Showing papers in "Metrologia in 1977"
TL;DR: In this article, the optimum operating point of the trap and the average ion energy were determined in preparation of an ODR experiment to determine the ground state hyperfine splitting of the odd isotopes.
Abstract: The observation of D1-fluorescence light from trapped Ba+ ions, using a pulsed tunable dye laser as a light source, leads to a sensitive detection of the confined particles. In preparation of an ODR-experiment to determine the ground state hyperfine splitting of the odd isotopes we found the optimum operating point of the trap and measured the average ion energy.
72 citations
TL;DR: In this paper, the length change vs time for several low thermal expansion materials maintained in evacuated environments at constant temperature (near 300 K) was measured over a period of 170 days to a precision of two to three parts in 109.
Abstract: We have measured length change vs time for several low thermal expansion materials maintained in evacuated environments at constant temperature (near 300 K). Materials were two types of fused silica, Cer-Vit, ULE, Zerodur, Invar, and super Invar. ΔL/L was measured over a period of 170 days to a precision of two to three parts in 109. In addition, we have measured time-dependent changes in optical contact interfaces and have placed an upper limit on drift of optical phase shift on reflection from multilayer dielectric coatings.
67 citations
TL;DR: In this paper, a method of combining the data from several primary cesium frequency standards is presented, which is applied to the International Atomic Time scale using all the available data from primary standards.
Abstract: Primary cesium frequency standards provide physical realizations of the second of the International System of Units, and these are compared with the scale unit of time scales. A method of combining the data from several standards is presented. As an example, this method is applied to the International Atomic Time scale using all the available data from primary standards.
63 citations
TL;DR: In this article, the ratio of the electron g-factor in hydrogen to the proton gfactor in a spherical sample of H2O was measured by comparing the electron spin frequency, as measured with a hydrogen maser, to the Proton spin flip frequency as measured by NMR, at a temperature of 34.7°C.
Abstract: We have measured the ratio of the electron g-factor in hydrogen to the proton g-factor in a spherical sample of H2O by comparing the electron spin frequency, as measured with a hydrogen maser, to the proton spin flip frequency, as measured by NMR. The result is gj(H)/gp = 658.216 0091(69) [10 parts per billion (ppb)] at a temperature of 34.7°C. This yields a value for the proton moment in Bohr magnetons of μp/μB = 0.001 520 992 983(17) (11 ppb). Our result differs from the best previous value by 150 ppb.
50 citations
TL;DR: In this article, a CW singlemode GaAs laser was used to excite selectively the hyperfine components of the D2 resonance line (8521 A) in a Cs133 atomic beam.
Abstract: A CW single-mode GaAs laser has been used to excite selectively the hyperfine components of the D2 resonance line (8521 A) in a Cs133 atomic beam. The hyperfine optical pumping was displayed by using a Rabi-type detection method. Frequency locking of the GaAs laser to individual hyperfine transitions was performed by monitoring the atomic beam fluorescence. On the basis of these experimental results, the realization of optically-pumped cesium beam frequency standards is discussed.
49 citations
TL;DR: In this paper, a time domain fractional frequency stability of σy(τ) 6 × 10-12 τ-1/2 was measured with independently line-center locked 1.5m grating controlled CO2 lasers.
Abstract: Significant improvement in signal-to-noise ratios is achieved with new, low pressure CO2 stabilization cells external to the lasers. A time domain fractional frequency stability of σy(τ) 6 × 10-12 τ-1/2 was measured with independently line-center locked 1.5 metre grating controlled CO2 lasers. Accurate, repeatable determination of pressure shift is demonstrated.
44 citations
TL;DR: In this paper, a method of correcting measurements in optical or photoelectric pyrometry to a reference wavelength is described, which enables the wavelength to be given as an instrumental constant in intercomparisons of results, and allows the effects of uncertainties in the characteristics of the pyrometer or the source to be studied without lengthy computations, and using only physically significant factors.
Abstract: A method of correcting measurements in optical or photoelectric pyrometry to a reference wavelength is described. This enables the wavelength to be given as an instrumental constant in intercomparisons of results. It also allows the effects of uncertainties in the characteristics of the pyrometer or the source to be studied without lengthy computations, and using only physically significant factors.
39 citations
TL;DR: In this paper, the most important factors which limit the reproducibility of He-Ne lasers stabilized on a hyperfine component of the R 127 127I2 line are examined, including curvature of the laser power profile, second and third frequency harmonic distortions, overlapping of neighbouring lines, molecular collisions.
Abstract: The most important factors which limit the reproducibility of He-Ne lasers stabilized on a hyperfine component of the R 127 127I2 line are examined. The considered factors are the following: curvature of the laser power profile, second and third frequency harmonic distortions, overlapping of neighbouring lines, molecular collisions. The reproducibility limitations connected to more fundamental effects (residual first order Doppler effect, second order Doppler effect and recoil effect) are stated. Guidelines for the control and the improvement of the reproducibility are given.
33 citations
TL;DR: A brief survey of various types of light-shifts corresponding to different physical situations is presented in this paper, using a dressed atom approach allowing simple physical discussions and simple calculations and some new suggestions are made.
Abstract: Atomic or molecular energy levels are shifted by a non-resonant electromagnetic irradiation. These so-called light-shifts must be carefully taken into account in high resolution spectroscopy experiments since they perturb the atomic Bohr frequencies which one wants to measure or to use as frequency standards. In this paper, we present a brief survey of various types of light-shifts corresponding to different physical situations. We use a dressed atom approach allowing simple physical discussions and simple calculations. Some new suggestions are made.
29 citations
TL;DR: The NBS primary frequency standard NBS-4 has been operating since January 1973 as discussed by the authors, and the standard was modified significantly and redesignated NBS6 in March 1975, and the extent and character of these design changes are discussed.
Abstract: The NBS primary frequency standard NBS-4 has been operating since January 1973. NBS-5 operated from January 1973 until March 1974. At this time NBS-5 was modified significantly and redesignated NBS-6. The extent and character of these design changes are discussed. NBS-6 operation and evaluation began in March 1975. Results obtained from NBS-4, NBS-5 and NBS-6 are given, along with intercomparisons of some significant parameters. During 1975, NBS-4 was operated as a clock and a time dispersion of 2.5 ns was obtained for one day. The NBS approach to long term clock operation of the primary standards is discussed. These techniques will probably involve "accuracy servo" methods, and may lead to very accurate clocks with time dispersion less than 1 ns per day.
29 citations
TL;DR: In this article, the current temperature scales for the region 1.1 to 30 K have been compared by means of 31 germanium resistance thermometers originating from eight national laboratories.
Abstract: The current temperature scales for the region 1.1 to 30 K have been intercompared by means of 31 germanium resistance thermometers originating from eight national laboratories. The scales compared include the International Practical Temperature Scale of 1968, the helium vapour pressure scales and various national scales based on gas, acoustic and magnetic susceptibility thermometry. While the overall scatter between these scales is some 15 mK, the intercomparison reveals agreement of the order of 1 mK between the most recent scales based on magnetic susceptibility measurements and using common fixed points. The values of the superconductive transition temperatures of aluminium, indium and lead on each of the scales have been determined.
TL;DR: In this paper, the Allan variance of argon lasers stabilized on iodine saturation peaks in external absorption cells at 5145 A (10-10 m) was found necessary for the commercial lasers used in this work.
Abstract: Preliminary results are given for the Allan variance of argon lasers stabilized on iodine saturation peaks in external absorption cells at 5145 A (10-10 m). A prestabilization on Fabry-Perot transmission fringes was found necessary for the commercial lasers used in this work. A flicker floor at 8 × 10-13 is reached between 0.1 and 1 second. Line pressure broadening and shift are studied by the frequency offset locking technique. This new optical frequency standard appears to offer many advantages with respect to accuracy because of the high molecular weight of I2 and of the possibility of using narrow three level resonances free of recoil structure.
TL;DR: In this article, the line width has been reduced from 20 MHz to about 10 kHz and a long term stability of 7 × 10-14 has been achieved by using an I2 molecular beam as a reference.
Abstract: Multiwatt Argon Lasers have been short-term and long-term stabilized. The laser line width has been reduced from 20 MHz to about 10 kHz and a long term stability of 7 × 10-14 has been achieved by using an I2 molecular beam as a reference. Frequency reproducibility of 1.5 × 10-12 has been demonstrated.
TL;DR: In this article, a new design for higher stability was proposed and the frequency stability was found to be better than three parts in 1011 when the lasers were free-running and two orders of magnitude better when they were stabilized on saturated absorption resonances of SF6.
Abstract: Carbon dioxide lasers have been built with a new design for higher stability. The frequency stability is found to be better than three parts in 1011 when the lasers are free-running and two orders of magnitude better when they are stabilized on saturated absorption resonances of SF6. We discuss the present limitations of stability, reproducibility and accuracy in these experiments.
TL;DR: In this article, a simplified theory for random sampling of magnetic field gradients in atomic hydrogen masers predicts shifts of the spin exchange tuned maser oscillation frequency at levels which affect resettability and long term stability of hydrogen maser standards.
Abstract: Model calculations based on a simplified theory for random sampling of magnetic field gradients in atomic hydrogen masers predict shifts of the spin exchange tuned maser oscillation frequency at levels which affect resettability and long term stability of hydrogen maser standards Strategies for minimizing and compensating such effects are presented
TL;DR: In this article, the effect of catalysis on the rate of ortho-paraconversion was extensively investigated and it was found that the catalyst should be in contact with most of the sample at low temperatures, if stirring is not possible, in order that conversion takes place rapidly.
Abstract: The vapour pressure versus temperature relationship for equilibrium H2 was obtained between its normal boiling and melting points. It was found that impurities other than Ne have no effect on the vapour pressure behaviour, presumably because the non-volatile impurities freeze out onto the cold walls of the apparatus and the only volatile impurity, He, appears to be insoluable in H2 and thus can easily be removed by pumping. The effect of catalysis on the rate of ortho-paraconversion was extensively investigated. It was found that the catalyst should be in contact with most of the sample at low temperatures, if stirring is not possible, in order that conversion takes place rapidly. Catalyst in contact with part of the condensed sample only does not work efficiently, probably because of the slow rate of ortho-para interdiffusion. The triple point pressures were found to be 52.763 mmHg (7034.5 N/m2) and 54.082 mmHg (7210.3 N/m2) for equilibrium and normal H2 respectively. The temperatures of the normal boiling and triple points of normal H2 were found to be 117 mK and 148 mK higher respectively than those of equilibrium H2. Boiling points (at 76 and 25 cmHg vapour pressures) and the triple point of equilibrium hydrogen are all defining fixed points on the International Practical Temperature Scale of 1968 (IPTS-68). This paper describes some experiments performed at the National Research Council of Canada aimed at realizing these thermometric fixed points. In addition vapour pressure versus temperature behaviour for liquid H2 samples of differing purities was also investigated.
TL;DR: In this article, an improved theory of the instrumental corrections applied to absolute radiometers, with the exception of the effect of sensitivity variations across the receiver surface, is derived and a possible experimental procedure for the determination of the various correction factors is described.
Abstract: An improved theory of the instrumental corrections applied to absolute radiometers, with the exception of the effect of sensitivity variations across the receiver surface, is derived. After a brief review of the historical emergence of correction factors and finally of a formal correction theory, as formulated by Geist, some shortcomings of this theory are pointed out. Based on a set of strict definitions and the conservation of energy principle a revised theory is derived and a possible experimental procedure for the determination of the various correction factors is described. The new theory also takes into account the influence of deviations from linear response, which to a certain extent are present in all practical absolute radiometers. The ratio of the mean sensitivities for radiant and electrical heating is expressed in terms of either the equivalent or non-equivalent heat losses. By analyzing the one-dimensional heat flow through a representative model of an absolute radiometer the equivalent and non-equivalent losses are identified. At the same time a formal proof for the conception of the equivalence of the heat loss through the heater wires is provided. All correction terms in the new theory are treated as functions of the applied power and can also be determined as such. In conclusion both the scope and the limitations of the theory are discussed.
TL;DR: In this paper, the main characteristics of the caesium beam time and frequency standard CS1 of the PTB are summarized, and current research work on the improvement of CSI is reported: reduction of the mean beam velocity and the velocity range in the beam; detection of small asymmetries of the Ramsey resonance, e.g., due to a shifted Rabi resonance; development of improved analyser deflection systems.
Abstract: First the main characteristics of the caesium beam time and frequency standard CS1 of the PTB are summarized. Then current research work on the improvement of CSI is reported: (1) Reduction of the mean beam velocity and the velocity range in the beam; (2) detection of small asymmetries of the Ramsey resonance, e.g., due to a shifted Rabi resonance; (3) development of improved analyser deflection systems. The efficiencies of beam polarizers using quadrupole magnets or hexapole magnets, or combinations of both, have been studied for CS1 achieving the reduction of the mean beam velocity to about 100 m/s and the half-width velocity range in the beam to about 16%. For the analyser a shaped quadrupole magnet or a combination of hexapole and quadrupole magnets should be advantageous. The square root of the sum of squares of the uncertainty contributions of CS1 amounts to 0.26 · 10-13, the official relative uncertainty of CS1 being 1 · 10-13.
TL;DR: In this paper, the authors demonstrated that total spin angular momentum is conserved in the near resonant charge transfer collisions between oriented helium ions and oriented cesium atoms, and the resulting spin dependence of the total charge transfer cross-sections was described using singlet and triplet channels based on the molecular potential energy curves of the collision pair.
Abstract: The experiment demonstrated that total spin angular momentum is conserved in the near resonant charge transfer collisions between oriented helium ions and oriented cesium atoms. The resulting spin dependence of the total charge transfer cross-sections is described using singlet and triplet channels based on the molecular potential energy curves of the collision pair. The experiment was performed with helium ions stored in a rf-quadrupole trap in interaction with an optically pumped beam of cesium atoms. Total spin dependent charge transfer cross-sections were measured in the energy range of a few eV.
TL;DR: In this paper, the present and future roles of the cesium beam frequancy standard in time and frequency metrology are discussed briefly, and the present limitation of the CBE device is the uncertainty in the determination of the first and second-order Doppler shifts.
Abstract: The present and future roles of the cesium beam frequancy standard in time and frequency metrology are discussed briefly. The present limitation of the cesium beam device is the uncertainty in the determination of the first- and second-order Doppler shifts. These are fundamental problems of all frequency standards, and possible solutions in cesium clocks and other standards are mentioned.
TL;DR: Comparisons with the best NRC secondary HP high performance cesium clock and with UTC(USNO) and TAI indicate that, after compensation for Loran C discontinuities, the best relative value of 2, 60 days is about 2 ?
Abstract: Performance of the new 2.1 metre NRC cesium standard during its first year of operation as a continuously running primary clock is described. Comparisons with the best NRC secondary HP high performance cesium clock and with UTC(USNO) and TAI indicate that, after compensation for Loran C discontinuities, the best relative value of ?(2, 60 days) is about 2 ? 10-14.
TL;DR: In this paper, a method for the detection of the hyperfine structure resonance of 135Ba+ or 137Ba+ ions was proposed, which benefits from the existence of a metastable 5D level.
Abstract: We propose a method for the detection of the hyperfine structure resonance of 135Ba+ or 137Ba+ ions. It benefits from the existence of a metastable 5D level. The observation of the fluorescence light which is emitted in the 62P3/2 → 52D5/2 transition of Ba+ ions trapped in an alternating and inhomogeneous electric field is reported.
TL;DR: In this paper, it is shown that the FEP wall behaviour is different according to the temperature range, when the wall behaves like a perfect solid and the H atoms are perturbed during weak physical adsorption.
Abstract: Measurements have been performed of wall effects (atomic loss rate, wall relaxation and wall shift for a FEP 120 coating) and spin exchange effects (spin exchange cross-section, spin exchange frequency shift) in a hydrogen maser for various temperatures of the wall and the atomic hydrogen gas in the range 77-363 K. These experimental results allow a discussion of the phenomena involved in atom-wall collisions. It is shown that the FEP wall behaviour is different according to the temperature range. When the temperature is smaller than 202 K, the wall behaves like a perfect solid and the H atoms are perturbed during weak physical adsorption. When the temperature is greater than 202 K, the wall is no longer a perfect solid: the adsorption sites are modified, or new sites appear, the effects of this change being stronger and stronger when the temperature rises. The phenomena responsible for the loss of atoms on the wall are not modified at 202 K. For temperatures above 296 K, new phenomena appear, which introduce strong positive wall shift and atomic loss, when the temperature rises. These changes of the wall behaviour are connected with second order transitions affecting FEP. The experimental results relative to spin exchange effects are in good agreement with theoretical calculations by Allison: at room temperature the experimental values for the spin exchange cross section is σ = 23.1 ± 2.8 A2 and for the spin exchange frequency shift is λ = 2.5 ± 2.5 A2 (the theoretical values are respectively σ = 23.5 ± 2.4 A2 and λ = 4.5 ± 0.45 A2). We observe small variations of σ in the considered temperature range and a change of the sign of λ at a temperature around 205 K, as predicted by the theoretical calculations.
TL;DR: In this paper, a systematic frequency shift was observed and explained in terms of the Millman effect, and the authors suggest that an alternative explanation be sought for the observed results, which is the case in this paper.
Abstract: In a recent paper entitled "The Millman Effect in Cesium Beam Atomic Frequency Standards" (Mungall A G 1976 Metrologia 12 151) a systematic frequency shift was observed and explained in terms of the Millman effect. The purpose of this note is to suggest that an alternative explanation be sought for the observed results.
TL;DR: In this article, a photo-electric microscope for line standard measurement is described, where the source of light is a 0.6328 μm HeNe one milliwatt laser whose beam passes through an astigmatic lens system to produce a quasi line image at the scale and a birefringent crystal splits the beam to produce two such images of variable separation so that both sides of the scale line are sensed simultaneously.
Abstract: A novel photo-electric microscope for precise measurement of Line Standards is described. Its two distinctive features are: (i) the source of light is a 0.6328 μm HeNe one milliwatt laser whose beam passes through an astigmatic lens system to produce a quasi line image at the scale and (ii) a birefringent crystal splits the beam to produce two such images of variable separation so that both sides of the scale line are sensed simultaneously. These result in a capability of reading good lines to a sensitivity of ± 0.02 μm while the lines move at constant velocity under the microscope.