Daniel Claus

Institut für Lasertechnologien in der Medizin und Meßtechnik an der Universität Ulm · Messtechnik

Interferometric detection enables the acquisition of the amplitude and phase of the optical field. By making use of the synthetic wavelength as a computational construct arising from digital processing of two off-axis digital holograms, it is possible to identify the shape of an object obscured by fog and further increase the imaging range due to t...

In this paper, we demonstrate digital holographic imaging through a 27-m-long fog tube filled with ultrasonically generated fog. Its high sensitivity makes holography a powerful technology for imaging through scattering media. With our large-scale experiments, we investigate the potential of holographic imaging for road traffic applications, where...

Thermal diffusion results in spatiotemporally evolving temperature distribution in material mediums. In dielectric mediums it will also lead to change in local refractive index. Digital holographic interferometry can be used for high contrast quantitative phase imaging of spatially and temporally evolving refractive index variations in dielectric m...

In this manuscript, we describe the development of a single shot, self-referencing wavefront division, multiplexing digital holographic microscope employing LED sources for large field of view quantitative phase imaging of biological samples. To address the difficulties arising while performing interferometry with low temporally coherent sources, a...

We demonstrate single-shot digital holographic imaging and two-wavelengths shape measurement through fog.

This article discusses the fabrication and performance of a multi-channel fibre switch, consisting of 19 single-mode fibres, with enhanced coupling efficiency due to micro-optics, directly printed via two-photon-polymerization on the end-face of each fibre. The use of high-resolution two-photon-polymerization not only allows the enhancement of the...

Digital holographic microscopes provide quantitative phase images of transparent objects like biological cells. These phase images can in turn provide a host of parameters based on the object morphology, which could be used for object identification. But one of the biggest challenges in digital holographic microscopy is the design of compact setups...

In this paper we describe a phase retrieval algorithm using constraints given by diffraction patterns and phase difference obtained from bidirectional interference. Wave propagation and linear phase ramps are used to connect the recordings. At least three patterns are recorded and processed (two diffraction patterns and one interference pattern). T...

In this Letter, we describe a method for retrieving the phase of a wavefield from a volume diffraction pattern. We show at first that the magnitude of the 3D Fourier transform of a diffracted volume wavefield is concentrated around a paraboloid. For the phase retrieval, we apply iteratively the constraints of the measured intensity and the parabolo...

This Letter discusses the generation of 3D-printed micro-optics to obtain the desired beam profile from a multimode vertical-cavity surface-emitting laser (VCSEL) with a significantly reduced divergence angle via the usage of high-resolution two-photon polymerization. Due to the low cost and compact packaging, the VCSEL array is a novel light sourc...

This paper addresses the effect and influence of wave optical aberrations and surface roughness on the chromatic confocal signal and resulting measurement errors. Two possible approaches exist for implementing chromatic confocal imaging based on either refraction or diffraction. Both concepts are compared and an expression for the expected chromati...

A novel algorithm for reconstruction of hyperspectral 3D complex domain images (phase/amplitude) from noisy complex domain observations has been developed and studied. This algorithm starts from the SVD (singular value decomposition) analysis of the observed complex-valued data and looks for the optimal low dimension eigenspace. These eigenspace im...

Conventional confocal 3D microscopes suffer from a slow measurement speed due to its requirement of scanning in three directions. Although lateral slit scanning has been proven to perform similarly to single point scanning, a direct area confocal scanning microscope is commonly considered impossible as the system is reduced into a wide-field micros...

In this paper, we have applied a recently developed complex-domain hyperspectral denoiser for the object recognition task, which is performed by the correlation analysis of investigated objects’ spectra with the fingerprint spectra from the same object. Extensive experiments carried out on noisy data from digital hyperspectral holography demonstrat...

We describe the development and verification of an optical, powder-free, intraoral scanner based on a chromatic confocal imaging system, which has been realized in a single-shot multifocal approach. The system is based on a combination of micro-optical and dispersion optical elements. The methodology of recording and analyzing the acquired data are...

A new denoising algorithm for hyperspectral complex domain data has been developed and studied. This algorithm is based on the complex domain block-matching 3D filter including the 3D Wiener filtering stage. The developed algorithm is applied and tuned to work in the singular value decomposition (SVD) eigenspace of reduced dimension. The accuracy a...

in the presented paper we propose the dual wavelength method based on compact VCSEL laser diode. This type of source has many applications due to its small size and high temporal and spatial coherence. Another advantage of VCSELs is the possibility to adjust the output wavelength in the range of 2 nm by changing the current or temperature. This pro...

Superresolution in lensless near-field ptychography is demonstrated via the application of a strongly curved illumination function. The reconstruction is performed using the Rayleigh–Sommerfeld diffraction integral, which is implemented via a pixel-size adjustable angular spectrum method. In this manner, the reconstructed object details, which are...

Quantitative phase imaging can reveal morphological features without having to stain the biological sample. This property has important implications for intraoperative applications since the time spent during histopathology can be reduced from a few minutes to a few seconds. However, most common quantitative phase imaging techniques are based on th...

Early detection of cancer can significantly increase the survival chances of patients. Palpation is a traditional method in order to detect cancer; however, in minimally invasive surgery the surgeon is deprived of the sense of touch. We demonstrate how shearing elastography can recover elastic parameters and furthermore can be used to localize stif...

Due to a number of benefits mainly concerning orthodontic treatment planning and issues of documentation and sharing of patient records, digital models of the dental arches are more and more replacing conventional stone models in clinical orthodontics. To date, the most common approach for generating digital models of the dental arches comprises th...

This paper demonstrates the usefulness of spectrally resolved digital holography for dual-wavelength optical metrology. Based on the large degree of phase information available, multiple de-correlated dual-wavelength phase maps can be generated, which, when averaged, result in a signal-to-noise-ratio improvement. Compared with single-wavelength ave...

The topography of surface relief gratings was studied by digital holographic microscopy. The applicability of the method for quantitative measurements of surface microstructure at nanoscale was demonstrated. The method for wavefront reconstruction of surface relief from a digital hologram recorded in off-axis configuration was also applied. The mai...

Surface relief gratings and refractive index gratings are formed by direct holographic recording in amorphous chalcogenide nanomultilayer structures As 2 S 3 − Se and thin films As 2 S 3 . The evolution of the grating parameters, such as the modulation of refractive index and relief depth in dependence of the holographic exposure, is investigated....

The topography of surface relief gratings patterned on As2S3–Se nanomultilayers was investigated by digital holographic microscopy. For the high-accuracy phase reconstruction of the topography we used the sparse wavefront modeling. Experimental results are presented.

The pupil scanning modulation is a maneuverable method for retrieving the phase of the complex-valued object. It is based on changing the extent of the illumination function using an adaptive aperture. The apertures are fixed on the same border or point of intersection that ensures the location of the aperture. We sequentially increase the size of...

This paper introduces the concept of spectrally resolved digital holography. The measurement principle and the analysis of the data will be discussed in detail. The usefulness of spectrally resolved digital holography is demonstrated for colour imaging and optical metrology with regards to the recovery of modulus information and phase information,...

[This corrects the article DOI: 10.1117/1.JMI.4.1.014505.].

This paper relates to the improvement of conventional surgical stereo microscopy via the application of digital recording devices and adaptive optics. The research is aimed at improving the working conditions of the surgeon during the operation, such that free head movement is possible. The depth clues known from conventional stereo microscopy in i...

In this Letter, we demonstrate the application of light field imaging to endoscopy. By introducing a microlens array into the image plane of a conventional endoscope, the 4D light field can be captured in one snapshot. This information can be used to obtain perspective images and to digitally refocus to different planes. These features allow for th...

An alternative phase retrieval technique is discussed in this paper, which offers some advantages for the obtained resolution and reconstruction procedure. In contrast to commonly applied iterative phase retrieval routines, diffraction patterns with varying distance between the illumination source and the object are recorded. This has the same effe...

In minimally invasive surgery the haptic feedback, which represents an important tool for the localization of abnormalities, is no longer available. Elastography is an imaging technique that results in quantitative elastic parameters. It can hence be used to replace the lost sense of touch, as to enable tissue localization and discrimination. Digit...

Modern microsurgery is a long and complex task requiring the surgeon to handle multiple microscope controls while performing the surgery. Eye tracking provides an additional mean of interaction for the surgeon that could be used to alleviate this situation, diminishing surgeon fatigue and surgery time, thus decreasing risks of infection and human e...

The surface of holographic grating, directly written by polarization holography on chalcogenide nanomultilayers, has been studied by DHM. The quantitative phase map was converted in a two dimensional topography map of nanometric accuracy. In addition an AFM in contact mode was likewise used to obtain the topography.

Diffraction patterns with varying distance between illumination-source and the object are recorded. This has the same effect as changing the object sensor distance, with the advantage of preserving the resolution. Its usefulness for biomedical imaging, to assist the discrimination between tumorous and healthy tissue, is demonstrated.

This paper describes how the complex amplitude of a wavefront can be obtained via the application of a scanning diffraction element and a reference pinhole. The theoretical background and the experimental proof are presented.

During minimally invasive surgery the visual (3 dimensional) and mechanical (haptic) feedback is restricted or even non-existing, which imposes a serious loss of important information for decision making. Information about the mechanical properties of the biological tissue helps the surgeon to localize tissue abnormalities (benign vs. malign tissue...

The reconstruction of the smallest resolvable object detail in digital holography and coherent diffractive imaging when the detector is mounted close to the object of interest is restricted by the sensor’s pixel size. Very high resolution information is intrinsically encoded in the data because the effective numerical aperture (NA) of the detector...

Besides the many advantages minimally invasive surgery offers, the surgeon suffers from the loss of information, visual and mechanical (haptic feedback). The latter is an important tool, which helps the surgeon to localize tissue abnormalities (benign vs. malign tissue). We are aiming to generate a reliable constitutive FE model of the organ descri...

During minimally invasive surgery the visual (3 dimensional) and mechanical (haptic) feedback is restricted or even nonexisting, which imposes a serious loss of important information for decision making. Information about the mechanical properties of the biological tissue helps the surgeon to localize tissue abnormalities (benign vs. malign tissue)...

Ptychography is a lensless coherent imaging technique. It therefore offers all advantages known from other lensless coherent imaging methods such as digital holography (high phase sensitivity, non tactile, non destructive, wide field imaging, diffraction limited optical resolution). Moreover, it offers new possibilities for radiations outside the v...

We show for the first time that ptychography (a form of lensless diffractive imaging) can recover the spectral response of an object through simultaneous reconstruction of multiple images that represent the object's response to a particular mode present in the illumination. We solve the phase problem for each mode independently, even though the int...

Holograms of 3D images are combined with noise suppression and off-axis projection to image arbitrary patterns onto a vertically oriented plane. This has important applications in microfabrication, for instance writing on the edges of silicon chips.

We describe an experimental implementation of ptychography to optical metrology, in particular topography measurement, in combination with the dual wavelength method. This is the first published account of the application of the dual wavelength method to ptychography or any other phase retrieval method in order to obtain surface height information...

This paper considers some of the most important optical parameters that characterize a digital holographic microscope (DHM) and presents their mathematical derivation based on geometrical and diffraction-based models. It supports and justifies the use of the out-of-focus recording of holograms by showing that the field of view can be increased when...

Digital holography is a modern imaging technique whereby a propagated object wave interferes with a known (spherical or plane) reference wave at a plane where a digital sensor is situated. The resulting intensity distribution is recorded by a CCD or CMOS sensor array to produce a digital hologram. This digital hologram can be processed in several w...

In this paper the coherence requirement for different holographic setups (Fresnel hologram, Fourier hologram, and image-plane hologram) is compared. This analysis is based on the investigation of the recorded interference pattern from the superposition of reference wave and object wave in in-line and off-axis mode. The outcome of this investigation...

This paper introduces ptychography, a novel and very exciting phase retrieval technique, to the field of optical metrology. Its working principle is explained and a useful application in combination with the dual wavelength method for topography measurement is presented. Advantages of the dual wavelength method compared to other optical topography...

The Lunar Dust Analysis package (L-DAP) is a suite of payloads which have been designed to operate in synergy with each other at the Lunar Surface. The benefits of combining these payloads in a single package allow very precise measurements of a particular regolith sample. At the same time the integration allows mass savings since common resources...

This paper presents a comparison of the most commonly applied digital holographic setups, namely Fourier hologram, Fresnel hologram and Image-plane hologram.

This paper shows that visible-light ptychography can be used to distinguish quantitatively between healthy and tumorous unstained cells. Advantages of ptychography in comparison to conventional phase-sensitive imaging techniques are highlighted. A novel procedure to automatically refocus ptychographic reconstructions is also presented, which improv...

The microscopic properties of the lunar regolith such as the shape, the surface texture and the size distribution are required for an understanding of both past surface processes and potential hazards for future human exploration [1]. To reveal the particle morphology at the sub micrometer scale, scanning-probe microscopy (SPM), first used on the 2...

The space-bandwidth product (SBP) is a measure for the information capacity an optical system possesses. The two information processing steps in digital holography, recording, and reconstruction are analyzed with respect to the SBP. The recording setups for a Fresnel hologram, Fourier hologram, and image-plane hologram, which represent the most com...

The most commonly used configurations in digital holography—namely Fourier holograms, Fresnel holograms, and image-plane holograms—are analyzed with respect to Seidel’s wave aberration theory. This analysis is performed by taking into account the phase terms involved in the recording and reconstruction processes. The combined phase term from both p...

This paper discusses ptychography, a coherent diffraction imaging technique. Advantages of ptychography with respect conventional imaging techniques for cell visualisation are highlighted and demonstrated using unstained healthy and tumorous mouse cells as the object under investigation. A novel procedure to automatically refocus a possible slightl...

A novel (to our knowledge) approach for resolution improvement in digital holography is presented in this paper. The proposed method is based on recording the incoming interference field on a complementary metal-oxide semiconductor (CMOS) camera with subpixel resolution. The method takes advantage of the small pixel size of the CMOS sensor, while o...

In the last two decades digital holography emerged as one of the most promising techniques for obtaining the complex object-wave (amplitude and phase). However, due to the coherent nature of the light source used in digital holography, the reconstructed hologram is subjected to speckle noise. Moreover, the resolution and size of the sensor employed...

This paper is intended to introduce ptychography, a novel and very promising phase retrieval technique. It is based on the lens-less recording of a series of diffraction patterns caused by coherent object illumination. In the visible region of light, ptychography has successfully been implemented for visible light microscopy and optical metrology....