We propose a new phase contrast filtering technique based on a combination of a focused and a defocused point-spread-function. This way, an axial shear is introduced in the imaging system. Compared to conventional differential interference contrast, an isotropic behavior is achieved. The lateral resolution is improved compared to conventional defocusing. Furthermore, the digital combination of multiple images leads to strongly enhanced visualization of small structures. We show simulated results as well as experimental results using a spatial-light modulator-based microscope.
In microscopy, several different phase contrast methods (e.g. Zernike contrast, differential interference contrast)
have been developed to image phase objects. For these methods specialized microscopic equipment (modified
microscope objectives, filters, etc.) is needed. The static elements within such microscopes are a trade-off,
because phase contrast imaging depends strongly on the object and the information to be visualized. We show
results of an implementation of many different phase contrast methods using a high resolution phase-only spatial
light modulator (SLM) in the pupil plane. All implemented methods are realized by software. Therefore, it is not
only feasible to change the different phase contrast methods in real time, but it is also possible to optimize the
parameters. Images obtained from different settings are combined digitally to improve the final image quality.
Furthermore, completely new phase contrast filters can be tested easily because the phase of each pixel can be
changed arbitrarily. We use this method to implement a new phase contrast filter that is obtained by combining
a focused and a defocused point spread function. We will present theoretical as well as experimental results of
this vertical differential interference contrast filter.
Heterodyne interferometry is a very accurate and robust technique for measuring vibrations under industrial
conditions. Typically, instruments based on this principle measure on a single point and scanning is employed to
obtain operational deflection shapes. For the simultaneous measurement of vibrations (e.g. to detect transients)
it is possible to use a fixed arrangement of measurement beams. Dynamic steering of multiple beams, however, is
not easy to achieve. In this contribution we present a solution for multipoint vibrometry using a high resolution
(HDTV) programmable spatial light modulator as the core element. By using a liquid crystal display (LCD)
for displaying a dynamic hologram it is possible to independently control multiple measurement spots in three
dimensions with high repeatability and accuracy. Mechanical movements that might introduce noise do not
oocur. The main challenge in designing such an LCD-based multipoint vibrometer is to avoid problems due to
the unwanted spurious diffraction orders that will be present when using commercially available spatial light
modulators for reconstructing holograms. We present a system in which the illuminating as well as the detection
is programmable. One half of the high resolution LCD is used for illumination and the other half is responsible for
the detection. Different possible methods to avoid spurious diffraction orders are shortly discussed. Emphasis will
be laid on a method based on complex multiplexing (using hologram optimization) and a spatial multiplexing
method based on Golay arrays. We show the optical design as well as first experimental results for a single
detector. Hologram computation is based on a joint optimization of the detection and the illumination hologram
using a modified Gerchberg-Saxton algorithm together with combinatorial optimization of the spot/detector
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.
Spatial light modulators (SLM) are used in different microscopy setups. Examples are optical tweezers, programmable
phase contrast imaging, confocal imaging, and aberration correction. We report on a method that
measures and corrects specimen-induced aberrations in wide-field microscopy without additional optical components
(e.g. Shack-Hartmann sensors) by taking advantage of the SLM that is already used in the setup.
Different local gratings are written into the SLM which is positioned in a plane conjugate to the pupil of the
imaging system. Multiple images are recorded and based on the shift of subimages we deduce the wavefront. We
demonstrate first experimental results of this method for a system using a high resolution LCoS modulator.
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.