Introduction

It is now over thirty years since Lock-in amplifiers: principles and applications was first published. In the intervening period it has become established as a minor classic, being amongst the most widely cited text books of its kind. Remarkably, despite a lapse of almost 25 years since the final printing, there is continuing interest and regular requests from researchers and students seeking a copy – hence the decision to create an 'authorised' electronic version and make it freely available. Unlike the PDF held by Google Books (and numerous plagiarised versions circulating elsewhere) this e-edition has been newly compiled from the original typescript and diagrams. No apologies are offered for leaving the content substantially the same as before, with no extensive revisions or additions. This reflects the view that, while there have been significant developments in the technology and implementation of lock-in systems, the greater part of the book, dealing with principles and guides to good practice, remains valid and useful. Although there is no new material, time has been spent in correcting obvious mistakes and in improving the type-setting of equations which was less than satisfactory in the printed edition. There is, of course, the danger that this reworking is prone to fresh errors and, here, the author is fully prepared to amend and reissue any pages where errors are reported.

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