Abstract : Report describes a resonance enhanced multiphoton ionization (REMPI) technique to measure vapor leakage from fuel tanks. The technique is a nonlinear optical process where two photons are simultaneously absorbed by an analyte resulting in the ejection of an electron to form a positively charged parent ion. Leak detector is comprised of three major components: a pulsed UV laser, an ionization cell, and electronics to convert the generated ion current to a measurable voltage.