# Theses 2014

## Amin Pour, Hamed

## 3D Dynamic Opto-Mechanical Modeling of Diode-Pumped Trapezoid Yb:YAG/YAG Thin Disk Laser

**Abstract: **In this master thesis, we present a 3D modelling of thermal lensing effect in an edge-pumped trapezoid Yb:YAG/YAG thin disk laser. At first, a Monte-Carlo ray tracing method and finite element analysis (FEA) is used to calculate the absorbed pump power from our sides in such a way, that the pump light are totally trapped inside the crystal after total reflections. To study this configuration we performed a detailed simulation of our delivery system in our laser simulation code software ASLD. Secondly, we optimized the absorption efficiency of our laser which is obtained 66.7% due to the optimum Yb:YAG dopant of 10% and efficient thickness of 0.2 mm. Then, using the result of absorbed pump light distribution as a heat source for the crystal to compute the temperature distribution inside the crystal and perform the consequences of opto-mechanical properties including Von Mises stress and deformation components distribution inside the crystal via Finite Element Analysis (FEA). Furthermore, the thermal lens power is considered in our modelling as an important consequence of opto-mechanical effect which is compared in different output powers. Finally, we applied the Dynamic Multimode Analysis (DMA) method to solve the rate equation and calculate the output powers respect to different length of cavities and different output coupler curvatures respect to the dealing beam quality in multimode operation.

## Gebremichael, Wendwesen

## Optical Characterization of a New Amplifier Media

**About this project: **The advances made in laser technology must address vast and continuously evolving needs in multiple application areas [1]. Among different types of lasers, the all-solid-state lasers, ideally diode pumped (DPSSL) are best placed to address majority of these needs because of a robust and compact setup, a relatively high efficiency with corre-sponding low thermal cooling requirements, and a long lifetime [2]. Research and de-velopment on nonlinear optics and laser physics have been growing fast over the past twenty years. Behind such an impressive growth is the need for excellent thermal prop-erties and high damage threshold for high power and high energy applications, a large emission spectrum for ultra-short pulse generation, a long lifetime of the excited state for high-energy extraction and the access to new wavelength ranges [1]. Depending on the type of problem to be addressed, these issues demand the development of materials which have a host and a dopant specific in each case. Thus, research on and charac-terization of new laser materials is inevitable to answer to the above mentioned chal-lenges or societal needs of today and tomorrow in general [2].

Efficient use of laser materials requires full characterization of their absorption and emission properties. For most classes of crystals, measurements of these properties can be done along dielectric frame axes which are best described with 3-by-3 second rank linear permittivity tensor. However, in the case of monoclinic crystals, the maximum values of absorption and fluorescence are not along the principal axes of the dielectric frame, but tilted at an angle with respect to one of the axes of the dielectric frame [1]. In general, monoclinic crystals are biaxial crystals such that the imaginary part of refrac-tive index is different than principal refractive indices in the tri-rectangular dielectric frame (x, y, z) [3].

In this master thesis project, we have studied Yb-doped borate type-Yb:Li6(Y/Gd)(BO3)3-monoclinic crystals. The use of these new amplifier media was explored for the devel-opment of new solid-state lasers in different spectral domains: the near-infrared with Ytterbium-doped crystals for short-pulse generation. The project was done in the Short lasers: applications & materials (SLAM) research group which is mainly focusing on pho-tonics at the University of Bordeaux, France. Characterization and tests of new laser materials is one of the themes of the group. Based on previous experiments, some of the anisotropic properties of highly concentrated Ytterbium-doped monoclinic gain me-dia with hosts from borate family, Yb-doped borate type crystals were characterized. As a continuation of these studies on borate-type crystals [2, 4-6], the relationship between linearly polarized light, absorption and emission of these crystals with the real and imaginary refractive index surfaces was studied with a new and relatively simple approach.

**Conclusions: **With a consideration of the so called dielectric frame, the relative dielectric permittivity tensor of monoclinic crystals is described by a 3×3 diagonal real matrix plus imaginary matrix with diagonal and two similar off-diagonal elements. The off-diagonal elements depict the relative rotation of the imaginary plane with respect to the principal dielectric plane that are perpendicular to one of the dielectric axes which is parallel to the 2 fold axis or perpendicular to the mirror m. With this concept, from each host matrix, two types of Yb-doped monoclinic crystal samples were prepared and the dependence of the absorption coefficient on the polarization angle for a linearly polarized source at the maximum absorption wavelength of the samples was studied.

From the result of these experiments, the orientation of the dielectric axes were identi-fied with respect to the crystallographic orientations. Consequently, this leads to the full description of the imaginary index surfaces of the LGB:Yb and LYB:Yb monoclinic sam-ples.

However, for laser operations, the “good” absorption axis is not necessarily the “best” emission axis. Therefore, further investigations should be made on the lasing and gain experiments which was already tried during the course of this project [Appendix B, Ap-pendix C]. The absorption experiments should also be improved with a better mechanics for the crystal mounts to minimize angular misalignment of the samples.

Generally, in this master thesis project, we were able to develop rather simple and complete theoretical and experimental approach to characterize the absorption of Yb-doped borate type monoclinic crystals or monoclinic crystals in general. Given the po-tentiality of Yb-doped crystals for future laser performances, it was an amazing journey.

## Gebredikan, Medhanie Tesfay

## Shifted Excitation Raman Difference Spectroscopy for Identification of Oral Squamous Cell Carcinoma

Abstract: In recent decades, the research and development activities related to medical diagnosis have emphasized the development of real time, fast, and accurate methods of cancer screening. Raman spectroscopy has been typically proposed to replace conventional histopathological examination.

Identification of oral squamous cell carcinoma with a real time, portable and highly specific method is under investigation at the Lehrstuhl für Technische Thermodynamik (LTT) of the Friedrich-Alexander-Universität Erlangen-Nürmberg to increase the survival rate of patients of the cancer diseases by extracting its earlier information. Fluorescence rejection, which affects the overall accuracy of the useful information delivered by the Raman spectroscopy, is part of the research. The goal of this thesis is the development of a shifted excitation Raman difference spectroscopy (SERDS) technique combined with a baseline correction method which removes the overwhelming effect of fluorescence without losing relevant and significant Raman spectral features which hold the molecular profile. It is also the aim of this thesis to classify tissues based on the reconstructed pure Raman spectra with a minimum misclassification errror.

The overall work of this thesis is organized in three main parts. The first part of the work reviews Raman spectroscopy, its challenges and the available methods developed to tackle them. The second part is the implementation of a reconstruction algorithm of Raman spectra from a fluorescence corrupted spectra. A shifted excitation principle is applied to get rid of the fluorescence followed by baseline correction method to completely remove the fluorescence. The reconstruction method was able to get rid of the fluorescence without losing significant Raman information. The final part of the thesis is devoted to the results and discussions. Effect of excitation wavelength shift and strength of fluorescence are analyzed. Nine different tissues from four different pigs are differentiated with a misclassification error of 1.74%. Tissues of soft bone and hard bone showed the highest misclassifications. Significant differences, which are attributed to the spectral feature of lipids and proteins, among the Raman spectra of normal tissue and tumor tissue of the oral cavity of human are also observed..

## Hosseini, Pooria

## Dispersive Fourier Transformation Method to Investigate the Nonlinear Dynamics of Photonic Crystal Fibre Ring Cavities

**Abstract: **By means of a conventional spectrum analyser for oserving the real-time spectrum of a pluse train up to 100 megahertz repetition rate, we can only view an average of the spectra because of the low scanning rate of the device. To overcome this limitation, one can use the time-stretching method, also kknown as the Dispersive Fourier Transform (DFT) technique, to map the spectral intensity on the temporal pulse and observe the shot-do-shot spectrum by employing a normal oscilloscope with few gighertz bandwidth.

In this thesis we investigated the nonlinear dynamics of a passive photonic crystal fibre ring cavity, pumped in the fs regime, by analysing the shot-do-shot spectrum obtained by the DFT technique. Afterward, we used the obtained spectral information of the cavity to determine the bifurcation diagrams and pointed out different nonlinear dynamical states such as steady, perodic, and highly complex dynamics.

Furthermore, we presented the concept of the spectral correlation maps and applied it on the ensembles of the different dynamical states. Outstandingly, we observed highly correlated areas on the map that remained persistent even when the number of the considered consecutive pulses increased up to few hundreds.

## Huang, Jiapeng

## Speckle Detection of Surface Plasmon Polaritons

**Abstracts:** Sensors based on surface plasmon polaritons are of great utility in the eld of biosensing. By detecting the resonance angle or wavelength change, it is possible to sensitively measure surface modication which changes the refractive index. In this thesis, we take a new approuch to SPP biosensing by observing changes in the re-radiatied light from directionally scattered surface plasmon polaritons. We show that changes in the resulting speckle pattern can be used to detect single nanoparticle, breaking through previous performance limitations in surface plasmon polariton biosensing.

## Jeevanandam, Guadhaman

## Generation of Optical Activity by Bilayered Chiral Metamaterials and Planar Metamaterials in the Visible Spectrum

**Abstract:** Chiral metamaterial are a class of metamaterials that show optical activity, ellipticity and negative refraction. Optical activity and ellipticity generally occurs together. The aim of this thesis is to obtain a high optical activity with low ellipticity. A bi-layered structure comprising of both a negative and a positive structure was used for this purpose. These structures were fabricted by using focussed ion beam (FIB). The transmission spectrum for the structures is measured by a light microscope equipped with a spectrometer. The bi-layered structures were attempted to be fabricated by using FIB and by micromanipulators. Also, different arrangements of the bi-layered structures were modelled by the finite difference time domain (FDTD) method. From the modelled structures, an optical activity of 61° was obtained with zero ellipticity.

## Kayal, Yaman Ahmad

## Khodaei, Yashar

## Improved Design of a Raman-based Optical Sensor for the Identification of Oral Cancer

**Conclusion: **In this thesis, the high potential of Raman spectroscopy (RS) to differentiate tumour from normal tissue was studied. Because of its capability to provide an objective „chemical fingerprint“ of the examined region, RS can be used for the identification of molecular changes through specific spectral patterns in oral cancer tissue. I showed the potential of identifying oral tumour with high sensitivity and specificity in an *ex vivo* setting.

The hardware and software of the former set up was improved to reach high spectral resolution and intensity with lower excitation power (100 mW) and very short integration time (100 ms) giving rise to high diagnostic speed of the clinical Raman sensor, too. Hardware development was carried out through utilizing the Ventana spectrometer with twice higher spectral resolution than the QE65000 spectrometer (that was calculated theoretically and was confirmed by the experiment) and high sensitivity, wide numerical aperture hand-held Raman probe which has 2.5 times larger solid angle than the former Raman probe.

Development of software was done with the aim of having highly automated spectral data acquisition and analysis. Thus, a robust and user-friendly software, which can synchronize all process of shifting wavelength, spectra acquisition and spectral analysis for physicians was established which allows for a time-saving and cost-reducing application.

The suppression of the fluorescence background was done with the SERDS (shifted-excitation Raman difference spectroscopy) method followed by a polynomial fit. And, the reconstructed Raman spectrum of normal tissue represented intense peaks at 1258, 1308, 1458 and 1667 cm^{-1}. In contrast, the Raman spectrum of oral tumour had lower peak intensities at 1291, 1342, 1458 and 1667cm^{-1}. Hence, the Raman spectral difference between normal and tumour oral tissue of human was used for tumour diagnosis. There are obvious shifts from 1258cm^{-1} of normal tissue to 1291cm^{-1} peak of tumour tissue and from 1308cm^{-1} peak of normal tissue to 1342cm^{-1} peak of tumour tissue that were applied as criterion for differentiation. Besides, there is a clear intensity difference between normal and tumour tissue in 1458 cm^{-1} peak that was also used for discrimination. Accordingly, a statistical method will be implemented for the classification of the reconstructed Raman signal to convert the Raman spectrum into a diagnosis that would be carried out by my colleague in the other study.

## Littau, Benjamin

## Design and Implementation of a Frequency Modulated Continuous Wave Terahertz Tomography System for the Development of Hybrid Reconstruction Algorithms

**Abstract: **The electromagnetic properties of synthetic materials at terahertz frequencies offer great opportunities for non-destructive testing in quality assurance or production process control. Terahertz tomography systems providing three-dimensional images of specimens have several advantages over conventional X-ray or ultrasonic systems including the opportunity of a spectral analysis of the material properties. However, terahertz tomography systems are still a current field of research and the demand for applicable improvements in both, system design and reconstruction algorithms is still highly topical.

The here developed tomographic imaging system is one of the first hybrid systems that combines transmission and reflection system architecture. Transmission terahertz tomography using reconstruction algorithms similar to X-ray tomography allows to analyse material properties but resolution in the propagation direction of the beam and use algorithms based on the synthetic aperture radar principle adopted from ultrasound tomography. The increased amount of collected information in a hybrid system combining both architectures enables the development of more efficient algorithms providing significantly higher resolution.

The hybrid system consists of an electronic terahertz source and four heterodyne detectors which simultaneously measure the transmitted and reflected radiation. The system works similar to a frequency-modulated continuous wave radar. It sweeps the emitted signal frequency between 70 and 110 GHz, detecting both, amplitude and phase of every single frequency component. As advancement the development of a system using optically generated terahertz pulses allowing spectral analysis of specimens is already planned. The time of flight is determined by detecting the frequency difference between the emitted and received signal. Telescopes consisting of two lenses provide facile alignment of optics as well as the opportunity to modify beam parameters by exchanging lenses easily. One rotational and two translational stages are used for scanning the specimen. First results show reconstructed three-dimensional images of samples with dimensions up to 140 millimetres where the development of hybrid reconstruction algorithms promises significant improvement in resolution.

## Lu, Xiaofeng

## Optimization of 4-Dimensional Modulation and Coherent Receiver Processing in Optical 28-Giga-Baud Lab Transmission System

**Summary: **Today 100-Gbit/s optical transmission systems are based on coherent detection of the transmitted optical carrier which is independently phase and amplitude modulated in two orthogonal polarizations at a symbol rate of 28-Gbaud. Digital signal processing (DSP) algorithms implemented in receiver ASIC perform adaptive demultiplexing, distortion equalization, and phase estimation of the detected optical signal as well as error-correcting decoding if channel coding is applied.

In frame of the Master thesis a coherent receiver DSP algorithm shall be refined for processing of 4-dimensional (4D) modulated signals. Specifically receiver phase, frequency estimation and butterfly FIR filter shall be extended to full 4D operation and nonlinear filtering such as decision feedback equalization shall be developed and implemented. Performance shall be numerically analyzed by simulation and by application of measurement data which have to be generated by experiment regime of the fiber shall be evaluated.

Soft-decision error correction tailored to 4D formats, which are provided by Bell Labs, Alcatel-Lucent, shall be implemented in the receiver algorithm and the operation -joint with other processing- shall be investigated. Specifically the tradeoff between constellation order rates shall be discussed.

Moreover, different existing options of 4D modulation formats (POLQAM) shall be evaluated the 32, 64 and more point constellations shall be optimized by Sphere Packing algorithm, Densest Lattice Packing algorithm or other methods. The method should also be extended to a higher dimensional modulation. Attention should be paid to the optimization of bit mapping to constellations points in view of efficient error correction decoding using heuristic (Ant Colony Optimization) and other algorithm.

## Mulugeta, Kumneger Demeke

## Surface Light Scattering Under Considertation of Line Broadening Effects

**Conclusion:** In the present work, the instrumental line broadening of an existing SLS experiment was investigated by the reference fluid toluene and the results were applied to a semitransparent IL [BMIM][TCM].

During the measurement with toluene several problems like the impurity of the fluid due to the measurement cell and a contamination of the top window of the measurement cell due to the preparation procedure were faced. At the end, for relatively large incident angles of about 3°, the measured thermophysical properties of surface tension and dynamic viscosity were in very good agreement with the reference data. Based on this, an experimental analysis of the setup was performed with the focus on small incident angles where line broadening effects become dominant. It could be shown that the experimental setup is complex and cannot be easily treated theoretically. Therefore an experimental calibration with the reference fluid toluene, whose thermophysical properties σ and η are well-known, should be preferred.

In accordance with the SLS theory, a mathematical concept was developed and programmed to extract the instrumental line broadening effect from the measurements with toluene. These measurements were performed for the first time in a range of incident angles between 0.3° and 1°. The instrumental line broadening Δq was calculated and additionally an unexpected error in the wave number q_{0} was found. Both Δq and q_{0} depend on the adjusted wave number and have a large variance for individual measurements. This result shows that the experimental setup is not optimal for the use with small incident angles, but excellent results can be obtained at larger angles. The unexpected error in the wave number q_{0} and its variance might be related to the adjustment of the laser beam in horizontal direction by hand.

Nevertheless a possible correction of the measured semitransparent IL [BMIM][TCM] was investigated but it turned out that a correction is not possible. The corresponding calculated thermophysical properties possess errors of more than 10% in σ and η.

A major task for the future will be an analysis of the unexpected error in the wave number q_{0}. The assumed origin is the horizontal movement of the laser by hand which should be verified by an experiment. In the next step a mechanism has to be invented which allows an exact positioning of the laser beam. Without such modifications the current setup is of limited use at small incident angles.

Another important point refers to the programming of an algorithm that allows the calculation of σ and η as suggested. The main problem here is the time consuming evaluation of the dispersion relation which could be possibly solved by a pre-calculation of the dispersion relation and the use of an interpolation function. I.e. the dispersion relation calculates ω_{q} and Γ_{q} for many input combinations of σ, η and q a priori; an interpolation function uses this information and can answer function calls for all possible input combinations by interpolation; the algorithm of the minimization problem calls the interpolation function instead of the dispersion relation.

## Ringel, Thomas

## Surface Light Scattering Under Considertation of Line Broadening Effects

**Conclusion:** In the present work, the instrumental line broadening of an existing SLS experiment was investigated by the reference fluid toluene and the results were applied to a semitransparent IL [BMIM][TCM].

During the measurement with toluene several problems like the impurity of the fluid due to the measurement cell and a contamination of the top window of the measurement cell due to the preparation procedure were faced. At the end, for relatively large incident angles of about 3°, the measured thermophysical properties of surface tension and dynamic viscosity were in very good agreement with the reference data. Based on this, an experimental analysis of the setup was performed with the focus on small incident angles where line broadening effects become dominant. It could be shown that the experimental setup is complex and cannot be easily treated theoretically. Therefore an experimental calibration with the reference fluid toluene, whose thermophysical properties σ and η are well-known, should be preferred.

In accordance with the SLS theory, a mathematical concept was developed and programmed to extract the instrumental line broadening effect from the measurements with toluene. These measurements were performed for the first time in a range of incident angles between 0.3° and 1°. The instrumental line broadening Δq was calculated and additionally an unexpected error in the wave number q_{0} was found. Both Δq and q_{0} depend on the adjusted wave number and have a large variance for individual measurements. This result shows that the experimental setup is not optimal for the use with small incident angles, but excellent results can be obtained at larger angles. The unexpected error in the wave number q_{0} and its variance might be related to the adjustment of the laser beam in horizontal direction by hand.

Nevertheless a possible correction of the measured semitransparent IL [BMIM][TCM] was investigated but it turned out that a correction is not possible. The corresponding calculated thermophysical properties possess errors of more than 10% in σ and η.

A major task for the future will be an analysis of the unexpected error in the wave number q_{0}. The assumed origin is the horizontal movement of the laser by hand which should be verified by an experiment. In the next step a mechanism has to be invented which allows an exact positioning of the laser beam. Without such modifications the current setup is of limited use at small incident angles.

Another important point refers to the programming of an algorithm that allows the calculation of σ and η as suggested. The main problem here is the time consuming evaluation of the dispersion relation which could be possibly solved by a pre-calculation of the dispersion relation and the use of an interpolation function. I.e. the dispersion relation calculates ω_{q} and Γ_{q} for many input combinations of σ, η and q a priori; an interpolation function uses this information and can answer function calls for all possible input combinations by interpolation; the algorithm of the minimization problem calls the interpolation function instead of the dispersion relation.

## Ströhl, Florian

## Structured Illumination Microscopy (SIM). Theory, Implementation and Conmparison of TIRF-SIM, SROS-SIM and MSIM

**Abstract: **One of the most important tools for biomedical research is fluorescence microcsopy. Selective labelling of molecules enables the observation of process kinetics within living cells but is limited due to diffraction to a maximum resolution of half the wavelength in use. To further increase resolution it is possible e.g. to use structured instead of homogeneous illumination light. The spatial frequencies of illumination and flurophore distribution will mix, thus encoding fine details of the structure, which would usually be lost, in observable spatial frequency bands. The so obtained additional information is computationally decoded afterwards to offer super-resolution. Depending on the particular structure of the illumination light the respective reconstruction algorithms vary a lot. In addition, the set-ups and acquisition procedures need to be adapted to generate the needed patterns and record the appropriate amount of different raw image data. Therefore, it is useful to compare different illumination geometries as they all have their strength, weaknesses and optimal fields of application. For example, sinusoidal illumination in a total internal reflection configuration (TIRF-SIM) allows extremely fast, high-contrast imaging with the theoretical possibility of unlimited resolution improvement via the use of non-linear effects (SSIM) but is restrained to two-dimensional imaging. In contrast, three-dimensional sinusoidal illumination (3D-SIM) requires more reconstruction and hardware efforts but is capable of removing out-of-focus light computationally and enables volumetric data at even higher imaging rates than 3d-SIM but lacks resolution improvement in the axial direction. Diffraction limited multi-focal spot pattern illumination (MSIM), similarly to SROS-SIM, does not offer super-resolution in the axial direction but enhances penetration depth and contrast and therefore is useful in thick sample imaging. To optimally compare these techniques, the standard reconstruction algorithms were implemented in Matlab and a SIM microscope was built that is switchable between TIRF-SIM, SROS-SIM and MSIM. It is therefore ideal to comparatively evaluate the respective performances regarding resolution, imaging speed, and reduction of out-of-focus-light. Additionally, a new kind of reconstruction algorithm was developed, joint Richardson-Lucy deconvolution for widefield MSIM, that improves reconstruction results from noise corrupted raw data.

## Unberath, Mathias

## 3D + t Statistical Human Heart Phantom for X-Ray Projection Imaging

The long acquisition times of about 5s in rotational angiography using C-arm CT systems requires the incorporation of the heart’s dynamics into the reconstruction algorithms. Meaningful evaluation and comparison of such algorithms requires projection data from computerized 4D phantoms. Changing clinical parameters of the model or incorporating pathologies, however, may decrease clinical relevance. In order to tackle this problem, we develop a 4D open-source statistical shape model of the whole heart.

We compare two registration-based segmentation based on Thirion’s Demons and mutual information driven B-spline transforms, respectively, for automatic training set generation from four-chamber enhanced ten phase CT angiography. The model, built from nine male and eleven female patient’s data sets, exhibits a generalization ability of 5:00 0:93mm and specificity of 7:30 0:97mm. We investigate the use of kernel principal component analysis in classification of pathologies with manifestations in anatomical alteration.

The model is implemented in CONRAD, an open-source simulation and reconstruction framework. The algorithms and high resolution projection data are available online. To the best of our knowledge, this is the first open-source statistical shape model of its kind.

## Yahyapour, Milad

## Implementation and Characterization of Imaging Routines into a Continuous-Wave Terahertz Photomixing System

Conclusion and Future Work: In this thesis, a beam profile imaging routine and a sample inspection imaging routine were implemented into a continuous-wave terahertz photomixing system. The beam profile measurement was performed to recognize and characterize the emitter (photomixer) properties and to examine the alignment of the terahertz beam with an opto-mechanic setup. The emitter was whown to form a beam focus in front of its facet, with frequency dependent properties. A similar frequency dependent behaviour was found for the intermediate focus, which is formed by the opto-mechanic setup for sample inspection purposes.

A sample inspection routine was developed based on two scan methods: as step-by-step scan and a continuous scan. Both methods were throughly tested for various parameters.

Finally, both scan methods were used to inspect an envelope, where the teraherzt images of the envelope clearly revealed its content. But, one of the objects could not be identified with terahertz imgaing. Based on its spectral fingerpringts the unknown object’s material was identified with an additional spectroscopic analysis.

There are some works left for the future:

- An automatic data analysis is desired for beam profile imaging routine.
- So far there is only one emitter characterized. For statistiscal validations, the beam profile routine should be applied for different emitters.
- The implemented sample inspection routine is compatible with TOPTICA’s incoherent photomixing setup. In future, the routine should be extended to a coherent system for phase-sensitive sample inspection.

## Yousefi Amin, Amir Abbas

## Solution-processed Fabrication and Characterization of Light-Emitting Electrochemical Cells with Silver Nanowirde Electrodes

**Conclusion and Outlook:** The focus of this thesis was to investigate LEC architectures that can be fabricated by solution processing. In particular, the aim wa to replace the ITO electrode with silver nanowires.

It was shown that AZO and additional buffer layers as ETLs couldn’t be successful to inject electrons into the organic semiconductor and therefore the inefficient injection cannot provide electrons and holes for radiative recombination and the light output from the device is low.

In the normal structure of LECs, we applied a new structure design which didn’t utilize any ETLs. Equally interesting are the results of the performance optimization of the different HTL and active layer thicknesses and it was demonstrated how to utilize thick active material layers.

In the last step, both ITO and the evaporated silver top electrode were successfully replaced with silver nanowire as anode and cathode, respectively.

In conclusion, this thesis has demonstrated LEC fabrication and operation under ambient conditions, and fully solution-processed devices that feature silver nanowire electrodes.

Successful implementation of solution processing methods could allow LECs to become an ultra-low-cost lighting alternative for various large area fabrications, using roll to roll coating and slot die casting.

The gap between LECs and currently available lighting technology has become smaller indicating the potentials of LECs in future’s technology. Nevertheless, further development could primarily address the limited lifetime of LECs by increasing ionic conductivity of active layer ink, and also improve efficiency using solution processed reflector bottom electrode like silver ink in order to increase the light emission.