Prof. Jürgen Mohr Profile

Prof. Jürgen Mohr

Deputy Director at Karlsruher Institut für Technologie

Profile Summary

more than 20 years experience in X-ray lithography, micro technology and micro systems for optical applications
interest in micro optics and photonics, x-ray optics, x-ray lithography

Publications (69)

PROCEEDINGS ARTICLE | May 2, 2017

First experience with x-ray dark-field radiography for human chest imaging (Conference Presentation)

Proc. SPIE. 10132, Medical Imaging 2017: Physics of Medical Imaging

KEYWORDS: Chest, Tissues, Imaging systems, Signal attenuation, X-rays, Radiography, Diagnostics, Lung, X-ray imaging, Chest imaging

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SPIE Journal Paper | January 12, 2017

Large area gratings by x-ray LIGA dynamic exposure for x-ray phase-contrast imaging

Tobias Schröter, Frieder Koch, Pascal Meyer, Martin Baumann, Daniel Münch, Danays Kunka, Sabine Engelhardt, Marcus Zuber, Tilo Baumbach, Jürgen Mohr

JM3 Vol. 16 Issue 01

KEYWORDS: Photomasks, X-rays, X-ray imaging, Synchrotrons, Scanners, Visibility, Gold, Sensors, Phase shifts, Interferometers

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SPIE Conference Volume | September 26, 2016

Micro-Optics 2016

SPIE Conference Volume | May 19, 2014

Micro-Optics 2014

PROCEEDINGS ARTICLE | May 2, 2014

Three-dimensional buried polymer waveguides via femtosecond direct laser writing with two-photon absorption

Proc. SPIE. 9130, Micro-Optics 2014

KEYWORDS: Refractive index, Femtosecond phenomena, Waveguides, Cladding, Polymers, Diffusion, Integrated optics, Neodymium, Multiphoton lithography, Absorption

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Integrated optics has emerged as a promising solution to the electronic interconnect bottleneck, enabling high bandwidth density and low power consumption. Recently, confining photochemical and physical reactions in a micro-volume has given an extra dimension to optical interconnection using glass or polymer. Three-dimensional waveguides can then connect, combine, or split the optical signal among any blocks in all dimensions. However, the refractive index increase is still a challenge to fabricate free-form, stable and single-mode three-dimensional buried waveguides.<p> </p>This paper presents a new concept to tackle this challenge using the combination of femtosecond direct laser writing (FsDLW) in polymer and external diffusion of a gaseous monomer. FsDLW with two-photon absorption was used to initiate cross-linking following a programmed trajectory to form the waveguide core. A thermal treatment was then needed to complete cross-linking. Afterwards, a low-index monomer from a gas atmosphere was diffused into the uncross-linked cladding. Since this diffusion hardly occurred in the already cross-linked pattern, the subsequent UV flood exposure only cross-linked the diffused monomer with host oligomer in the cladding. This low-index monomer decreased the refractive index of the cladding and, therefore, created enough refractive index contrast for total internal reflection. Finally, the whole structure was hard-baked for polymerization and stabilization.<p> </p>The peak refractive index change of 0.012 was revealed using refractive near field method. Measured near-field intensity at the end facet of waveguides showed single-mode Gaussian profiles. We further demonstrated how feature sizes can be linearly adjusted in the range of 5-12 μm by varying scanning speed and laser intensity. Moreover, changing the voxel shape by a field aperture in front of the objective was investigated. Our fabrication method requires only one layer of a single material without masks, contact or wet processing. Free-form waveguides with high index contrast have high potential to improve the density and flexibility of optical interconnects at board level. Some applications of this concept are three-dimensional arrays of optical waveguide network routers, optofans, pitch converters or splitters.

PROCEEDINGS ARTICLE | March 19, 2014

Increasing the field of view of x-ray phase contrast imaging using stitched gratings on low absorbent carriers

Proc. SPIE. 9033, Medical Imaging 2014: Physics of Medical Imaging

KEYWORDS: Biomedical optics, Phase contrast, Scattering, X-rays, Silicon, Image restoration, Interferometry, X-ray imaging, Semiconducting wafers, Absorption

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PROCEEDINGS ARTICLE | March 19, 2014

Design of a compact high-energy setup for x-ray phase-contrast imaging

Proc. SPIE. 9033, Medical Imaging 2014: Physics of Medical Imaging

KEYWORDS: Optical design, Interferometers, Sensors, X-rays, Interferometry, X-ray imaging, Binary data, Visibility, Phase shifts, Absorption

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PROCEEDINGS ARTICLE | March 6, 2013

Compact hard X-ray grating interferometry for table top phase contrast micro CT

Proc. SPIE. 8668, Medical Imaging 2013: Physics of Medical Imaging

KEYWORDS: Phase contrast, X-ray computed tomography, Imaging systems, Interferometers, Sensors, X-rays, Image resolution, Interferometry, Visibility, Absorption

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SPIE Conference Volume | May 18, 2012

Micro-Optics 2012

PROCEEDINGS ARTICLE | May 10, 2012

Low-loss single mode light waveguides in polymer

Proc. SPIE. 8431, Silicon Photonics and Photonic Integrated Circuits III

KEYWORDS: Refractive index, Waveguides, Polarization, Cladding, Signal attenuation, Polymers, Near field, Wave propagation, Near field optics, Polymer multimode waveguides

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PROCEEDINGS ARTICLE | September 21, 2011

X-ray refractive large aperture rolled prism lenses as condensers for x-ray tubes

Proc. SPIE. 8167, Optical Design and Engineering IV

KEYWORDS: Prisms, X-ray optics, Lenses, Sensors, Glasses, X-rays, X-ray diffraction, X-ray microscopy, Collimators, Neodymium

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At the Institute of Microstructure Technology (IMT) at Karlsruhe Institute of Technology (KIT), refractive X-ray optics are developed. These optics are proposed to be used as condenser optics in X-Ray spectroscopy and microscopy applications with an X-ray tube as a source. To produce the lenses, a thin structured foil with equidistant fins in triangular form is casted from a structured silicon wafer. The foil is then wound around a glass fibre core. Due to this fabrication method, it is possible to produce large-aperture lenses with low absorption in comparison to other types of refractive X-Ray optics, like X-ray lenses with continuous parabolic shape or prism lenses. The first are limited due to their absorption while the latter are limited due to their mechanical stability of the prism columns. The optimisation of the so called X-Ray rolled prism lenses (RXPL) is underway at the institute and involves several parameters. One important property of the lenses is the correct form of the wound foil layers. This determines the number of necessary refractive elements at a given radius, which in turn determines the refracted slope and focal position of the transmitted beam. The spatial extent of the x-ray source is also being accounted for in the lens design. Another important point is the diameter of the winding core, which should be as small as possible due to the fact that the winding core reduces the active area of the lens. The rolling process itself is also revised to produce lenses with the above-mentioned small diameter winding cores and bend foil layers while sustaining a tight- fitting foil bundle. The lenses are studied at different energies and types of X-Ray tubes, as well as synchrotron sources, to gain additional information of the internal structure of the lens after the winding process. In this paper the current status of the lens development and results at X-Ray tube sources for use in diffractometers is presented.

PROCEEDINGS ARTICLE | May 4, 2011

Advances in the development of x-ray refractive large aperture rolled prism lenses

Proc. SPIE. 8076, EUV and X-Ray Optics: Synergy between Laboratory and Space II

KEYWORDS: Optical components, Prisms, X-ray optics, Lenses, X-rays, Silicon, Geometrical optics, Semiconducting wafers, X-ray technology, Absorption

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At the Institute of Microstructure Technology (IMT) at Karlsruhe Institute of Technology (KIT) X-ray refractive line focus lenses have been developed. They consist of a large number of concave bi-parabolic lens elements made of SU8. To form a point focus two of these lens stacks, tilted by 90° with respect to each other around the optical axis, need to be arranged in the optical path. To increase their transmission, the Fresnel principle can be applied to the lenses to provide higher ratios of refractive power to absorption. The lenses are fabricated by deep X-ray lithography which allows to pattern high aspect ratio structures and gives the possibility to fabricate the lens elements tilted by 90° with respect to each other on a single substrate by tilted double exposure. Nevertheless, the aspect ratio is limited, due to the fact that the columns tend to collapse from capillary forces during fabrication if they exceed a certain height. To overcome this issue and to simplify the fabrication process a new type of lenses as well as a method to fabricate refractive large aperture lenses has been developed recently at IMT. These lenses are fabricated out of a structured polyimide film which is cut into a calculated shape and rolled around a glass-fiber core. The structure on the film itself consists out of triangular shaped ribs. The lenses provide the advantage of Fresnel lenses and also provide a point focus through their approximate rotational symmetry. The full width at half maximum (FWHM) of the focal spot of such lenses is mainly determined by the height of the triangular ribs. Such X-ray optical elements are well suited to be used as condenser lenses, because they provide efficient illumination of an area in the exit working distance. To increase the lens performance, the lens fabrication process has been optimized. In the paper we provide information on how the lenses where improved and present results from tests with X-ray tube sources.

PROCEEDINGS ARTICLE | September 20, 2010

Micro-and nano-tomography at the GKSS Imaging Beamline at PETRA III

Proc. SPIE. 7804, Developments in X-Ray Tomography VII

KEYWORDS: Optical components, X-ray optics, Lenses, Sensors, Photons, Crystals, X-rays, Tomography, Spatial resolution, Monochromators

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PROCEEDINGS ARTICLE | September 20, 2010

X-ray grating interferometer for imaging at a second-generation synchrotron radiation source

Proc. SPIE. 7804, Developments in X-Ray Tomography VII

KEYWORDS: Optical design, Magnesium, Interferometers, X-rays, Radiography, Tomography, Aluminum, Synchrotron radiation, X-ray imaging, Synchrotron x-ray imaging

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PROCEEDINGS ARTICLE | September 3, 2010

Recent developments in x-ray Talbot interferometry at ESRF-ID19

Proc. SPIE. 7804, Developments in X-Ray Tomography VII

KEYWORDS: Beam splitters, Phase contrast, Modulation, Interferometers, Sensors, X-rays, Interferometry, Wavefronts, Tomography, Synchrotron radiation

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PROCEEDINGS ARTICLE | September 2, 2010

Front- and backside structuring of gratings for phase contrast imaging with x-ray tubes

Proc. SPIE. 7804, Developments in X-Ray Tomography VII

KEYWORDS: Phase contrast, Tissues, Interferometers, X-rays, Tomography, Computed tomography, X-ray imaging, Visibility, Phase shifts, Absorption

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PROCEEDINGS ARTICLE | May 14, 2010

Micro-retroreflector array fabricated by the LIGA process

Proc. SPIE. 7716, Micro-Optics 2010

KEYWORDS: Gold, Lithography, Retroreflectors, Polymethylmethacrylate, Teeth, Optical fabrication, Micro optics, Photomasks, X-ray lithography, Tolerancing

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PROCEEDINGS ARTICLE | May 13, 2010

Refractive x-ray optics made from polymer microstructures

Proc. SPIE. 7716, Micro-Optics 2010

KEYWORDS: Prisms, X-ray optics, Lenses, Polymers, X-rays, X-ray microscopy, X-ray imaging, X-ray lithography, Photorefractive polymers, Synchrotron technology

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PROCEEDINGS ARTICLE | May 13, 2010

Active modular microsystems based on Mach-Zehnder interferometers

Proc. SPIE. 7716, Micro-Optics 2010

KEYWORDS: Optical components, Prisms, Beam splitters, Interferometers, Glasses, Interfaces, Photodiodes, Microactuators, Optical alignment, Phase shifts

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PROCEEDINGS ARTICLE | May 12, 2010

Replication of optical components by hot embossing

Proc. SPIE. 7716, Micro-Optics 2010

KEYWORDS: Optical components, Lithography, Polymethylmethacrylate, Waveguides, Lenses, Polymers, Metals, Nickel, Polymer thin films, Temperature metrology

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SPIE Conference Volume | May 6, 2010

Micro-Optics 2010

PROCEEDINGS ARTICLE | August 21, 2009

Polymer biophotonic lab-on-chip devices with integrated organic semiconductor lasers

Proc. SPIE. 7418, Organic Semiconductors in Sensors and Bioelectronics II

KEYWORDS: Microfluidics, Polymethylmethacrylate, Deep ultraviolet, Waveguides, Polymers, Scanning probe lithography, Semiconductor lasers, Lab on a chip, Organic semiconductors, Polymer multimode waveguides

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PROCEEDINGS ARTICLE | August 11, 2008

Tomographic studies of 3D refractive index and birefringence distribution in M-O elements replicated by hot embossing technology

Proc. SPIE. 7064, Interferometry XIV: Applications

KEYWORDS: Optical components, Refractive index, Photoelasticity, Birefringence, Glasses, Interferometry, Tomography, Head, 3D metrology, Prototyping

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SPIE Conference Volume | May 29, 2008

Micro-Optics 2008

PROCEEDINGS ARTICLE | May 15, 2008

Replication of micro-optical components and nano-structures for mass production