a photodiode

Estimation of the line width for a laser marking on the silicon wafer is very important to improve the productivity of the final product which use nonpackaged chip. Until now, only theoretical and numerical estimation models have been studied. However, it is not easy for these models to apply to real systems. In this study, a process monitoring system was used to develop an estimation model for the laser marking width. The plasma produced by interaction between the laser and the wafer was measured using an optical sensor. For each laser power setting, the correlation between the signal acquired from the optical sensor and the resulting line width was analyzed. Estimation models were developed for laser marking width through statistical regression analysis and an artificial neural network algorithm.     

A laser system for the spectroscopy of highly charged bismuth ions

We present and characterize a laser system for the spectroscopy on highly charged ²⁰⁹Bi⁸²⁺ ions at a wavelength of 243.87?nm. For absolute frequency stabilization, the laser system is locked to a near-infra-red laser stabilized to a rubidium transition line using a transfer cavity based locking scheme. Tuning of the output frequency with high precision is achieved via a tunable rf offset lock. A?sample-and-hold technique gives an extended tuning range of several THz in the UV. This scheme is universally applicable to the stabilization of laser systems at wavelengths not directly accessible to atomic or molecular resonances. We determine the frequency accuracy of the laser system using Doppler-free absorption spectroscopy of Te₂ vapor at 488?nm. Scaled to the target wavelength of 244 nm, we achieve a frequency uncertainty of σ _{244 nm}=6.14?MHz (one standard deviation) over six days of operation.     

Mechanisms for formation of a population inversion in the levels of metal atoms and ions in a plasma jet

The mechanisms for formation of population inversions in plasma jets of lithium, sodium, cadmium, and strontium vapor are studied. The primary contribution to forming a population inversion over the transitions of the alkali atoms is found to be three-body electron-ion recombination, and for transitions between the ion levels of strontium and cadmium, inelastic collisions with the buffer gas play an important role. Using helium instead of argon as a buffer leads to a substantial increase in the magnitude of the inversion. Zh. Tekh. Fiz. 68, 134–135 (June 1998)     

A diode laser system for spectroscopy of the ultranarrow transition in ytterbium atoms

A narrow-line diode laser system has been developed for high-resolution spectroscopy of the magnetic quadrupole transition in ytterbium (Yb) atoms at 507 nm. The system consists of an extended-cavity laser diode at 1014 nm, a tapered amplifier and a periodically poled lithium niobate nonlinear crystal which converts the wavelength from 1014 nm to 507 nm. We have stabilized the laser frequency and reduced the linewidth below 1 kHz by tightly locking the laser to a high-finesse optical cavity. By using the developed laser system, we have successfully observed the ultranarrow transition in Yb atoms. Furthermore, our simple and compact laser system could be a high performance and portable frequency reference using iodine spectra whose linewidth becomes less than 50 kHz around 507 nm. We have also demonstrated spectroscopy of iodine molecules. PACS 32.30.-r; 07.60.-j     

Inclusion of the exchange-correlation effects in Ab initio methods for calculating the plasmon dispersion and line width in metals

A self-consistent analog of the Hubbard local-field factor accounting for a real band structure of the metal under investigation is proposed for the calculation of the exchange-correlation corrections to the randomphase approximation. The plasmon energy and the plasmon line width for potassium are calculated as a function of the wave vector. The calculations are performed within the random-phase approximation and with corrections for the local field. It is shown that the results of the calculations are in good agreement with the experimental data. This indicates that, first, the corrections to the random-phase approximation should be taken into account for metals with a low electron density and, second, the local-field factor approximation is an appropriate approach.     

Zeeman effect of atomic uranium in the high lying odd levels measured by laser induced fluorescence spectroscopy

We measured Zeeman effect of atomic uranium spectra using laser induced fluorescence spectroscopy, and derived the J-value and g-factor of the second step levels. J-values and g-factors of high lying odd levels could be obtained. These data, especially the g-factors, have almost been unknown so far. We could verify our method which can be useful to measure J-values and g-factors of high lying levels of complex atoms like uranium. Received 27 July 1999 and Received in final form 30 November 1999     

Radio-frequency laser double-resonance spectroscopy of trapped171Yb ions and determination of line shifts of the ground-state hyperfine resonance

The paper reports on radio-frequency laser double-resonance experiments on¹⁷¹Yb ions confined in a cylindrically symmetric electrodynamic trap in the presence of helium buffer gas. The optical-excitation scheme relies on the selective excitation of a cycling hyperfine component of the = 370 nm resonance transition. Additional excitation of a transition at = 935 nm prevents population trapping of ions in the metastable² F _7/2 level. Using a maser reference, the ground-state hyperfine resonance frequency is measured under conditions of a systematic variation of confinement conditions. Kinetic temperatures and the resulting relativistic resonance shifts are inferred from the inhomogeneous broadening of the optical resonance transition. Shifts of the hyperfine resonance frequency due to quadratic Stark effect and collisions are determined. By extrapolation, the unperturbed transition frequency is determined as 12 642 812 118.471 (9) Hz.