S. Noehte

Fast laser beam position control with submicroradian precision

Abstract Precise control of spatial position and pointing stability of the output beam of a cw free-jet ring dye laser was realized. The fast opto-electronic feedback device, based on four-quadrant photodiode detectors and piezo-driven mirrors, limits beam angle variations to 4 × 10 -7 rad. The importance of the method is discussed and the efficiency is illustrated.

Dye laser saturation spectroscopy of the 23S1-23P transition in6, 7Li+ ions

The metastable 23S1 state and the short lived 23P states of the helium-like6, 7Li+ ion spectra have been investigated by dye laser saturation spectroscopy in a low-energy Li+ ion-beam and fluorescence light detection. The hyperfine structure splittings of all the levels, the 23P fine structure intervals and the isotope shift of the 23S1-23P transitions have been measured. These measurements were made by application of a specially constructed tunable dye laser system capable of single-mode laser scans over more than 60 GHz.

Laser-microwave spectroscopy of lithium ions: 23S1 hyperfine structure of7Li+

The hyperfine structure (hfs) splittings of the metastable 1s2s3S1 state of7Li+ have been measured with combined laser optical pumping and microwave resonance. A lowenergy Li+ ion beam, optically excited by an intersecting laser beam, passed a waveguide where radio frequency transitions were induced. The resulting population transfer among the hfs levels of the3S1 was detected via the change in intensity of the fluorescence light from a second crossing region of laser light and ion beam located past the waveguide. The magnetic hfs constantA(7Li+, 1s2s3S1) was measured and compared with theory. A deviation of the two transition frequenciesν(F=3/2−F=5/2) andν(F=1/2−F=3/2) from the interval rule is due to a depression of theF=3/2 hfs sublevel, caused by mixing of the 23S1 and 21S0 states via hyperfine interaction. This shift was never observed so far in a two-electron spectrum, because of absence ofI>1/2 isotopes in He, the only two-electron atom investigated spectroscopically with high precision. The size of the shift is in fair agreement with a theoretical estimate.

An automatic michelson interferometer with frince dropout correction

Abstract An automatic Michelson-type fringe counting interferometer (Lambda-meter) allowing for interpolation to 1/50 of a wavelength is described. The movable part of the interferometer consists of a carriage which slides on two polished steel bars and transports two corner cube retroreflectors. A missing-fringe digital control logic identifies and instantaneously corrects for laser interference fringe dropouts, caused by short-time laser light instabilities. By exact superposition of the beams of a He 22 Ne laser stabilized to a line of I 2 and the laser to be measured in the interferometer, absolute wavelength measurements with a precision of 1 to 2 parts in 10 8 were performed. Real-time control of the measurement, data acquisition and calculation of the wavelength are provided by a microcomputer.

Confocal Fabry-Perot microwave resonator at 48 GHz for high-resolution spectroscopy

A high-Q confocal Fabry-Perot microwave resonator for precision spectroscopy of atoms, ions and molecules is described, giving convenient access to the overlap region of interacting species, microwave field and light. Microwave power is coupled with almost 100% efficiency into the interferometer by means of a small copper wire dipole antenna. The concept of an uncomplicated and inexpensive frequency stabilisation of microwave sources through coupling to a Fabry-Perot reference resonator is discussed.

Triplet-singlet interaction in the 1s 2s3S1 hyperfine splitting of he-like Li+

The hyperfine structure (hfs) interaction between the metastable 23S1 and 21S0 states in6, 7Li+ causes very small equal and opposite energy level shifts,δ, in the two levels having the same total angular momentum quantum numberF=I. This amounts to 12ppm with respect to the total hfs splitting of 30 GHz for the7Li+ 23S1 state and has been measured for the first time directly for the case of a core-free electronic system by combined laser-microwave spectroscopy. A new calculation ofδ with accurate integral-transform 21S0 and 23S1 wave functions is reported. Configuration interactions and electron exchange and correlation effects, which differ for parallel (3S1) and antiparallel (1S0) spins, are treated in detail in order to obtain very good agreement between measured and theoretical values for this tiny perturbation. A complete understanding ofδ is indispensable for extracting fundamental constants from two-electron spectroscopic data.

Effects of nuclear structure and triplet-singlet interaction in the 1s2s3S1 hyperfine multiplet of Li+

From combined laser-microwave spectroscopy of the 1s2s3S1 hyperfine structure (hfs) splittings in helium-like6,7Li+ ions, the magnetic dipole hfs interaction constantA and a small displacement σ of theF=1 substate, caused by 1s2s3S1−1s2s1S0 hyperfine mixing, have been obtained. Analysis ofA yields nuclear structure effects in the hfs splittings of the isotopes6,7Li+. The result of a calculation of6,7δ with accurate integral-transform 21S0 and 23S1 wave functions is presented.

Laser-Microwave Spectroscopy of Li+ Ions

The Li+ ion, a two-electron system like He is of fundamental interest as a testing ground for atomic structure theory. This paper reports on combined laser-microwave measurements of hyperfine structure (hfs) splittings of the metastable (τ ≈ 50 sec) ls2s 3S1 state in 6,7Li+ and of the short-lived (τ ≈ 43 nsec) ls2p 3P multiplet in 7Li+. The precise data from this experiment should stimulate improved ab initio calculations of the 2 3S1 hfs not available yet. It is also an aim of this experiment to test the very precise theoretical hfs [1] and fine structure [2] values existing for the 2 3P states. For very accurate 2 3P fine structure measurements in 4He see [3].

A Computer-Controlled Two-Dye-Laser Heterodyne Spectrometer of High Precision

A computer-controlled heterodyne spectrometer [1,2], consisting of two self-built free-jet ring dye lasers (output power 600 mW each), was constructed for optical measurements of high precision and excellent signal-to-noise ratio. It substitutes 1. Fabry-Perot interferometers of exactly known and constant free spectral range for the precise calibration of laser frequency scans; 2. expensive microwave systems, including different sets of microwave sources, amplifiers, waveguides, tunable resonant cavities, etc. in order to cover large frequency ranges, e.g. from 1 to 150 GHz.