David Hopp

Nanoscale imaging using deep ultraviolet digital holographic microscopy

A deep ultraviolet off-axis digital holographic microscope (DHM) is presented. The microscope has been arranged with as least as possible optical elements in the imaging path to avoid aberration due to the non-perfect optical elements. A high resolution approach has been implemented in the setup using oblique illumination to overcome the limitation introduced by the optical system. To examine the resolution of the system a nano-structured template has been designed and the result confirms the submicron and nanoscale resolution of the arranged DHM setup.

A novel diffractive encoding principle for absolute optical encoders

Rotary and linear position sensors are used in numerous manufacturing and automotive applications, where cost effectiveness and the ability of integration are major goals. To meet the increasing demand for competitive optical rotary encoders, in recent years a novel type of optical encoders have been proposed and demonstrated using a micro grating based encoding scheme. This proceeding will give details on the operation principle of this novel kind of position encoder and will show its performance on two exemplary implementations: A compact absolute rotary encoder with a micro-structured plastic disc, which can be manufactured in a conventional and cost effective DVD-molding process and a linear encoder which is based on a pseudo-random coding scheme. The implementation as well as results from their experimental characterization are presented.

Optischer inkrementaler Drehgeber in Low-Cost-Bauweise

Zusammenfassung Um der wachsenden Nachfrage nach hochauflösenden und dennoch kostengünstigen optischen Drehgebern gerecht zu werden, entstand die Idee, in optischen Drehgebern anstelle der typischerweise verwendeten Kodierscheibe aus Glas eine mikrostrukturierte Kunststoffscheibe ähnlich einer CD oder DVD einzusetzen. Diese kann auf einfache Weise in einem effizienten Spritzprägeprozess hergestellt werden. Damit wird es möglich, die hochgenaue Maßverkörperung mittels eines kostengünstigen Verfahrens in hohen Stückzahlen zu fertigen. Abstract We have developed a new concept for low-cost optical encoders to come up to meet the increasing demand for inexpensive rotary sensors. The principal idea is to use a micro patterned plastic disc with metal coating, as it is used for Compact Discs or DVDs. Such encoder discs can be manufactured by an efficient injection compression moulding process. With this well established technique it is possible to achieve highly precise micro patterns while running a cost effective process for high volume production.

Deep-ultraviolet digital holographic microscopy for nano-inspection

We present an off-axis digital holographic setup in the deep ultraviolet to improve the resolution of the optical microscopy down to the nanoscale. A deep (193 nm) UV laser has been used as a source and the setup arranged in a way to avoid aberrations due to the non-perfect optical elements. A cost-effective high aperture objective ( NA = 0.75 ) has been designed which is aberration-corrected for a long working distance. A high resolution approach has been implemented in the setup using oblique illumination to overcome the limitation introduced by the optical system. The system has the capability to investigate samples in both reflection and transmission mode.

Different approaches to increase resolution in DHM

Different approaches to increase the resolution in digital holographic microscopy (DHM) are presented. A high resolution approach has been implemented in the off axis Deep UV DHM setup using oblique illumination to overcome the limitation introduced by the optical system and the theoretical resolution limit of 250 nm (according to Abbe criterion) has been verified, experimentally. A two view DHM system operating in the visible wavelength is also introduced to increase the resolution and contrast in 3D imaging of complex biological samples.

Resolution enhanced technologies in digital holography

We present different systems based on digital holography suitable for the investigation of microscopic objects. A deep UV laser source (193 nm) and high numerical aperture geometry have been used to increase the resolution of the reconstructed amplitude and phase. Furthermore we show how digital holographic interferometry can be used to measure the deformation of microsystems down to the nanometer scale.