A low-pass filtering compensation (LPFC) method is proposed to compensate for phase aberrations in point diffraction-based common-path digital holographic microscopy. This method estimates the phase aberration from the object hologram by Fourier transform and low-pass spatial filtering. The estimated phase aberration is subtracted from the object phase image to achieve single-hologram phase compensation. The accuracy and capability of LPFC for phase compensation were demonstrated by experiments on a Ronchi grating and a human blood smear. LPFC provides phase compensation for both smooth objects and objects containing abrupt edges, in the special case of a system with relatively high-frequency objects and low-frequency slight phase aberrations. LPFC operates without the need for fitting procedures, iterative steps, or prior knowledge of the optical parameters, which substantially simplifies the process of phase compensation in quantitative phase imaging.

The characteristics of a surface, particularly the roughness, play an important role in different fields of the industry and have to be considered to ensure quality standards. Currently, there are numerous sophisticated methods for measuring surface roughness but plenty of them cause long-term damage because they are in contact with the sample. This article presents a non-contact method to accurately determine small surface roughnesses resulting from the consideration of the depolarization effects caused by the rough surface. This technique can be applied as an extension in various roughness measurements and improves the approach of Chandley’s technique, which does not take into account the depolarization of the light scattered by the sample. The experimental setup and the measurements are easy to perform. The essential component is a quarter wave plate, which is incorporated into a Michelson interferometer. With the resulting two different contrasts and the recorded intensities of the sample and the reference mirror, the surface roughness can be estimated straightforwardly. This article details the theoretical approach, followed by the experimental results and the corresponding uncertainties. The experimental results are compared with Chandley’s method. In order to have reference roughness values of the samples, measurements with a stylus profilometer and with a confocal microscope are performed and compared.

To guarantee quality standards for the industry, surface properties, particularly those of roughness, must be considered in many areas of application. Today, several methods are available on the market, but some damage the surface to be tested as they measure it by contact. A non-contact method for the precise estimation of sub-micron roughness values is presented, which can be used as an extension of existing roughness measurement techniques to improve them further considering the depolarized light reflected by the sample. This setup is based on a Michelson interferometer, and by introducing a quarter-wave plate on a half part of the reference mirror, the surface roughness can be directly derived by measuring the fringe contrasts. This article introduces a simple model describing the intensity distortions resulting from the microscopic roughness in divided interferograms when considering depolarization. This work aimed to extend the measurement range of the technique developed in a previous work, in which depolarization effects are taken into account. For verification, the experimental results were compared with the fringe contrast technique, which does not consider the depolarization of the scattered light, especially regarding the extended wavelength interval, highlighting the limits of the technique. In addition, simulations of the experiments are presented. For comparison, the reference values of the sample roughness were also generated by measurements with a stylus profiler.

Zusammenfassung: Die Oberflächeneigenschaften, insbesondere die Rauheit, sind in der Industrie von großer Bedeutung. Derzeit gibt es zahlreiche Verfahren zur optischen Rauheitsmessung. Ziel der in diesem Artikel beschriebenen Arbeiten ist es, eine Verbesserung der in [1, 2] beschriebenen Verfahren zu erzielen. Da bei realen Rauheitsmessungen gekrümmte Streifen auftreten, wird das Verfahren durch eine lokale Ermittlung der Streifenausrichtung im Interferogramm erweitert. Durch die Richtungsbestimmung der Streifen kann eine hohe laterale Auflösung erzielt und Oberflächenunregelmäßigkeiten besser erkannt werden. Als Referenz im Messsystem wird ein räumlicher Lichtmodulator verwendet.