Geometrical cross-sectional imaging by a heterodyne wavelength-scanning interference confocal microscope

Digital Hilbert transformation for separation measurement of thicknesses and refractive indices of layered objects by use of a wavelength-scanning heterodyne interference confocal microscope

A wavelength-scanning heterodyne interference confocal microscope quickly accomplishes the simultaneous measurement of the thickness and the refractive index of a sample by detection of the amplitude and the phase of the interference signal during a sample scan. However, the measurement range of the optical path difference (OPD) that is obtained from the phase changes is limited by the time response of the phase-locked loop circuit in the FM demodulator. To overcome this limitation and to improve the accuracy of the separation measurement, we propose an OPD detection using digital signal processing with a Hilbert transform. The measurement range is extended approximately five times, and the resolution of the OPD is improved to 5.5 from 9 microm without the electrical noise of the FM demodulator circuit. By applying this method for simultaneous measurement of thickness and the refractive index, we can measure samples 20-30-microm thick with refractive indices between 1 and 1.5.

Geometrical tomographic imaging of refractive indices through turbid media by a wavelength-scanning heterodyne interference confocal microscope

A wavelength-scanning heterodyne interference confocal microscope has proved to provide the tomographic image of the refractive indices of transparent and turbid media on the scale of geometrical depth when weakly reflected light with an optical power as low as of the order of 10(-14) W is used. The refractive indices of the transparent object and the turbid media were measured with accuracies of -0.5% and approximately 3%, respectively. This imaging method is advantageous for evaluating quantitative refractive indices and internal structures.