ABSTRACT
We describe a simple method to measure the back-bombardment heating temperature rise as a function of time in pulsed microwave thermionic guns using a fast rise-time InGaAs detector and optical pyrometer. Gaining knowledge of the nature of that temperature rise and the corresponding current out of the gun are the first steps in devising a scheme to counteract the back-bombardment heating which lengthens the micropulses, limits the macropulse length, and increases the energy spread of the emitted electron beam. We measured a temperature rise of 59 K in our LaB6 cathode which delivered a peak of 600 mA over a 5 µs RF pulse in our 0.33 MV/cm peak field, 2.856 GHz thermionic electron gun.
ABSTRACT
This report describes a mobile Raman lidar system that has been developed for spectral measurements of samples located remotely at ranges of hundreds of meters. The performance of this system has been quantitatively verified in a lidar calibration experiment using a hard target of standardized reflectance. A new record in detection range was achieved for remote Raman systems using 532 nm laser excitation. Specifically, Raman spectra of liquid benzene were measured with an integration time corresponding to a single 532 nm laser pulse at a distance of 217 meters. The single-shot Raman spectra at 217 meters demonstrated high signal-to-noise ratio and good resolution sufficient for the unambiguous identification of the samples of interest. The transmitter consists of a 20 Hz Nd:YAG laser emitting at 532 nm and 1064 nm and a 178 mm telescope through the use of which allows the system to produce a focused beam at the target location. The receiver consists of a large custom telescope (609 mm aperture) and a Czerny-Turner monochromator equipped with two fast photomultiplier tubes.
