Laser Detection of Very Rare Long—Lived Radioactive Isotopes

Abstract

Laser spectroscopy techniques have made it possible to solve the cardinal problems of optical spectroscopy: (1) the spectral resolution of the Doppler-free nonlinear spectroscopy techniques has already reached a value of R = v/∆v ≃ 10¹¹ at a spectral resonance width of ∆v ≃ 10³Hz, the development of methods for further reduction of ∆v being under way;¹ (2) where femtosecond mode-locked tunable lasers are used, the time resolution amounts to a few tens of femtoseconds, i.e. only a few tens of light oscillation periods;² (3) the sensitivity of some techniques, atomic and molecular photoionization spectroscopy in particular,³ reaches ultimate values - single atoms and molecules. There is one more, perhaps the last, problem of optical spectroscopy that is still to be solved; (4) highselectivity detection of trace atoms and molecules in a real environment, particularly the detection of trace rare isotope atoms in the presence of an abundant isotope or the detection of trace molecules of a certain species in a molecular mixture. Subject to intensive development are now being various approaches that can combine a maximum possible sensitivity with an exceptionally high detection selectivity. The present lecture treats in short of some possible ways to solve the first of these problem — to attain a high selectivity of optical detection of very rare isotopes. This problem was introduced in Ref.⁴ and discussed in Refs.^5,6.