<title>Wavelength scanning confocal interference microscope for separate measurement of refractive index and geometrical thickness</title>

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ABSTRACT We previously proposed a system based on a combination of a confocal microscope and a wavelength scanning heterodyneinterferometer, for separate measurement of refractive index and geometrical thickness of lens and plates. However, we usedtwo optical systems successively although they share the same optical system. In this paper, we propose a new measurementscheme which enable us to measure both the confocal profile and the optical path difference of the interferometer by singlescanning of an object. We describe here the measurement principle, the apparatus, signal processing means, and some experi-mental results.Keywords: Interferometry, microscopy, thickness measurement, refractive index measurement, wavelength tuning 1. INTRODUCTION Optical measurement of thickness usually gives the optical thickness that corresponds to a product of refractive index andgeometrical thickness. We have proposed recently separate measurement of refractive indices and geometrical thicknesses ofmultiple layers.1 This technique was based on a combination of a low-coherence interferometer (LCI) and a confocal micro-scope. Similar technique, in which a heterodyne microscope is used instead of the confocal microscope for focus detection, hasbeen proposed independently by Ohmi et aL2 For quicker measurement we further promoted to replace the LCI, which requiresmechanical scanning, by a wavelength scanning heterodyne interferometer (WSHI). We have already shortened the measure-ment time for optical path length to about 1 s. from 60 s. taken in the low-coherence interferometry. For separate measurement,however, we used the confocal microscope and the interferometer successively although they share one optical system and arepetition of sample movement was required for each measurement. Here, we propose a new measurement scheme whichenable us to measure both confocal profile and optical path difference (OPD) of the interferometer by single movement of asample.