Abstract

It has recently been shown¹ that extremely large values of the second-order nonlinear suceptibility can be obtained through use of Rydberg atomic states perturbed by an external electric field.² In these experiments a value of χ⁽²⁾ = 10^-9 esu was obtained using a sodium vapor of number density ~10¹⁴ atoms cm^-3 and a dc electric field of magnitude 1 kV/cm. One laser was tuned close to the sodium D₂ resonance line while a second laser completed the two-photon resonance with a Rydberg state. A strong coherent UV beam at the sum frequency was generated in the forward direction. The splitting of the highly excited atomic levels induced by the external electric field created a broad region of overlapping levels, leading to continuous tunability. This technique can be applied to any system displaying a Rydberg series, and should be capable of producing coherent, tunable radiation in the extreme ultraviolet.

© 1984 Optical Society of America