Dismiss
InnovationQ will be updated on Sunday, Oct. 22, from 10am ET - noon. You may experience brief service interruptions during that time.
Browse Prior Art Database

Flight Height Monitoring by Differential Interferometer

IP.com Disclosure Number: IPCOM000107565D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 72K

Publishing Venue

IBM

Related People

Makosch, G: AUTHOR

Abstract

This article describes a novel technique for contactless flight height measurements between a recording head and a spinning glass plate. Until recently, the flight height was measured in digital flight height testers by white light interferometry and spectroscopy. However, such systems will be of limited use in future head/disk assemblies where the flight height is likely to be less than 100 nm.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Flight Height Monitoring by Differential Interferometer

       This article describes a novel technique for contactless
flight height measurements between a recording head and a spinning
glass plate.  Until recently, the flight height was measured in
digital flight height testers by white light interferometry and
spectroscopy.  However, such systems will be of limited use in future
head/disk assemblies where the flight height is likely to be less
than 100 nm.

      The proposed technique, which is based on a differential
interferometer (Fig. 1) combined with digital phase measurement, has
a measuring range from several hundred nm down to zero.

      The beam of an He-Ne laser is split by a birefringent crystal W
into two partial beams.  A lens system L focuses one of the beams,
the reference beam, outside the magnetic slider on the bottom
boundary face of a glass plate, the other beam, the measuring beam,
being focused in the area of the air gap to be measured.  The phase
difference of the two reflected beams may be very accurately measured
by the known LASSI (laser spot scanning interferometry) method.  The
phase characteristic (a) as a function of the air gap h is depicted
in Fig. 2 which also shows that the phase signal is not a linear
function of the air gap h between disk and head.

      As the reference beam is phase-invariable, the non-linearity of
the phase characteristic must be attributable to a non-linear phase
change of the measuring bea...