Photonics problems (light in interaction with matter, electrons or atoms)
We are mainly working in Photonics problems; this is everything related to light and it’s interaction with matter, electrons or atoms. We focus in novel materials called metamaterials, taming light using scattering or nano-structures. We have projects for students interested in experimental optics, theory building via mathematical analysis and numerical simulations. The projects are usually very applied with a clear problem to solve for various domain such as lighting, energy harvesting or illumination.
- Nanoshells and NanoEggsfor efficient scattering and light trapping
In this project we use a new method to fabricate Nanoshell (dielectric sphere fully covered with metal) and NanoCups (dielectric sphere partially cover with metals). We need to characterise them and model their response in order to design accurately their optical behaviour. In a second stage, we would like to control the orientation of the NanoCups via Optical trapping in order to control their scattering properties. In a short introductory period, you will learn the basic principles of Nanoshell (fabrications, usage) and plasmonics, then characterize the optical properties of different nanoshells; model and optimise the parameters to fit the measurements and think over a way to control the orientation of this Nanoparticules and measure their scattering efficiency. For this project, we are working in collaboration with Aachen University and TNO-Optics.
- Hyperbolic Metamaterials for Sub-wavelength Detection of Particules
In this project we use a new use of Hyperbolic Metamaterials for detection of sub-wabvelength ob ject which traditionally can not be detect in far-field. in the past we have develop a concept of waveguide based on such metamaterials. Now we have engineer a way to have only information related to the particule to be transmitted and measured in the far field. This requires both theory/optimisation and fabrication/characterisation of this novel detectors. The work is very challenging both in term of theory and in term of fabrication. For this project, we are working in collaboration with EWI and TNO-Optics
- Photonics interrogator beyond the coherence length built on chip
A recent way to detect stimulus (acoustic, motion, pressure) is to use light and a fiber. The external stimulus changes the wavelength of the light travelling inside the fiber. A high-resolution wavelength detector called the interrogator is required to detect the typically small wavelength changes. We here propose a new type of photonics interrogator that would work faster then current technology, unabling us to perform measurement at a higher pace. The student is asked to design, simulate and optimised the photonics circuit. He will have to validate them with experiments made on a self-made setup. This works is a collaboration with TNO-Optics and the Else Kooi Lab.
- Fluoresence in a multilayer stack: improving efficiency of LEDs
Most of the new luminair nowadays uses Light Emitting Diodes (LEDs). They usually are based on a Blue LED and a layer contains fluophores that will partly absorb the blue light to produce other colors and finally give a “white” color to the emitter light. Improvement can be done in way the light is re-emitted. We propose here a control of this reemission using multilayers where the different phosphorescent dyes are trapped. To study the process we need to make theoritical model and perform time-resolved measurement of the ligth using very sophisticated instruments (Femto-second layer, Frequency doubler, Streak camera). The student would need to study the theory, design choosen multilayer configuration, measure and validate his calculation with the measurements. This works is a collaboration with Philips Lighting.
- Using fine (nano)structures at the surface of an optical element for control of light illumination
One major problem for the light industry is to produce uniform light illumination with the use of single/mulitple LEDs. The LED are partly coherent source almost equivalent to single point source. It is very difficult to obtain a desired illumination from such points sources. A general idead is to use scattering surface that would mix the light and improce the illumination. We introduce a novel approach for the characterization and optimization of micro-featured grating structures implemented in a diffractive optical element (DOE) in combination with low coherent LED light to produce better illumination than currently achieve with simple scattering elements. The student would need to extend our model and perform experimental studies in order to confirm his model. The model being predictive, it would be easy to create any illumination once the source are known. This work is in collaboration with Philips Lighting and other partners.
Insight in imaging and patterning on the nano-scale
Using focused electron beams we study the mechanisms of 3Dnanostructure fabrication and we develop the necessary instrumentation: a ‘3D-printer’ at nano-scale. To characterize these tiny structures we develop quantitative metrology methods based on electron microscopy and atomic force microscopy. The state-of-the art Monte Carlo simulations that we develop, using fast parallel computing on graphics cards, help us to understand the mechanisms at work.
Both BSc- and MSc-students are welcome to collaborate with us in projects that may vary from being purely experimental and applied to rather theoretical and simulation-based. Projects, to be defined in consultation with the student, may contain the following aspects, or combinations thereof:
- Use of scanning electron microscopes for nanofabrication
- Unravel the mechanisms of the formation of nanostructures
- Design, construction and testing of electron optical components
- Design, construction and testing of components for a ‘3D-printer at nano-scale’
- Development of simulations of electron scattering with matter
Use of electron scattering simulations in lithography, metrology, or particle detection The majority of the projects will have an industrial component in the sense that either industry is funding the
project or that a direct industrial application is aimed for.
Revolutionary tools for fabricating nano-structures and inspection of the nanoworld
- Secondary electron detection in the multi-beam Scanning Electron Microscope
The group has a unique electron microscope to speed up imaging by a factor >100. The secondary electrons from 196 beams are projected onto a fluorescent screen in order to detect them. The deflectors to separate the secondary electrons from the primary electrons are now influencing the primary beam resolution. The student is asked to analyse the problem, find a solution and then to design, build and test the improved separation optics.
- Focused ion beam nano aperture source
In a cooperation with FEI Company the group is developing a new ion source. At the core of this source is a nanostructure with 50 nm thin foils in which we drill 100nm holes. Within this gas cell electrons create ions. We are in the middle of testing the source inside a scanning electron microscope. The student is asked to add a test set-up that allows us to measure the spread in kinetic energies of the ions.
In optical metrology, we are busy with the development of techniques that uses optical fields for very accurate measurements. Think about extremely sensitive sensors and noninvasive inspection of subwavelength structures or particles on surfaces. The most important area of application of our technique at the moment is in the semiconductor industry in the development of lithographic machines for integrated circuit fabrication. But we expect that other new areas such as plastic based technology for fabrication of cheap solar cells, organic LEDS and flexible electronics will profit of our approach. We have projects for students interested in experiments as well as theory, and we have close contacts with TNO, ASML, Philips research.
- Optical metrology for lithography based on scatterometry
Optical scatterometry is a technique where light scattered by an object is collected at several directions. With this technique, it is possible to recover information about the object by analysing the scattered light properties such as angular intensity distribution, phase and polarisation. In this project you will use this technique to recover information of subwavelength structures that are important for the semiconductor industry. The project is experimental and you will have opportunity to work and improve an optical setup, take data and analyse it. As an example, in the picture you see a mini-scatterometer designed and fabricated by students.
- Analysis of the polarisation properties of light scattered from insect cuticula
The goal of this project is to detect physical properties of insect cuticula such as beetles and butterflies. As a first property to test, we will look at the polarisation properties of the light that is reflected from these insects at various incident angles. These effects are usually due to complicated nanostructures and sometimes stacks of nanostructures that occur in insect cuticula. For this goal, you will build a Mueller matrix polarimeter in order to quantify these polarisation effects. These findings could inspire us to develop and fabricate new types of nanostructures to manipulate the polarisation properties of the light.
- Quantum theory of super-resolution for two incoherent optical point sources
Recently, there have been some new work on super resolution for two incoherent point sources. It is based on a new way to estimate the separation between two point sources with measurements involving linear optics and photon counting. With this proposed scheme is shown that the famous Rayleigh criterion for resolution (see figure) does not play a role and its application can be very important in for example, astronomy. The proposed measurement is based on a multimode rectangular waveguide where the light from the two point sources is split into an infinity number of modes and each mode is detected by a photon counter. The goal of this project is to try another expansion of modes based on Laguerre Gaussian modes (spiral modes) which would make the experimental realisation much easier than the one that has been proposed in the literature. If successful, this project could become the starting point of the realisation of such experiment in Delft. This project will be theoretical and good mathematical skills are necessary.
Optics is still very much alive and is a fascinating subject to study and to pursue a career in. Examples of exciting topics are e.g. holography and optical cloacking. Optics also has many applications and is very important for industry. If you do your master or bachelor project in the Optics Group you can choose between a more applied or a more theoretical subject. We maintain a close link with TNO Optics through the Dutch Optical Centre which is an initiative of the Optics Groups of TU Delft and of TNO. We also have close ties with ASML, Carl Zeiss in the field of scatterometry and computational imaging, and with Datalogic in the field of bar code readers, and also with other companies. If you prefer fundamental topics, you can explore for example transformation optics, hyperbolic materials, nano-optics using special focused beams or optical communication with singular vector beams.
- Hyperspectral imaging using computational optics
Obtaining images for many wavelengths is important in several applications such as monitoring crops, imaging human tissue etc. Often the optical components such as lenses are not very good for the entire spectrum of entrance. Furthermore, using conventional techniques there is a kind of trade-off between spectral and spatial resolution of the images. By replacing the imaging components by computational optics, a high spatial resolution can be obtained with at the same time high spectral resolution. The aim of the project is to extend the existing computational model and to carry out experiments to verify the technique. Extensions to light sources that are partial spatially coherent may also be studied. You will be supervised on a daily basis by a PhD who is expert in the field.
- Ptychography by using a liquid lens
Ptychography is a lensless method of imaging in which the scattered light is measured for a number of overlapping illumination patterns and applying an iterative algorithm to retrieve the complex transmission function of the object. Instead of using overlapping illumination patterns, one can alternatively introduce sufficient diversity in the illumination by using a spatial light modulator (SLM). The aim of this project is to attempt to replace the SLM by a much cheaper solution using liquid lens which is excited at some mechanical resonance frequency. The shape of the lens surface is then given by a standing wave with Bessel shape as function of the radius of the lens. This resonant shape alters the phase pattern of the beam that illuminates the object. The aim is to verify this idea by simulations and experiments. Your daily supervisors will be two PhD students
- Diffraction tomography using dual comb technology
In diffraction tomography a (microscopic) sample is illuminated from many angles of incidence and the scattered intensity is measured. The refractive index of the sample as function of position is retrieved from the scattering data. The aim of the project is touse a frequency comb as a source and to assign to every angle of incidence a different wavelength of the comb. The scattered light is spectrally analyzed using dual comb technology. In this way both amplitude and phase data can be obtained very fast so that living cells can be imaged. The proposed method is new and has not been studied before. The project is theoretical and requires good skills in electromagnetic modelling and simulation.
- Ellipsometry with a frequency comb
In conventional ellipsometry a multi-layer sample is characterized by illuminating with a plane wave and measuring the reflected light for two polarisations. The refractive indices of all layers and the thicknessesare determined by scanning the angle of incidence of the plane wave. In this project the aim is to use a multi-wavelength source for only one angle of incidence such at frequency comb or a white laser instead of a monochromatic source at many angles of incidence. In this way the dispersion of the materials (i.e. the dependence of the refractive index on wavelength) can be retrieved.
- Optimization of focused optical fields
In this project we optimize the field in the pupil of a lens to obtain a focused field that is a close as possible to a desired resolution. The difference between the desired and the actual distribution is measured in terms of the energy norm. By applying a variational principle one derives that the optimum pupil field is Eigenfield corresponding to the largest eigenvalue of a self-adjoint integral operator. In the project this integral operatorwill be studied, if time permits, a numerical solution method will be implemented in Matlab.
Advanced and high-resolution seismic imaging techniques
Just like ultrasound techniques, seismic imaging uses acoustic reflection energy to create an image of the internal structures of a medium, the Earth in this case. With thousands of sources and receiver put at or close to the Earth’s surface, we aim at characterizing small heterogeneities at a few km depth. The challenge is to use all complex propagation effects and multiple scattering to obtain results at a resolution and reliability beyond today’s capabilities. As doing actual measurements is usually not feasible, the main emphasis of the research projects is in the development of new algorithms and testing them on either simulated or measured seismic responses. Furthermore, cross-fertilization to applications at a small scale for non-destructive testing of materials takes place.
- Acoustic detection of the wall thickness of a blast furnace
M.Sc. topic under supervision of D.J. (Eric) Verschuur in cooperation with Tata Steel IJmuiden
A blast furnace (BF) is the ‘oven’ in which molten metal (iron) is produced by steel companies. Because of the extreme heat inside the furnace a layer with insulating (refractory) material has been deposited at the inner side of the steel wall. During operation this inner layer will slowly degrade. It is very important to monitor the thickness of the total insulating layer in order to avoid overheating of the outside wall with potential disastrous results. Impact Echo (IE) is a technique for detecting interfaces in solids, like solid to solid and solid to air. The equipment was developed and is primarily used for testing concrete structures. At Tata Steel R&D this technique is used to detect imperfections (cracks & open voids) in the refractory of the BF hearth.
The IE can be done with a simple pulse-echo method, where a hammer is used to hit the wall and an accelerometer records the resulting signal. If the wall has a simple layered structure, the resonance frequencies can be analyzed and the thickness can be determined. However, in more complex situations (with air between the insulating refractory materials) the response can be more complex.
This M.Sc. project will consist of 3 parts:
- Forward modeling of the reflection response of layered media that resemble typical cross-sections of blast furnace walls. Find out if resonance peaks are indeed a good indicator for the wall thickness in case the wall has a more complex structure.
- Performing and analyzing actual wall thickness measurements and compare this with forward modeled responses.
- Derive an inversion method that estimates the cross-section of the furnace wall for given measurements. This can be a parametric inversion process or an imaging-driven method.
- Knowledge on acoustics and good programming skills.
- The MSc student should be able to work independently and to be able to systematically explore the main mechanisms and explain results.
- Good communication skills.
The work will mainly consist of literature research, modeling and programming. Practical tests at the BF could be done, if necessary. The student will be supervised by Eric Verschuur from the TU Delft and Gerard Louwerse and Joost Storm from Tata Steel R&D. Depending on the needs, the work will be performed at TU Delft and Tata Steel.
Typical recording of an impact Echo experiment, with the time signal at the top and the frequency spectrum shown at the bottom.
- Full Wavefield Migration
One of the current challenges we are facing is to take all multiple scattering – that happens in a heterogeneous, high-contrast medium like the Earth – into account in order to illuminate areas in the medium that are difficult to reach by primary wave propagation. This effect is particularly strong in situations where the acquisition geometry is sparse, yielding very limited illumination by primary waves (see example on the right).