White-light interferometry is a powerful tool for high resolution measurements on rough surfaces. The technology can be used for roughness measurements on technical surfaces with sub-micrometers tolerances. However, in automotive industry the surface of interest may be located inside a small drilling. In this case the surface properties cannot be measured by conventional white-light interferometry. For this purpose we introduce the concept of white-light interferometry via an endoscope. The setup uses a Michelson-Interferometer and the endoscope is placed into the object arm. The endoscope produces several intermediate images of the object within the object arm. In order to approximately gain a Linnik-setup we insert a second endoscope into the reference arm. We investigate different concepts in order to perform a depth scan: A scan of the reference mirror, a scan of the object and a new intermediate image scan. By using this intermediate image scan, the measuring range in depth is not limited by the aperture of the endoscope and each point of the object is measured with the maximum lateral resolution. Feasibility experiments have been performed in our laboratory. First measurement results are presented and benefits and limitations of white-light interferometry via an endoscope are discussed.
Spectral radar is an optical sensor for tomography, working in the Fourier domain, rather than in the time domain. The scattering amplitude a (z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary. One important property of optical coherence tomography (OCT) sensors is the dynamic range. We will compare the dynamic range of spectral radar with standard OCT. The influence of the Fourier transformation on the dynamic range of spectral radar will be discussed. The clinical relevance of the in vivo measurements will be demonstrated.
Important aims in dermatology are the measurement of pathological alterations of human skin and on the other hand the quantification of the influences caused by pharmaceutic and cosmetic products. We present modifications of the well- established coherence radar that allow in vivo measurement of human skin, in spite of involuntary body movements and bloodflow. The measuring field can be varied from 100 X 100 micrometers 2 to 5 X 5 mm2. The measuring time is 5 to 15 s and the longitudinal measuring uncertainty is about 2 micrometers . A fiber optical implementation allows the separation of the sensor head from the mechanical scan. The mobile and compact sensor head can now be freely positioned and adjusted to each part of the patient's skin. Disturbances caused by unavoidable movement of the patient can be compensated by modified setups of the coherence radar. We show measurements of clinical and cosmetic relevance.
The 'spectral radar' is an optical sensor for the acquisition of skin morphology. The scattering amplitude a(z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary. We discus the theory of the sensor, including the dynamical range and we show in vivo measurements of human skin by a fiber optical implementation of the sensor.
Optical coherence profilometry (OCP) may be a useful tool for medical diagnosis of human skin. Different medical indications show distinct alterations of the skin surface. We measure the 3D shape of the surface of the skin by the use of the 'coherence radar', which is based on short- coherence-interferometry. The measuring uncertainty is less than 3 micrometers . The measuring time takes about 4 seconds. We perform in vivo 3D skin mapping of naked skin without preparation. We describe methods to compensate for the movement of the patient during the measurement. In order to realize the sensor for clinical application a fiber optical implementation is introduced.
We discuss different modifications of white light interferometry, for the acquisition of human skin morphology. In a first experiment we display the diffusion of light within tissue, versus time. Light is focused onto the surface of the sample, penetrates the sample, is scattered and partly emerges from the surface again. For each point of the surface we can measure a certain run time profile of the emerging photons, via the speckle contrast. The local scattering behavior of the skin is encoded in the run time profile. Further we present a sensor for the acquisition of cross-sectional images of volume scatterers, we call it 'spectral radar.' The scattering amplitude a(z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary, hence a short measurement time is possible. The depth uncertainty within a range of 1000 micrometer is about 10 micrometer. In first measurements we distinguished a melanoma maligna from healthy skin, in vitro and we measured the thickness of a fingernail in vivo. We further demonstrate a third method, the 'coherence radar' for in vivo measurements of skin surface topology, with an accuracy of a few micrometers, and a field of 512 by 512 pixels.
We present a sensor for acquisition of cross-sectional images of volume scatterers, we call it 'spectral radar'. Medical and technical applications are possible. The sensor is a modified Michelson interferometer, with a broad bandwidth light source. The scattering amplitude a(z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary. Measurement results of stationary and non stationary scattering phantoms, human skin and of a fish eye in vitro are shown.
We adapted a method, the 'coherence radar', that was originally developed for the precise measurement of surface topology, to measure bulk properties within strongly scattering media. The sensor is based on short-coherence- interferometry. It enables the 2D observation of light propagation in scattering media with a high temporal resolution. The measurements are carried out by observing photons that traveled form an entrance focus through the bulk of the sample, and back to the surface. The source of information is the speckle contrast. One important result is that during the propagation a sharp photon horizon evolves. This photon horizon can be used for the detection on inhomogeneities in the scattering properties. In solid samples we measured absorbing obstacles with a depth of 320 micrometers and a depth uncertainty of < 5 percent. The measuring time is about 30 seconds. The observation of the photon horizon can also be realized in 'life' volume scatterers with moving scattering particles. First in vivo measurements of human skin have been successful.