Peter Lehmann

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A new approach for determining the roughness of engineering surfaces that is applicable to industrial in-process measurements is introduced. Laser speckle patterns, arising from light scattered from rough surfaces that are illuminated by polychromatic laser light, are detected in the far-field region. The incoherent superposition of these light intensities(More)
The statistical properties of speckle patterns generated from a rough surface under a fully developed static speckle-pattern illumination are examined. The roughness dependence of the intensity autocorrelation function is studied and utilized to characterize typical engineering surfaces with anisotropic roughness. The speckle patterns under investigation(More)
The shape of droplets in liquid-liquid systems influences their mass and momentum transfer processes. The deviation from sphericity of rising droplets in liquid-liquid systems was investigated for different droplet sizes. Rainbow refractometry permits one to test, in this case, whether the use of laser-optical particle sizing will be correct or faulty.(More)
Here polychromatic speckle patterns generated either by a polychromatic light source that emits at discrete frequencies or by a light source showing a continuous narrow-band spectral distribution are studied. The purpose here is the application of polychromatic speckle-pattern analysis to an in-process surface roughness characterization. To compare the(More)
Vertical scanning white-light interferometry (SWLI) is a well-established method that is widely used in high precision surface topography measurement. However, SWLI results show characteristic slope-dependent errors due to dispersion effects and lateral chromatic aberrations of the optical imaging system. In this paper, we present methods to characterize(More)
Although white-light interferometers have become well-established tools for measuring smooth, rough, and microstructured surfaces, there are some limitations in certain applications, e.g., if tilted surface areas or small radii of curvature are to be measured. Since the correction of chromatic aberrations is not perfect over the total field of view or the(More)
Fiber-optical sensors have some crucial advantages compared with rigid optical systems. They allow miniaturization and flexibility of system setups. Nevertheless, optical principles such as low-coherence interferometry can be realized by use of fiber optics. We developed and realized an approach for a fiber-optical sensor, which is based on the analysis of(More)
White-light interferometry has turned into a standard tool in the field of high-accuracy topography measurements. Nevertheless, surfaces with relatively large local surface tilts or height steps often give rise to systematic measuring errors. The reasons are diffraction and dispersion effects, which cause deviations between height values obtained from the(More)
In this Letter, the transfer characteristics of rectangular periodic phase objects are studied. It turns out that there are significant differences compared to amplitude objects. The imaging of an amplitude object can be understood as a linear process, whereas phase objects behave nonlinearly. It is shown that under certain conditions the correct shape of a(More)
Besides the illumination wavelength also the numerical aperture (NA) of a microscope objective affects the fringe spacing in interference microscopy. Therefore, at high NA values an effective wavelength should be obtained by calibration. At step height structures both, the effective wavelength and the batwing effect strongly depend on the(More)