• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 194
  • 81
  • 43
  • 22
  • 13
  • 11
  • 4
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 2062
  • 627
  • 593
  • 516
  • 512
  • 187
  • 175
  • 129
  • 126
  • 122
  • 106
  • 100
  • 95
  • 92
  • 89
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

The non linear optical properties of materials

Kernthaler, J. E. January 1973 (has links)
No description available.

Studies with an energy analysing electron microscope

Ditchfield, R. W. January 1972 (has links)
No description available.

Electron channelling in the scanning electron microscope

Woolf, R. J. January 1972 (has links)
No description available.

Theoretical description, optimisation and implementation of multi-wavelength interferometric methods for absolute distance metrology

Falaggis, Konstantinos January 2010 (has links)
Optical interferometry has been applied for distance metrology since the time of Michelson and Benoit. One of the current challenges in interferometric metrology is to achieve long range unambiguous measurement, for example of gauge blocks up to 500 mm in length and in interferometric telescopes, where path length differences can be 10's of meters. A theoretical analysis of multi-wavelength interferometry describing the relationship between unambiguous measurement range, reliability and the measurement wavelengths is the main focus of this research. The results of this analysis allow the derivation of a theoretical model that can be used to develop wavelength selection strategies. Hence, it is possible to maximize the reliability in the calculated fringe order for a given measurement range, number of wavelengths, and level of phase noise. Optimum wavelength selection strategies have been implemented in a fibre optic four-wavelength interferometer and experiments have been carried out showing an overall dynamic range of 1 part in 2x10 6, or a resolution of 8 nm in >18 mm.

Pulsed optical stimulation of luminescence from quartz

Chithambo, M. L. January 2000 (has links)
A light emitting diode based pulsing system capable of producing luminescence time-resolved spectra was developed for study of optically stimulated luminescence from quartz and feldspar. The aim of the pulsed optical stimulation method is to separate in time stimulation and detection of luminescence so that luminescence can be measured in the absence of scatter from stimulating light unlike in conventional continuous stimulation where luminescence monitored includes such scatter. Pulsed optical stimulation not only offers the possibility of improvements in signal to background ratio but also the ability to investigate the time dependence of luminescence emission relative to the time of stimulation. Although study of pulsed luminescence has been dominated by laser-based systems, a pulsing system based on light emitting diodes offers, in comparison, advantages of simplicity and economy. The present system has been used over a wide range of pulse widths (25 ns (FWHM) - 30 <i>m</i>s) and dynamic ranges (40 ns - 64 <i>m</i>s). The system can be adapted for use with a wide range of wavelengths with pulse widths from 25 ns (FWHM) to as long as desired. Luminescence time-resolved spectra have been recorded from feldspar and quartz. Half lives measured from feldspar range from 25 ns and from quartz, 20 - 28 <i>m</i>s. Properties of luminescence half lives from quartz were studied in detail as a function of experimental parameters such as stimulation time, temperature, radiation dose, and preheating method. The influence of temperature on luminescence intensity was studied for time-resolved spectra recorded at long stimulation times. Explanations are proposed to account for experimental results.

Photonic effects in microstructured conjugated polymer films and light emitting diodes

Matterson, Benjamin James January 2002 (has links)
This thesis reports an investigation into the photonic effects caused by wavelength scale micro structure patterned onto films of conjugated polymers. The efficiency of light emitting diodes (LEDs) made from conjugated polymers is limited in part by the trapping of light into waveguide modes caused by the high refractive index of these materials. Waveguide modes in films of poly(p-phenylene vinylene) (PPV) and poly(2-methoxy, 5-(2'ethylhexyloxy)-p-phenylene vinylene) (MEH-PPV) are analysed and the refi-active index of these materials is calculated. The photoluminescence of conjugated polymer films that have been spun onto textured substrates is analysed. It is found that the photoluminescence quantum yield of a film spun onto a substrate inscribed with a grating is increased. It is also found that the photoluminescence spectrum of the film is dramatically altered and varies substantially with viewing angle. The features in the spectrum caused by the grating are strongly polarized. These effects are analysed and are attributed to the scattering of waveguided light out of the film. It is found that films spun onto metal gratings exhibit especially strong scattering. The effect of metal gratings with various grating depths is analysed. The possible contribution of band gaps to the photoluminescence spectrum from polymers on strong metal gratings is discussed. LEDs that include grating structures are constructed and analysed. It is found that having grating structures on the metal layers that are used as electrodes in the LED does not adversely affect the electrical properties of the LED. It is demonstrated that the grating in the LED is able to substantially increase the light emission without using extra electrical power. The emission spectra from LEDs are observed to vary with angle, and exhibit considerable polarization.

Nonlinear effects in quantum cascade lasers

Gambari, Johannes January 2011 (has links)
No description available.

Luminescent complexes for cell imaging

Saad, Suad January 2017 (has links)
Chapter One: Gives a general introduction the history of, and types of, luminescence and the non-radiative processes that result from the absorption of light. It gives an introduction about the generation of Ir(III), Re(I) and Os(II) emission according to the electronic transitions. This chapter also includes the principles of energy transfer between two metal centres that are linked together through bridging ligands and the effect of such ligands on the energy transfer. Finally, it gives the importance of using these metal complexes as probes in cell imaging as some of the prepared complexes in this thesis have been used in cell imaging. Chapter Two: Deals in detail with the luminescent cyclometalated mononuclear Ir(III) complexes starting from their syntheses and the general formula to their emission tuning by changing the coordinating ligands. By this modification, different mononuclear Ir(III) complexes with colours covering the visible region could be obtained. This chapter also shows the generation and the importance of blue emission cyclometalated mononuclear Ir(III) complexes in energy transfer to other metal centres, in the fabrication of OLEDS and in cell imaging. It also shows the syntheses of the bridging ligands based on 3-(2-pyridyl)pyrazole and their complexes with cyclometalated Ir(III) complexes and how these different ligands affect the complexes photophysical properties. These Ir3+ complexes were used as starting materials to synthesize the dinuclear Ir/Re and Ir/Os complexes in chapter 3 and 4 respectively. Chapter Three: Gives a general introduction about the optical properties of mononuclear [Re(CO)3(diimine)L] complexes, where L is a halogen, and the effect of swapping this ligand with neutral monodentate ligands such as pyridine on the photophysical properties such as the emission and the quantum yields. This chapter also shows the energy transfer in other complexes containing Ir and Re such as Ir/Ru and Ru/Re dyads and comparing them with the energy transfer in the Ir/Re system. Furthermore, this chapter deals with the syntheses of the dinuclear Ir/Re complexes from the prepared mononuclear Ir3+ complexes in chapter 2. The synthesis was followed by obtaining the crystal structure of some of these dyads. Moreover, their photophysical properties were studied, including the absorption, emission, excitation, (aerated and degassed) lifetime, quantum yields and extinction coefficients. The energy transfer between Ir? Re was studied with the effect of the bridging ligands and the solvents. Chapter Four: Includes an introduction to the optical properties of mononuclear 2,2- bipyridine Os(II) complexes with different diimine ligands. Also it shows the energy transfer in Ir/Ru systems and comparing it with the energy transfer in Ir/Os systems. This chapter also shows the syntheses of mononuclear [Os(2,2-bipyidine)2Cl2] complexes with 3-(2-pyridyl)pyrazole containing ligands and their Ir/Os dyads. This chapter involves the photophysical studies of the mononuclear osmium complexes and the dyads. The energy transfer from Ir?Os was studied also and was compared with that shown in Ir/Re dyads. Chapter Five: Explains the procedures that were used to synthesize the new ligands, all mononuclear complexes and all the dyads. It also shows the instruments that have been used to characterize and purify all the prepared compounds. This chapter also contains table for the crystal structure data of some complexes.

Problems in the quantum theory of radiation

Boyer, R. H. January 1957 (has links)
No description available.

Spectroscopic properties of conjugated systems

Packer, John Charles January 1968 (has links)
The resonance energy transfer of electronic excitation between two weakly coupled molecules is discussed. The energy transfer mechanism between an isolated ground state acceptor and an excited sensitizer is studied in the dipole-dipole approximation , and the limitations of this model noted. Using the single acceptor-sensitizer pair interaction the behaviour, of a whole system of transferring species is investigated. A new cell-model is proposed for the statistical treatment of the transfer in solution and the results of a computer simulation of a random solution presented. The effect of diffusion on the transfer rate is also theoretically investigated. The time-dependent luminescence of a randomly distributed collection of sensitizer and acceptor molecules is discussed using a Green's function method when the exciting light is an arbitrary function of time . This theory is applied to the interpretation of phase-fluorimetry results. Theoretical expressions describing the effect of light attenuation in fluorescing solutions are given, and a model for secondary fluorescence and the trivial effect is proposed and tested against experimental results . An account of an apparatus for the observation and measurement of resonance energy transfer is given , and the results of an experimental investigation presented. The treatment of molecular π-electrons in the semi-empirical self-consistent field (SCF) approximation is discussed. A derivation of the Hartree-Fock SCF equations for both closed-shell ground states and half open-shell states is given. The nature and validity of the semi-empirical SOF approximation and the π-δ electron separability is considered. The Pople-Pariser-Parr approach is followed throughout.

Page generated in 0.1613 seconds