Absolute Frequency Measurement Research Articles

Absolute frequency measurements on the 5s5p3P0 → 5s6d3D1 transition in strontium

We report the first absolute frequency measurements for the 5s5p3P0→5s6d3D1 transition at 394 nm for all the stable strontium isotopes by utilizing repumping induced spectroscopy in a magneto-optical trap. Absolute transition frequency is measured to be 760524409251(25) kHz for Sr88. With reference to Sr88, the isotope shifts are measured to be 91052(35), 54600(33), and 51641(28) kHz for Sr84, Sr86, and Sr87, respectively. We calculate the hyperfine constants A and B for the fermionic isotope Sr87 at kHz level. Furthermore, we perform King plot analysis by combining isotope shifts on the 689-nm transition to our data. Published by the American Physical Society 2024

171Yb+ optical clock with 2.2×10−18 systematic uncertainty and absolute frequency measurements

A full evaluation of the uncertainty budget for the ytterbium ion optical clock at the National Physical Laboratory (NPL) was performed on the electric octupole (E3) 2S1/2→2F7/2 transition. The total systematic frequency shift was measured with a fractional standard systematic uncertainty of 2.2×10−18 . Furthermore, the absolute frequency of the E3 transition of the 171Yb+ ion was measured between 2019 and 2023 via a link to International Atomic Time (TAI) and against the local caesium fountain NPL-CsF2. The absolute frequencies were measured with fractional standard uncertainties between 3.7×10−16 and 1.1×10−15 , and all were in agreement with the 2021 BIPM recommended frequency.

Hyperfine structure and isotope shifts of the (4s2)S01→(4s4p)P11 transition in atomic zinc

We report absolute frequency, isotope shift, radiative lifetime, and hyperfine structure measurements of the (4s2)S01→(4s4p)P11 (213.8 nm) transition in Zn I using a cryogenic buffer gas beam. Laser-induced fluorescence is collected with two orthogonally oriented detectors to take advantage of differences in the emission pattern of the isotopes. This enables a clear distinction between isotopes whose resonances are otherwise unresolved, and a measurement of the Zn67 hyperfine structure parameters, A(Zn67)=20(2)MHz and B(Zn67)=10(5)MHz. We reference our frequency measurements to an ultralow expansion cavity and achieve an uncertainty at the level of 1 MHz, about 1 percent of the natural linewidth of the transition. Published by the American Physical Society 2024

Pesquisas científicas sobre zumbido no Brasil: Um compilado observacional

ABSTRACT Purpose: to identify the profile of tinnitus research in Brazil and the main procedures adopted by professionals in the field in the national territory. Methods: an observational, descriptive, and cross-sectional study, in which an active search was made on digital platforms to identify researchers in Brazil who have tinnitus as a study focus. After identifying the tinnitus study groups, an online Form was sent to the researchers comprising 21 questions, so as to know the works in development. The collected responses were extracted and tabulated intoMicrosoft Excel Professional Plus2019 through the absolute and relative frequency measurements of the final sample. Results: 117 researchers were identified, of these, 21 participated in the study, being (90.5%) females, specifically from public universities (81%) in the Southeast region of Brazil (47.7%). These professionals develop clinical research (76.1%), focusing on therapies and/or treatments (38.1%), and use sound therapy (52.38%) as the main technological resource of their studies. Conclusion: the research profile is clinical, with a main focus on therapies and/or treatments for tinnitus. As for the procedures, there is a predominant application of the Visual Analogue Scale- VAS and the Tinnitus Handicap Inventory- THI as evaluation protocols and sound therapy as the main technological resource of their studies.

Absolute frequency measurement of molecular iodine hyperfine transitions at 554 nm and its application to stabilize a 369 nm laser for [formula omitted] ions cooling

We investigate 13 hyperfine structures of transition lines of 127I2 near 554 nm, namely, the R(50) 22-0, P(46) 22-0, P(121) 24-0, P(69) 25-1, R(146) 25-0, R(147) 28-1, P(160) 26-0, P(102) 26-1, R(96) 23-0, R(49) 22-0, P(45) 22-0, P(92) 23-0, and R(72) 25-1 transitions, and measure their absolute frequencies with an optical frequency comb. A 369 nm frequency-tripled laser is frequency stabilized by locking the 554 nm harmonic-frequency laser to the R(146) 25-0 a15 line of 127I2 via modulation transfer spectroscopy. A frequency stability of 5×10−12 is observed over a 1000 s integration time. The measurement of the molecular iodine spectroscopy at 554 nm enriches high-precision experimental data, and also enables theoretical predictions. Meanwhile, the 369 nm frequency-tripled laser stabilized by molecular iodine spectroscopy has wide applications in frequency metrology, and quantum information processing based on Yb+ ions.

Evaluation of systematic frequency shift and uncertainty of an optical clock based on Bayesian hierarchical model

Optical clocks are the most accurate time–frequency measurement devices currently available. In order to evaluate the performance quickly and conveniently, we build a Bayesian hierarchical model to initially evaluate the systematic frequency shift and the corresponding uncertainty of the 171Yb optical lattice clock. Significant time savings is achieved through the Bayesian model compared to the traditional method during the absolute frequency measurement. The model is implemented via the R2jags package in R, samples are drawn from the target posterior distribution of the parameters by the Markov Chain Monte Carlo simulation (MCMC). The simulation result of the total systematic frequency shift is −1.595 Hz, with an uncertainty of 6.71 × 10−16, which is close to the actual measurement value. This method provides us a new way to evaluate optical clocks.

Absolute frequency measurements with a robust, transportable 40Ca+ optical clock

We constructed a transportable 40Ca+ optical clock (with an estimated minimum systematic shift uncertainty of and a stability of ) that can operate outside the laboratory. We transported it from the Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan to the National Institute of Metrology, Beijing. The absolute frequency of the 729 nm clock transition was measured for up to 35 d by tracing its frequency to the second of International System of Units. Some improvements were implemented in the measurement process, such as the increased effective up-time of 91.3% of the 40Ca+ optical clock over a 35-day-period, the reduced statistical uncertainty of the comparison between the optical clock and hydrogen maser, and the use of longer measurement times to reduce the uncertainty of the frequency traceability link. The absolute frequency measurement of the 40Ca+ optical clock yielded a value of 411 042 129 776 400.26 (13) Hz with an uncertainty of , which is reduced by a factor of 1.7 compared with our previous results. As a result of the increase in the operating rate of the optical clock, the accuracy of 35 d of absolute frequency measurement can be comparable to the best results of different institutions in the world based on different optical frequency measurements.

Intercombination line frequencies in 171Yb validated with the clock transition.

We have carried absolute frequency measurements of the (6s 2) 1 S 0-(6s6p) 3 P 1 transition in 171 Y b (intercombination line), where the spin-1/2 isotope yields two hyperfine lines. The measurements rely on sub-Doppler spectroscopy to yield a discriminator to which a 556 nm laser is locked. The frequency reference for the optical frequency measurements is a high-quality quartz oscillator steered to the GNSS time scale that is bridged with a frequency comb. The reference is validated to ∼3×10-12 by spectroscopy on the 1 S 0- 3 P 0 (clock) line in laser cooled and trapped 171 Y b atoms. From the hyperfine separation between the F=1/2 and F=3/2 levels of 3 P 1, we determine the hyperfine constant to be A(3 P 1)=3957833(28)k H z.

Absolute frequency measurement of a Yb optical clock at the limit of the Cs fountain

We present the new absolute frequency measurement of ytterbium (171Yb) obtained at INRiM with the optical lattice clock IT-Yb1 against the cryogenic caesium (133Cs) fountain IT-CsF2, evaluated through a measurement campaign that lasted 14 months. Measurements are performed by either using a hydrogen maser as a transfer oscillator or by synthesizing a low-noise microwave for Cs interrogation using an optical frequency comb. The frequency of the 171Yb unperturbed clock transition SP0 results to be 518 295 836 590 863.44(14) Hz, with a total fractional uncertainty of that is limited by the uncertainty of IT-CsF2. Our measurement is in agreement with the Yb frequency recommended by the Consultative Committee for Time and Frequency. This result confirms the reliability of Yb as a secondary representation of the second and is relevant to the process of redefining the second in the International System of Units on an optical transition.

Suppression of the Equivalent Magnetic Noise Caused by Electron Spin Polarization in a Xe Isotope Comagnetometer

The Xe isotope comagnetometer in the nuclear magnetic resonance regime can be used as a promising high-precision inertial measurement unit because of the absolute frequency measurement and high bandwidth. The fluctuation of the electron spin polarization leads to equivalent magnetic noise in the Xe isotope comagnetometer, which is one of the main factors limiting the stability of the comagnetometer. Here, we demonstrate systematic research of equivalent magnetic noise suppression and analyze the influence of the electron spin polarization on the Xe isotope comagnetometer. Based on the spin–exchange method between Xe isotopes and alkali metal atoms through the Fermi contact hyperfine interaction, the error equation of the Xe Larmor frequency is established. The equivalent magnetic noise can be suppressed by controlling the static magnetic field. This suppression method for Xe isotope comagnetometers improved the stability while maintaining high bandwidth. The experimental results show that this method can reduce the fluctuations of the 129Xe and 131Xe frequencies by 75% and 68.6%, respectively.

High-resolution isotope-shift spectroscopy of Cd i

We present absolute frequency measurements of the ${}^{1}\text{P}_1 \leftarrow {}^{1}\text{S}_0$ ($229$nm) and ${}^{3}\text{P}_1 \leftarrow {}^{1}\text{S}_0$ ($326$nm) transitions for all naturally occurring isotopes of cadmium. The isotope shifts and hyperfine intervals of the fermionic isotopes are determined with an accuracy of 3.3MHz. We find that quantum interference in the laser-induced fluorescence spectra of the ${}^{1}\text{P}_1 \leftarrow {}^{1}\text{S}_0$ transition causes an error of up to 29(5)MHz in determining the hyperfine splitting, when not accounted for with an appropriate model. Using a King-plot analysis, we extract the field- and mass-shift parameters and determine nuclear charge radius differences for the fermions. The lifetime of the $^1\text{P}_1$ state is determined to be 1.60(5)ns by measuring the natural linewidth of the ${}^{1}\text{P}_1 \leftarrow {}^{1}\text{S}_0$ transition. These results resolve significant discrepancies among previous measurements.

Absolute frequency measurement of the 87Sr optical lattice clock at NTSC using international atomic time

We report the absolute frequency measurement of the transition in 87Sr optical lattice clock (Sr1) at National Time Service Center. Its systematic frequency shifts are evaluated carefully with a total relative uncertainty of . The measured absolute frequency is 429 228 004 229 872.91(18) Hz with a relative uncertainty of , with reference to the ensemble of primary and secondary frequency standards published in the Circular T bulletin by BIPM through a global navigation satellite system link.

Accurate absolute frequency measurement of the S(2) transition in the fundamental band of H2 near 2.03 μm.

A series of spectra of the quadrupolar electric S(2) transition of H2 in the 1-0 band near 4917 cm-1 has been recorded at seven pressure values between 2 and 100 Torr. The comb-referenced cavity ring down spectroscopy (CR-CRDS) technique was used for the recording of this very weak transition. The accuracy of the spectrum frequency axis is achieved by linking the CRDS setup to an optical frequency comb referenced to a GPS-referenced 10 MHz rubidium clock. Applying a multi-spectrum fit procedure to the seven averaged spectra with a quadratic speed dependence Nelkin-Ghatak profile, the transition frequency is determined (ν0 = 147 408 142 357 kHz) with an uncertainty of 150 kHz (∼1 × 10-9 in relative). This represents the smallest uncertainty achieved so far for a transition in the fundamental band of H2. The experimental frequency reported in this work is 1.53 MHz higher than the best-to-date theoretical value. This difference represents 1.5 times the 1σ-uncertainty (about 1 MHz) of the calculated frequency. The measurements also allow for the determination of the absolute intensity value of the S(2) line which shows an agreement with the ab initio value at the per mil level. In addition, the cross section of the collision induced absorption (CIA) underlying the S(2) line is accurately retrieved from the quadratic pressure dependence of the baseline level of the recorded spectra.

Improved absolute frequency measurement of the strontium ion clock using a GPS link to the SI second

We report on an improved absolute frequency measurement of the – optical transition of a single trapped strontium ion using a Global Positioning System (GPS) link to the SI second. Compared to our previous measurement, the systematic uncertainty of the optical clock has been reduced from to . The measurement campaign was performed over a two-week period in June 2017, with a total measurement time of 92 h. The traceability to the SI second through International Atomic Time was achieved through a GPS link using the Precise Point Positioning method. The dead time uncertainty of the link between the optical clock and the maser was evaluated using standard methods based on a model of the maser noise and on the optical frequency measurement uptimes. The measured frequency of the 88Sr+ ion – transition is Hz. This result is in excellent agreement with our previous measurements and the uncertainty has been reduced by almost a factor of four, from a fractional frequency uncertainty of to .

Absolute frequency measurement of the 6s21S0 → 6s6p3P1F = 3/2 → F' = 5/2 201Hg transition with background-free saturation spectroscopy.

We report the development of a method for eliminating background-induced systematic shifts affecting precise measurements of saturation absorption signals. With this technique, we measured the absolute frequency of the 6s21S0 → 6s6p3P1 transition in 201aHg (F = 3/2 → F' = 5/2) to be 1181541111051(83) kHz. The measurement was referenced with an optical frequency comb synchronized to the frequency of the local representation of the UTC. This specific atomic line is situated on the steep slope of the Doppler background at room temperature, which results in a frequency systematic shift. We determined the dependence of this shift on the properties of both the spectral line and the background of the measured signal.

Traceability of optical frequency to SI second via UTC(NIM)

Absolute frequency measurement of an optical clock is a milestone towards the redefinition of second in the International System of Units. This work summarizes briefly the measurement of frequency ratio between an optical clock and the second, applying the frequency comparison link from UTC(NIM) to International Atomic Time. Some strategies and suggestions are proposed to reduce the uncertainty introduced by the measurement system and dead time, which guided the frequency measurement of three optical clocks at 10−16 level in the past 3 years.

Rydberg Microwave-Frequency-Comb Spectrometer

The developing frequency-comb spectral technologies have potential applications and prospects in the wide fields of cosmology, meteorology, and microwave measurement. Here, we demonstrate a Rydberg microwave-frequency-comb spectrometer via multiple-microwave field dressing, providing precise microwave measurement. The Rydberg microwave-frequency-comb spectrum provides a real-time and absolute-frequency measurement with a range of 125 MHz and gives the relative phase of a single-frequency microwave signal. The reported experiment helps real-time sensing of an unknown microwave signal over a wide range using Rydberg atoms, which are vital for Rydberg-atom-based microwave metrology.

A compact, transportable optical clock with 1×10−17 uncertainty and its absolute frequency measurement

We report a robust, compact, and transportable optical clock (TOC-729-2) based on a trapped single 40Ca+ ion with a systematic uncertainty of 1.1×10−17, which is limited by the black-body radiation shift uncertainty at room temperature. By comparing it with the previous transportable optical clock (TOC-729-1) similar but completely independent, the instability was measured to be better than 1.2×10−14/τ. Benefiting from the modular and integrated design, this TOC was constructed in a volume of ∼0.33 m3 excluding the controlling electronics in 19-in. racks. After being moved ∼1200 km away by express delivery, the single-ion signal was restored within 24 h. With the TOC uptime of 92% in 35-day period, the absolute frequency of the 729 nm transition of 40Ca+ was measured using a satellite link to International Atomic Time (TAI) to provide traceability to the SI second, and the result is 411 042 129 776 400.15(22) Hz, corresponding to a relative uncertainty of 5.3×10−16.

Absolute frequency measurement of the 3ν1 band of N2O with comb-locked rapid scan spectroscopy using a multi-pass cell

The 3ν1 vibration band of 14N2O at 1.52 µm is observed with a frequency comb referenced CW laser. Utilizing the high sensitivity and frequency accuracy of a spectrometer, we have determined 47 transition frequencies from P(28) to P(6) and from R(5) to R(28) under a sample pressure of about 40 Pa (300 mTorr) with a measurement uncertainty of 0.55 MHz. We also determined that the self-induced pressure shift coefficient for the P(12) transition is −1.76(7) kHz/Pa (−0.235(9) MHz/Torr). Three molecular constants of the upper state are yielded by fitting the line positions with a standard deviation of 0.71 MHz. The line positions and molecular constants that we determined are consistent with previous work on cavity ring down spectroscopy [G. –L. Liu, et al., J. QUANT. SPECTROSC RADIAT, 229 (2019) 17–22].

Absolute frequency measurement of the 6D5/2 level of neutral Cs133 using two-photon spectroscopy

We report absolute frequency measurements on the $6{D}_{5/2}$ level of neutral $^{133}\mathrm{Cs}$ using sub-Doppler two-photon spectroscopy. The absolute center-of-gravity energy for the $6{D}_{5/2}$ level is determined to be $22\phantom{\rule{0.16em}{0ex}}631.683\phantom{\rule{0.16em}{0ex}}877(6)\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, a factor of 170 times improvement over the previous measurement from 1964 of $22\phantom{\rule{0.16em}{0ex}}631.6863(10)\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. This measurement also corrects a $2.4\ensuremath{\sigma}$ discrepancy with the previously measured value. The hyperfine coefficients were found to be $A=\ensuremath{-}4.629(14)$ and $B=\ensuremath{-}0.10(15)\phantom{\rule{0.28em}{0ex}}\mathrm{MHz}$, which are consistent with previous results.