IEEE Transactions on Instrumentation and Measurement

This paper proposes a Kalman filter-based attitude (i.e., roll and pitch) estimation algorithm using an inertial sensor composed of a triaxial accelerometer and a triaxial gyroscope. In particular, the proposed algorithm has been developed for accurate attitude estimation during dynamic conditions, in which external acceleration is present. Although external acceleration is the main source of the attitude estimation error and despite the need for its accurate estimation in many applications, this problem that can be critical for the attitude estimation has not been addressed explicitly in the literature. Accordingly, this paper addresses the combined estimation problem of the attitude and external acceleration. Experimental tests were conducted to verify the performance of the proposed algorithm in various dynamic condition settings and to provide further insight into the variations in the estimation accuracy. Furthermore, two different approaches for dealing with the estimation problem during dynamic conditions were compared, i.e., threshold-based switching approach versus acceleration model-based approach. Based on an external acceleration model, the proposed algorithm was capable of estimating accurate attitudes and external accelerations for short accelerated periods, showing its high effectiveness during short-term fast dynamic conditions. Contrariwise, when the testing condition involved prolonged high external accelerations, the proposed algorithm exhibited gradually increasing errors. However, as soon as the condition returned to static or quasi-static conditions, the algorithm was able to stabilize the estimation error, regaining its high estimation accuracy.

A temperature standard in the body temperature (clinical) region would be helpful in calibrating fever thermometers, now largely electronic. Temperature standards (fixed points) commonly use the freezing point of a pure material, often a metallic element. A check of the periodic table reveals only one suitable candidate, rubidium, which melts at 38.89° C(102.00°F). Rubidium, however, is an awkward material to handle. A hydrocarbon plastic (polystyrene, polyethylene, polypropylene) would make a suitable container for the same reason. The device should require only a small quantity of rubidium. Detecting the melting/freezing transition should not be difficult, as rubidium has two helpful properties, either one of which may be used for the purpose. On melting its volume expands 3.7%, and its electrical resistivity rises 58%, from 14.21 to 22.52 μohm-cm. A unity ratio ac bridge might be used, one arm being a solenoid surrounding the rubidium container, and the other a solenoid surrounding a metal of similar dimensions, with resistivity intermediate between that of liquid and solid rubidium, e.g., tin-lead alloys. A three-coil arrangement of the type used in linear displacement transducers might also be used with the two metals

A short-circuited-ring electrodynamic ammeter is described. The short-circuited ring is supported by a fine quartz fiber and is suspended midway between the inner and outer conductors of a coaxial transmission line. The current on the line is found by measuring the torque exerted against the ring by the current on the coaxial line. A new technique is given for determining the relationship between the torque on the ring and the current on the transmission line, and is compared with the technique used in the past. The new method is an application of the resonator action theorem used by Cullen for calibrating a torque-operated microwave wattmeter. The major weakness in the previous evaluations of the torque-current relation is discussed. The ammeter is useful for measuring current from 1 to 100 amperes over the frequency range 1 MHz to 1 GHz, with an uncertainty of the order of 0.5 percent.

We present the results of a gravitational experiment which is based on a microwave resonator. The gravitational force of a test mass acting on the resonator is measured as a function of distance. No deviation from Newton's law on a level of a few parts in 10^-4 in the near range has been found and the gravitational constant G has been determined with a relative accuracy of 1.1×10^-4 to be: G=(6.6719±0.0008)×10^-11 Nm² kg ^-2

Many industrial processes and scientific experiments utilize large amounts of ac power at frequencies from 3 kHz to 500 kHz. The phase angle and the impedances of these loads often vary over a wide range. This paper describes an instrument to provide an accurate measurement of currents (1 A to 1000 A), voltages (100 V to 20 kV), and powers (100 W to 20 MW) over the frequency range from 25 kHz to 500 kHz. It deals with loads having power factors down to nearly zero and with load impedances from 10 Ω to 20 kΩ. The paper contains practical details of both the design and the calibration of the front-end voltage and current transducers. The characteristics of a nearly ideal broadband current transducer are presented. Overall instrument calibration, verification and traceability problems are considered in detail

At a frequency of 30 MHz-a commonly used intermediate frequency-two micropotentiometers have been intercompared at a voltage level of 0.001 V and in a second exercise two thermal converters at a level of 100 V. Seven national laboratories of metrology from China, Finland, the former German Democratic Republic, Hungary, the United States (U.S.A.), India, and the Federal Republic of Germany with the PTB as pilot laboratory participated in the first comparison and three of them also in the second one. In this paper, the methods for determining the RF-dc transfer differences are described and the results of the intercomparison are presented. The results proved that uncertainties between 0.002 and 0.005 can be obtained for the transfer difference at 30 MHz with the stepping-up and stepping-down procedures used to perform accurate high and low voltage measurements referred to a national RF voltage standard at 1 V

A magnetic-field measurement probe capable of a resolution of 0.001 per cent is described. The probe employs bifilar wound heating pads and a platinum resistance thermometer to maintain the temperature of its enclosure within 0.1°C. A thermistor-resistor network compensates for the effects of self-heating due to changing power dissipation in the control side of the sensitive element. The probe was calibrated and tested with nuclear magnetic resonance equipment. The results obtained are discussed.

This paper describes an inexpensive implementation of a dual six-port microwave network analyzer that features extensive use of on-hand facilities. The system's performance compares favorably with that of more expensive, fully automated, self-contained systems with one exception: significantly more time is required to change measurement frequencies.

A series-resistors-type voltage divider is one of the most commonly used dividers. We have carefully analyzed various error sources such as leakage current, normal mode rejection ratio of the voltmeter, temperature coefficient, and others. The KRISS' 10:1 divider which was used for 10-V calibration was chosen for this study. Here, we would like to describe some common error sources and their effects which should be taken into account in the level of 10^-8 or below for the series-resistors type voltage dividers

A frequency-to-voltage converter is described, for use as a control circuit in a voltage-controlled oscillator with a 100-kHz central frequency, varying within an octave on either side. Conversion is effected by averaging standard pulses of constant width and constant height, corresponding to the zero cross of each cycle of the measured frequency. Accuracy of 0.01 percent and better is secured by determining the pulsewidth by an exact digital system and determining the pulseheight by switching an exact current source. The range of measurement and response time may be varied by the user in accordance with his optimization requirements.

Thermal voltage converter structures have been modeled theoretically and studied experimentally to determine their AC-DC differences in the 0.1-100-MHz frequency range. Estimated uncertainties, corresponding to the one standard deviation confidence level, for these AC-DC differences vary from 20 p.p.m. at 1 MHz to 2000 p.p.m. at 100 MHz

Prompted by the need to support vibration and pressure measurements at frequencies down to 0.5 Hz (with expected future needs to 0.1 Hz), NBS now offers a calibration service for voltage standards and rms voltmeters in the range of 0.1-10 Hz. The means for the service is an "ac Voltmeter/Calibrator," an NBS-developed instrument containing an rms digital voltmeter and ac and dc voltage calibrators. The methods used to calibrate the ac voltage calibrator are discussed; also, application of the ac Voltmeter/Calibrator to the calibration of customers' voltage and voltmeter standards is described. Finally, a multifrequency voltage reference source with frequency-independent amplitude is proposed as a more suitable transfer standard than thermal voltage converters (TVC's) for the 0.1-10-Hz range.

The Dielectric Specimen Bridge has been developed to measure polyethylene's dissipation factor of approximately 60× 10-6 to an accuracy of approximately 10-6 over the frequency range of 0.1 MHz to 10 MHz. The specimen holder is of the liquid displacement type employing silicone fluid. A specimen consists of two 0.050-inch thick sheets, 2.7 inches wide by 2.0 inches high. Low-impedance coaxial spring fingers provide a highly reproducible connection between the holder and the bridge. The bridge is of the unity ratio type with 100-picofarad ratio arms and adjustable capacitance and conductance standards. The conductance standard contains four decades, each consisting of a small fixed capacitor in series with a resistance decade. A specially developed phase-sensitive detector prevents capacitance changes of several parts per million from obscuring the observation of the desired conductance balance. This detector has continuous tuning and uses heterodyne techniques. The bridge is calibrated with an external conductance standard which consists of a capacitor in series with an interchangeable resistor, and has a geometry and element values such that the radio frequency conductance can be determined from low-frequency measurements. Since the liquid displacement method measures the difference between the dissipation factors of the polyethylene and the silicone fluid, the bridge is being used to make measurements of the dissipation factor of the fluid itself. In addition, measurements are being made of the dissipation factor of air.

The single ion Penning trap mass spectrometer at M.I.T. now compares masses with an accuracy of 0.1 part per billion. We have created a table of fundamental atomic masses and made measurements useful for calibrating the X-ray wavelength standard, and determining Avogadro's number, the molar Planck constant, and the fine structure constant

A 10-kV stabilized supply with a dc capacity of 10 mA has been constructed. Its drift rate measured over time intervals greater than about 1 minute and extending to times of more than 10 hours is about 1 part in 107 per hour. For shorter times from 1 second to 1 minute the peak-to-peak deviation from the mean is about 2 mV at 9.2 kV or ±1 part in 107. This performance has been achieved by the use of an initially well regulated commercial 10-kV supply in a closed-loop control system. High dc loop gain has been achieved by the use of a chopper-stabilized amplifier, and a guarded resistive divider of special design. The reference voltage is made up of a bank of unsaturated standard cells enclosed in a temperature-controlled air bath whose short term temperature stability is ±0.001°C. The control resistive divider, together with a measuring divider and a guard divider, are enclosed in an oil bath whose temperature is controlled near ambient to within ±0.01°C.

A wide-range low-permanent-field standard measurement system is described, intended for use within the geomagnetic range of natural magnetic fields on the earth's surface (20-100 μT), fields of near and distant outer space (0.1-20 μT), and precision current-carrying high-uniform-field coil systems used in fundamental and applied research (up to 1.5 mT).

The author describes a standard time-division-multiplexing (TDM) wattmeter with a constant average carrier frequency, no inherent phase error, and known systematic magnitude frequency error, as well as efforts to increase frequency bandwidth. The residual error of the wattmeter, after corrections, is below 100 p.p.m. up to 5 kHz. The meter is expected to find application in accurate power measurements under distorted and low power factor conditions, and as a transfer standard for interlaboratory comparisons

The results are presented of an international comparison of measurements of the complex reflection coefficient in the G 900-14 mm/50 Ω coaxial line technique at 0.5 GHz, 3 GHz and 7 GHz in which eleven national laboratories of metrology participated. The standards showed very small drifts of the reflection coefficient over a period of nine years. With few exceptions, good agreement between the mean values reported by the various participants is observed

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

Nuclear spin systems follow the Curie law down to far below 1 mK and can provide an accurate standard of temperature below 0.5 K. Pulsed nuclear magnetic resonance (NMR) techniques are used to measure the susceptibility to an accuracy of one part in one thousand in a copper sample below 4.2 K. The method has been found experimentally to be useful down to 25 mK; the theoretical limit is much lower.

A robust high-accuracy analog-signal-processing 0.5-mum CMOS chip for real-time heart-rate (HR) extraction is presented. A novel peak-detector architecture is proposed and implemented to facilitate on-chip integration. The system is capable of processing electrocardiogram (ECG) signals with a peak-to-peak amplitude as low as 5 mV, without any prefiltering. Experimental results with prerecorded and real-time ECG signals have demonstrated the obtained R-R interval accuracy on the order of milliseconds. The system was also used to successfully extract HR intervals with Doppler radar. Such a system may significantly reduce ADC resolution and sampling speed requirements while providing high immunity to noise and DC offset drift.

We report the successful observation of high-fields optically pumped nuclear magnetic resonance (NMR) of helium-3 and electron spin resonance (ESR) of atomic hydrogen, both at 0.6 T. Also described are our findings on the relative optical pumping efficiencies of the various components of the 1083 nm line in helium-3. These are a precursor to a measurement of the magnetic moment of the helion in Bohr magnetons. For this measurement the two signal frequencies must be measured sucessively in the same apparatus. This work is aimed at overcoming the limitations for high-accuracy magnetometry of using water as an NMR substance

A reevaluation of the NIST standards of ac-dc difference was undertaken in an effort to reduce the calibration uncertainty offered by NIST for thermal voltage converters (TVC's) at frequencies below 100 Hz. This paper describes the measurements taken in support of this effort, as well as the devices used for the reevaluation process and the analysis of the uncertainty of the measurements. This reevaluation of the NIST low-frequency standards will permit a significant reduction in uncertainty for ac-dc difference calibrations at 10 Hz in the voltage range from 0.6-100 V

Over the last several years, we have made many improvements to NIST-F1 (a laser-cooled cesium fountain primary frequency standard) resulting in nearly a factor of 2 reduction in the uncertainty in the realization of the SI second at the National Institute of Standards and Technology. We recently submitted an evaluation with a combined standard fractional uncertainty of 0.61×10^-15 to the Bureau International des Poids et Mesures (BIPM). The total fractional uncertainty of the evaluation (including dead time and time transfer contributions) was 0.88×10^-15. This is the smallest uncertainty in a frequency standard yet submitted to the BIPM.

The design and implementation of a complete gas sensor system for liquified petroleum gas (LPG) gas sensing are presented. The system consists of a SnO₂ transducer, a lowcost heater, an application specific integrated circuit (ASIC) with front-end interface circuitry, and a microcontroller interface for data logging. The ASIC includes a relaxation-oscillator-based heater driver circuit that is capable of controlling the sensor operating temperature from 100degC to 425degC. The sensor readout circuit in the ASIC, which is based on the resistance to time conversion technique, has been designed to measure the gas sensor response over three orders of resistance change during its interaction with gases.

We report on the frequency stabilization of extended-cavity diode lasers against rotovibrational absorption lines of water vapor at around 0.94 mum, by means of the frequency modulation spectroscopy technique. A minimum frequency instability of ~ 30 kHz has been obtained for integration times in the range from 1 to 100 s

A method is described for testing precision current transformers, particularly devices with very high values of rated primary current and rated secondary currents up to 200 A. It makes use of the well-known differential method (Arnold, Hohle), substituting, however, the common resistor with an electronic operational amplifier, thus yielding an almost negligible resistance and a very high sensitivity of 0.01 ppm. Results of ratio error measurements are reported at values of primary currents between 500 and 100 000 A.

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A 100000-A, high precision device of the magnetic modulation current comparator type, which can be used in industrial heavy direct current systems for online calibration and measurement, is presented. Testing of the comparator indicates that its current ratio accuracy is 5×10^-5, and that measurements of voltage with a standard resistor achieve an accuracy of 5×10^-4. These are slightly degraded to 3×10^-4 for on-site calibration and 1×10^-3 for on-site measurement. The device, which has a toroidal configuration, can be opened for each installation on a busbar, with a variation in accuracy of less than 2×10^-5. Its magnetic shielding renders it insensitive to magnetic fields up to 1×10^-2 Tea. Its accuracy is better by a factor of two than that of similar industrial measuring devices. The principle of operation and the characteristics of the comparator, the double shielded design, and an analysis of its errors are discussed

A standard apparatus is described for realization of the unit of ac electric power at power factors close to zero and for investigation of the angular error of voltage dividers in the frequency range 40 Hz to 20 kHz. The uncertainty of the reference apart from the current shunt angular error is estimated to be 15 μrad at 40–400 Hz and 60 μrad at 20 kHz. The quadrature between the test voltage and current is established by the equality of the sum and difference magnitudes of the test voltage and the voltage drop across the shunt with the use of two thermal voltage converters. A thermal multiplier unit with adjustable angular error is used for investigation of the voltage dividers.

The Mars Pathfinder, Mars Surveyor '98, and Mars Surveyor '01 lander designs all utilize CCD-based cameras to conduct scientific investigations, assist with navigation of surface reverse and/or confirm sample acquisition and delivery by robotic arms. The extreme temperature and pressure environment of the Martian surface, the vibration and shock experienced during launch and landing, and the tight volume, mass, and power budgets challenge the designer and scientist alike to develop instruments and associated electronics that will function properly to provide the desired data. This paper provides an overview of the optical and mechanical design of two of the camera configurations, as well as a detailed description of the camera electronics. The cameras described are a gimbal-mounted stereo multi-spectral imager with 1 mrad/pixel resolution, and a variable focus robotic arm camera capable of 23-μm/pixel resolution and provided with a self-contained three-color illumination system. The electronics, housed in the cameras and in separate enclosures, utilizes such subsystems as FPGAs for digital control, VME bus-mapped video memory, and multiplexed stepper motor select/phase driver circuitry

From August 1995 to May 1998, the CCE 92-05 intercomparison of ac-dc voltage transfer standards at high frequencies was carried out. Two travel standards were measured by 15 national standards institutes. The results in the frequency range from 1 to 50 MHz show a good agreement between the majority of participants. The span of the majority of the reported ac-dc differences at 50 MHz is less than 1000 mu V/V, which is similar to a previous intercomparison but with a greater number of participants.

The detection statistics of a molecular beam are analyzed, taking into account fluctuations in emission, transition and detection. It is discovered that the over-all process has a Poisson distribution. Because of the nature of this distribution, it is noted that the optimum method of estimating the average number of molecular transitions is by means of a long-time average of the detected current. The degree to which the detector current is a measure of the average number of molecular transitions in the device is established, with a certain minimum confidence, by use of the Tchebycheff Inequality.

The broadband dielectric properties of 10 % formalin and 1,4 dioxane are presented in this paper. A variable temperature, variable thickness interferometer was assembled to perform dispersive Fourier transform spectroscopy on liquids. Using the two thickness method, the refractive index, absorption coefficient, real and imaginary permittivity, and loss tangent were obtained as a continuous function of frequency from 60 to 600 GHz (2-200 cm). Knowledge of these properties can facilitate future research in examining certain tissues and mixtures. Tests on chlorobenzene were also conducted as a calibration reference

The broadband millimeter-wave dielectric properties of chlorobenzene, cyclohexane, 10% formalin, and 1,4-dioxane are presented for the first time in this paper. A variable-temperature variable-thickness interferometer was assembled to perform dispersive Fourier transform spectroscopy on liquids at millimeter and submillimeter waves. Using the two-thickness method, the refractive index, absorption coefficient, real and imaginary permittivities, and loss tangent were obtained as a continuous function of frequency from 60 to 600 GHz (2-20, 5-0.5 mm). Resonance patterns for cyclohexane, 10% formalin, and 1,4-dioxane were detected. Knowledge of these properties can facilitate future research in examining biological tissues and mixtures.

This paper summarizes the calibration of precision coaxial air lines in a 3.5-mm line size. The standard system of the National Metrology Institute of Japan (NMIJ) is used to accurately obtain mechanical measurements of the diameters and lengths of lines. Length compression of approximately 6.0 mum and diameter distortions caused by connections with specified torques have been observed in 3.5-mm air lines. A small insertion loss in the millimeter-wave frequency range has also been detected. Furthermore, NMIJ has established standards for scattering parameters in the frequency range up to 110 GHz for coaxial air lines in the 1.0-mm line size by the enhancement of mechanical measurement systems.

The authors describe a new automated measurement system for the direct calibration of the 1.018-V outputs of Zener-based electronic voltage standards with a programmable Josephson array. It features a programmable bias supply and a multiplexer that introduces negligibly small thermal EMFs in the critical circuits. Detailed descriptions of the two devices are given in this paper. A validation program is in progress in parallel with the previous chain, as no instruments are shared between the two

A longitudinally pumped, widely tunable, solid-state Yb:KYF₄ laser was developed with special design for applications to optical frequency metrology and absolute frequency stabilization. The KYF₄ crystalline host, combined with efficient diode pumping, allows for wide wavelength tunability at about 1.03 mum in a single transverse mode. Two different laser cavity designs were experimentally investigated. The combined use of an intracavity birefringent filter and uncoated glass etalons provides single-frequency output power at the 100-mW level in a folded-cavity resonator. A second hemispherical linear cavity was also developed with one or two coated intracavity etalons for single-frequency operation. The novel laser sources were thoroughly characterized in terms of output power and beam quality, amplitude noise, wavelength tunability, and single-axial-mode operation. High-quality TEM₀₀ single-frequency laser radiation opens the way to the development of a new optical frequency standard based on the I ₂ molecule at 0.5- mum wavelength.

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

An accurate self-adjusting CMOS RC oscillator for capacitive and resistive sensor applications has been designed and manufactured. The oscillator operates with supply voltages from 1.2 to 3 V and achieves an internal accuracy of plusmn0.7% with a temperature range from -20degC to 60degC. The RC oscillator was fabricated in a 0.35-mum standard n-well CMOS process with threshold voltages of 0.5 and -0.65 V. Its design and operation are described, and results of measurements performed on the fabricated chips are presented.

A Doppler-free stimulated-emission technique using an optically pumped I₂ laser with applications in spectroscopy and infrared frequency standards is reported. A single mode CW Ar ion laser, locked on a hyperfine component of the 13P(43-0) line of the B-X electronic transition ¹²⁷I₂ iodine molecule, is used as laser pump. Continuous wave oscillation is observed on transitions belonging to the B-X system into highly excited vibrational levels of the ground state. The long term stability of the Ar laser (Δν/ν≈10^-13 in 100 s) can be transferred to the iodine laser

A single-mode distributed feedback (DFB) fiber laser has been frequency locked to a CO₂ absorption line at 1578.665 nm to demonstrate its potential as a wavelength standard. A frequency stability of 10^-8 (≈2 MHz) was achieved on a time scale of minutes. A mechanical lead screw provided coarse wavelength tuning, white wavelength modulation and fast frequency corrections were applied by straining the fiber laser with piezoelectric transducers. With a suitable choice of absorption line, such a system may serve as an absolute frequency reference for dense wavelength-division multiplexing grids in telecommunication

We have made a frequency standard operating at the 1.5 μm region using the saturated absorption of the v₁+v₃ band of ¹³C₂H₂. To enhance the moderate power from a laser diode and to saturate a very weak molecular overtone transition, we used a Fabry-Perot (FP) cavity and inside of it we put an acetylene cell. In order to obtain a longer life time for the cell, we designed a new scheme consisting of a cavity with a ULE (ultralow expansion) glass spacer and a baked and sealed-off cell with Brewster windows. We observed the saturated spectrum having a 1 MHz spectral linewidth. The signal obtained using the same cell ten months later had the same signal-to-noise ratio (SNR) and spectral linewidth. We made two versions of the frequency standard and observed a beat note between these two lasers from which we derived the frequency stability, in terms of the square root of the Allan variance σ(τ)=2.4×10^-13 at an integration time τ=1000 s

Group velocity dispersion (GVD) measurement is presented utilizing supercontinuum (SC) white pulses generated in an optical fiber by 15 μm compact laser sources. This provides 1) ultrawide continuous spectral measurement range >600 nm from a single optical source without the use of interpolation formulae and 2) stable far-end measurements by the simultaneous multi-wavelength nature of the SC pulses. A novel method that is independent of the detector bandwidth is proposed which measures λ-dependent phase shifts of one of the Fourier components of a short pulse train. Fiber GVD's of unusual dispersion characteristics were measured using SC pulses extended over the spectral range of 1150-1770 nm. It is shown that fiber lengths of up to 130 km can be measured with a group delay resolution of 0.01 ps/km

Non-linear spectroscopy of the acetylene molecule has been performed in the wavelength range from 1532 nm to 1549 nm, by means of a novel diode-pumped Er-Yb:glass laser with single frequency emission and narrow linewidth (<50 kHz over 1 ms). In order to saturate the acetylene lines, the gas sample was placed within an external high finesse resonator. Measurements of the spatial beam quality, linear polarization state and sensitivity to pump amplitude noise have been performed

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We report on the absolute frequency stabilization of Yb-Er:glass lasers against different acetylene absorption lines in the 1.5 μm spectral region. An external frequency modulation technique was adopted to independently stabilize two diode-pumped erbium microlasers against the P(15) rovibrational line at 1534.099 nm. A long-term frequency stability below 10^-9 (200 kHz) was measured on both the closed-loop error signal and on the beat note frequency. From the beat signal analysis, a 1 ms laser linewidth of 50 kHz was observed. The Allan standard deviation of the beat frequency was below 10^-10 for integration times between 10 ms and 1 s and as low as 4×10^-11 around 0.1 s

A novel and compact Er-Yb:glass laser was developed with single-frequency output power >10 mW in a wavelength range from 1531 to 1547 nm. The laser output was efficiently frequency doubled at 770.1 nm in a single-pass periodically poled lithium niobate waveguide and a second harmonic power in excess of 15 μW was achieved, with an internal conversion efficiency of ∼220% W^-1. This frequency-doubled beam was used for high-resolution saturated spectroscopy of the ³⁹K 4S₁2 /-4P₁2 / absorption line. The best resolved crossover peak showed 16% line contrast and 10-MHz linewidth. In a second experiment, working at the fundamental frequency, saturation spectroscopy of ¹³C₂H₂ was achieved using a low-pressure gas cell inside a build-up cavity. The measured absorption dip has 3% line contrast and 1.2 MHz linewidth. Both the atomic and molecular saturated lines are very well suited for frequency locking in order to establish accurate frequency standards in the optical communication band.

Frequency-modulation spectroscopy of the CH₃D molecule is performed to assess a novel optical frequency standard at 1.54-μm wavelength. Numerical integration of the demodulated first derivative signals provides the Voigt absorption profiles for the R(6,3) transition at 1543.78 nm at different gas pressures. Deconvolution with the Gaussian (Doppler) line provides the corresponding Lorentzian (collisional) line as a function of the gas pressure. Measurements of the collisional broadening contribution, at three different gas pressures, provide a collisional broadening coefficient of 37 MHz/kPa for the R(6,3) line.

A quantized Hall resistance (QHR)-based capacitance measurement chain has been developed. The chain comprises an AC resistance bridge together with an AC-DC calculable resistor, a multifrequency quadrature bridge, and a capacitance bridge. The use of the multifrequency quadrature bridge enables the measurement of the frequency dependence of capacitors in the range between 1-1.592 kHz. The results demonstrate that the frequency dependence of 10-pF standard capacitors can be measured based on the QHR with a relative standard uncertainty of 3×10^-8