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We report on an external cavity diode laser at 972 nm stabilized to a mid-plane mounted Fabry-Perot (FP) resonator with a finesse of 400000. The 0.5 Hz optical beat note line width between two similar lasers (Allan deviation 2 × 10-15) is limited by thermal noise properties of two independent FP resonators. The long term drift of the FP resonator and mirror substrates made from Ultra-Low-Expansion glass (ULE) is small and can be well predicted on time intervals up to many hours if the resonator is stabilized at the zero thermal expansion temperature Tc. Using a Peltier element in a vacuum chamber for temperature stabilization allows stabilization of the FP cavity to Tcwhich is usually below the room temperature. Beat note measurements with a femtosecond optical frequency comb referenced to a H-maser during 15 hours have shown a well defined linear drift of the FP resonance frequency of about 60 mHz/s with residual frequency excursions of less than ±20 Hz.

Les propriétés de cohérence ainsi que la très courte durée des impulsions de la génération d'harmonique d'ordre élevé ont été appliquées à des applications de type pompe/sonde utilisant l'interférométrie dans le domaine XUV. Nous avons pour la première fois mesuré dans deux expériences différentes les densités électroniques de plasmas par interférométrie fréquentielle et spatiale dans le domaine XUV avec une résolution temporelle de quelques dizaine de femtosecondes.

The magneto-optical properties of cesium vapor near a glass surface have been studied by using selective reflection. We have observed sub-Doppler structures in the magneto-rotation and magnetic circular dichroism spectra. The spectral narrowing can be explained by the transient polarization behavior of cesium atoms due to wall collisions. A simple model, which takes atom-wall collisions and the mixing of hyperfine levels by the magnetic field into account, gives a good qualitative description of the observed spectra. Small discrepancies are likely to be due to long-range atom-surface interactions.

Abstract: We report on an external cavity diode laser at 972 nmstabilized to a mid-plane mounted Fabry-Perot (FP) resonator with afinesse of 400000. The 0.5 Hz optical beat note line width betweentwo similar lasers (Allan deviation 2 × 10-15) is limitedby thermal noise properties of two independent FP resonators. Thelong term drift of the FP resonator and mirror substrates made fromUltra-Low-Expansion glass (ULE) is small and can be well predictedon time intervals up to many hours if the resonator is stabilized atthe zero thermal expansion temperature Tc. Using a Peltierelement in a vacuum chamber for temperature stabilization allowsstabilization of the FP cavity to Tc which is usually below theroom temperature. Beat note measurements with a femtosecond opticalfrequency comb referenced to a H-maser during 15 hours have shown awell defined linear drift of the FP resonance frequency of about 60 mHz/s with residual frequency excursions of less than ±20 Hz.

We describe the theory and experimental realization of an ultrafast phase-matched electrooptic modulator, working with 486 nm light and a modulation frequency of 84 GHz. To achieve phase matching for arbitrarily high modulation frequencies the laser beam is guided with several internal total reflections along a zig-zag path through a LiTaO3 crystal. The method was studied experimentally with a 84 GHz modulator and a highly stable 486 nm dye laser. The maximum modulation index of this setup was about 5.0%. Beat signals between either the first- or the second-order sidebands and another laser were observed. This modulator was used to directly measure the 671 GHz 1S–2S isotope shift of hydrogen and deuterium with radio-frequency accuracy.

Conclusion Recently developed high-power semiconductor laser amplifiers offer new ways to construct laser sources for high-resolution spectroscopy in the blue and ultraviolet. Such sources overcome a number of limitations that are connected to the standard single-mode ring laser systems. A source of this kind can contribute significantly to the feasibility of antihydrogen spectroscopy. Experiments with hydrogen will also benefit greatly. The construction of an optical hydrogen frequency standard becomes realistic and experiments with demanding atomic preparation techniques as, for instance, optical cooling in magnetic traps are facilitated.

Experiments with electrons and ions in a combined trap are reported. The unique capability to confine particles with opposite charge and very different mass simultaneously in the same spatial region makes the combined trap a promising device for future synthesis of antihydrogen.

Doppler-free saturation spectroscopy in the regime of strong pumping intensities and optically thick atomic samples is investigated experimentally and theoretically. It is shown that a very high signal-to-background ratio can be obtained and, at the same time, subnatural linewidths can be reached. Further contrast and linewidth improvements can be attained by supplementing the primary depleted pumping beam with a second pumping beam. By using the signal beam from a first setup as the pumping beam for a second identical arrangement, extreme values for contrast and linewidth should be attainable.

A method that allows the calculation of magnetic fields produced by cylindrically symmetric configurations of permanent magnets and high permeability materials is presented. The method is based on a non-iterative finite-element algorithm and can be utilized on small-scale computing facilities. As an example, the design of a magnetic trap for neutral atoms is discussed. Comparisons of calculations with analytical and experimental data are also reported.

By use of a cw dye laser, the resonance-fluorescence method is used to make absolute density measurements of sodium vapor from 10^2 atoms/cm^3 at -28°C to 10^11 atoms/cm^3 at 144°C. The results are compared with other measurements at higher temperature by a thermodynamic analysis. A new vapor-pressure curve is derived, which is slightly different from previous curves based on the higher-temperature measurements. The application of laser resonance fluorescence to other species is also discussed. In particular, a scheme for detecting sodium-quark atoms, if they exist, with a sensitivity of n_q/n_B~10^-15, is proposed.

Generation of 22 mW of narrow-band radiation near 430 nm was achieved by frequency doubling the 100-mW output of a single-mode GaAlAs diode laser near 860 nm. A monolithic potassium niobate ring resonator serves as the nonlinear medium and at the same time as a reference cavity for the diode-laser frequency, which optically self-locks to a cavity resonance frequency. Continuous scans of the second-harmonic frequency over 330 MHz are achieved with the electro-optic effect. The results demonstrate a portable, economical, and efficient source of coherent blue light.

We have observed optical pumping signals from Cs atoms trapped in solid4He. While the longitudinal electronic spin relaxation timeT1 is found to be in the range of 1–2 s, the transverse relaxation timeT2, as inferred from magnetic resonance linewidths has a lower bound of 150 µs, and is determined by magnetic field inhomogeneities. We present a quantitative discussion of how paramagnetic species trapped in solid He might be used in a highly sensitive search for permanent atomic electric dipole moments.

The first implantation of neutral Ba and Cs atoms into solid4He is reported. We discuss details of the experimental setup and techniques used to load the helium with atoms at concentrations of 108 cm-3. If photodissociation of Cs molecules and clusters is performed twice per hour this atomic concentration can be kept without a second implantation for almost a day. From the optical spectra of Ba in solid helium we infer no significant difference in the trapping site with respect to that in liquid helium.

We show that for atoms trapped in a liquid He matrix the excitation and emission spectra can be quantitatively described by the bubble model which treats the matrix as an incompressible continuous medium. Comparison with experimental results shows that the model also holds for a solid matrix. The model is only valid in the case where the attractive He-He interaction dominates the attractive part of the foreign atom-helium interaction. Its failure in the case of implanted Na atoms is discussed.

Construction details and operating characteristics are given for a narrowband pulsed dye laser system, pumped by a nitrogen laser, that offers very linear reproducible frequency tuning over continuous ranges of 150 GHz and more, at a bandwidth down to 25 MHz. A diffraction grating in Littrow configuration, a tilted Fabry-Perot interferometer inside the cavity, and an optical external confocal filter interferometer are the wavelength-selective elements. Simultaneous scanning of these elements is accomplished without mechanically moving parts by changing the gas pressure in an enclosing chamber.

One can enhance second-harmonic generation in angle-tuned crystals by focusing the fundamental to an elliptical waist in the crystal. We present a general analysis for type I phase-matched uniaxial and biaxial crystals that will find particular application in the generation of harmonics from diode lasers.

A pulsed tunable dye laser with a bandwidth of less than 0.004 Å, repetitively pumped by a nitrogen laser, is described. An intracavity beam expanding telescope together with a diffraction grating in Littrow mount and a tilted Fabry-Perot etalon provide convenient, very reproducible wavelength tuning and good stability. Output peak powers in the kilowatt range at 5–100 nsec pulse width and repetition rates up to 100 pps can be generated from the near-ultraviolet throughout the visible spectrum.

Dual-comb spectroscopy is extended to the visible spectral range with two short-pulse frequency-doubled free-running ytterbium-doped fiber lasers. When the spectrum is shifted to other domains by nonlinear frequency conversion, tracking the relative fluctuations of the femtosecond oscillators at their fundamental wavelength automatically produces the correction signal needed for the recording of distortion-free spectra. The dense rovibronic spectrum of iodine around 19,240  cm^−1 is recorded within 12 ms at Doppler-limited resolution.

We report on the first (to our knowledge) demonstration of nonlinear dual-frequency-comb spectroscopy. In multi-heterodyne femtosecond Raman-induced Kerr-effect spectroscopy, the Raman gain resulting from the coherent excitation of molecular vibrations by a spectrally narrow pump is imprinted onto the femtosecond laser frequency comb probe spectrum. The birefringence signal induced by the nonlinear interaction of these beams and the sample is heterodyned against a frequency comb local oscillator with a repetition frequency slightly different from that of the comb probe. Such time-domain interference provides multiplex access to the phase and amplitude Raman spectra over a broad spectral bandwidth within a short measurement time.

We report on a low-noise diode laser oscillator at 972?nm actively stabilized to an ultrastable vibrationally and thermally compensated reference cavity. To increase the fraction of laser power in the carrier we designed a 20?cm long external cavity diode laser with an intracavity electro-optical modulator. The fractional power in the carrier reaches 99.9%, which corresponds to an rms phase noise of φrms2=1?mrad^2 in 10?MHz bandwidth. Using this oscillator, we recorded 1S–2S spectra in atomic hydrogen and have not observed any significant loss of the excitation efficiency due to phase noise multiplication in the three consecutive two-photon processes.

We report a new absolute frequency measurement of the Cs 6s-8s two-photon transition measured using frequency comb spectroscopy. The fractional frequency uncertainty is 5×10^−11, a factor of 6 better than previous results. The comb is derived from a stabilized picosecond laser and referenced to an octave-spanning femtosecond frequency comb. The relative merits of picosecond-based frequency combs are discussed, and it is shown that the AC Stark shift of the transition is determined by the average rather than the much larger peak intensity.

We have created a broad spectrum spanning more than an optical octave by launching femtosecond pulses from a battery operated Cr:LiSAF laser into a photonic crystal fiber. Despite the massive broadening in the fiber, the comb structure of the spectrum is preserved, and this frequency comb is perfectly suited for applications in optical frequency metrology.

The absolute frequency of the In^+5s^2 S1_0–5s5p P3_0 clock transition at 237 nm was measured with an accuracy of 1.8 parts in 10^13. Using a phase-coherent frequency chain, we compared the S1_0–P3_0 transition with a methane-stabilized He–Ne laser at 3.39 µm, which was calibrated against an atomic cesium fountain clock. A frequency gap of 37 THz at the fourth harmonic of the He–Ne standard was bridged by a frequency comb generated by a mode-locked femtosecond laser. The frequency of the In^+ clock transition was found to be 1?267?402?452?899.92?(0.23) kHz, the accuracy being limited by the uncertainty of the He–Ne laser reference. This result represents an improvement in accuracy of more than 2 orders of magnitude over previous measurements of the line and now stands as what is to our knowledge the most accurate measurement of an optical transition in a single ion.s

We demonstrate that high-order harmonics generated by short, intense laser pulses in gases provide an interesting radiation source for extreme ultraviolet interferometry, since they are tunable, coherent, of short pulse duration, and simple to manipulate. Harmonics from the 9th to the 15th are used to measure the thickness of an aluminum layer. The 11th harmonic is used to determine the spatial distribution of the electron density of a plasma produced by a 300-ps laser. Electronic densities higher than 2–10^20 electrons/cm^3 are measured.

We have used the comb of optical frequencies emitted by a mode-locked laser as a ruler to measure differences of as much as 20 THz between laser frequencies. This is to our knowledge the largest gap measured with a frequency comb, with high potential for further improvements. To check the accuracy of this approach we show that the modes are distributed uniformly in frequency space within the experimental limit of 3.0 parts in 10^17. By comparison with an optical frequency comb generator we have verified that the mode separation equals the pulse repetition rate within the experimental limit of 6.0 parts in 10^16.

We have generated up to 1 mW of single-mode cw ultraviolet radiation between 243 and 247 nm by mixing the outputs of an ultraviolet argon-ion laser at 363.8 nm and a red LD700 dye laser in ammonium dihydrogen phosphate. The dye-laser intensity within the crystal is enhanced by using an actively locked passive ring cavity. Wavelengths near 243.1 nm are of particular interest for the high-resolution two-photon spectroscopy of atomic hydrogen.

Two frequency components of an IR laser beam near 980??nm are simultaneously coupled into two adjacent longitudinal modes of a passive ring resonator. A potassium niobate crystal inside the resonator converts the circulating IR light into coherent blue radiation. The total conversion efficiency is enhanced by a factor of 1.4 compared with that of conventional single-mode intracavity second-harmonic generation with the same circulating total power, and we obtain a total output power of 560??mW from 780-mW IR light incident upon the cavity. The spectra of the generated blue radiation and the circulating IR light contain a number of equidistant frequency components that are due to consecutive sum- and difference-frequency mixing.

He4 2 ^3S_1?2 P3 transitions at 1083??nm were laser probed in the presence of radiation that coupled the 2 P3 level with the 3 ^3S_1 level in a ladder scheme. The metastable helium that was used was produced in a rf discharge. Significant atomic birefringence was detected, in addition to complete electromagnetically induced transparency. A simple theoretical model explains the experimental results.

We study a new type of optical lattice in which the localized atoms experience a much reduced optical pumping and fluorescence rate. An optical standing wave is tuned to the blue of the F = 2 ? F = 2 transition of the ^87Rb D_2 line and induces periodic optical potentials by coupling the F = 2 ground state to both the F = 2 and F = 3 excited states. A Sisyphus mechanism efficiently cools the atoms into the lattice sites. We adiabatically release the atoms from the optical lattice and measure their momentum distribution with a resolution of one third of a single photon recoil. This allows us to determine the population of the two lowest energy bands in the optical lattice (44% and 20%).

We demonstrate specular reflection of a thermal rubidium beam with low-power laser light. The atoms are reflected by the gradient force of an evanescent wave enhanced by surface plasmons excited in a thin silver layer. With only 6 mW of diode laser power we achieve a deflection angle of 2.5 mrad. Analysis of the velocity distribution of the reflected atoms yields an enhancement factor of 60 ± 20 for the amplitude square of the evanescent wave.