Fundamental standards for acoustics based on optical methods - phase three report for sound in water.

This report documents the progress of work towards the development of fundamental standards for acoustics based on optical methods for sound in water between 1 kHz and 500 kHz. The favoured approach for achieving this is particle velocity measurement using heterodyne interferometry and a reflecting membrane in the acoustic field. This report focuses on investigations into a suitable design of reflecting membrane and the performance of the ‚all-fibre™ heterodyne interferometer. Some new developments on the new ‚all-fibre™ heterodyne interferometer are also reported together with the recent comparison results with a reference hydrophone calibrated using the reciprocity method. The report also presents some different optical techniques that can be employed for the transducer characterisation and mapping of acoustic fields. This report is the Deliverable for the Phase Three Work Package for Project 3.6 of the NMS Quantum Metrology Programme for the UK Department of Trade and Industry. The sound in water aspect of the project is being undertaken by a consortium of the National Physical Laboratory and Loughborough University, with Laser Optical Engineering Ltd. as a subcontractor.