Susanne Picard

Absolute frequency atlas of molecular I/sub 2/ lines at 532 nm

With the aid of two iodine spectrometers, we report for the first time the measurement of the hyperfine splittings of the P(54)32-0 and R(57)32-0 transitions near 532 nm. Within the tuning range of the frequency-doubled Nd:YAG laser, modulation transfer spectroscopy recovers nine relatively strong ro-vibrational transitions of /sup 127/I/sub 2/ molecules with excellent SNR. These transitions are now linked together with their absolute frequencies determined by measuring directly the frequency gaps between each line and the R(56)32-0:/spl alpha//sub 10/ component. This provides an attractive frequency reference network in this wavelength region.

A new method to determine the absolute mode number of a mode-locked femtosecond-laser comb used for absolute optical frequency measurements

The generation of optical frequency combs, directly referenced to the SI second, can be used to make measurements of optical frequencies. This provides a supreme method for the realization of the meter. However, an approximate knowledge of the frequency of the radiation is normally needed for such measurements in order to determine the integral order of the comb component used. Such information is usually obtained by prior wavelength measurements of the radiation under study. This paper demonstrates a new method to determine the absolute mode number in optical frequency measurements using mode-locked femtosecond lasers, thus eliminating the need for complementary wavelength measurements. Measurements of the frequency of an iodine-stabilized He-Ne laser at /spl lambda/=633 nm and a Nd:YAG laser at /spl lambda/=532nm are given as examples.

The BIPM laser standards at 633 nm and 532 nm simultaneously linked to the SI second using a femtosecond laser in an optical clock configuration

The study of an optical clock based on an iodine-stabilized Nd:YAG laser has been performed using a femtosecond laser. The optical frequency of the iodine-stabilized He-Ne laser at 633 nm and the Nd:YAG laser at 532 nm have been measured simultaneously with a relative uncertainty below 1/spl times/10/sup -12/.

Determination of the specific heat capacity of a graphite sample using absolute and differential methods

An experimental assembly has been constructed to measure the specific heat capacity of macroscopic graphite samples at room temperature. The same batch of graphite constitutes the core of a graphite calorimeter, which is currently being realized to measure the absorbed dose due to ionizing radiation. Two different experimental procedures have been applied. In the first method the specific heat capacity of graphite was measured directly, where its value is corrected for the influence of impurities. The second method, to our knowledge not previously applied to macroscopic samples, is based on a series of differential measurements where no correction for added impurities is needed. By its nature, the second method reduces systematic effects. The specific heat capacity of a particular graphite sample is determined to be 706.9 J K−1 kg−1 with a combined relative standard uncertainty of 9 parts in 104 at 295.15 K. The specific heat capacity of cyanoacrylate has also been determined.

First international comparison of femtosecond laser combs at the International Bureau of Weights and Measures

The first international comparison of femtosecond laser combs has been carried out at the International Bureau of Weights and Measures (BIPM). Three comb systems were involved: BIPM-C1 and BIPM-C2 from the BIPM and ECNU-C1 from the East China Normal University (ECNU). The agreement among the three combs was found to be on the subhertz level in the vicinity of 563 THz. A frequency difference measurement scheme was demonstrated that is suitable for general comb comparisons.

Improved iodine-stabilized Nd:YAG laser

In 1977 the 532 nm radiation obtained by frequency-double iodine-stabilized Nd:YAG lasers was included in the revised list of recommended radiations for the practical realization of the definition of the meter. In a planned group of reference lasers at this wavelength at the BIPM, the first two have been completed and a series of beat measurements has been made. The relative short-term stability was typically 5 (DOT) 10-14. Over longer durations a typical minimum stability floor of about 6 (DOT) 10-15 is reached. The frequency difference between the BIPM lasers measured over a 10-day period was found to be 63 Hz with a standard uncertainty of 161 Hz. The hyperfine spectrum of the R(56)32-0 line in iodine has been measured using beat frequency techniques and excellent agreement with theory is found, with a residual of the fit of only 400 Hz.

Direct measurement of the absolute frequency of the international reference laser BIPM4

Direct phase-coherent measurements of the absolute frequency of the 11-5, R(127) transition in 127I2 at 633 nm of the BIPM4 He–Ne laser have been made. This laser has been used as a reference laser for a large number of international comparisons over the years and, as such, has served as the connecting point for the national implementation of the SI metre in the member states of the Metre Convention. The frequency value found for the f-component was 473 612 353 605.4 kHz with a combined uncertainty of 1.8 kHz, a value in close agreement with the value adopted for this radiation in the list of recommended radiations for the realization of the metre, which is 473 612 353 604 kHz.

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

Establishment of degrees of equivalence of national primary standards for absorbed dose to water in accelerator photon beams

The basis for the degrees of equivalence of national primary standards for absorbed dose to water in accelerator photon beams established by the BIPM.RI(I)-K6 comparison was adopted by the Consultative Committee for Ionizing Radiation in May 2013. The degrees of equivalence for the comparisons with reports published or having reached a draft B stage before the adoption in May 2013 have been determined and are presented. Comparison reports published after that date will each contain the established degrees of equivalence including those for the new comparison. 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 CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).