An Optical Technique for Analysis of the Behaviour of Flying Heads in Computer Disc Files

The evolution of computer disc files to the current levels of high density information storage
has resulted in the development of high sensitivity, low-flying recording heads. An interferometer
is described which was designed especially for the analysis of the flight characteristics of such
heads. It is capable of detecting nano-metres differential motion between a head and disc in the
presence of several tens of micro-metres of disc run-out. To achieve this mode of operation, differential
design and polarisation effects have been employed. The final instrument has, in addition
to fulfilling its design requirement, proved to be a versatile high precision measurement tool.