James B. Clark

Population and rotational kinetics of the rhodamine B monomer and dimer: Picosecond transient spectrometry

We use picosecond excite‐and‐probe techniques at 532 nm, a subnanosecond fluorescence spectrometer, and a transient‐transmission spectrometer with picosecond temporal resolution to measure the population kinetics and rotational diffusion of aqueous rhodamine B monomer and dimer. The excited‐state lifetimes of the monomer and dimer are determined to be 1.6 ns and 100 ps, respectively, and the rotational randomization time of the monomer is measured to be 250 ps. The dimer rotational diffusion time is determined to be longer than that of the monomer, indicating that there is a large molecular species in equilibrium with the monomer.

Level decay and orientational kinetics of the rhodamine B monomer and dimer

Abstract The population kinetics and the rotational diffusion of the rhodamine B monomer and dimer were measured by using picosecond pulses from a mode-locked Nd : YAG laser to induce and time resolve the concentration-dependent transient absorption saturation of various aqueous solutions of this organic dye.

The vacuum ultraviolet spectrum of bromosilane

Abstract The vacuum ultraviolet absorption spectrum of bromisilane in the vapor phase is reported. Assignments are made using photoelectron data and oscillator strengths. The absorptions of this compound are related to absorptions of chlorosilane, methyl bromide and methyl chloride. The results of this work indicate the presence of dπ-pπ (SiBr) delocalizations and concomitant stabilization of halogen nonbonding electrons.

Frequency doubling of narrowband high-energy optical parametric oscillators

Poor beam propagation is a typical characteristic of most pulsed optical parametric oscillators. We describe the design and operation of a tunable narrow linewidth (< 0.2 cm-1) high energy (> 100 mJ), low divergence (< 0.5 mrad) OPO system to overcome this problem. Frequency doubling efficiencies of this OPO are 185 when using BBO and 28% in KDP. These high efficiencies are attributed to the use of an unstable resonator in the OPO.

Broadly tunable, beta-barium-borate-based, pulsed optical parametric oscillators and their potential applications in medicine

With the recent availability of Beta Barium Borate (BBO) crystals in useful sizes at acceptable market prices, the promise of Optical Parametric Oscillators (OPOs) becoming practical tunable systems is finally being realized. Wavelength coverage from such systems extends from 420 nm to over 2400 nm when pumped in the UV. For medical applications their usage will be limited in the near term to low repetition rates (< 50 Hz) nanosecond pulsed systems. The pump lasers of choice will be flashlamp pumped Q-switched Nd:YAG lasers. As higher repetition rate (kHz) Q-switched diode pumped solid state continue to increase in energy and decrease in price, they are likely to also become viable pump sources for lower energy OPO systems. Energy output in excess of 100 mJ from low repetition rate OPO systems may make them suitable for selective absorption applications in medicine such as colored tattoo removal or treating vascular lesions. For such high energy devices peak powers necessitate the use of articulating arms for beam delivery. For high repetition rate systems, energy outputs will be in the range of 100 to 500 (mu) J at kHz frequencies (up to 1 W average power). Peak powers are low enough that fiber optic delivery is possible. These systems may find selective absorption applications in ophthalmology.