Diese Arbeit entstand im Rahmen des Schwerionenexperiments NA49 am CERN. Auf der Suche nach einem... more Diese Arbeit entstand im Rahmen des Schwerionenexperiments NA49 am CERN. Auf der Suche nach einem neuen Zustand von Kernmaterie, dem Quark-Gluon-Plasma, werden dort im SPS (Super-Proton-Syncrhotron Bleiionen auf eine Energie von 158 GeV pro Nukleon beschleunigt und dann auf eine dünne, im Laborsystem ruhende, Bleifolie (Target) gelenkt. Ziel ist es, in zentralen Stößen zweier Bleikerne ein ausgedehntes Volumen hochkomprimierter und heißer stark wechselwirkender Materie zu erzeugen. Kernmaterie im Grundzustand besitzt eine Dichte von rho o ~ 0,14 Nukleonen pro Kubikfermi. Damit ergibt sich mit der Masse der Nukleonen von etwa 939 MeV/c exp 2 eine Energiedichte im Grundzustand von 130 MeV/fm exp 3. Theoretische Überlegungen im Rahmen der Quantenchromodynamik (QCD, die Eichtheorie der starken Wechselwirkung) sagen voraus, daß sich bei einer Energiedichte von etwa 2-3 GeV/fm exp3 und einer Packungsdichte der hadronischen Materie von 10-15 rho 0 die normalerweise in den Hadronen eingesch...
A novel mixture of low molar mass organosiloxane liquid crystals, with an optimum tilt angle of 2... more A novel mixture of low molar mass organosiloxane liquid crystals, with an optimum tilt angle of 22.5 , exhibits very good alignment. A liquid crystal binary intensity switch with a high, 60 dB, extinction ratio and an analogue response atten- uator, with 54 dB of attenuation, suitable for telecommunication applications at nm were constructed based on such a mixture. The switch and attenuator operate with fast rise times of sa nd s, respectively, at moderate electric fields of up to V m .
Journal of the Society for Information Display, 2006
Liquid-crystal lasers exhibit narrow linewidth, large coherence area, and low threshold laser emi... more Liquid-crystal lasers exhibit narrow linewidth, large coherence area, and low threshold laser emission. Moreover, the wavelength of the laser line can be readily tuned using a variety of different external stimuli, including electric fields. These combined features make them particularly attractive as compact tunable laser light sources. Recent experimental results with regards to the emission characteristics of chiral nematic photonic band-edge lasers are discussed. This type of liquidcrystal laser consists of a self-organizing one-dimensional photonic band structure and a gain medium in the form of a laser dye. Some of the generic features that are observed for these lasers are discussed, including the typical emission linewidth of the laser line, the change in emission energy of the laser for high excitation energies and high pump repetition rates, and the dependence of the excitation threshold and slope efficiency on the cell thickness. In addition, how the performance changes when either the molecular structure of the chiral nematic host or the gain medium is varied is considered. To conclude, results are presented on the laser emission for a wide-temperature-range blue phase I band-edge laser which consists of a self-organizing three-dimensional photonic band structure. Keywords-Photonic band-edge laser, dye, chiral nematic, blue phase. 3 Generic features For the following measurements, a dye-doped chiral nematic liquid-crystal sample was prepared.
This paper describes the behaviour of bulk superconductors when subjected to a varying magnetic f... more This paper describes the behaviour of bulk superconductors when subjected to a varying magnetic field. A magnetic model is described together with experimental results which explain and describe the behaviour of superconducting bulks when subjected to varying magnetic fields. We demonstrate how the behaviour is dependent on the magnitude and period of the perturbations in the fields. The model which we use has been implemented using the Comsol TM pde solver. It is a fully integrated model which uses a variable heat source to regulate the magnetic circuit and thereby to achieve flux pumping. Comsol TM is used for post solution visualization and the model is presented alongside experimental results which support and confirm the conclusions from the model.
In order to understand how the performance of a liquid-crystal laser depends on the physical prop... more In order to understand how the performance of a liquid-crystal laser depends on the physical properties of the low molar mass nematic host, we have studied the energy threshold and slope efficiency of ten optically pumped liquid-crystal lasers based on different hosts. Specifically, this leads to a variation in the birefringence, the orientational order parameter, and the order parameter of the transition dipole moment of the dye. It is found that low threshold energies and high slope efficiencies correlate with high order parameters and large birefringences. To a first approximation this can be understood by considering analytical expressions for the threshold and slope efficiency, which are derived from the space-independent rate equations for a two-level system, in terms of the macroscopic liquid crystal properties.
Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009
1. Introduction Deploying high-bandwidth optical interconnects at the board level is recognised a... more 1. Introduction Deploying high-bandwidth optical interconnects at the board level is recognised as a promising technological alternative to high-speed multi-gigabit short-reach electrical links. In particular, passive multimode polymer waveguides are perceived to offer a cost-...
This thesis presents the development of two new types of polarimetric distributed feedback (DFB) ... more This thesis presents the development of two new types of polarimetric distributed feedback (DFB) fibre laser sensors for simultaneous strain and temperature measurements. These fibre Bragg grating (FBG) based sensors offer strain and temperature measurement accuracies of ±0.3 - ±15 µ.epsilon and ±0.04 - ±0.2°C which are suitable for many applications. The main advantage of these DFB fibre laser sensors over other FBG based sensors is the simplicity of their interrogation system. The first type of sensor operates stably in a single longitudinal mode which splits into two orthogonally polarised modes. This sensor utilises the wavelength of one polarisation mode and the RF beat frequency between the two polarisation modes. The system complexity is reduced to a minimum in the dual longitudinal mode polarirnetric DFB fibre laser sensor which utilises the RF beat frequencies between two longitudinal modes and their associated orthogonal polarisations, therefore requiring only a simple and...
The three-dimensional imaging of mesoscopic samples with Optical Projection Tomography (OPT) has ... more The three-dimensional imaging of mesoscopic samples with Optical Projection Tomography (OPT) has become a powerful tool for biomedical phenotyping studies. OPT uses visible light to visualize the 3D morphology of large transparent samples. To enable a wider application of OPT, we present OptiJ, a low-cost, fully open-source OPT system capable of imaging large transparent specimens up to 13 mm tall and 8 mm deep with 50 μm resolution. OptiJ is based on off-the-shelf, easy-to-assemble optical components and an ImageJ plugin library for OPT data reconstruction. The software includes novel correction routines for uneven illumination and sample jitter in addition to CPU/GPU accelerated reconstruction for large datasets. We demonstrate the use of OptiJ to image and reconstruct cleared lung lobes from adult mice. We provide a detailed set of instructions to set up and use the OptiJ framework. Our hardware and software design are modular and easy to implement, allowing for further open micr...
Many countries have a rapidly ageing population, placing strain on health services and creating a... more Many countries have a rapidly ageing population, placing strain on health services and creating a growing market for assistive technology for older people. We have, through a student-led, 12-week project for 10 students from a variety of science and engineering backgrounds, developed an integrated sensor system to enable older people, or those at risk, to live independently in their own homes for longer, while providing reassurance for their family and carers. We provide details on the design procedure and performance of our sensor system and the management and execution of a short-term, student-led research project. Detailed information on the design and use of our devices, including a door sensor, power monitor, fall detector, general in-house sensor unit and easy-to-use location-aware communications device, is given, with our open designs being contrasted with closed proprietary systems. A case study is presented for the use of our devices in a real-world context, along with a co...
Http Dx Doi Org 10 1080 15421400590954371, Aug 31, 2006
ABSTRACT We demonstrate three electro-optic telecommunication devices operating at a wavelength λ... more ABSTRACT We demonstrate three electro-optic telecommunication devices operating at a wavelength λ = 1550 nm: an optical switch or modulator, a variable attenuator, and a rotatable waveplate. These devices make use of the electroclinic and ferroelectric properties of a chiral smectic organosiloxane liquid crystal. Under moderate electric fields of ≤23 V/μm we observed an optical power modulation of up to 38 dB and a switching time of ∼100 μs. The waveplate could be continuously rotated over 38°. We also present birefringence data of this liquid crystal at λ = 1550 nm as a function of temperature and the implications on the development of liquid crystal telecommunication devices.
Technical Digest. Summaries of papers presented at the Conference on Lasers and Electro-Optics. Postconference Edition. CLEO '99. Conference on Lasers and Electro-Optics (IEEE Cat. No.99CH37013), 2000
ABSTRACT We demonstrate three electro-optic telecommunication devices operating at a wavelength λ... more ABSTRACT We demonstrate three electro-optic telecommunication devices operating at a wavelength λ = 1550 nm: an optical switch or modulator, a variable attenuator, and a rotatable waveplate. These devices make use of the electroclinic and ferroelectric properties of a chiral smectic organosiloxane liquid crystal. Under moderate electric fields of ≤23 V/μm we observed an optical power modulation of up to 38 dB and a switching time of ∼100 μs. The waveplate could be continuously rotated over 38°. We also present birefringence data of this liquid crystal at λ = 1550 nm as a function of temperature and the implications on the development of liquid crystal telecommunication devices.
Proceedings of SPIE - The International Society for Optical Engineering
This paper reports on progress with the coherence-domain method for interrogation of Bragg gratin... more This paper reports on progress with the coherence-domain method for interrogation of Bragg grating pairs, presenting for the first time a simple theoretical analysis of the interrogation procedure and describing the first measurements of useful engineering parameters (strain, pressure) with the system.
We employ two different theoretical methods to calculate the optical prop-erties of photonic band... more We employ two different theoretical methods to calculate the optical prop-erties of photonic band gaps in thin chiral nematic liquid crystal layers. We find that the photonic band gap of chiral nematic liquid crystals can be described by the same equations found in coupled mode theory used for 1D distributed feedback structures comprising of a large number of periods.
Diese Arbeit entstand im Rahmen des Schwerionenexperiments NA49 am CERN. Auf der Suche nach einem... more Diese Arbeit entstand im Rahmen des Schwerionenexperiments NA49 am CERN. Auf der Suche nach einem neuen Zustand von Kernmaterie, dem Quark-Gluon-Plasma, werden dort im SPS (Super-Proton-Syncrhotron Bleiionen auf eine Energie von 158 GeV pro Nukleon beschleunigt und dann auf eine dünne, im Laborsystem ruhende, Bleifolie (Target) gelenkt. Ziel ist es, in zentralen Stößen zweier Bleikerne ein ausgedehntes Volumen hochkomprimierter und heißer stark wechselwirkender Materie zu erzeugen. Kernmaterie im Grundzustand besitzt eine Dichte von rho o ~ 0,14 Nukleonen pro Kubikfermi. Damit ergibt sich mit der Masse der Nukleonen von etwa 939 MeV/c exp 2 eine Energiedichte im Grundzustand von 130 MeV/fm exp 3. Theoretische Überlegungen im Rahmen der Quantenchromodynamik (QCD, die Eichtheorie der starken Wechselwirkung) sagen voraus, daß sich bei einer Energiedichte von etwa 2-3 GeV/fm exp3 und einer Packungsdichte der hadronischen Materie von 10-15 rho 0 die normalerweise in den Hadronen eingesch...
A novel mixture of low molar mass organosiloxane liquid crystals, with an optimum tilt angle of 2... more A novel mixture of low molar mass organosiloxane liquid crystals, with an optimum tilt angle of 22.5 , exhibits very good alignment. A liquid crystal binary intensity switch with a high, 60 dB, extinction ratio and an analogue response atten- uator, with 54 dB of attenuation, suitable for telecommunication applications at nm were constructed based on such a mixture. The switch and attenuator operate with fast rise times of sa nd s, respectively, at moderate electric fields of up to V m .
Journal of the Society for Information Display, 2006
Liquid-crystal lasers exhibit narrow linewidth, large coherence area, and low threshold laser emi... more Liquid-crystal lasers exhibit narrow linewidth, large coherence area, and low threshold laser emission. Moreover, the wavelength of the laser line can be readily tuned using a variety of different external stimuli, including electric fields. These combined features make them particularly attractive as compact tunable laser light sources. Recent experimental results with regards to the emission characteristics of chiral nematic photonic band-edge lasers are discussed. This type of liquidcrystal laser consists of a self-organizing one-dimensional photonic band structure and a gain medium in the form of a laser dye. Some of the generic features that are observed for these lasers are discussed, including the typical emission linewidth of the laser line, the change in emission energy of the laser for high excitation energies and high pump repetition rates, and the dependence of the excitation threshold and slope efficiency on the cell thickness. In addition, how the performance changes when either the molecular structure of the chiral nematic host or the gain medium is varied is considered. To conclude, results are presented on the laser emission for a wide-temperature-range blue phase I band-edge laser which consists of a self-organizing three-dimensional photonic band structure. Keywords-Photonic band-edge laser, dye, chiral nematic, blue phase. 3 Generic features For the following measurements, a dye-doped chiral nematic liquid-crystal sample was prepared.
This paper describes the behaviour of bulk superconductors when subjected to a varying magnetic f... more This paper describes the behaviour of bulk superconductors when subjected to a varying magnetic field. A magnetic model is described together with experimental results which explain and describe the behaviour of superconducting bulks when subjected to varying magnetic fields. We demonstrate how the behaviour is dependent on the magnitude and period of the perturbations in the fields. The model which we use has been implemented using the Comsol TM pde solver. It is a fully integrated model which uses a variable heat source to regulate the magnetic circuit and thereby to achieve flux pumping. Comsol TM is used for post solution visualization and the model is presented alongside experimental results which support and confirm the conclusions from the model.
In order to understand how the performance of a liquid-crystal laser depends on the physical prop... more In order to understand how the performance of a liquid-crystal laser depends on the physical properties of the low molar mass nematic host, we have studied the energy threshold and slope efficiency of ten optically pumped liquid-crystal lasers based on different hosts. Specifically, this leads to a variation in the birefringence, the orientational order parameter, and the order parameter of the transition dipole moment of the dye. It is found that low threshold energies and high slope efficiencies correlate with high order parameters and large birefringences. To a first approximation this can be understood by considering analytical expressions for the threshold and slope efficiency, which are derived from the space-independent rate equations for a two-level system, in terms of the macroscopic liquid crystal properties.
Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009
1. Introduction Deploying high-bandwidth optical interconnects at the board level is recognised a... more 1. Introduction Deploying high-bandwidth optical interconnects at the board level is recognised as a promising technological alternative to high-speed multi-gigabit short-reach electrical links. In particular, passive multimode polymer waveguides are perceived to offer a cost-...
This thesis presents the development of two new types of polarimetric distributed feedback (DFB) ... more This thesis presents the development of two new types of polarimetric distributed feedback (DFB) fibre laser sensors for simultaneous strain and temperature measurements. These fibre Bragg grating (FBG) based sensors offer strain and temperature measurement accuracies of ±0.3 - ±15 µ.epsilon and ±0.04 - ±0.2°C which are suitable for many applications. The main advantage of these DFB fibre laser sensors over other FBG based sensors is the simplicity of their interrogation system. The first type of sensor operates stably in a single longitudinal mode which splits into two orthogonally polarised modes. This sensor utilises the wavelength of one polarisation mode and the RF beat frequency between the two polarisation modes. The system complexity is reduced to a minimum in the dual longitudinal mode polarirnetric DFB fibre laser sensor which utilises the RF beat frequencies between two longitudinal modes and their associated orthogonal polarisations, therefore requiring only a simple and...
The three-dimensional imaging of mesoscopic samples with Optical Projection Tomography (OPT) has ... more The three-dimensional imaging of mesoscopic samples with Optical Projection Tomography (OPT) has become a powerful tool for biomedical phenotyping studies. OPT uses visible light to visualize the 3D morphology of large transparent samples. To enable a wider application of OPT, we present OptiJ, a low-cost, fully open-source OPT system capable of imaging large transparent specimens up to 13 mm tall and 8 mm deep with 50 μm resolution. OptiJ is based on off-the-shelf, easy-to-assemble optical components and an ImageJ plugin library for OPT data reconstruction. The software includes novel correction routines for uneven illumination and sample jitter in addition to CPU/GPU accelerated reconstruction for large datasets. We demonstrate the use of OptiJ to image and reconstruct cleared lung lobes from adult mice. We provide a detailed set of instructions to set up and use the OptiJ framework. Our hardware and software design are modular and easy to implement, allowing for further open micr...
Many countries have a rapidly ageing population, placing strain on health services and creating a... more Many countries have a rapidly ageing population, placing strain on health services and creating a growing market for assistive technology for older people. We have, through a student-led, 12-week project for 10 students from a variety of science and engineering backgrounds, developed an integrated sensor system to enable older people, or those at risk, to live independently in their own homes for longer, while providing reassurance for their family and carers. We provide details on the design procedure and performance of our sensor system and the management and execution of a short-term, student-led research project. Detailed information on the design and use of our devices, including a door sensor, power monitor, fall detector, general in-house sensor unit and easy-to-use location-aware communications device, is given, with our open designs being contrasted with closed proprietary systems. A case study is presented for the use of our devices in a real-world context, along with a co...
Http Dx Doi Org 10 1080 15421400590954371, Aug 31, 2006
ABSTRACT We demonstrate three electro-optic telecommunication devices operating at a wavelength λ... more ABSTRACT We demonstrate three electro-optic telecommunication devices operating at a wavelength λ = 1550 nm: an optical switch or modulator, a variable attenuator, and a rotatable waveplate. These devices make use of the electroclinic and ferroelectric properties of a chiral smectic organosiloxane liquid crystal. Under moderate electric fields of ≤23 V/μm we observed an optical power modulation of up to 38 dB and a switching time of ∼100 μs. The waveplate could be continuously rotated over 38°. We also present birefringence data of this liquid crystal at λ = 1550 nm as a function of temperature and the implications on the development of liquid crystal telecommunication devices.
Technical Digest. Summaries of papers presented at the Conference on Lasers and Electro-Optics. Postconference Edition. CLEO '99. Conference on Lasers and Electro-Optics (IEEE Cat. No.99CH37013), 2000
ABSTRACT We demonstrate three electro-optic telecommunication devices operating at a wavelength λ... more ABSTRACT We demonstrate three electro-optic telecommunication devices operating at a wavelength λ = 1550 nm: an optical switch or modulator, a variable attenuator, and a rotatable waveplate. These devices make use of the electroclinic and ferroelectric properties of a chiral smectic organosiloxane liquid crystal. Under moderate electric fields of ≤23 V/μm we observed an optical power modulation of up to 38 dB and a switching time of ∼100 μs. The waveplate could be continuously rotated over 38°. We also present birefringence data of this liquid crystal at λ = 1550 nm as a function of temperature and the implications on the development of liquid crystal telecommunication devices.
Proceedings of SPIE - The International Society for Optical Engineering
This paper reports on progress with the coherence-domain method for interrogation of Bragg gratin... more This paper reports on progress with the coherence-domain method for interrogation of Bragg grating pairs, presenting for the first time a simple theoretical analysis of the interrogation procedure and describing the first measurements of useful engineering parameters (strain, pressure) with the system.
We employ two different theoretical methods to calculate the optical prop-erties of photonic band... more We employ two different theoretical methods to calculate the optical prop-erties of photonic band gaps in thin chiral nematic liquid crystal layers. We find that the photonic band gap of chiral nematic liquid crystals can be described by the same equations found in coupled mode theory used for 1D distributed feedback structures comprising of a large number of periods.
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Papers by Oliver Hadeler