Microdisk Resonators with Two Point Scatterers

Optical microdisk resonators exhibit modes with extremely high Q-factors. Their low lasing thresholds make circular microresonators good candidates for the realization of miniature laser sources. They have, however, the serious drawback that their light emission is isotropic, which is inconvenient for many applications. In our previous work, we showed that the presence of a point scatterer inside the disk can lead to highly directional modes in various frequency ranges while preserving the high Q-factors. In the present paper we generalize this idea to two point scatterers. The motivation for this work is that the strength of a point scatterer is difficult to control in experiments, and the presence of a second scatterer leads to a higher dimensional parameter space which permits to compensate this deficiency. Similar to the case of a single scatterer in a circular disk, the problem of finding the resonance modes in the presence of two scatterers is to a large extent analytically tractable.

Internal and External Resonances of Dielectric Disks

Circular microresonators (microdisks) are micron sized dielectric disks embedded in a material of lower refractive index. They possess modes with complex eigenvalues (resonances) which are solutions of analytically given transcendental equations. The behavior of such eigenvalues in the small opening limit, i.e. when the refractive index of the cavity goes to infinity, is analysed. This analysis allows one to clearly distinguish between internal (Feshbach) and external (shape) resonant modes for both TM and TE polarizations. This is especially important for TE polarization for which internal and external resonances can be found in the same region of the complex wavenumber plane. It is also shown that for both polarizations, the internal as well as external resonances can be classified by well defined azimuthal and radial modal indices.Comment: 5 pages, 8 figures, pdflate

Spectral statistics in chaotic systems with a point interaction

We consider quantum systems with a chaotic classical limit that are perturbed by a point-like scatterer. The spectral form factor K(tau) for these systems is evaluated semiclassically in terms of periodic and diffractive orbits. It is shown for order tau^2 and tau^3 that off-diagonal contributions to the form factor which involve diffractive orbits cancel exactly the diagonal contributions from diffractive orbits, implying that the perturbation by the scatterer does not change the spectral statistic. We further show that parametric spectral statistics for these systems are universal for small changes of the strength of the scatterer.Comment: LaTeX, 21 pages, 7 figures, small corrections, new references adde

Japanese American Internment Camps: Resistance and Perseverance

This thesis examines the internment of Japanese Americans during World War II from the internees’ side, the side of the United States government and the general non-Japanese American population’s side. It examines three key aspects of internment from the Japanese American perspective: initial feelings of the camps and their conditions; the ways in which Japanese Americans maintained a traditional life during internment or, particularly in the case of Japanese American women, found new opportunities through internment to break with certain traditions; and how both age and gender played a role in their perception of events as well as their ability to resist internment. Oral history interviews with Japanese Americans who were interned provide the main primary source information. Military documents of camp examinations and newspaper articles show the racist climate of the United States during internment. Using these primary sources in conjunction with secondary scholarship from some of the most respected names in Asian American Studies, Roger Daniels, Linda Tamura and Valarie Matsumoto, who have all written extensively on the topic, a better understanding of the experiences Japanese Americans had in the internment camps can be gained. Japanese Americans resisted both racism and internment during this time

Doctor of Philosophy

dissertationThe ability to sense metabolic status and coordinately regulate specific aspects of metabolism is central to human health and disease. The second chapter of this dissertation defines a role for the Drosophila nuclear receptor, DHR96, as a key regulator that coordinates triacylglycerol (TAG) and cholesterol homeostasis. Studies presented in this dissertation show that DHR96 maintains whole animal TAG levels by promoting the breakdown of dietary TAG through regulation of the intestinal lipase Magro. Previous studies have shown that DHR96 binds cholesterol in its ligand-binding domain and regulates the transcriptional response to dietary cholesterol. The third chapter of this dissertation describes how, in conjunction with its role in promoting dietary TAG digestion, DHR96 functions through magro to prevent the accumulation of excess sterols in the fly. Magro exerts this role in cholesterol homeostasis through its cholesterol esterase activity, cleaving stored cholesterol esters to promote sterol excretion. Taken together, these studies define a key role for DHR96 in coordinating dietary TAG digestion and maintaining cholesterol homeostasis through its regulation of magro. Observations made during my studies of Drosophila lipid metabolism suggested that the metabolic state of the progeny is dependent on the health and nutritional status of their parents. The fourth chapter of this dissertation shows that temporary dietary restriction during the parental iv generation influences TAG and glycogen levels in the resulting progeny, as well as specific changes in metabolic gene expression. This work also defines roles for both DHR96 and HP1 as key regulators of these transgenerational effects on metabolism, suggesting that transcriptional regulation and chromatin are a central part of this pathway. Overall, these studies establish a new genetic system and framework for detailed molecular characterization of the mechanisms that facilitate the transgenerational regulation of metabolism, including an investigation of nuclear receptor and chromatin factors in this process

Partner orbits and action differences on compact factors of the hyperbolic plane. Part I: Sieber-Richter pairs

Physicists have argued that periodic orbit bunching leads to universal spectral fluctuations for chaotic quantum systems. To establish a more detailed mathematical understanding of this fact, it is first necessary to look more closely at the classical side of the problem and determine orbit pairs consisting of orbits which have similar actions. In this paper we specialize to the geodesic flow on compact factors of the hyperbolic plane as a classical chaotic system. We prove the existence of a periodic partner orbit for a given periodic orbit which has a small-angle self-crossing in configuration space which is a `2-encounter'; such configurations are called `Sieber-Richter pairs' in the physics literature. Furthermore, we derive an estimate for the action difference of the partners. In the second part of this paper [13], an inductive argument is provided to deal with higher-order encounters.Comment: to appear on Nonlinearit

List of Birds from Durian

ABSTRACT NOT AVAILABL

Doppler-free two-photon spectrum of the 000 band of the Ã1B1←X1A1 transition in difluorodiazirine, F2CN2

The Doppler-free two-photon excitation spectrum of the vibrationless Ã1B1←Image 1A1 transition of difluorodiazirine (F2CN2) has been recorded with a resolution of 15 MHz using a cw single-mode dye laser coupled to an external concentric resonator. The asymmetric rotor spectrum has been analysed and more than 350 lines randomly selected from all five branches were assigned in order to fit the ground- and excited-state rotational and quartic centrifugal distortion constants. From the rotational constants the rNN and rFF distances in the ground Image 1A1 and excited Ã1B1 state were determined. The geometry change upon excitation is found to be ΔrNN = 3.89(2) pm and ΔrFF = −4.09(2) pm. No perturbation in the rotational structure of the 000 band has been found. This points to a small singlet-triplet coupling matrix element in the small molecule limit

Intensity distribution in rotational line spectra

Completely resolved Doppler-free rotational line spectra of six vibronic two-photon bands in benzene C6 H6 and C6 D6 are presented. The excited final states possess different excess energies in S1 (1567 to 2727 cm−1 ) and are embedded in dense manifolds of background states with differing densities of states (1<rho<60 1/cm−1 ). The bands are analyzed by a statistical procedure. The intensity distribution of several hundreds of lines of each band is investigated. It is found that all weakly perturbed bands display a similar, peaked intensity distribution while in strongly perturbed bands the number of lines decreases monotonically with increasing intensity. The origin of this difference is discussed in terms of coupling to the many background states. The Journal of Chemical Physics is copyrighted by The American Institute of Physics

Semiclassical universality of parametric spectral correlations

We consider quantum systems with a chaotic classical limit that depend on an external parameter, and study correlations between the spectra at different parameter values. In particular, we consider the parametric spectral form factor $K(\tau,x)$ which depends on a scaled parameter difference $x$. For parameter variations that do not change the symmetry of the system we show by using semiclassical periodic orbit expansions that the small $\tau$ expansion of the form factor agrees with Random Matrix Theory for systems with and without time reversal symmetry.Comment: 18 pages, no figure