Observation of rubidium 5S1/2 --> 7S1/2 two-photon transitions with a diode laser

The 5S1/2 --> 7S1/2 two-photon transition of atomic rubidium, which is 100 times weaker than the 5S-5D transition, is observed with an extended-cavity diode laser and a vapor cell. Signals with a signal-to-noise ratio of 280 are obtained with a laser power of 10 mW, and the observed linewidth is 3 MHz. The laser wavelength is 760 nm and is locked on the transitions to a stability of 2 x 10(-11). For the first time to our knowledge, the isotope shift of this transition is measured to be 130(4) MHz in atomic frequency.     

Direct frequency comb measurements of absolute optical frequencies and population transfer dynamics

A phase-stabilized femtosecond laser comb is directly used for high-resolution spectroscopy and absolute optical frequency measurements of one- and two-photon transitions in laser-cooled 87Rb atoms. Absolute atomic transition frequencies, such as the 5S1/2 F=2-->7S1/2 F"=2 two-photon resonance measured at 788,794 768,921 (44) kHz, are determined without a priori knowledge about their values. Detailed dynamics of population transfer driven by a sequence of pulses are uncovered and taken into account for the measurement of the 5P states via resonantly enhanced two-photon transitions.     

Hyperfine splitting,isotope shift,and level energy of the 3S states of (6,7)Li

We study the 2S-3S transition of (6,7)Li by high-precision laser spectroscopy using two-photon Doppler-free excitation and photoionization detection. Interferometric cross referencing to metrologic Rb 3S-5D two-photon transitions allowed measurement of the transition isotope shift and hyperfine splitting in the 3S state with precision at the 30 kHz level. The results are IS=11 453.734(30) MHz, A(3S)(6Li)=35.263(15) MHz, and A(3S)(7Li)=93.106(11) MHz. Combined with recent theoretical work, the isotope shift yields a new value for the change in squared nuclear charge radii DeltaR(2)=0.47(5) fm(2). This is compared with other work and some existing discrepancies are resolved.     

Phase coherent vacuum-ultraviolet to radio frequency comparison with a mode-locked laser

We demonstrate a versatile new technique that provides a phase coherent link between optical frequencies and the radio frequency domain. The regularly spaced comb of modes of a mode-locked femtosecond laser is used as a precise ruler to measure a large frequency gap between two different multiples (harmonics or subharmonics) of a laser frequency. In this way, we have determined a new value of the hydrogen 1S-2S two-photon resonance, f(1S-2S) = 2 466 061 413 187.29(37) kHz, representing now the most accurate measurement of an optical frequency.     

Absolute frequency measurements of the 2(3)S1-->2(3)P 0,1,2 atomic helium transitions around 1083 nm

We measure the frequency of the 2(3)S1-->2(3)P(0,1,2) transitions of helium in a metastable beam using an optical frequency comb synthesizer. The relative uncertainty of these measurements ranging from 5x10(-11) to 7x10(-12) is, to our knowledge, the most precise result for any optical helium transition. Considering existing accurate values of the 2(3)P fine structure, we measure a centroid value of the 2(3)S-2(3)P frequency of 276 736 495 624.6(2.4) kHz, improving the previous interferometric measurement by 30 times. New accurate values of the 2(3)S-2(3)P and 2(3)P Lamb-shift energies are obtained.     

Doppler-free two-photon spectrum of SF(6) for metrological purposes

We report on our systematic investigation of strong Doppler-free two-photon absorption in the middle infrared. The absorption frequencies for two counterpropagating waves of identical frequencies are predicted. Five of these transitions were observed with sub-Doppler resolution with a sideband CO(2) laser and were measured with 10-kHz accuracy. Knowledge of these strong two-photon absorptions frequencies will allow the improvement of secondary frequency standards in the infrared.     

Interferometric frequency measurements of 130Te2 transitions at 486 nm

Doppler-free spectra of ¹³⁰Te₂ have been investigated in the region of 486 nm, close to the Balmer-β transitions atomic hydrogen and deuterium. The frequency ratios between a 633 nm He-Ne laser stabilized to the 11-5 R(127) “i” transition in ¹²⁷I₂ and two of these ¹³⁰Te₂ Doppler-free components have been measured interferometrically to a precision of 2 parts in 10¹⁰ (one standard deviation). These measured components constitute useful transfer standards for the measurement of absolute frequencies of both the Balmer-β transitions and the 243-nm two-photon 1S-2S transitions in hydrogen and deuterium.     

High-resolution 133Cs 6S-6D, 6S-8S two-photon spectroscopy using an intracavity scheme

This Letter presents an intracavity scheme for diode laser based two-photon spectroscopy. To demonstrate generality, three (133)Cs hyperfine transition groups of different wavelengths are shown. For the 6S-6D transitions, we achieved a 10(2) times better signal-to-noise ratio than in previous work [J. Phys. Soc. Jpn. 74, 2487 (2005)] with 10(-3) times less laser power, revealing some previously vague and unobserved spectra. Possible mutual influences between the two-photon absorber and laser cavity were investigated for the first time to our knowledge, which leads to the application of a reliable hand-sized optical frequency reference. Our approach is applicable for most of the two-photon spectroscopy of alkali atoms.     

Contribution of the tensor component to the light shift of the rf optical microwave resonance frequency in rubidium vapor

We have calculated the tensor component of the light shift for the frequency of the rf optical microwave resonance on the magnetically independen 0−0 and 1, −1 transitions in rubidium-87 atoms under conditions of isotope filtering of the resonant pump light. We have observed a difference between the temperatures of the filter cell at which a zero frequency shift is achieved for the rf optical resonance for these transitions. We have noted that selective optical pumping on theD ₁ lines is advisable when using a two-photon microwave transition in rubidium vapor in applications. St. Petersburg State Technical University, St. Petersburg. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 2, pp. 86–90, February, 1999.     

Magic Wavelengths for the 1S-2S and 1S-3S Transitions in Hydrogen Atoms

The dynamic dipole polarizabilities for 1S,2S and 3S states of the hydrogen atom are calculated using the finite B-spline basis set method,and the magic wavelengths for 1S-2S and 1S-3S transitions are identified.In comparison of the solutions from the Schrodinger and Dirac equations,the relativistic corrections on the magic wavelengths are of the order of 10~(-2) nm.The laser intensities for a 300-E_r-deep optical trap and the heating rates at 514 and 1371 nm are estimated.The reliable prediction of the magic wavelengths would be helpful for the experimental design on the optical trapping of the hydrogen atoms,and in turn,it would be helpful to improve the accuracy of the measurements of the hydrogen 1S-2S and 1S-3S transitions.     

Frequency stabilization of a frequency-doubled 1556-nm source to the 5S(1/2) ? 5D (5/2) two-photon transitions of rubidium

Improvements in the power level of sources near 1550 nm and in the efficiency of waveguide frequency doublers enabled us to lock a frequency-doubled source directly to the 5S(1/2) ? 5D(5/2) two-photon transitions near 778 nm. We obtained a sufficiently powerful second-harmonic signal, exceeding 2 mW, by doubling an external-cavity diode laser that was amplified by an erbium-doped fiber amplifier in a periodically poled LiNbO(3) channel waveguide. Our experimental scheme can be used for realizing compact, high-performance frequency standards near 1550 nm for fiber-optic communication and sensing applications.     

Rb（7^2D）态与基态K原子的碰撞能量转移

Ｋ－Ｒｂ混合蒸汽中，使用Ｒｂ光谱灯和染料激光器，将基态Ｒｂ原子二步激发到７＾２Ｄ态用荧光法测量了过程Ｒｂ（７＾２Ｄ）＋Ｋ（４Ｓ）→Ｒｂ（５Ｓ）＋Ｋ（７Ｓ，５Ｄ），的碰撞转移截面，Ｋ７Ｓ，５Ｄ对Ｒｂ７＾２Ｄ的荧光比中，含Ｋ７Ｓ＾←→５Ｄ碰撞转移的影响，第二个实验可以消除这个影响，利用Ｋ光谱灯和染料激光器产生Ｋ７Ｓ或５Ｄ态，探测Ｋ７Ｓ（５Ｄ）对５Ｄ（７Ｓ）的荧光比，Ｒｂ７Ｄ→Ｋ７Ｓ，５Ｄ碰撞转移截面（     

Measurement of the hydrogen 1S- 2S transition frequency by phase coherent comparison with a microwave cesium fountain clock

We report on an absolute frequency measurement of the hydrogen 1S-2S two-photon transition in a cold atomic beam with an accuracy of 1.8 parts in 10(14). Our experimental result of 2 466 061 413 187 103(46) Hz has been obtained by phase coherent comparison of the hydrogen transition frequency with an atomic cesium fountain clock. Both frequencies are linked with a comb of laser frequencies emitted by a mode locked laser.     

Development of two-color laser system for high-resolution polarization spectroscopy measurements of atomic hydrogen

We have developed a high-spectral-resolution laser system for two-photon pump, polarization spectroscopy probe (TPP-PSP) measurements of atomic hydrogen in flames. In the TPP-PSP technique, a 243-nm laser beam excites the two-photon 1S-2S transition, and excited n=2 atoms are then detected by polarization spectroscopy of the n=2 to n=3 transition using 656-nm laser radiation. The single-frequency-mode 243 and 656-nm beams are produced using injection-seeded optical parametric generators coupled with pulsed dye amplifiers. The use of single-mode lasers allows accurate measurement of signal line shapes and intensities even with significant pulse-to-pulse fluctuations in pulse energies. Use of single-mode lasers and introduction of a scheme to select nearly constant laser energies enable repeatable extraction of important spectral features in atomic hydrogen transitions.     

Trapped ion optical clocks

A single laser-cooled ion confined in a radiofrequency ion trap comes close to the spectroscopic ideal of an absorber at rest in a perturbation-free environment. Narrow optical transitions in such systems are therefore very promising for the realisation of optical frequency standards with accuracy significantly exceeding that of current microwave primary frequency standards. When combined with femtosecond optical frequency combs, these standards can be operated as optical clocks generating a direct microwave output, raising the possibility of a future redefinition of the SI second. In this article, the fundamental aspects and current state-of-the-art of trapped ion optical clocks are reviewed, and the improvements that are likely to occur over the next few years are considered.     

Accurate spectroscopy of Sr atoms

We report the frequency measurement with an accuracy in the 100 kHz range of several optical transitions of atomic Sr: 1S0-3P1 at 689 nm, 3P1-3S1 at 688 nm and 3P0-3S1 at 679 nm. Measurements are performed with a frequency chain based on a femtosecond laser referenced to primary frequency standards. They allowed the indirect determination with a 70 kHz uncertainty of the frequency of the doubly forbidden transition of 87Sr at 698 nm and in a second step its direct observation. Frequency measurements are performed for 88Sr and 87Sr, allowing the determination of 3P0, 3P1 and 3S1 isotope shifts, as well as the 3S1 hyperfine constants.     

Absolute frequency determination of the 5P3/2-->7S1/2 transition in 87Rb

We report the absolute frequency of the important 5S(1/2)-->7S(1/2) two-photon transition in (87)Rb. We access the upper state using two dipole-allowed transitions via the intermediate 5P(3/2) state. This allows us to use much lower laser intensities compared to directly driving the two-photon transition, thereby avoiding potential errors due to the AC Stark shift. Collisional shifts are also minimized because the atomic density required is several orders of magnitude smaller. Our values are consistent with earlier frequency-comb measurements.     

The dispersive properties of an excited-doubletfour-level atomic system

We have investigated the dispersive properties of excited-doublet four-level atoms interacting with a weak probe field and an intense coupling laser field. We have derived an analytical expression of the dispersion relation for a general excited-doublet four-level atomic system subject to a one-photon detuning. The numerical results demonstrate that for a typical rubidium D1 line configuration, due to the unequal dipole moments for the transitions of each ground state to double excited states, generally there exists no exact dark state in the system. Close to the two-photon resonance, the probe light can be absorbed or gained and propagate in the so-called superluminal form. This system may be used as an optical switch.     

A compilation of wavelengths and energy levels for the spectrum of neutral rubidium (Rb I)

We are presenting a complete list of wavelengths for all classified lines of Rb I. The data are based mainly on the observations and analysis of this spectrum by many authors. The tabulated data include 615 observed lines in the spectral range 103-, classified as transitions among 22 even-parity and 414 odd-parity levels. Vacuum wavelengths are given for all the lines, and wavelengths in air are also included for the region above . We also present the results of the doppler-free two-photon absorption spectrum for the transition n2S←52S and n2D←52S of atomic rubidium.