Phase-shifting fringe projection is an effective method for three-dimensional shape measurements. Conventional fringe projection systems utilize a digital projector that images fringes into the measurement plane. The performance of such systems is limited to the visible spectral range (VIS), as most projectors experience technical limitations in ultraviolet (UV) or infrared (IR) spectral ranges. However, for certain applications these spectral ranges are of special interest. A novel fringe projector was developed on the basis of a single-tailored free-form mirror. The free-form mirror generates a sinusoidal fringe pattern by redistribution of light. Phase shifting can be realized by a slight rotation of the free-form mirror. In this system, the fringe pattern is generated by illuminating the free-form surface and not by the classical imaging technique. As the system is based on a single mirror, it is wavelength-independent in a wide spectral range and therefore applicable in UV and IR spectral ranges. Additionally it does not feature any chromatic aberrations. We present the design and an experimental setup of this novel fringe projection system. Fringe projection is realized in different wavelength ranges (VIS and UV) and the advantage of fringe projection in the UV spectral range can be shown for certain materials.
A simulation model for the development of an aspheric lens adjustment system that is based on multi-point optical
distance measurement is presented. Adjustment of aspheric lenses means the correction of decentering and tilt errors
within the mount of the lens. The presented model includes the determination of decentering and tilt errors using distance
measurement variation of the lens surface at certain radial positions over 360° rotation of the lens. However, the
occurring noise in the distance measurement as well as an uncertainty in the distance sensor positioning lead to errors
remaining after the determination of decentering and tilt by the new method. The size of these residual errors can be
estimated by the presented simulation tool with statistical significance. The simulation model provides the possibility to
use arbitrary noise values as input quantity. The individual aspheric lens design data, the number of chosen measurement
positions, and the specified noise level determine the statistically expected residual error after lens adjustment. It
provides the possibility to determine the optimal arrangement of the positions of the distance sensor and the number of
repetitions for every given aspheric lens for the enforcement of the requested measurement accuracy. The newly
developed simulation model is a necessary tool for a novel metrology method of the adjustment of aspheric lenses.
Recent developments in design algorithm allow the calculation of free form surfaces that generate a picture in
the target plane with the help of one optical surface. In contrast to conventional imaging, light modulation is
done by a ray-optical redistribution of the incident light which is comparable to incoherent beam shaping.
Such picture-generating surfaces normally exhibit very complex surface sags, that are manufactured using
diamond turning machining. The knowledge of manufacturing tolerances is important to generate the desired
intensity distribution with the required accuracy and at the same time reduce manufacturing effort.
However, compared to the tolerancing of conventional optical elements (e.g. spheres), the tolerancing of
picture-generating free form optical elements is a demanding task. The complexity of their surface shapes and
the target intensity distribution are challenging considering the finding of tolerance parameters and performance
Tolerance parameters strongly depend on the manufacturing process. Therefore they can be obtained by a
detailed analysis of their manufacturing process. In this contribution we focused on picture-generating free form
optical elements manufactured using diamond turning with slow tool servo support. Astigmatism and spherical
aberration are typical manufacturing errors caused by this tool exhibiting low spatial frequency. Errors with
middle to high spatial frequency have not been investigated so far.
Conventional software tools for tolerancing, as e.g. implemented in Zemax, provide only such tolerance
parameters as radius, thickness or tilt, corresponding to conventional manufacturing methods of classical optical
elements (e.g. spheres). Therefore we implemented a software tool developed in Matlab and using Zemax for
raytracing in order to perform sensitivity analysis and Monte Carlo analysis.
Conventional performance criteria like spot radius or wavefront error to evaluate the tolerance analysis cannot
be applied for picture-generating free from elements. Consequently, other performance criteria were investigated.
The correlation between the desired and the generated intensity distribution was chosen to be an appropriate
performance criterion for the tolerancing analysis.
Phase-shifting fringe projection is an effective method for 3D-shape measurements. Conventional fringe projection systems utilize a digital projector that images fringes into the measurement plane. The performance of such systems is limited to the visible spectral range, as most projectors experience technical limitations in UV or IR spectral ranges. However, for certain applications these spectral ranges are of special interest. A novel fringe projector was developed on the basis of a single tailored free-form mirror. The freeform mirror generates a sinusoidal fringe pattern by redistribution of light. Phase-shifting can be realized by a slight rotation of the free-form mirror. In this system, the fringe pattern is generated by illuminating the free-form surface and not by the classical imaging technique. As the system is based on a single mirror, it is wavelength independent in a wide spectral range and therefore applicable in UV and IR spectral ranges. Additionally it does not feature any chromatic aberrations. We present the design and realization of this novel fringe projection system. The tailored freeform mirror is realized using ultra-precision turning. Experimental results demonstrate the functionality of the novel measurement system in VIS and UV spectral range.
Recent developments in design algorithm enable to design freeform surfaces that generate intensity distributions
with middle to high spatial frequency. Such freeform surfaces can generate a picture in a defined plane. In
contrast to conventional imaging, the light modulation is done by a ray-optical redistribution of the incident light
comparable to incoherent beam shaping. Such picture-generating freeform surfaces have various advantages. As
only one single optical element is needed to generate the intensity distribution, very compact optical systems can
be designed. Additionally, they are highly energy efficient, as nearly 100% of the incident light is directed into the
image plane. In case of a freeform mirror, the system is wavelength independent, which offers the possibility for
applications in UV or IR spectral range, as well as the polychromatic projection without any chromatic aberration.
As no classical imaging is performed, conventional evaluation criteria concerning the resolution of this picturegenerating
system like e.g. the Rayleigh criterion cannot be applied. In order to simulate diffraction effects in
the picture plane, the wave-optical propagation has to be simulated. However, depending on the geometrical
arrangement of such systems, the surface modulation of the freeform can be up to several millimeters. This
leads to a violation of the thin element approximation and to significant sampling problems using conventional
propagation algorithms. Therefore, we used a propagation method based on the Huygens-Fresnel principle. The
physical formation of the intensity distribution of a picture-generating freeform system was simulated and the
diffraction limit evaluated. We will show that such systems have a significantly lower resolution than conventional
imaging systems. However, they are very well suited for middle- and low-resolution applications.
Phase-shifting fringe projection is one of the most effective methods for shape measurement. Conventional
systems are based on a projector imaging fringes into the measurement plane. These systems are mainly limited
to the spectral range of visible light, as projectors in UV- or
IR-range suffer from technical problems. However,
for certain applications these spectral ranges can be of interest. We introduce a novel fringe projector based
on beamshaping using a freeform mirror. The fringes in the measurement plane are generated by redistributing
light with the freeform mirror. This projection system is
wavelength-independent and highly energy efficient,
which makes it suitable for applications in UV and IR spectral ranges. Additionally, a measurement field with
axially very large dimension can be realized. We present here the system design as well as system simulation
results, that demonstrate the principle of our novel approach.
Typical optical metrology systems for surface and shape characterization are based on a separated camera and
projection unit, yielding to a limitation concerning the miniaturization of the sensor. We present a compact,
highly integrated optical distance sensor applying the inverse confocal principle using a bidirectional OLED
microdisplay (BiMiD). This microdisplay combines light emitting device (AM-OLED microdisplay) and photo
sensitive detectors (photodiode matrix) on one single chip based on OLED-on-CMOS-technology. Comparable to
conventional confocal sensors, the object is shifted through the focal plane (±▴z) and the back reflected/scattered light is collected via an special designed optic and detected by the photo sensitive detector elements. The detected
photocurrent depends on movement (▴z) of the measurement plane. In contrast to conventional confocal sensors,
our inverse confocal sensor detects a minimum of reflected/scattered light if the object is positioned in the focal
plane. We present a novel sensor concept as well as system and optical simulations that demonstrate the principle
of the novel inverse confocal sensor setup.
We report on the implementation of different phase contrast methods using an SLM in a microscope. The ease of
generating complex phase filters with the SLM opens the possibility to realize standard filters adapted to the specimen
and the possibility to develop new phase contrasting methods. Due to the real-time addressing we can obtain a number of
different images from each specimen recorded nearly simultaneously with the same microscope objective. We
demonstrate how to realize different versions of differential interference contrast imaging, Zernike-type imaging and
dark-field imaging and the combination of the different images by simple post processing. Experimental results for
biological as well as technical specimens are presented.
We present a method that enables the generation of arbitrary positioned dual-beam traps without additional
hardware in a single-beam holographic optical tweezers setup. By this approach stable trapping at low numerical
aperture and long working distance is realized with an inverse standard research microscope. Simulations and
first experimental results are presented. Additionally we present first steps towards using the method to realize
a holographic 4π-microscope. We will also give a detailed analysis of the phase-modulating properties and
especially the spatial-frequency dependent diffraction efficiency of holograms reconstructed with the phase-only
LCOS spatial light modulator used in our system. Finally, accelerated hologram optimization based on the
iterative Fourier transform algorithm is done using the graphics processing unit of a consumer graphics board.
Modern spatial light modulators (SLM) enable the generation of more or less arbitrary light fields in three
dimensions. Such light fields can be used for different future applications in the field of biomedical optics. One
example is the processing/cutting of biological material on a microscopic scale. By displaying computer generated
holograms by suitable SLMs it is possible to ablate complex structures into three-dimensional objects without
scanning with very high accuracy on a microscopic scale. To effectively cut biological materials by light, pulsed
ultraviolet light is preferable. We will present a combined setup of a holographic laser scalpel using a digital
micromirror device (DMD) and holographic optical tweezers using a liquid crystal display (LCD). The setup
enables to move and cut or process micro-scaled objects like biological cells or tissue in three dimensions with
high accuracy and without any mechanical movements just by changing the hologram displayed by the SLMs.
We will show that holograms can be used to compensate aberrations implemented by the DMD or other optical
components of the setup. Also we can generate arbitrary light fields like stripes, circles or arbitrary curves.
Additionally we will present results for the fast optimization of holograms for the system. In particular we will
show results obtained by implementing iterative Fourier transform based algorithms on a standard consumer
graphics board (Nvidia 8800GLX). By this approach we are able to compute more than 360 complex 2D FFTs
(512 × 512 pixels) per second with floating point precision.
Holographic tweezers offer a very versatile tool in many trapping applications. Compared to tweezers working with acousto optical modulators or using the generalized phase contrast, holographic tweezers so far were relatively slow. The computation time for a hologram was much longer than the modulation frequency of the modulator. To overcome this drawback we present a method using modified algorithms which run on state of the art graphics boards and
not on the CPU. This gives the potential for a fast manipulation of many traps, for cell sorting for example, as well as for a real-time aberration control. The control of aberrations which can vary spatially or temporally is relevant to many real world applications. This can be accomplished by applying an iterative approach based on image processing.