Resonance-enhanced multiphoton ionization

Resonance-enhanced multiphoton ionization (REMPI) is a technique applied to the spectroscopy of atoms and small molecules.

REMPI is usually generated by a focused frequency tunable laser beam to form a small-volume plasma.

In REMPI, first m photons are simultaneously absorbed by an atom or molecule in the sample to bring it to an excited state.

An advantage of the REMPI technique is that the ions can be detected with almost complete efficiency and even time resolved for their mass.

Coherent microwave scattering from electrons in REMPI-induced plasma filaments adds the capability to measure selectively-ionized species with a high spatial and temporal resolution - allowing for nonintrusive determinations of concentration profiles without the use of physical probes or electrodes.

It has been applied for the detection of species such as argon, xenon, nitric oxide, carbon monoxide, atomic oxygen, and methyl radicals both within enclosed cells, open air, and atmospheric flames.

They can significantly increase the detection sensitivity by suppressing the noise and follow sub-nanosecond plasma generation and evolution.

These high SNRs allow the temporal behavior of the microwave signal to be followed on a sub-nanosecond time scale.