Publications

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We present the bandwidth enhancement of an EAM monolithically integrated with two mutually injection-locked lasers. An improvement in the modulation efficiency and bandwidth are shown with mutual injection locking.

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Remote optical detection of molecules, agents, and energetic materials has many applications to national security interests. Currently there is significant interest in determining under what circumstances THz frequency coverage will aid in a complete sensing package. Sources of coherent THz frequency (i.e. 0.1 to 10 THz) electromagnetic radiation with requisite power levels, frequency agility, compactness and reliability represent the single greatest obstacle in establishing a THz technology base, but recent advances in semiconductor-based quantum cascade lasers (QCLs) offer huge improvements towards the ultimate THz source goals. This project advanced the development of narrow-linewidth THz quantum cascade lasers. We developed theoretical tools to guide the improvement of standard THz quantum cascade lasers, the investigation of nonlinear optics employing infrared QCLs, and the exploration of quantum coherence to improve QCL performance. The latter was aimed especially towards achieving high temperature operation. In addition we developed a computer algorithm capable of shifting the frequencies of an existing THz QCL to a different frequency and invented a new type of laser that may enable room temperature THz generation in a electrically driven solid-state source.

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The emission from a radiating source embedded in a photonic lattice is investigated. The photonic lattice spectrum was found to deviate from the blackbody distribution, with intracavity emission suppressed at certain frequencies and significantly enhanced at others. For rapid population relaxation, where the photonic lattice and blackbody populations are described by the same thermal distribution, it was found that the enhancement does not result in output intensities exceeding those of the blackbody. However, for slow population relaxation, the photonic lattice population has a greater tendency to deviate from thermal equilibrium, resulting in output intensities exceeding those of the blackbody.

A quantum optical approach is proposed and analyzed as a solution to the problem of detecting weak coherent radiation in the presence of a strong incoherent background. The approach is based on the extreme sensitivity of laser dynamical nonlinearities to the coherence of external perturbation. This sensitivity leads to dynamical phase transitions that may be employed for detecting the presence of external coherent radiation. Of particular interest are the transitions between stable and chaotic states of laser operation. Using a baseline scheme consisting of a detector laser operating with a Fabry-Perot cavity, we demonstrated significant qualitative and quantitative differences in the response of the detector laser to the intensity and coherence of the external signal. Bifurcation analysis revealed that considerable modification to the extension of chaotic regions is possible by tailoring active medium and optical resonator configurations. Our calculations showed that with semiconductor lasers, destabilization can occur with a coherent external signal intensity that is over six orders of magnitude smaller than the detector laser's intracavity intensity. Discrimination between coherent and incoherent external signal also looks promising because of the over four orders of magnitude difference in intensity required for inducing chaos-like behavior. These results suggest that the proposed approach may be useful in laser sensor applications, such as satellite Laser Threat Warning Receivers (LTWR).

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The potential for implementing quantum coherence in semiconductor self-assembled quantum dots has been investigated theoretically and experimentally. Theoretical modeling suggests that coherent dynamics should be possible in self-assembled quantum dots. Our experimental efforts have optimized InGaAs and InAs self-assembled quantum dots on GaAs for demonstrating coherent phenomena. Optical investigations have indicated the appropriate geometries for observing quantum coherence and the type of experiments for observing quantum coherence have been outlined. The optical investigation targeted electromagnetically induced transparency (EIT) in order to demonstrate an all optical delay line.

This report describes an investigation of the piezoelectric field in strained bulk GaAs. The bound charge distribution is calculated and suitable electrode configurations are proposed for (1) uniaxial and (2) biaxial strain. The screening of the piezoelectric field is studied for different impurity concentrations and sample lengths. Electric current due to the piezoelectric field is calculated for the cases of (1) fixed strain and (2) strain varying in time at a constant rate.

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