We examined the applicability of Raman spectroscopy as a laser remote sensing tool for monitoring the gases dissolved in water and gas bubbles. A frequency doubled Q-switched Nd:YAG laser (532 nm) is irradiated to CO2 gas bubbles generated by an air pump. The Raman signals at 1383 cm-1 from CO2 and 1645 cm-1 from water were detected. It has been shown that the CO2/H2O Raman signal ratio is dependent on the CO2 bubble rate.
We have been developing a coherent "white light" lidar using a terawatt laser system at 800 nm with a 9m length
krypton gas cell, which emits a coherent supercontinuum from UV to near infrared regions. Linearly polarized
supercontinuum was transmitted to the atmosphere, and backscattered light was collected with a telescope of 31.8 cm in
a diameter and the light was separated into 3 to 5 wavelengths using dichroic mirrors and interference filters. Mainly, we
used the wavelengths of 450, 550, 700nm and 800 nm with each bandwidth of 10 to 40 nm. Although, the energy of light
included in each wavelength range is restricted, the advantage of multi-spectral features on the same optical axis of this
system enables us to use preferred spectral lines for various measurements. The system was successfully applied as a
depolarization lidar as well as a multi line Mie scattering lidar for cloud particles and Aeolian dusts. By comparing the
response for each spectrum, we can determine the size of particles with information on their shapes. Current research is
focused to find applications in near infrared region of the white light.
Extreme ultraviolet (EUV) emission from laser produced plasma attracts much attention as a next generation lithography
source. The characterization of EUV emission has been carried out using GEKKO XII laser system. The twelve beams
irradiated tin or tin-oxide coated spherical targets uniformly and dependence of EUV spectra on laser intensity were
obtained with a transmission grating spectrometer and two grazing incidence spectrometers. The EUV Conversion
Efficiency (CE, the ratio of EUV energy at the wavelength of 13.5 nm with 2 % bandwidth to incident laser energy) was
measured using an absolutely calibrated EUV calorimeter. Optimum laser intensities for the highest conversion were
found to be 0.5- 1x10<sup>11</sup> W/cm<sup>2</sup> with CE of 3 %. The spectroscopic data indicate that shorter wavelength emission
increases at higher laser intensities due to excessive heating beyond optimum temperatures (20- 40 eV). The CE was
almost independent on the initial coating thickness down to 25 nm.
A computer simulation code to treat atomic excitation and laser beam propagation simultaneously in an atomic laser isotope separation system has been developed. The three- level Bloch-Maxwell equations are solved numerically to analyze the change of pulse shapes, the modification of laser frequencies and the time-varying atomic populations. The near- resonant effects on the propagation of frequency chirped and non-chirped laser pulses have been analyzed. It was found that there are serious differences in pulse shapes, frequency modifications and propagation velocities between laser pulses with and without chirping.
A 5 kpps copper vapor laser (CVL) switched by semiconductors has been demonstrated for the first time. The solid state power exciter consists of static induction (SI) thyristors and two stage magnetic pulse compression circuits with saturable inductors. The maximum electric efficiency was 67%. The exciter showed the high transfer efficiency in the input energy range of 2.9kW to 6.5kW by optimizing the reset currents for saturable inductors. The average laser power was 21W at a 5kpps repetition rate. An overall system jitter for synchronization was successfully reached down to a very small value of +/- 2.5ns.