Optical Shop Testing

Chapter 6 - Multiple-Beam Interferometers

6.1.  BRIEF HISTORICAL INTRODUCTION

The historical origin of multiple-beam interference was found as early as 1836, when
Airy derived an expression for the multiple-beam interference pattern that would be
produced by a plane parallel plate. However, the idea remained unexploited since
high-reflectance coatings were not available and uncoated glass plate has a
reflectance of only 0.04. It can produce good visibility fringes but of a two-beam
type in reflection; no recognizable fringes can be seen in transmission.1 Then Fizeau
(1862a, 1862b) devised his celebrated interferometer, which now bears his name (see
Chapter 1). His invention led to the idea of studying surface topography by optical
interferometer (Laurent, 1883). The interferometer, being formed by two uncoated
glass plates, gives interference fringes of a two-beam (cosine) type in reflection that
contour the surface topography. Then Boulouch (1893) revived Airy’s (1836)
derivation of multiple-beam interference and demonstrated that with increasing
reflectance of the Fizeau surfaces the multiple-beam fringes, both in reflection and
in transmission, become increasingly sharper.

A few years later Fabry and Perot (1897) recognized the potential of the
interferometer that consists of two plane parallel surfaces of high-reflection coating
with variable separation, now known as the Fabry–Perot interferometer. Today it is
still one of the most compact and highest resolving power spectrometers (Cook,
1971). To exploit this capability for high resolving power, the Fabry–Perot plates
were usually used with a large separation that obscured the great potential of this
instrument for mapping surface microtopography with ultrahigh local precision.
Then in 1913, Benoit, Fabry, and Perot used a Fizeau interferometric arrangement
with coated surfaces for their determination of the standard meter. They also missed
the "optimum conditions" under which this multiple-beam Fizeau interferometer
could be used for precision surface testing.


1The relative strengths of the first three reflected beams are 0.04, 0.037, and 0.000059, and those of the
transmitted beams are 0.92, 0.0015, and 0.0000024.

 

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