A hollow-core photonic band-gap (PBG) lattice in a dielectric fiber has been proposed as a highgradient low-cost particle accelerator operating in the optical regime where the accelerating mode confined to a defect in the PBG fiber can be excited by high-power lasers [X. Lin, Phys. Rev. ST Accel. Beams 4, 051301 (2001)]. Developing efficient methods of coupling laser power into these structures requires a thorough examination of the propagating mode and its near and far-field radiation. In this paper, we develop a simulation method using the parallel finite-element electromagnetic suite ACE3P to calculate the radiation of the propagating accelerator mode into free space at the end of the fiber. The far-field radiation will be calculated and the mechanism of coupling power from an experimental laser setup will be discussed.

It is observed that the discharge current in a copper vapor laser rises prior to the voltage breakdown. This current, which appears almost 50 ns before the discharge breakdown and is equivalent to almost 70% of the peak current at the time of breakdown, is termed the phantom current. It is reported that by reducing the residual electron density (phantom current) in a metal vapor laser (MVL), its performance can be significantly improved. Metallic pins are used in the electrode to facilitate discharge in the long discharge tube. Besides augmenting the discharge during the initial stage, it has a significant impact on the laser performance. In this paper, we find out the correlation between the phantom current and the electrode pin geometry and then present the optimum electrode geometry for improved laser performance. It was observed that the number of pins in the electrode affects the localized electric field in the nearby region and plays a dominant role in the quantum of the phantom current in the discharge tube of the laser. The MVL system was tested with electrodes that had a different number of pins (zero, eight and 36) and it was found that the phantom current is minimum when the electrode has zero pins and highest with an eight-pin electrode.

A dye cell was designed and fabricated to facilitate high repetition rate single longitudinal mode (SLM) operation with low viscosity solvents such as ethanol. The flow circulation (vortex) in the dye cell was eliminated by reducing the flow cross section from 10 to 5 mm 2 with optimized flow entry. The physical dimension of dye cell is very important for short cavity SLM lasers in terms of keeping the cavity length small. Flow visualization of various geometries in the dye cell was carried out using commercial computational fluid dynamics (CFD) software. It was found that the slit as well as tubular entry to the dye cell of cross section 1 × 10 mm 2 shows flow circulation (a vortex) near the entry to the dye cell. The SLM was obtained from a 10 mm 2 flow cross section dye cell with a high viscosity solvent such as binary solvent (200 cP) or glycerol (1400 cP) with a higher bandwidth. The pulse to pulse fluctuations in the bandwidth and wavelength are generally associated with dye flow instabilities. These flow related instabilities reduced with higher viscosity solvents, which results in an increased bandwidth of the SLM dye laser (by nearly 40%). A specially designed dye cell was fabricated and used for SLM operation at two different pump lasers having different pulse repetition rates ranging from 20 to 6000 Hz. SLM operation was demonstrated for longitudinal pumping of the dye cell with low viscosity solvents. Time averaged SLM line widths of 400 and 175 MHz were obtained with a copper vapor laser (CVL) and Nd:YAG laser, respectively. A single pulse line width of 315 MHz was obtained with a CVL pumped dye laser.