Date of Award


Document Type

Campus Access Thesis


Chemistry and Biochemistry



First Advisor

Michael S. Angel


The following thesis presents investigations of resonant enhanced multiphoton ionization of solid high explosives following laser desorption. This study is driven by the need for new, fast and reliable in-situ detection techniques for hazardous materials such as high explosives, in order to reduce the danger of exposure of first responders, to provide early warning and prevent US military and civilian casualties.

In Resonance Enhanced Multiphoton Ionization (REMPI), the molecule of interest, in the gas phase, is resonantly excited and subsequently ionized from that state using a pulsed laser, leading to the formation of a plasma. A platinum probe electrode is used to measure the intensity of the laser-induced plasma and the magnitude of the probe current is proportional to the concentration of the analyte. REMPI is a very sensitive and selective ionization technique for molecular vapors, providing a spectral "fingerprint" by scanning the laser wavelength.

Because most high explosives have low volatility it is necessary to use a laser to desorb the analyte, producing gas phase molecules that are then measured by REMPI. Desorption can use the same laser beam that is used for the REMPI measurement. While a pulsed laser was most often used for analyte desorption, in some cases the use of a UV continuous wave (CW) laser system showed gave better sensitivity and selectivity.

In an attempt to develop a standoff REMPI capability, microwave detection of a laser-induced plasma was investigated, using both homodyne and heterodyne microwave detection schemes. If successful, this could lead to a standoff REMPI technique for remote HE measurements.