MHz Accuracy Research Articles

Saturation-dip measurements for the ν_8 C-O stretching band of CH_3OH with a CO_2-laser-microwave-sideband spectrometer

Saturation-dip measurements for the ν8 C-O stretching band of CH3OH have been systematically carried out with a CO2-laser-microwave-sideband spectrometer operating on low- and high-J 9.6 μm P-branch CO2 laser lines. Frequencies of nearly 500 spectral lines, including overlapped and doublet lines unresolved in dense Doppler-limited spectra, have been measured with a resolution of 0.4MHz and absolute accuracy of the order of ±100 kHz. Over 200 frequency combination loops have been formed from the present and previous sub-Doppler observations, unambiguously confirming the infrared transition assignments, and refined term values have been determined for 623 excited vibrational levels. These results constitute a substantial database of high-accuracy frequency reference standards for CH3OH in the 10 μm region, with applications in frequency calibration, in detailed studies of the complicated methanol intermode vibrational interactions, and in the interpretation of optically pumped far-infrared laser emission.

Stable lightwave frequency synthesiser using discrete-timenegative frequency feedback with polarisation diversity technique

A stable lightwave frequency synthesiser has been realised by combining discrete-time negative frequency feedback with a polarisation diversity technique. It is confirmed that this synthesiser operated stably for 24 h by using an optical frequency counter with 100 MHz accuracy.

Frequency-stabilization of a diode laser with ultra-low power through linear selective reflection

Linear selective reflection spectroscopy stabilizes the emission frequency of a diode laser. A 10 nW beam intensity is sufficient to lock the nominal frequency on the 852 nm Cs line with 1 MHz accuracy. Applications may concern laser cooling as well as stabilization of 1.5 μm lasers on atomic references.

A Dense Grid of Reference Iodine Lines for Optical Frequency Calibration in the Range 571–596 nm

A high precision dense grid of reference lines in the hyperfine structure of theB–Xsystem of molecular iodine (127I2) is presented. A simple parametrization has been derived, predicting the hyperfine line positions of the “t” components for vibrational bands (13-1) up to (18-1) and rotational quantum numbersJ= (9–140). The analysis in this paper is based on Doppler-free saturation spectroscopy spectra used for calibration of more than 100 new components in the hyperfine structure of127I2. The data presented contains a prediction (with 2 MHz accuracy) for the positions of 1584 “t” components in the rotational structure of iodine, covering the wavelength interval 571–596 nm.

Power system frequency estimation

A new algorithm of power system frequency estimation is presented. The algorithm applies orthogonal signal components obtained with use of two orthogonal FIR filters. The essential property of the algorithm presented is its outstanding immunity to both signal orthogonal component magnitudes and FIR filter gains variations which ensures 1.5 mHz accuracy of estimation over typical (±2 Hz) range of measured frequency deviation. The results of the algorithm simulation tests using the EMTP software package are also included. It was confirmed that the algorithm dynamics are good enough to track power system frequency even under transient conditions.

High-resolution infrared and infrared radiofrequency double-resonance spectroscopy of the ν2 band of CD 3I

Approximately 175 transitions in the ν 2 band of CD 3I near 949.360 cm −1 have been recorded at Doppler-limited resolution and 2–10 MHz accuracy by means of an infrared microwave sideband laser spectrometer. About 150 radiofrequency resonances, half each in the ground and v 2 = 1 states, have been recorded at 70 kHz resolution and 5–20 kHz accuracy by using the infrared microwave sideband system as a pumping source for infrared radiofrequency double resonance. In addition to demonstrating the usefulness of this technique for systematic infrared radiofrequency double resonance, the radiofrequencies have been combined with previous measurements of microwave, millimeter-wave, and infrared radiofrequency double-resonance spectra to determine nuclear quadrupole coupling parameters, including centrifugal distortion effects, and spin-rotation parameters for the iodine nucleus. The infrared frequencies have been converted to hypothetical unsplit frequencies and combined with similarly converted microwave and millimeter-wave frequencies to obtain improved rotational and centrifugal distortion constants for the ground and v 2 = 1 states in CD 3I. These constants have been used to calculate coincidences with CO 2 laser frequencies for J ≤ 40 and K ≤ 10 and to assign three previously reported submillimeter-wave laser transitions.

MILLIMETER-WAVE SPECTROSCOPY OF CESIUM RYDBERG STATES AND POSSIBLE APPLICATIONS TO FREQUENCY METROLOGY

An extensive high-resolution study of the millimeter-wave spectrum of Cesium Rydberg states is presented, yielding new precise values of the nS, nP, nD and nF states quantum defects (23 ⩽ n ⩽ 45), and of their fine and hyperfine structures. The quantum defects values allow us to predict the frequency of any n,l → n',l' (n ⩾ 20, l ⩽ 3) transition, with a MHz accuracy. This precise mapping of the Cesium Rydberg states can provide a new secondary frequency standard in the 50 GHz - 10 THz range. Possible interesting metrological applications are discussed.