Final report on APMP regional key comparison APMP.L-K6: Calibration of ball plate and hole plate

open14sìThe comparison in this Final Report is part of the CIPM-MRA (Comité International des Poids et Mesures - Mutual Recognition Arrangement). The Report is also available in the open-access KCDB (Key Comparison Data Base) through the website of the BIPM (Bureau International des Poids et Mesures, www.bipm.org).The results of the APMP key comparisons on ball plate and hole plate (APMP.L-K6.2007) are reported. Both transfer standards were provided by NMIJ, Japan. The ball plate standard is 532 mm by 532 mm in nominal dimension and 25 spheres are embedded. Thirteen National Metrology Institutes (8 from APMP, 5 from other Regional Metrology Organizations) participated in the ball plate measurement comparison. The hole plate standard is 550 mm by 550 mm in nominal dimension and there are 44 cylindrical holes in it. Nine National Metrology Institutes (5 from APMP, 4 from other Regional Metrology Organizations) participated in the hole plate measurement comparison. The comparison started in May 2006 and finished in October 2008. The participants used different measurement techniques which were used for their routine calibration services. For determining the key comparison reference values, a two-dimensional coordinates-based analysis was performed. The measurement results on the ball plate show good agreement in ten out of thirteen participants. In contrast, those on the hole plate are in agreement for five out of nine participants.Takatsuji, Toshiyuki; Eom, Taebong; Tonmueanwai, Anusorn; Yin, Ruimin; van der Walt, Floris; Gao, Sitian; Thu, Bui Quoc; Singhal, R P; Howick, Eleanor; Doytchinov, Kostadin; Valente de Oliveira, José Carlos; Lassila, Antti; O'Donnell, Jim; Balsamo, AlessandroTakatsuji, Toshiyuki; Eom, Taebong; Tonmueanwai, Anusorn; Yin, Ruimin; van der Walt, Floris; Gao, Sitian; Thu, Bui Quoc; Singhal, R. P; Howick, Eleanor; Doytchinov, Kostadin; Valente de Oliveira, José Carlos; Lassila, Antti; O'Donnell, Jim; Balsamo, Alessandr

A method to lower the detection limit for optical beat signals from a frequency-dithered stabilized laser

A narrow absorption feature in an atomic or molecular gas (such as iodine or methane) is used as the frequency reference in many stabilized lasers. As part of the stabilization scheme an optical frequency dither is applied to the laser. In optical heterodyne experiments, this dither is transferred to the RF beat signal, reducing the spectral power density and hence the signal to noise ratio over that in the absence of dither. We removed the dither by mixing the raw beat signal with a dithered local oscillator signal. When the dither waveform is matched to that of the reference laser the output signal from the mixer is rendered dither free. Application of this method to a Winters iodine-stabilized helium-neon laser reduced the bandwidth of the beat signal from 6 MHz to 390 kHz, thereby lowering the detection threshold from 5 pW of laser power to 3 pW. In addition, a simple signal detection model is developed which predicts similar threshold reductions

APMP L-K4 Key Comparison, Calibration of diameter standards

A regional key comparison, APMP.L-K4, was held in 2008. To demonstrate the equivalence of routine calibration services offered by NMIs to clients, participants in this APMP.L-K4 comparison agreed to use the same apparatus and methods as routinely applied to client gauges. There are 14 laboratories from NMIs involved this key comparison, which included CMS/ITRI, NMIJ/AIST, NPL-I, NIMT, Puslit KIM-LIPI, NMISA, MSL, NMIA, NML-SIRIM, VMI, KRISS, SCL, NMC/A*STAR and NSCL. This report describes the measurement results of five diameter standards including two rings and three plugs. The calibrations of this key comparison were carried out by laboratories during the period from May 2008 to November 2010. 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 (CIPM MRA

Testing process for the WEAVE prime focus corrector lenses for the William Herschel Telescope

International audienceA new prime focus corrector for the WEAVE project for the William Herschel Telescope is being produced. The corrector consists of six lens elements, the largest being 1.1 m in diameter. It also incorporates an Atmospheric Dispersion Corrector. Testing procedures for the WEAVE prime focus corrector lens elements are described here. Critical issues encountered in practice, including the influence of the lens size, wedge and weight on the testing procedure are discussed. Due to large lens dimensions, a dedicated test tower and lens support system has been developed to measure the optical surface form errors of the concave surfaces and the transmitted wavefront of each lens. For some of the lens elements, sub-aperture measurements have been performed using an off-axis Hindle sphere and the resultant OPD maps have been stitched together. The challenge of testing a wedged lens with a combination of a long radius convex surface and a short radius concave surface has been resolved by using another lens from the system as an auxiliary lens. The practice of testing convex surfaces via internal reflection/transmission through the lens element has been avoided entirely in this case and some discussion justifying the choices of metrology approach taken is given. The fabrication and acceptance testing of the lens elements has been completed within the expected time and budget, and all elements have been shown to meet requirements

Testing process for the WEAVE prime focus corrector lenses for the William Herschel Telescope

A new prime focus corrector for the WEAVE project for the William Herschel Telescope is being produced. The corrector consists of six lens elements, the largest being 1.1 m in diameter. It also incorporates an Atmospheric Dispersion Corrector. Testing procedures for the WEAVE prime focus corrector lens elements are described here. Critical issues encountered in practice, including the influence of the lens size, wedge and weight on the testing procedure are discussed. Due to large lens dimensions, a dedicated test tower and lens support system has been developed to measure the optical surface form errors of the concave surfaces and the transmitted wavefront of each lens. For some of the lens elements, sub-aperture measurements have been performed using an off-axis Hindle sphere and the resultant OPD maps have been stitched together. The challenge of testing a wedged lens with a combination of a long radius convex surface and a short radius concave surface has been resolved by using another lens from the system as an auxiliary lens. The practice of testing convex surfaces via internal reflection/transmission through the lens element has been avoided entirely in this case and some discussion justifying the choices of metrology approach taken is given. The fabrication and acceptance testing of the lens elements has been completed within the expected time and budget, and all elements have been shown to meet requirements

Testing process for the WEAVE prime focus corrector lenses for the William Herschel Telescope

International audienc