Temporal characteristics of compressed femtosecond KrF pulses are measured with the help of a single-shot phase-sensitive autocorrelator for the UV. The performance of a prism compressor and the influence of higher order phase dispersion on the ultimate pulse width of compressed pulses is investigated. Self-phase modulation of high intensity femtosecond KrF pulses in MgF$\sb2$ is reported. The nonlinear refractive index n$\sb2$ (7.4 $\times$ 10$\sp{-16}$ $\pm$ 1.5 $\times$ 10$\sp{-16}$ cm$\sp2$/W) of MgF$\sb2$ is derived from the recorded broadened spectra. Implications of self-phase modulation in solids for compression of femtosecond KrF pulses are discussed.

The optical properties of metallic nanoshell systems are investigated using the Finite Difference Time Domain (FDTD) method. The method provides a convenient and systematic approach for calculating several physical properties of nanostructures, including the optical absorption and scattering cross sections as well as the local electromagnetic fields and induced charge densities near and on the surfaces of the nanoparticles. The method is applied to single uniform nanoshells as well as nanoshells with surface defects and structural distortions. The results show that, while defects can significantly affect local electric field enhancements, far field results such as extinction spectra can be remarkably insensitive to defects and distortions. Calculations are also presented for both homodimers and heterodimers. The results show that retardation effects must be taken into account for an accurate description of realistic size nanoparticle dimers. The optical properties of the nanoshell dimer are found to be strongly polarization dependent. Maximal coupling between the nanoshells in a dimer occurs when the electric field of the incident pulse is aligned parallel to the dimer axis. The wavelengths of the peaks in the extinction cross section of the dimer are shown to vary by more than 100 nm depending on the incident electric field polarization. The calculations show that electric field enhancements in the dimer junctions depend strongly on dimer separation. The maximum field enhancements occur in the dimer junction and at the expense of a reduced electric field enhancement in other regions of space. We investigate the usefulness of nanoshell dimers as substrates for surface enhanced Raman spectroscopy (SERS) by integrating the fourth power of the electric field enhancements around the surfaces of the nanoparticles as a function of dimer separation and wavelength. The SERS efficiency is shown to depend strongly on dimer separation but much weaker than the fourth power of the maximum electric field enhancement at a particular point. The SERS efficiency is also found to depend strongly on the wavelength of the incident light. Maximum SERS efficiency occurs for resonant excitation of the dimer plasmons. Specific implementation details as well as issues of numerical convergence are also discussed.

Photonic crystals are materials having a periodicity in their refractive index. This results in the inhibition of select frequencies of light from propagating within the crystal causing the formation of a gap in the photonic band structure. Analogous to semiconductors, the presence of a photonic band gap makes these materials tremendously promising for a new revolution in the technology industry. Their periodic nature make them ideal for two-dimensional lithographic fabrication. However self assembly methods with colloids offer the most promising route to fabricating three-dimensional structures, so as to affect the confinement of light in all directions. The work presented in this thesis strives to advance the understanding of colloidal crystals to ultimately facilitate the construction of real, working, commercial devices. We probe the optical properties of such colloidal crystals and describe techniques to engineer them into novel structures, such as crystals of hollow spherical shells, to enhance the performance of the photonic band gap. We examine novel architectures like colloidal photonic superlattices to generate propagation modes within the band gap and show that such structures can be fabricated to have uses as filters and optical resonators. We investigate incorporating colloidal crystal structures into organic light-emitting devices to improve device performance by spatially modifying the light output. Finally, as it is critical to fabricate high quality devices approaching the accuracy obtained by lithography, we conduct a systematic and quantitative study of the nature of defects in these colloidal crystals and correlate structural defects during fabrication to altered optical properties.

Optical transmission studies of three-dimensionally ordered photonic crystals of close-packed spherical shells are presented. These samples are fabricated using a double-template method, which allows for extensive control over shell thickness. The transmission spectra exhibit an optical stop band, whose spectral position and width depend on the thickness of the shell and on the overlap between adjacent spheres, in a manner consistent with numerical simulations. These parameters can be controlled over a wide range, thus permitting systematic studies of the optical properties, and providing a valuable method for engineering the characteristics of the optical stop band in colloidal photonic media.

A detailed investigation of tunable, high power excimer lasers, particularly of the electron-beam pumped XeF(C $\to$ A) laser, is presented. A numerical model is described which simulates the performance of such lasers. The output energy and temporal profile of an injection controlled XeF(C $\to$ A) excimer laser were successfully predicted for a wide range of experimental conditions. The XeF(C $\to$ A) excimer laser was demonstrated as a wideband tunable source of radiation capable of accessing a wavelength range from 455 to 530 nm. A high energy output of 1.2 J per pulse at a repetition rate of 1 Hz was accomplished by the use of a transverse gas flow cell. Injection controlled operation provided a narrow laser linewidth of 0.001 nm and three times diffraction limited spatial beam quality. Stimulated Raman scattering of the XeF(C $\to$ A) laser in hydrogen and liquid nitrogen was used to generate continuously tunable radiation between 525 and 650 nm with pulse energies exceeding 100 mJ. An energy conversion efficiency of 38% and a peak power of 35 MW were achieved. The XeF(C $\to$ A) excimer transition was characterized as a new gain medium for ultrashort pulse amplification. A gain bandwidth of 60 nm, as measured with 100 ps pulses, and a saturation energy density of 50 mJ/cm$\sp2$ for 250 fs pulses constitute a 20-fold improvement over other short pulse excimer laser systems. An ultrahigh power, short pulse amplifier system was designed and built, based on the gain measurements. An unstable resonator, particularly adapted to low gain conditions and high temporal purity was developed for the XeF(C $\to$ A) excimer amplifier. A maximum output energy of 275 mJ was obtained for amplified 250 fs pulses, resulting in terawatt peak power. A spatial beam quality of 2.4 times the diffraction limit was measured, which makes it possible to achieve an intensity of larger than 1 $\cdot$ 10$\sp{19}$ W/cm$\sp2$ in a focused beam. Therefore, the XeF(C $\to$ A) excimer laser amplifier can be used in an exciting new field of studies involving the interaction of ultrahigh intensity light with matter.

This paper presents a quantum cascade (QC) laser having an active region designed for both pump radiation emission and third order nonlinear emission. This design produces third harmonic generation from an InGaAs/AlInAs QC laser based on a three-well diagonal transition active region with an integrated third-order nonlinear oscillator. This design ensures efficient coupling of pump photon energy hv to the intersubband transitions of the nonlinear element and maximal overlap of interacting waveguide modes in the nonlinear active region. The problem of pump absorption is solved since the pump is generated in the nonlinear medium.

Prometheus I, a low-energy ($\sim$0.06-12.0 MeV), balloon-borne gamma ray telescope has been developed and successfully flown. It consists of a central NaI(Tl) detector that is segmented into an array of 9 x 9 crystals and an active anticoincidence shield of thick plastic scintillator. Implemented on Prometheus are several background reduction techniques which allow it to be 10 times more sensitive to aperture gamma rays than previous generations of low-energy gamma ray telescopes. First, a $\beta$ ray rejection method is used. Next, a low-Z shield minimizes cosmic ray activation. Also layers of Li$\sp6$ absorb slow neutrons, thereby reducing background caused from inelastic neutron scattering and neutron capture. Finally the use of lightweight, low-Z construction materials minimizes locally produced background. Semi-analytical calculations and preliminary in-flight count rate data confirm the usefulness of these techniques.

Two color center laser spectrometers have been developed using an F(,A)(II) and F(,B)(II) color center laser system for the 2.2-3.3 (mu)m region, and a powerful single mode F(,2)('+) color center ring laser for the 0.82-1.05 (mu)m region. Both lasers are interfaced to a minicomputer to provide long range scanning, high resolution data acquisition, and automatic calibration. Single mode scans with a resolution of 0.01cm('-1) are possible over the entire tuning range of the lasers; continuous single mode scans with a resolution of 10('-4)cm('-1) are possible over 1 cm('-1) ranges. An extensive set of software algorithms and a stable hardware interface between the laser and computer are necessary to reliably control and calibrate the lasers. Evaluation of the F(,A)(II) and F(,B)(II) laser spectrometer led to the development of a method to improve the sensitivity of absorption spectroscopy. The method, described as magnetic rotation spectroscopy, uses the Faraday effect to modulate the polarization of a beam travelling through a paramagnetic specie. This technique has been tested on NO, and has led to the first observations of the free radical OH('-) in the 2.7 (mu)m region, and the complete ('2)P(,1/2) (<---) ('2)P(,3/2) transition in B(,r). An F(,2)('+) color center has been built in a ring configuration to obtain maximum single mode output power. Design criteria for the laser resonator, the "optical diode" which forces unidirectional operation of the laser, and the tuning system have been developed to prolong the lifetime of the F(,2)('+) crystal, and to insure stable and unidirectional single mode operation.

Laser characteristics were studied extensively for the broadband rare gas halide excimers Xe(,2)Cl, Kr(,2)F, and XeF (C(--->)A). The trimer Kr(,2)F was first observed to lase during these investigations, while Xe(,2)Cl and XeF (C(--->)A) had been previously demonstrated. Since all three excimers have unbound ground states, a spectrally wide emission bandwidth is available for wavelength tuning. Other excimers with wide band fluorescence emissions--Ar(,2)F and KrF (C(--->)A) at 290 nm, XeCl (C(--->)A) at 345 nm, and Xe(,2)F at 630 nm--were studied but had gains too small to achieve laser threshold in a 10 cm transversely pumped laser cavity. Several system parameters were studied for each of the lasers. These included mixture optimization, variation of optical resonator configuration, and influence of different halogen donors and buffer gases. Tuning was accomplished by using cavity mirrors with different center wavelengths. Littrow prisms were not suitable as dispersive elements because of the relatively high insertion loss and the low gain-length product of the 10 cm cavity. The trimer Xe(,2)Cl had a nominal peak wavelength of 518 nm, with a tuning range of ('(TURN))15 nm and a (DELTA)(lamda) of 20 nm (FWHM). Laser pulse widths were about 36 nsec, and were delayed by 35 nsec from the e-beam excitation current pulse. This delay was observed in the other lasers as well, and can be attributed to transient absorptions by molecular argon. Atomic absorptions by xenon metastables to Ryberg levels were identified in the laser spectrum. Kinetics of Xe(,2)Cl* were also studied, with the following results: a radiative lifetime of 135 (+75 -60) nsec; a CCl(,4) quenching constant of 6 (+OR-) 1 x 10('-10) cm('3) sec('-1); a xenon quenching constant of )A) had the largest laser output intensity. The peak wavelength was 486 nm, with a (DELTA)(lamda) of 10 nm and a tuning range of 30 nm. Pulse duration was ('(TURN))30 nsec. Xenon absorption lines were identified which belonged to the same series as observed for the Xe(,2)Cl laser.

The principal purpose of this work has been the studies of the broadband tunable excimer laser namely XeF(C $\to$ A). Wideband tunability of this excimer laser was first demonstrated with a simple compact dispersive stable cavity in a transverse e-beam pumped geometry. More recently, a series of experiments has been performed to control the XeF(C $\to$ A) by dye laser injection. In any low-gain, short-pulse laser systems, rapid build-up of the optical field within the resonator is critical to good laser performance and extraction efficiency. Simultaneous injection of a "seed" signal into the cavity with laser pumping excitation can create a much faster increase in the intensity of the optical field. This rapid build-up of the optical field will aid the competition against radiative emission from the high gain XeF(B $\to$ X) transition and non-radiative quenching of the XeF excimers by halogen donors and other constituents of the laser gas mixture. Efficient, ultranarrow (0.002 nm to 0.005 nm) spectral output from an electron-beam excited XeF(C $\to$ A) laser medium (Ar/Kr/Xe/F$\sb{2}$/NF$\sb{3}$ mixture) has been observed by injection tuning. Amplification of an injected tunable dye laser pulse was achieved throughout the entire blue-green spectral region from 435 nm to 535 nm. Several different confocal unstable resonator geometries with magnification of 1.05 to 1.23 were investigated. A maximum output of about 85 mJ was measured at 482.5 nm for a cavity with magnification M = 1.1, which corresponds to an energy density and intrinsic efficiency of 4.7 J/liter and $\sp\sim$5%, respectively. These values are comparable to those of UV rare gas-halide lasers. In order to gain a better understanding of the injection control process in XeF(C $\to$ A) laser, a semiempirical model using a pulsed regenerative amplifier approach has been established with good accuracy. A set of coupled rate equations are used for this purpose. Some key factors in cavity and pumping source design are addressed.