Frequency Scanning Interferometry FSI measurements PACMAN internal meeting

Frequency Scanning Interferometry (FSI) measurements PACMAN internal meeting 28/04/2014 Solomon William Kamugasa

Frequency Scanning Interferometry (FSI) Measurements Contents 1. 2. 3. 4. 5. 6. 7. 8. Background concepts Interferometry: (Displacement & FSI) Sources of error in FSI System components How to determine 3 D position using FSI in CLIC Other applications of FSI Ongoing work PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Background • Superposition: Resultant displacement produced by a number of waves at a point is the algebraic sum of displacements of the individual waves. • Interference: Combination of 2 waves to form composite waves. In phase Out of phase PACMAN internal meeting, 28/04/2014 Constructive interference Destructive interference

Frequency Scanning Interferometry (FSI) Measurements Background • λ PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Interferometry Michelson Interferometer • Technique based on interference that measures properties of light waves such as wave length and optical path length. Coherent light Requires: source • Coherent light source. Beam Splitter • Monochromatic light. • Measures displacement by observing fringes. Fixed Reflector Movable Reflector Detector PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Displacement Interferometry • Intensity minima Intensity maxima PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements FSI Tunable laser • PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements FSI Advantages • Measures absolute distance. • Beams can be interrupted as does not rely on fringe counting. • Ability to measure several interferometers simultaneously. Disadvantages • Tend to be less accurate than displacement interferometry (because it measurements are made relative to a physical reference). • Accuracy reduced by drift errors (dominant source of error in FSI). PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements • PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Drift management • Limited by control of environmental factors that cause drift. • Using faster electronics that make measurements quicker. • Using a stable reference such as Invar (nickel-iron alloy) with low CTE ≈ 1. 2 ppm per °C in range of 20 -100 °C. • Reference interferometer drift can be eliminated by replacing physical length reference. PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Drift cancellation • Tunable laser Measurement interferometer Reference interferometer Tunable laser PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements • PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Determining the position of fibre launchers • PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Determination of fiducial coordinates • PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Reference Interferometer Physical length standard • Reference needs to be calibrated in order to be traceable. • Measurements rely on stability of reference. Alternative • Wavelength of a He-Ne laser determined by energy levels in the gas atoms in the laser cavity (little dependence on ambient conditions). • Atomic transitions lines in an absorption gas cell (weak dependence on ambient conditions). • Benefit: Requires a single calibration, valid for the life of the instrument. PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Measurement interferometer • Each measurement interferometer consists of a quill (two parallel optical fibres and a beam splitter) and a reflector. Delivery fibre Return fibre Retroreflector Beam Splitter PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Main System components Laser • Narrow line width: Provides good fringe visibility. • Wide tuning range: Better measurement precision. • Diode laser most commonly used for FSI. • Replaced dye lasers. PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Main system components Optical fibres • Used to deliver light waves from laser to interferometer and to deliver the return signal from interferometer to photo detector. • Light propagated through fibres by total internal reflection. • Single mode fibres (D=8 -10μm). • Sharper light longer distances. PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Main system components Retroreflectors Incident light is reflected exactly in the direction of origin. Typically corner cube (3 mutually orthogonal surfaces). Retroreflectors are made of various materials. • Aluminium pellets coated with gold to enhance reflectivity (ATLAS). • Commercially - Glass prisms (utilise total internal reflection). • Mirror reflectors are also available. PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements • PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Monitoring and Control • CMMs show systematic deviations resulting from aging & elastic deformations etc. • FSI will be used to continuously monitor the CMM to provide control of systematic deviations. PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Other FSI applications FSI at ATLAS Used to remotely monitor shape changes of the SCT. • Measurement precision of 1μm. • 3 D coordinate reconstruction to 10μm. • 842 measurement interferometers. • Radiation-hard low mass components. • No maintenance over 10 years. ATLAS Experiment © 2014 CERN • Fibres 100 m long from interferometer to detector/laser. PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements Project 1. 2 Work in progress Develop fiducials measureable by FSI, Micro-triangulation & CMM. Why? More redundancy and ability to detect faults. Study the mechanics of fibre ends and targets in order to determine their systematic offsets/errors and those of the target holders. Study various configurations of the FSI network in order to select the best one through simulations. Extrapolate to a portable solution. PACMAN internal meeting, 28/04/2014

Frequency Scanning Interferometry (FSI) Measurements References • Coe P. A (2001) An Investigation of Frequency Scanning Interferometry for the alignment of the ATLAS semiconductor tracker. Dphil thesis, University of Oxford. • Dale J. (2009) A Study of Interferometric Distance Measurement Systems on a Prototype Rapid Tunnel Reference Surveyor and the Effects of Reference Network Errors at the International Linear Collider. Dphil thesis, University of Oxford. • Griffet S. , Cherif A. , Kemppinen J. , Mainaud Durand H. , Rude V. , Sterbini G. Strategy and validation of fiducialisation for the pre-alignment of CLIC components, CERN Geneva, Switzerland. • Griffet S (2010) Fiducialisation and Dimensional Control: Study of existing means and expected performances. EDMS 1097661. • Warden M. S (2011) Absolute distance metrology using frequency swept lasers. DPhil thesis, University of Oxford. • Absolute Multiline®-Technology A revolution in length metrology. Available on Indico, Presented by Mainaud Durand H. PACMAN internal meeting, 28/04/2014