Analysis of the light shift effect in the 87Rb frequencystandard

The ⁸⁷Rb cell frequency standard, optically pumped by a laser diode, is of great interest in the development of high-stability, short-term oscillators. We report the experiments performed on a rubidium-cell prototype aiming to evaluate the transfer of the laser and microwave noise to the hyperfine clock transition via the light-shift effect, which appears to be the main contribution to the observed short- and medium-term instabilities in this kind of a standard. Pulsed optical pumping is also examined in order to strongly reduce the light-shift effect: the experimental results show an improvement in medium term frequency stability     

H2O: a frequency and wavelength standard from 0.5 to 5THz (18-160 cm-1)

Frequencies of H₂O pure rotational transitions from 0.5 to 5 THz have been measured with an accuracy of 1 part in 10⁸ using a tunable far-infrared spectrometer. Measured frequencies of more than a hundred spectral lines provide an excellent wavelength and frequency calibration standard for the far infrared     

Absolute frequency control of a 1560 nm (192 THz) DFB laser lockedto a rubidium absorption line using a second-harmonic-generated signal

We demonstrate second-harmonic generation from a DFB laser at 1560 nm in a type I critically phase-matched KNbO₃ crystal. We obtain 2.2 nW at 780 mm with 11.3 mW at 1560 nm incident on the crystal. The conversion efficiency is 17.2 pW/(mW)². The 780 nm beam is used to interrogate a resonance of the ⁸⁷Rb-D₂ line at 780 nm and lock the laser frequency. To characterize the absolute frequency stability, two 1560 nm DFB lasers are respectively stabilized on a Doppler resonance of the ⁸⁷Rb-D₂ line (780.246 nm) and of the ⁸⁵Rb-D₂ line (780.244 nm). The square root of the Allan variance measured from the beat note is around 1.5×10^-9 for averaging times between 3 and 100 s. To improve the precision of the frequency locking, we realize a setup to observe a saturated absorption profile. We use a 780 nm stabilized laser as a pump and the SHG signal as a probe. A saturated absorption profile is observed over the Doppler envelope. Work is under progress to use this saturated resonance for an improved frequency control     

Observation of a Sub-10-Hz Linewidth 88Sr+ 2S1/2–2D5/2 Clock Transition at 674 nm

In this paper, a pair of diode lasers at 674 nm, locked to two independent ultralow-expansion high-finesse cavities, have been characterized by monitoring the beat frequency between them. The individual laser linewidth of 1.4 Hz for a 3-s averaging time broadened to 4 Hz at 30 s. The relative frequency stability of the beat at 1s is 2.5 10^-15. One of the lasers has been used to interrogate the ⁸⁸Sr^{+ 2}Si_1/2-²D _5/2 transition at 674 nm, and a transition linewidth of 9 Hz has been observed     

CO2/OsO4 lasers as frequency standards in the29 THz range

The CO₂ lasers, frequency stabilized on OsO₄ transitions around 29 THz, are successfully used as secondary references for visible frequency synthesis and also for high-accuracy spectroscopy in the infrared domain. The BNM-LPTF CO₂/OsO₄ frequency standards exhibit high metrological performances: a long term reproducibility of ±10 Hz (1σ=2×10^-13) and a stability σ_y=6.6×10^-14/√τ with a Flicker plateau of 4×10^-15 (Δν/ν=0.1) for 300 s to 10³ s averaging times. These results and a preliminary study of the main effects which can induce frequency shifts are reported     

International comparison of 127I2-stabilizedHe-Ne Lasers at λ≈633 nm using the third and the fifthharmonic locking technique

In an international comparison of ¹²⁷I₂-stabilized helium-neon lasers at λ≈633 nm, lasers from the CMI and the BIPM were stabilized by the third (THT) and the fifth (FHT) harmonic locking techniques. A frequency shift to the blue was measured when using the FHT technique. The influence of weak components of the rotational-vibrational transition P(33) 6-3 of the molecule ¹²⁷I¹²⁹I on the frequency shift of components d, e, f, and g of the line R(127) 11-5 is evaluated     

Precision frequency measurement of the 2S1/2 2D5/2 transition of Sr+ with a 674-nmdiode laser locked to an ultrastable cavity

We have measured the frequency of the 5s ²S_1/2 -4d ²D_5/2 clock transition of a single Sr ion confined in a Paul trap. A diode laser locked to an ultrastable Fabry-Perot (F-P) cavity was used to probe the transition with a resolution of 3.5 kHz. The absolute frequency was determined from heterodyne measurements referenced to an iodine stabilized HeNe laser and a CO₂ laser yielding a value for the S-D transition of (444 779 043 963±30) kHz. This work could lead to the development of a new optical frequency standard at 674 nm     

A 6130 keV gamma-ray source using the 13C(α, n)16O reaction

A high energy gamma-ray source has been produced by mixing the alpha emitter ²³⁸Pu with ¹³C to produce the 6130 keV gamma-ray from the de-excitation of the second excited state ¹⁶O. The gamma-ray spectrum and emission rate have been measured and the neutron emission rate and mean energy have been determined.     

Calibration of a Van de Graaf accelerator and determination of the threshold of the reaction 45Sc(p,n)45Ti using a covariance analysis

The resonances of the ²⁷Al(p, γ)²⁸Si reaction are used to determine the relation between the proton energy and the frequency of a nuclear magnetic resonance (NMR) meter controlling the magnetic induction of a 90° bending magnet used for proton energy analysis.The experimental results and their covariance matrix have been used to obtain a calibration function by a least-squares fit. In addition the threshold and the Q value of the reaction ⁴⁵Sc(p, n)⁴⁵Ti have been determined including all uncertainties and correlations in the analysis.     

Observation of the radiative transitions between 4d9(2D5/2,3/2)5s2nl and 4d105p(2P

Radiative transitions between the 4d ⁹(² D _5/2,3/2)⁵ s ² nl and 4d ¹⁰5p(² P ₁ ^2,3/2/0 )nl autoionization states of the cadmium atom, representing dielectronic recombination satellites of the laser lines of Cd⁺ ion with λ = 325.0 nm (4d ⁹5s ^{2 2} D _3/2 → 4d ¹⁰5p ² P ₁ ^2/0 ) and λ = 353.6 nm (4d ⁹5s ^{2 2} D _3/2 → 4d ¹⁰5p ² P ₃ ^2/0 ), have been observed for the first time in the regime of electron-ion collisions. The energy dependence of the effective cross sections for the electron-impact excitation of satellite lines has been studied in the interval from 7 to 10 eV. The effective cross sections for the excitation of dielectronic recombination satellites are on the order of ∼10⁻¹⁷ cm², which is comparable with the efficiency of excitation of the main laser lines.     

On the water distribution in K2[Pt(CN)4]Br0.3 · 3D2O a single crystal neutron diffraction structure analysis

A single crystal neutron diffraction analysis of the linear conductor K₂[Pt(CN)₄]Br_0.3 · 3D₂O is reported. Complementary to former X-ray investigations the distribution of the water molecules was studied and three different types of D₂O could be located. Besides the full and reduced occupied two- and four-fold D₂O-positions, a third site nearby the Br^?-position was clearly identified giving the picture of a filled center of the unit cell occupied partially by Br^? and D₂O. There is no argument left for a crystallographically different second Br^?-site.     

Ultrastable optical frequency reference at 1.064 μm using a C2HD molecular overtone transition

Saturated molecular overtone transitions in the visible and near infrared can be detected with record-high sensitivities using our cavity-enhanced frequency modulation technique. We have stabilized a Nd:YAG laser onto the P(5) line in (ν₂+3ν₃) overtone band of C₂HD at 1.064 μm and established its absolute frequency. Excellent signal-to-noise ratio produced an Allan variance of 3.4×10^-13 at 1 s averaging, improving to 1×10^-14 after 800 s. Selection of slow molecules with low power and gas pressure gave a linewidth 13 times below the room temperature transit time limit     

RBS depth profiling and optical characterization of multilayers of TiO2 (20 nm) and Ge (15 nm)

Rutherford Backscattering Spectrometry (RBS) has been employed for studying inter-layer diffusion and mixing of TiO₂ and germanium in the multi-layers grown on the soda lime glass substrate. TiO₂ layers were grown by electron-beam evaporation of titanium in an oxygen atmosphere and Ge layers were grown by resistive heating. UV–visible and Raman spectroscopy were carried out for optical characterization. RBS spectra were analyzed by SIMNRA which confirmed the successful formation of alternate layers of TiO₂ and Ge with a thickness of 20 nm and 15 nm, respectively. Annealing caused interface mixing. The approximate stoichiometry of interfaces was of GeTiO₂. The thickness of these layers increased with annealing temperature. Two to five top Ge layers also underwent oxidation to form GeO and GeO₂, depending on annealing temperature. Nuclear Reaction Analysis (NRA) signal of oxygen from top layers was also recorded to confirm the pick-up of oxygen from the annealing atmosphere. An increase in the transmission efficiency with blue shift of the absorption edge was also observed with annealing temperature, as associated with the decrease in the effective thickness of Ge layers. Shift of Raman peaks confirmed the stoichiometric changes as a result of annealing.     

The BIPM laser standards at 633 nm and 532 nm simultaneously linked to the SI second using a femtosecond laser in an optical clock configuration

A femtosecond laser comb was used in an optical clock configuration to measure simultaneously the optical frequency of an iodine-stabilized Nd:YAG laser at 532 nm and an iodine-stabilized He-Ne laser at 633 nm at the International Bureau of Weights and Measures (BIPM). The noise characteristics of the data corresponds well to those of the reference standards and the lasers under study. In a second series of measurements during which the comb was phase-locked to a hydrogen maser, laser standards at 532 nm and at 633 nm were measured. A standard deviation of 6/spl times/10/sup -15/ during 2 h of measurements for the Nd:YAG laser illustrates well the excellent stability of these standards and, at the same time, the capabilities of the comb techniques.     

Phase Separation in the Ternary Liquid System [Th(NO3)4(TBP)2]— [UO2(NO3)2(TBP)2]—Decane at Various Temperatures

The phase diagram of the ternary liquid system [Th(NO₃)₄(TBP)₂]— [UO₂(NO₃)₂(TBP)₂]—decane was studied within the 298.15–333.15 K range. The system has the area of homogeneous solutions and area of binary liquid subsystems (with separation); one phase (I) is enriched in [Th(NO₃)₄(TBP)₂] and [UO₂(NO₃)₂·(TBP)₂] and the other phase (II), in decane. The temperature does not substantially affect the area of phase separation. In two-phase systems, [UO₂(NO₃)₂(TBP)₂] is mainly concentrated in phase I, in spite of the fact that the binary system [UO₂(NO₃)₂(TBP)₂]—decane is single-phase in the entire temperature range studied. Concentration of [UO₂(NO₃)₂(TBP)₂] in phase I results in redistribution of [Th(NO₃)₄(TBP)₂] into phase II. The points of the critical composition of the ternary system are compositions with similar content of the solvates [Th(NO₃)₄(TBP)₂] and [UO₂(NO₃)₂(TBP)₂] at all the temperatures studied. __________ Translated from Radiokhimiya, Vol. 47, No. 6, 2005, pp. 520–522. Original Russian Text Copyright ? 2005 by Keskinov, Mishina, Pyartman.     

Synthesis of (Na2O,PbO)-Nb2O5, (Na2O,BaO)-Nb2O5, and (K2O,SrO)-Nb2O5 thin films using sol-gel method

Homogeneous pore-free Ba₂NaNb₅O₁₅, KSr₂Nb₅O₁₅, and 2·Na₂O-PbO-6·Nb₂O₅ thin films were fabricated on sapphire substrates using the sol-gel technique. By controlling the gelation and coating process, thickness of thin films fabricated was controllable from ~ 40 nm to ~ 10 μm. Synthesized thin films possessed highly preferred orientated microstructure. Another advantage of this method is the subsequent heat treatment temperature dramatically decreased compared with other methods. This increases stoichiometry control and makes the large scale fabrication more feasible and efficient.     

Phase equilibria in the liquid ternary system [Th(NO3)4(TBP)2]-[UO2(NO3)2(TBP)2]-Isooctane at different temperatures

The phase diagrams of the ternary systems [Th(NO₃)₄(TBP)₂]-[UO₂(NO₃)₂(TBP)₂]-isooctane in the temperature range 298.15–333.15 K were constructed. These diagrams contain the field of homogeneous solutions and the field of separation into two liquid phases (I, II). Phase I is enriched in [Th(NO₃)₄(TBP)₂] and [UO₂(NO₃)₂(TBP)₂], and phase II is enriched in isooctane. With increasing temperature from 298.25 to 333.15 K, the mutual solubility of Th(NO₃)₄(TBP)₂ and isooctane does not change noticeably, but the two-phase fields somewhat contract. In the two-phase systems [UO₂(NO₃)₂(TBP)₂] is preferentially distributed in phase I, although the binary system [UO₂(NO₃)₂(TBP)₂]-isooctane is single-phase over the entire temperature range examined. The preferential accumulation of [UO₂(NO₃)₂(TBP)₂] in phase I causes the redistribution of [Th(NO₃)₄(TBP)₂] and isooctane into phases II and I, respectively. The compositions of the ternary systems in the critical points at different temperatures were determined. The electronic absorption spectra of uranyl nitrate solvate with TBP in the homogeneous and two-phase systems were recorded and analyzed. Original Russian Text ? A.K. Pyartman, V.A. Keskinov, V.V. Lishchuk, Ya.A. Reshetko, 2007, published in Radiokhimiya, 2007, Vol. 49, No. 5, pp. 420–422.     

Growth and characterization of Cs(D1−x, Hx)2 AsO4 from aqueous solutions

Highly deuterated single crystals of Cs(D_1?x, H_x)₂ AsO₄ can be grown from D₂O by the temperature lowering method. The primary phase region, saturation and super-saturation concentrations of cesium dideuterium arsenate are reported. Typical deuteration levels in the crystal and the growth solution were determined. The transmission range, phase-match temperature and lattice constants of the most highly deuterated crystals were measured. Some of the difficulties associated with the aqueous growth of cesium dideuterium arsenate were eliminated by the adjustment of the solution P_H to values ≥ 7.76 and by careful seed selection.     

Dielectric properties of B2O3-doped (1 − x)LaAlO3-xSrTiO3 ceramic system at microwave frequency

The effects of B₂O₃ addition on the microwave dielectric properties and the microstructures of (1−x)LaAlO₃-xSrTiO₃ ceramics prepared by conventional solid-state routes have been investigated. Doping with 0.25 wt.% B₂O₃ can effectively promote the densification and the microwave dielectric properties of (1−x)LaAlO₃-xSrTiO₃ ceramics. It is found that LaAlO₃-SrTiO₃ ceramics can be sintered at 1400°C due to the liquid phase effect of a B₂O₃ addition observed by scanning electronic microscopy (SEM). The dielectric constant as well as the Q×f value decreases with increasing B₂O₃ content. At 1460°C, 0.46LaAlO₃-0.54SrTiO₃ ceramics with 0.25 wt.% B₂O₃ addition possesses a dielectric constant (ε_r) of 35, a Q×f value of 38,000 (at 7 GHz) and a temperature coefficients of resonant frequency (τ_f) of −1 ppm/°C.