Simultaneous Measurement of Phase and Group Indices of Transparent Plates Using the Low Coherence Interferometry

High-speed simultaneous measurement of refractive index and thickness of transparent plates by low-coherence interferometry and confocal optics

“…The calibration was made for a nearly 1 mm thick fusedquartz plate by substitution of the measured thickness D = 1498 µm, z = 703 µm and t = 1026 µm into equation (6). Here, the thickness t was measured with a micrometer gauge and the value of n p was experimentally determined from equations (3) and (5). Consequently, the calibrated value of ζ = 0.150 was obtained in our measurement.…”

“…and where ζ is the effective numerical aperture of the 20× objective which is calibrated before the simultaneous measurement of n and t. n p and n g are the phase index and group index of the sample plate, respectively [5,6]. Very recently, we found that the chromatic dispersion δn of the index is approximately expressed by…”

“…Here, we have L = D − z where D is the optical thickness of the sample. Measurement of these two quantities, z and L (or D), allows us to determine n and t [4][5][6]. In our previous paper, we demonstrated the automatic measurement method of z and L where the sample is scanned repeatedly by changing the reference mirror position in steps of 2-5 µm [7,8].…”