Precision Measurement of Gravitational Frequency Shift of Electromagnetic Signals in the RadioAstron Mission#

Recent developments in the trapping of ions and neutral atoms suggest that significant improvements in the precision of spectroscopic measurements on such systems can be expected. The application of these techniques to trapped antiprotons, positrons and antihydrogen atoms opens up new possibilities for precision tests of the weak equivalence principle (WEP) for antimatter. It is shown that constraints on WEP for positrons and antiprotons may be imposed by comparison of electron and positron, or proton and antiproton cyclotron frequencies, or of transition frequencies in hydrogen and antihydrogen, at the same height in a gravitational potential. The constraints that may be inferred from the results of existing particle-antiparticle cyclotron frequency comparisons are derived, and the improvements which will be possible from future, higher precision experiments are analysed.

Wideband microwave Doppler frequency shift measurement based on acousto-optic frequency shift and DP-QPSK receiver

Precision gravity tests and the Einstein Equivalence Principle

The two Galileo satellites launched in 2014 (E14 and E18) were injected in orbits with a significant eccentricity. Both the gravitational potential at the location of the satellites and their velocity thus change as a function of time. Since the Galileo satellites carry very stable clocks, these can potentially be used to set new bounds to the level of agreement between measurements of the clocks' frequency shifts and their prediction by the theory of relativity. This paper presents some initial results obtained by processing available data from Galileo satellite E18.

A photonic-assisted scheme based on optical frequency shift heterodyne and low-frequency power mapping is proposed and experimentally demonstrated to measure the Doppler frequency shift (DFS) and Angle-of-arrival (AOA) of the microwave signals. In the proposed system, the optical signal is divided into two paths. The upper optical signal is injected into a dual-drive Mach-Zehnder modulator (DDMZM) and modulated by the two echo signals with a phase difference. The lower path optical signal is frequency-shifted by an acousto-optic modulator (AOM) and then modulated by the transmitted signal via a Mach-Zehnder modulator (MZM). After an optical filter, the two first-order sideband optical signals heterodyne in the photodetector. The DFS without direction ambiguity and AOA are mapped to the frequency shift and power of the low-frequency microwave signal. By adjusting the DC bias of the DDMZM, two power-phase mapping curves are obtained to eliminate phase ambiguity in AOA measurement. The measurement accuracy is enhanced by adjusting the identity of the two power mapping curves in different measurement ranges. A proof-of-concept experiment demonstrates a DFS measurement at 20 GHz with errors less than ± 8 Hz in the range of ±100 kHz and an AOA measurement from -62.5° to 62.5° with no more than ±2.5° errors.

We present measurements of the frequency shift of the Rb electron-paramagnetic-resonance (EPR) line in the presence of nuclear-polarized $^{3}\mathrm{He}$ gas for the temperature range of 30 to 85 \ifmmode^\circ\else\textdegree\fi{}C. The frequency shift is due to the Fermi-contact interaction between the Rb valence electron and the polarized $^{3}\mathrm{He}$ nucleus. Expressions for both the frequency shift and the spin-exchange cross section are derived in terms of the strength of this contact interaction. From these expressions and the measured frequency shift, we estimate the Rb${\mathrm{\ensuremath{-}}}^{3}$He spin-exchange cross section. The Rb EPR frequency shift, which is 53 kHz for a 100% polarized 10-amagat $^{3}\mathrm{He}$ sample at 50 \ifmmode^\circ\else\textdegree\fi{}C, can be used to determine the absolute polarization of nuclear polarized $^{3}\mathrm{He}$ targets. From these measurements, one can also predict the shift of the $^{3}\mathrm{He}$ NMR line due to a polarized Rb vapor.

We present a new method based on a transfer of population by adiabatic passage that allows one to prepare cold atomic samples with a well-defined ratio of atomic density and atom number. This method is used to perform a measurement of the cold collision frequency shift in a laser cooled cesium clock at the percent level, which makes the evaluation of the cesium fountain accuracy at the 10(-16) level realistic. With improvements, the adiabatic passage would allow measurements of density-dependent phase shifts at the 10(-3) level in high precision experiments.

Over five years we have compared the hyperfine frequencies of /sup 133/Cs and /sup 87/Rb atoms in their electronic ground state using several laser cooled /sup 133/Cs and /sup 87/Rb atomic fountains with an accuracy of /spl sim/10/sup -15/. These measurements set a stringent upper bound to a possible fractional time variation of the ratio between the two frequencies: d/dt In (/spl nu/Rb//spl nu/Cs)=(0.2/spl plusmn/7.0)/spl times/10/sup -16/ yr/sup -1/ (1/spl sigma/ uncertainty). The same limit applies to a possible variation of the quantity (/spl mu/Rb//spl mu/Cs)/spl alpha//sup -0.44/, which involves the ratio of nuclear magnetic moments and the fine structure constant. To improve this test, one needs more accurate cesium fountain clocks, for which the major limiting factor is the cold collision frequency shift. This effect can now be evaluated with great accuracy using a new method which we also present here. It is based on a transfer of population by adiabatic passage that allows to prepare cold atomic samples with a well defined ratio of atomic density and atom number. This method is used to perform a measurement of the cold collision frequency shift in a laser cooled cesium clock at the percent level. With improvements, the adiabatic passage would allow measurements of density-dependent phase shifts at the 10/sup -3/ level in high precision experiments. With this precision, reaching an accuracy of 10/sup -16/ is possible.

A simple, sensitive, low-cost microwave sensor capable of conducting glucose concentration measurements has been developed without chemical bindings. The sensing device uses a microstrip transmission line to detect variation of the glucose component of the solutions placed in a cavity under it. The uniform and concentrated electric field distribution results in an accurate and sensitive measurement of the absorption frequency shift in the frequency response of the sensor. The sensor was fabricated on a FR4 substrate for low-cost purpose. The shift in the absorption frequency of the device was measured in the frequency range between 4.8 GHz and 5.7 GHz using solutions with different glucose concentrations in two ranges: (a) high concentration from 1000 mg dl−1 to 8000 mg dl−1 and (b) low concentration from 100 mg dl−1 to 300 mg dl−1. The experimental results showed a high sensitivity of 0.32 MHz (mg dl−1)−1 for the low concentrations in terms of absorption frequency.

The standard Quartz Crystal Resonator (QCR) and network analysis based methods in conjunction with curve fitting were used to investigate the sensing capability and characterize the properties of phthalocyanine films on vapour exposure. The measurement of frequency shift and resistance change (mass loading and film damping), caused by adsorption of organic vapour namely, Benzene, Hexane, Ethanol and Toluene were investigated. Confirmation of film properties using supplementary methods such as AFM, Ellipsometry and UV-visible spectrometer was also performed to provide a full characterization of the sensing membranes. The extracted values of Δƒ and ΔR from subsequent fitting of the spectra to the BVD model are observed on vapour exposure. A frequency shift (Δƒ) and change in magnitude (as related to ΔR of the BVD equivalent circuit) indicate changes in the films viscoelastic properties for the increasing concentrations of tested vapours. The sensitivity of the coating has been estimated from the slope of fitted trend line and gives values below LEL thresholds (the Lower explosive limit) and IDLH thresholds (Immediately Dangerous to Life or Health) for the ZnPcs films. The experimental results of the study demonstrate selected sensing membranes are easily applied through spin coating techniques evident from definitive shifts in resonance. Additionally when exposed to the target vapours tested, the film(s) exhibit fast and consistent responses, consequently giving significant potential for gas/vapour sensing applications. Changes in the film parameters have also been observed through the measurement of the admittance spectra. Shifts in both frequency and resistance are observed on exposures which indicate mass loading and changes in film viscosity caused by ad/absorption of the vapour. Response times appear to be quick and full recovery is observed. From the tested vapours, toluene gives the most significant frequency shift exhibiting the highest sensitivity for this compound; this can be attributed to relatively high saturated vapour pressure as compared to the other analytes. In addition, the film parameters extracted from this work were used to estimate the shear modulus parameters. It was found the shear modulus of viscous material (coating film) extracted electrical equivalent circuit parameters are dependent on film properties, thickness and analyte ad/absorption. Consequently, the QCR sensor can act iv as a gravimetric and non gravimetric sensitive device for thin film depending on load and adsorption characteristics. In most instances the studied film behaviour demonstrates a rubbery regime that was indicated from increase in resistance for the coating film at series resonant frequency typically. Consequently the calculation of change in film mass from frequency shift (Sauerbrey equation) is inaccurate except for suitably thin rigid films. A range of Phthalocyanine sensing membranes have been successfully evaluated; selected variants (mainly ZnPc) have given promising results to their viability as gas sensing membrane to detect a range of organic solvents at vapour concentrations below their lower explosive level, It was found suitably sensitive with detection limits in the low parts-per million ranges for the selected analytes. Furthermore, a comparison of gas sensor responses for the selected materials is included, and consequently a particular type of substituent is proposed as a suitable sensor coating for Quartz Crystal Resonator (QCR) gas sensor applications. Other phthalocyanine materials initially chosen proved less successful; demonstrating limited responsiveness to analytes ad/absorption and giving inconsistent results over the tested concentration range. Factors range from non-homogenous film surfaces to the structure and consequent suitability of the synthesised film(s). Moreover, further research is suggested to fully characterize the complete adsorption process with wide range of phthalocyanine material and various organic analytes.

Some considerations on the measurements of mean frequency shift and integrated backscatter following administration of albunex ®

As part of the scientific cooperation between Ukraine and Russia, a series of studies on the preparation of the ground segment of the RadioAstron mission has been carried out. A scientific program of measurements to be performed using the 22-m RT-22 radio telescope (Crimean Astrophysical Observatory) has been prepared. A substantial part of this program is the study of compact structures in extragalactic sources. Ground-based VLBI test experiments at 6 and 18 cm intended for testing a model of the ground segments of the RadioAstron mission have been carried out at RT-22 of the Crimean Astrophysical Observatory in Simeiz and RT-70 (P-2500) in Evpatoriya. The processing of the data recorded by each antenna resulted in obtaining and calibrating responses of cross-correlation functions using the ASC LPI correlator. The results of the experiment demonstrate the readiness of RT-22 and RT-70 to participate in the ground-space radio interferometer sessions in the RadioAstron mission.

Quantitative characterization of tip–sample interaction in scanning force microscopy isfundamental for optimum image acquisition as well as data interpretation. In this work wediscuss how to characterize the electrostatic and van der Waals contribution to tip–sampleinteraction in non-contact scanning force microscopy precisely. The spectroscopic techniquepresented is based on the simultaneous measurement of cantilever deflection, oscillationamplitude and frequency shift as a function of tip–sample voltage and tip–sampledistance as well as on advanced data processing. Data are acquired at a fixedlateral position as interaction images, with the bias voltage as fast scan, andtip–sample distance as slow scan. Due to the quadratic dependence of the electrostaticinteraction with tip–sample voltage the van der Waals force can be separated from theelectrostatic force. Using appropriate data processing, the van der Waals interaction, thecapacitance and the contact potential can be determined as a function of tip–sampledistance. The measurement of resonance frequency shift yields very high signal tonoise ratio and the absolute calibration of the measured quantities, while theacquisition of cantilever deflection allows the determination of the tip–sample distance.

A photonic approach for both wideband Doppler frequency shift (DFS) measurement and direction ambiguity resolution is proposed and experimentally demonstrated. In the proposed approach, a light wave from a laser diode is split into two paths. In one path, the DFS information is converted into an optical sideband close to the optical carrier by using two cascaded electro-optic modulators, while in the other path, the optical carrier is up-shifted by a specific value (e.g., from several MHz to hundreds of MHz) using an optical-frequency shift module. Then the optical signals from the two paths are combined and detected by a low-speed photodetector (PD), generating a low-frequency electronic signal. Through a subtraction between the specific optical frequency shift and the measured frequency of the low-frequency signal, the value of DFS is estimated from the derived absolute value, and the direction ambiguity is resolved from the derived sign (i.e., + or -). In the proof-of-concept experiments, DFSs from -90 to 90 kHz are successfully estimated for microwave signals at 10, 15, and 20 GHz, where the estimation errors are lower than ±60 Hz. The estimation errors can be further reduced via the use of a more stable optical frequency shift module.

A PM-based approach for Doppler frequency shift measurement and direction discrimination