Kaj Nyholm

Comparison of 127I2-stabilized frequency-doubled Nd:YAG lasers at the Bureau International des Poids et Mesures.

A frequency comparison was carried out between iodine-stabilized Nd:YAG lasers at 532 nm from the Bureau International des Poids et Mesures, the Centre for Metrology and Accreditation, the Czech Metrology Institute, and the Bureau National de Métrologie-Institut National de Métrologie. The frequency differences between lasers, as well as the frequency reproducibility of each system,were investigated. Pressure-, modulation-, and power-induced shifts were studied. A frequency dispersion (1 sigma) of 3.5 kHz (6.2 x 10(-12) in relative terms) with an average reproducibility for each laser of the order of 0.4 kHz (7.1 x 10(-13) in relative terms) was observed over the duration of the comparison. Relative stabilities better than 1 x 10(13) at 1 s were demonstrated for the third-harmonic systems.

Frequency stabilization of a diode-pumped Nd:Yag laser at 532 nm to iodine by using third-harmonic technique

A compact frequency standard was constructed by stabilizing the frequency of a diode-pumped Nd:YAG laser to the Doppler-free spectrum of iodine at 532 nm. The results show that by using standard third-harmonic locking technique good stability can be achieved in a relatively small, simple and inexpensive set-up.

An AC Josephson Voltage Standard for AC–DC Transfer-Standard Measurements

We describe the traceability chain of length measurements at Centre for Metrology and Accreditation (MIKES) from atomic clocks to the lasers of primary interferometers. Crucial part of the traceability chain, an optical frequency comb generator linking optical frequencies to atomic clocks, is described in detail. The frequency comb generator is used in frequency calibrations of iodine-stabilized lasers, which are operated in compliance with the recommendations of the practical realization of the definition of the meter. Measured absolute frequencies of iodine-stabilized lasers, time records of the measurements, and the respective Allan deviations demonstrate the solid performance of the MIKES laser frequency standards. The results are in good agreement with the recommended values, as well as with the independent characterizations of the measured lasers

Traceability of Laser Frequency Calibrations at MIKES

We describe the traceability chain of length measurements at Centre for Metrology and Accreditation (MIKES) from atomic clocks to the lasers of primary interferometers. Crucial part of the traceability chain, an optical frequency comb generator linking optical frequencies to atomic clocks, is described in detail. The frequency comb generator is used in frequency calibrations of iodine-stabilized lasers, which are operated in compliance with the recommendations of the Practical Realization of the Definition of the Meter. Measured absolute frequencies of iodine-stabilized lasers, time records of the measurements, and the respective Allan deviations demonstrate the solid performance of the MIKES laser frequency standards. The results are in good agreement with the recommended values, as well as with the independent characterizations of the measured lasers.

Results from international comparisons at the BIPM providing a world-wide reference network of /sup 127/I/sub 2/ stabilized frequency-doubled Nd:YAG lasers

Frequency comparisons have been carried out between iodine-stabilized Nd:YAG lasers from the Bureau International des Poids et Mesures, the Bureau National de Metrologie-Institut National de Metrologie, the Czech Metrology Institute, the Centre for Metrology and Accreditation, and the National Metrology Institute of Japan/National Institute of Advanced Industrial Science and Technology. The comparison data of these lasers can now be linked to the results of recent absolute frequency measurements of lasers from different institutes.

Fiber-based acetylene-stabilized laser

We describe a fiber-based acetylene-stabilized laser system in which light is coupled to free space only to pass through the acetylene cell. The system is constructed using standard components used in telecommunication networks, making the approach straightforward to implement. The Doppler-free spectrum of acetylene can be detected, even without a lock-in amplifier using simple collinear pump-probe geometry, when the length of the optical path in the spectroscopy arrangement is dithered to cancel interference that is inevitably present in a fiber-based setup. The laser was stabilized to five different transitions of 13 C2H2 at the (nu1 + nu3) band using the third-harmonic technique, and the absolute frequencies were measured with an optical frequency comb generator. All the results are in good agreement with the values recommended by the International Committee for Weights and Measures (CIPM). The method for canceling the interference presented here can conceivably be generalized to other types of stabilized lasers as well.

Portable frequency standard at 633 nm with compact external-cavity diode laser

A portable (32 cm × 13 cm × 6 cm) laser frequency standard has been constructed by frequency-stabilizing a miniaturized external-cavity diode laser to the Doppler-free spectrum of iodine. Compact structure is achieved using a novel transmission grating. The laser has excellent noise properties, which leads to a high signal-to-noise ratio (SNR) of detection and allows direct observation of the inverse Lamb dips. The frequency stability matches that of iodine-stabilized He-Ne lasers at 633 nm; the relative frequency stability (square root of the Allan variance) follows a slope of 7.9 × 10−12τ−1/2 (10 s < τ < 4000 s). The best stability, 1 × 10−13 (47 Hz), is reached at an integration time of τ = 4000 s. The observed day-to-day repeatability (1σ) is 4 × 10−12 (1.6 kHz). Extensive measurements were made to evaluate the dependence of the laser frequency on the various operational parameters.

Absolute frequency measurement of the R(12) 26-0 and R(106) 28-0 transitions in /sup 127/I/sub 2/ at /spl lambda/=543 nm

A direct phase coherent determination of the absolute frequency of the a15 component in the R(12) 26-0 and b10 component in the R(106) 28-0 transitions in 127I2 at 543 nm has been made at the International Bureau of Weights and Measures. Lasers from the Czech Metrology Institute (Czech Republic), the National Institute of Metrology (China), the Centro Nacional de Metrologia (Mexico), the Standards, Productivity and Innovation Board (Singapore), the Centre for Metrology and Accreditation (Finland), the Danish Institute of Fundamental Metrology (Denmark), the National Physical Laboratory (U.K.), and the International Bureau of Weights and Measures took part. The mean frequency values found are f(a15)=551579856480.4 kHz, uc=4.8 kHz and f(b10)=551580162397.1 kHz, uc=4.6 kHz for the current group of lasers, where uc is the combined standard uncertainty. This constitutes a 30-fold improvement in accuracy for this radiation, which is recommended for the realization of the definition of the meter. If only lasers equipped with an iodine cell temperature control are considered, the group of lasers shows a dispersion of 7 kHz. This value is indicative of the level of reproducibility that can be expected at present for this type of standard

Frequency stabilization of a diode-pumped Nd:YAG laser at 532 nm to iodine by using third-harmonic technique

A compact frequency standard was constructed by stabilizing the frequency of a diode-pumped Nd:YAG laser to the Doppler-free spectrum of iodine at 532 nm. The results show that by using standard third-harmonic locking technique good stability can be achieved in a relatively small, simple and inexpensive set-up.

Final report for the period 2007–2009 on the CCL-K11 ongoing key comparison

Lasers from nine national metrology institutes (NMIs) were compared as part of the CCL-K11 ongoing key comparison, initiated by the 13th meeting of the Comite Consultative des Longeurs (CCL) in 2007. The absolute frequency of the f component of the R(127) 11–5 transition of molecular iodine was measured for these lasers following the technical protocol for CCL-K11. The results of these measurements are compiled in the present report. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).