Chemical Depopulation of the Group State of Atoms in Plasma Lasers

Abstract

One of the most important current problems in applied physics is doubtless the construction of economical high-power light sources. At present the most promising method is lasing in a dense recombining plasma on transitions of atoms (molecules) from levels close to the continuum to ground state or low-lying levels. To obtain a population inversion on this type of transition there must exist rapid processes for the removal of “working” atoms (molecules) from the ground state. This is fairly difficult in a recombining plasma that efficiently amplifies light since the intensity of elementary processes leading to population of the lower energy levels is very great. Although the most effective populating processes involve light particles (electrons and photons), it appears that the most realistic relaxation processes for depopulating these states at the required rate are chemical reactions. The simplest chemical reactions of this type are the following:

EquationSource% MathType!MTEF!2!1!+- % feaagCart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamivaiabgU % caRiaadQfacaWGzbGaeyOKH4QaamivaiaadQfacqGHRaWkcaWGzbGa % aiilaaaa!3F82!]]</EquationSource><EquationSource Format="TEX"><![CDATA[$$T + ZY \to TZ + Y,$$

(1)

EquationSource% MathType!MTEF!2!1!+- % feaagCart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr % 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9 % vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x % fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamivaiaadQ % facqGHsgIRcaWGubGaey4kaSIaamOwaiaacYcaaaa!3CE4!]]</EquationSource><EquationSource Format="TEX"><![CDATA[$$TZ \to T + Z,$$

(2)

where T may, in principle, denote either an atom or a molecule. Of these, reaction (1) is intended to create conditions for lasing on transitions from highly excited electronic states T* to the ground state (T* → T + hw). We shall discuss this type of reaction here, and we may note the reactions of alkali metal atoms with the halogen molecules as an example. In the case of reaction (2), the decay of the ground state of an unstable or dissociating molecule TZ, it is reasonable to choose lasing on transitions of a large complex TZ from thermally stable excited terms into an unstable (or repulsive) ground-state term (TZ* → TZ + hw) rather than on transitions of the atom (or molecule) T. Lasing based on scheme (2) has already been realized in several types of lasers. A recombining plasma (at high pressure) of inert gases and their compounds serves as the active medium in these lasers.