Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 176-180).

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 159-170).

The fact that optical force is very significant in the microscopic world and can be used to manipulate microparticles has triggered an evolution in micromanipulation, in particular, the manipulation of biological species and colloidal particles. The induced optical force can easily be more than 103 times of the particle's weight. The particle size that are accessible to optical forces ranges from tens of nanometers to hundreds of micrometers. One of the most well-known tools in optical manipulation is called optical tweezers, which is, in essence, performing optical trapping by a strongly focused light beam. The optical force induced by the incident light wave can be generally decomposed into two mathematically and physically distinct components, namely the conservative (gradient force) and non-conservative (scattering and absorption force) forces. Such a split helps in the study of optical forces and elucidates the underlying physics (e.g., the optical trapping). For example, in optical trapping, the conservative gradient force drives the particles toward the intensity maxima and traps the particles there, whereas the non-conservative scattering and absorption force tends to push the particles away and thus has some destabilizing effects. However, while a significant portion of paper dealing with optical trapping explicitly mentioned gradient and scattering forces, the true and exact force profiles of the decomposed optical forces have been mysteries for decades. Researchers still use these concepts, and to certain extent, they imagine the force profile according to their own convenience. This thesis is mainly devoted to the analytical and numerical studies of the decomposition of optical forces. The intrinsic nature of the decomposed optical forces will be discussed, and the approaches of generating a purely conservative force field are presented.. First, the analytical approaches for decomposing the optical force into the gradient force and the scattering and absorption force are described. These approaches can be applied to different particle sizes (smaller than 40% of the wavelength if the multipoles are only considered up to the electric octopole or much larger than the wavelength under the geometrical optics limit), but they still cannot describe the experimentally accessible particle size, which is on the order of micrometer. Second, within the dipole limit, the origin of scattering force is shown to be resulted from the radiation reaction, the polarizations, and the topological charges. In addition, it is found that the conservativeness of the force is closely related to the force constant matrix (the linear term in the Taylor expansion of the optical force) at every point, and certain symmetries in these force constant matrix can guarantee the force to be conservative.. A numerical method that utilizes the fast Fourier transform (FFT) was developed to decompose the conservative and non-conservative forces. This approach is valid when the total force field is spatially localized and decayed sufficiently fast as we move away from the beam center (e.g., optical tweezers or alike) or is spatially periodic (e.g. plane incident waves). We also considered spherical aberration due to the mismatch of the refractive indices between the oil and water media in a typical optical tweezers setup within the FFT method. Various particle sizes, materials, and numerical apertures were also considered. For the periodic force field generated by a collection of plane waves, it is demonstrated that an incident 2-dimensional standing wave could generate a purely conservative force field. The accuracy of this fast Fourier transform approach is analyzed in details and shown to be quite accurate. Moreover, an incident 3-dimensional standing wave could also induce a conservative force field for intermediately sized particles.. Finally, three counter-intuitive examples obtained with the fast Fourier transform approach are presented. These examples clearly demonstrated the need to calculate the gradient and scattering forces accurately, as not doing so would lead to qualitatively wrong results.

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What we do possess to-day as 'art' a faked music, filled with exotic and showcard effects, that every ten years or so concocted out of the form-wealth of millenia some new "style'' which is no style at all since everyone does as he pleases. A lying plastic that steals from Assyria, Egypt and Mexico indifferently. Yet this and only this, the taste of the "man of the world" can be accepted as the expression and sign of the age. Everything else, everything that sticks to old ideals is for provincial consumption. This is the year 1965 - nearly fifty years since Oswald Spengler published "The decline of the West" The paragraph I have quoted by way of justification for this dissertation is in turn a justiification of the fact that Spengler is as valid today as he was in 1918.

This thesis encompasses a body of experimental work on the dynamics of twisted light. We first deal with the generation and reconstruction of twisted light for applications in classical and quantum physics, respectively. In the first case, we present a novel device that has the ability to generate twisted light in a manner that is completely wavelength-independent. Such a device may find applications in various fields of classical physics, ranging from nano to astronomical imaging. In the second work, we study the dynamics of twisted light in the case of laser-induced radial birefringence. This is done by studying the optical features resulting from elastic properties of silver-doped glass. In the last work on generation of twisted light, we present a nano-scale twisted light generator having the capacity to generate an optical mode with a controllable number of twists. In the context of quantum communication and quantum computations, this device has a great potential due to its small size and integrability. In the second part of the thesis, we study the propagation of twisted light both at the classical and quantum regime. In the first case, we observe exotic group velocities of light pulses in vacuum due to the twisting of its wavefront. In the second case, we study the effect of quantum decoherence of twisted light due to the coupling of photonic internal degrees of freedom. We present a technique to recover the lost coherence, which we name recoherence, by a practical unitary transformation.

This thesis concerns itself with the applicability of quantum field methods, in the fixed field approximation, to problems involving a weak gravitational field. After introducing general scattering relations, various classic problems are reviewed to illustrate various approaches to solving scattering problems. Newtonian and quantum mechanical field methods are illustrated using Coulomb scattering. Classical relativity is used to solve the bending of light rays by the sun. Finally, quantum field methods are used to solve the scattering of polarized photons by the sun. The additional problems of scattering of light by a mass distribution and by a rotating mass are calculable using this method. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In preparation for laser light scattering experiments on plasmas in magnetic fields a pulsed ruby laser has been developed in conjunction with a multichannel spectral analyser for detection of the scattered light. The laser, consisting of separate oscillator and amplifier rods has a spectral line width of .08 Å at powers up to 100 Megawatts. The use of a Pockels Cell as the Q-switch permits accurate synchronization with the spectral analyser and all external electronics. For the multichannel detection system five fiber optics slit bundles transmit light from the output of a monochromater to five photomultipiier tubes, which are gated on for 100 nsec during the laser pulse. The pulses are displayed sequentially to give an intensity vs. wavelength profile on an oscilloscope screen. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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