The dynamics of molecules in the gas and liquid phase is investigated using ultrafast optical techniques. The development of sub-25 fs ultrafast sources using noncollinear optical parametric amplification is discussed. These intense pulses are utilized in coherent anti-Stokes Raman scattering to investigate vibrational motion in I2 Br2 and IBr. For larger bio-molecules relevant dynamics may not be related to the absorption of light. Here, a new technique is introduced, in which an optically excitable molecule is incorporated into the bio-molecule. Photoisomerization of the trigger molecule initiates structural rearrangement in the larger system. To demonstrate this approach, azobenzene was synthesized into short strands of DNA to time-resolve base pair destacking dynamics and DNA melting. The isomerization of azobenzene in thin polymer films (and their corresponding change in optical properties) was also used to write birefringence and surface relief gratings. This method was used to demonstrate a rewritable Bragg filter for telecom wavelengths. Lastly, an alternative to typical crystal based wavemixing is presented for the generation of ultrafast tunable ultraviolet and deep ultraviolet pulses. The approach utilizes difference frequency four wave mixing in hollow waveguides filled with noble gas. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2011-08-31 14:55:11.636

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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.

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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.