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 Comité 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).

OCT measurements have a fundamental trade-off between the ability to resolve small details and the range over which the measurement is consistent. A measurement which is able to resolve small details is able to do so over a small range. A measurement which is consistent over a larger range is not able to resolve small details. While the axial resolution of the OCT measurement is determined by the optical bandwidth of the source, the lateral resolution (spot size) is determined by the focusing optics and the characteristics of the Gaussian beam. The spot size and the depth of field of a Gaussian beam are directly related in such a way that there is a trade-off between the spot size (details which can be resolved) and depth of field (distance over which the spot size is maintained). In this paper we analyze and discuss in detail the trade-off between the spot size and depth of field in OCT measurements. Some techniques to mitigate this limitation are mentioned and one is applied to measurements of cervical tissue with and without cervical intraepithelial neoplasia (CIN).

Interference microscopy is an important field of dimensional surface metrology because it provides direct traceability of the measurements to the SI base unit definition of the metre. With a typical measurement range from micrometres to nanometres interference microscopy (IM) covers the gap between classic metrology and nanometrology, providing continuous transfer of dimensional metrology into new areas of nanoscience and nanotechnology. Therefore IM is considered to be an indispensable tool for traceable transfer of the metre unit to different instruments. We report here the metrological study of an absolute Linnik interference microscope (IM) based on two frequency stabilized lasers. The design permits the flexible use of both lasers for measurements depending on the demand of the concrete measurement task. By principle of operation IM is combination of imaging and phase-shifting interferometry (PSI). The traceability is provided by the wavelength reference, that is, a He-Ne 633 nm stabilized laser. The second laser source, that is, a Blue-Green 488 nm grating stabilized laser diode, is used for improvements of resolution, and also for resolving integer fringe discontinuities on sharp features of the surface. The IM was optimized for surface height metrology. We have performed the study of the systematic effects of the measurements. This study allowed us to improve the hardware and software of IM and to find corrections for main systematic errors. The IM is purposed for 1D to 3D height metrology and surface topography in an extended range from nanometres to micrometres. The advantages and disadvantages of the design and developed methods are discussed.

This paper presents a methodology for providing traceability to OCT measurements linked to Length SI unit. The link to primary length standard is provided by an interference microscope (IM). The chosen transfer standard was a step height gauge block. The results for IM and OCT showed good agreement for step height standards, such that the OCT will be able to perform reliable measurements of complex surface topographies and to ensure traceability to the length scale. The main uncertainty components were evaluated for the OCT system. In addition, OCT also was used for measuring a surface roughness standard -a depth standard -in order to test this methodology for round groove profiles. Results were found to be in good agreement with the calibration certificate.

The imaging Linnik interferometer equipped with two lasers of different colors is under development and metrological study at National Metrology Institute of Brazil (INMETRO). This work reports the self-referenced method for practical calibration of the secondary laser wavelength. The method is based on accurate digitalization and comparison of the waveforms for both reference He-Ne stabilized laser at 633 nm and secondary laser diode at 488 nm. The process makes use of multiple step phase-shifting technique for waveform measurement and multi-parameter fit for wavelength extraction. The advantage of the method is that no extra hardware of realignment of interferometer is required to perform the calibration.