We propose and demonstrate a novel technique for simultaneous measurement of the phase index, n(p) , the group index, n(g) , and the thickness, t , of transparent plates by use of a low-coherence interferometer. The output light from a superluminescent diode is focused upon the front plane of a transparent plate that is used as the sample. The sample stage is subsequently moved until the light is focused upon the rear plane of the plate. Measurement of the stage movement distance and the corresponding optical path difference allows us to determine both n(p) and n(g) . By placing the sample between two glass plates, we measured n(p) , n(g) , and t simultaneously, with an error of 0.3% or less, for nearly 1-mm-thick transparent plates, including glass and electro-optic crystals.

We proposed and demonstrated in vitro simultaneous measurement of refractive index and thickness of biological tissue. The technique is based on the low coherence interferometry combined with precise translation stages. Refractive indices were determined with the accuracy of less than 1% for tissue samples of a few hundred micron thickness, including chicken tissue, human tooth and nail. Simultaneous measurement of refractive index and thickness of multilayer tissue are also demonstrated.

We have developed a low-coherence interferometer system used for the simultaneous measurement of refractive index n and thickness t of transparent plates. Both the phase index n(p) and group index n(g) can be determined automatically in a wide thickness range of from 10 microm to a few millimeters. Two unique techniques are presented to measure n(p), n(g), and t simultaneously. One allows us to determine n(p), n(g), and t accurately by using a special sample holder, in which the measurement accuracy is 0.3% for the thickness t above 0.1 mm. In the other technique the chromatic dispersion delta n of index is approximately expressed as a function of (n(p) - 1) on the basis of measured values of n(p) and n(g) for a variety of materials, and then the simultaneous measurement is performed with a normal sample holder. In addition, a measurement accuracy of less than 1% is achieved even when the sample is as thin as 20 microm. The measurement time is also 3 min or more.

Mental sweating is human sweating that is accelerated via the sympathetic nerve by application of mental or physical stress. In the neurosciences, there is keen interest in this type of sweating, because the amount of sweat in response to a stress applied to a volunteer directly reflects activity of the sympathetic nerve. It is therefore of particular value that optical coherence tomography (OCT) can provide clear in vivo imaging of the spiral lumen of an eccrin sweat gland in the epidermis with a spatial resolution around 10 mum. We demonstrate dynamic OCT of mental sweating of an eccrin sweat gland on a human fingertip, where the sweating dynamics can be tracked by time-sequential OCT images with a frame spacing of one second. An instantaneous amount of sweat stored in the spiral lumen is evaluated quantitatively in each OCT image, resulting in time variation measurements of excess sweat in response to mental or physical stress. In the dynamic OCT of mental sweating, as demonstrated here, we note for the first time internal sweating without ejection of excess sweat from the spiral lumen to the skin surface. Internal sweating has not been previously detected without the availability of our dynamic OCT technique. Until now, it has been commonly accepted that sweating is always accompanied with ejection of excess sweat to the skin surface. On the basis of our findings reported here, this type of sweating should now be referred to as external sweating. In this study, we demonstrate that internal sweating occurs more often in the case where mental stress is applied to a volunteer, and that it is more useful for evaluation of activity of the sympathetic nerve. The dynamic OCT for both external and internal sweating is demonstrated.

High-speed optical coherence tomography (OCT) makes it possible to perform a time-sequential imaging of biological tissue and small organs. In this paper, we demonstrate in vivo observation of dynamics of sweat glands of human finger tip using high-speed OCT with push–pull driven fiber-optic PZT phase modulators. Movement of a sweat droplet through a micro spiral duct can be tracked clearly. An interesting function of sweat glands is found out in time-sequential OCT imaging.