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| The UB Physical Optics Research Group | |
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The
UB Physical Optics Research Group Grup de Recerca en Òptica Física de la Universitat de Barcelona (GROF-UB)
The GROF focuses their efforts on several research lines:
1. Dynamic Holographic optical tweezers In this research line, we pursue
the study
and development of new optical tweezers based on the use of digital
holograms displayed on liquid crystal devices (LCD). The GROF has a
broad experience in the characterization and use of spatial light
modulators. Moreover, our expertise includes the design and calculation
of digital holograms for a wide range of purposes.
The goal of this
research is the design of dynamic traps using digital holography
methods. In this way, the movement of the optical traps is performed
without the need for mechanical manipulation, which is a strong
advantage of this technique
1. A highly focused
laser beam can trap microscopic particles, from nanometric scale to
biological samples. Moreover, the particles can be moved, and handled,
by changing the position of the focused light. This device is known as
an optical trap or optical tweezers and numerous applications have been
suggested
2. A suitable front-wave can be calculated as a digital hologram to produce the appropriate intensity pattern in the focal plane of a converging lens. If the hologram is displayed on an LCD, the pattern in the focus is dynamic because the front-wave distribution is refreshed in the screen at a high rate. The joint use of these two results allows the development of flexible and dynamic optical trapping devices. Click here to know more
2. Spatial Light Modulators and Digital Holography The calculation of holograms is based on the Scalar Theory of Diffraction. This approach is used as a way to obtain the complex values of the propagated scalar electric field from knowledge of this field in a reference plane. This process is known as wave-front design or wave-front engineering. The calculated field is encoded into a digital hologram and displayed on a spatial light modulator (SLM). The use of electronically controlled LCDs as modulators allows the information to be refreshed. A specific diffracted pattern (for instance, an optical trap array) can be dynamically modified by displaying a sequence of pre-calculated holograms on the LCD.
The set of points on the complex
plane
available to a modulator is known as the operative curve. A modulator
can produce different
operative curves depending on
(i) the polarization state of the light, (ii) the optical components in
the optical
setup and (iii) the SLM characteristics. In general, currently
available SLMs cannot modulate
large areas of the complex plane, and only a few points are
accessible to the operative curve. The amplitude and the
phase of
the points of the operative curve are strongly connected, so it is
difficult to achieve a specific configuration, such as an
amplitude-only or a
phase-only operation. Therefore, the modulator must be accurately
characterized to obtain the most suitable operative
curve.
The design of a hologram takes into account the SLM performance,
so holograms are calculated considering the
modulation.
Several algorithms have been proposed in order to obtain a
feasible diffracted field as close as
possible to the required one. Click here to know more
 3. Digital & Optical Image Processing
An emerging
technique in the
field of image formation and processing is known as the
‘wavefront coding’ method. This consists of
including a
phase plate in the exit pupil of the image forming instrument so that
the resulting PSF is virtually invariant with respect to the usual
aberrations, mainly with respect to defocus. The main disadvantage of
the method is the need to include the digital image processing
within the usual image detection stage, since good images
cannot
be obtained without digital processing. However, provided this
processing can be performed with relative easy, the wavefront coding
method
is a most promising procedure for vision systems.
Optical correlation
is one way to detect a 3D object in a complex scene.
Thus, current correlation methods take into account the different views
of the object to perform the recognition. Our group has developed
several optoelectronical setups for optical pattern
recognition. In
particular, we have built a real-time compact processor that performs
the correlation between a reference and the different views of
an object at high speed.
For years, we have
been working on medical image diagnosis in collaboration with the Faculty
of Medicine of the UB
and the Clinical Hospital of Barcelona. Our studies are centered on
gammagraphy (SPECT and PET). Currently we are developing a camera with
a pinhole collimator for the analysis of small animals.
Moreover, we are part of the IM3 network (Multimodal and Molecular Medical Imaging). In particular, we collaborate with the Institute of Optics (CSIC) working on classification of patterns using statistical and correlation-based methods. Click here to know more
At the GROF we have
developed software tools for the optical characterization of
thin film materials and multilayered stacks. We have implemented our
previous know-how in the algorithms for optical data reduction from
ellipsometric and/or spectrophotometric measurements.
Our experience is the result of our work in various scientific and industrial projects. This guarantees an state-of-the-art knowledge in the field of thin film applications, leading to suitable algorithms for the specific needs of the optical characterization problems. Go to the NKDGEn /NKDMATl / NKDStack page: http://www.ub.edu/optmat
This
research is carried out in collaboration
with the Physical Optics and
Laser Beams Group of the Universidad Complutense de
Madrid.. The objective is
the parametrization of the spatial and vectorial structure of light
beams. General solutions of Maxwell
equations in terms of the plane-wave spectrum of the
electromagnetic field are analyzed. The task of our
group is
centered on the numerical verification of the theoretical results.
Click here to know more
5. Research on Education in Optics
The JavaOptics Course is an ensemble of teaching resources for Physical Optics at university level as part of Physics The kernel of the resources developed is a software package, designed to simulate the physics of several optical phenomena. All the programs are freely available at We have recently started to investigate the connections between the learning progress of our students and the use of simulation programs. Information is collected by inquiring regularly of the students’ opinion and by analyzing their answers in exams. Preliminary results of the research show that concepts difficult to understand are more easily acquired if the students can experiment and manipulate the concepts using these applets. Click here to know more |
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Since 2000,
the members of the
GROF have been
developing materials in electronic format for teaching theoretical,
technological and experimental concepts related with optics and
photonics. The objective was to generate enough resources to allow
students to manipulate and investigate concepts, equations and images,
before study based on the exclusive use of a textbook. 