Abstract: A method and a system for increasing the lifespan of a plasma obtained in the atmosphere. The method includes the following steps: emitting a femtosecond laser pulse, referred to as a first pulse, generating a column of plasma by the filamentation phenomenon, and emitting a second YAG laser pulse, focused by way of an axicon on a line in the plasma column, the energy of the photons of the second laser pulse being greater than the attachment energy of the electrons in the plasma to neutral molecules such as oxygen molecules. The duration of the second pulse is greater than the duration of the first pulse, and the delay between the two pulses is greater than one microsecond.

Abstract: A method and a system for increasing the lifespan of a plasma obtained in the atmosphere. The method includes the following steps: emitting a femtosecond laser pulse, referred to as a first pulse, generating a column of plasma by the filamentation phenomenon, and emitting a second YAG laser pulse, focused by way of an axicon on a line in the plasma column, the energy of the photons of the second laser pulse being greater than the attachment energy of the electrons in the plasma to neutral molecules such as oxygen molecules. The duration of the second pulse is greater than the duration of the first pulse, and the delay between the two pulses is greater than one microsecond.

Abstract: The apparatus and method include adjusting two single frequency lasers to separate longitudinal modes of an interferometer, the plates of which are separated by a distance to be measured. A rough estimate of the distance is made using a tape measure or the like. The rough estimate, together with the frequency distance (.DELTA.F) of the lasers adjusted to the longitudinal modes of the interferometer is used to solve the equation: ##EQU1## where c is the speed of light and L.sub.1 is the rough estimate. The parameter k then calculated by rounding k.sub.