Optical Difference-Frequency Generation in Atomic Thallium Vapor

Abstract

Coherent radiation at the 1.28-μm electric-dipole-forbidden $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}-6\mathrm{}{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}$ transition in thallium vapor has been produced by the simultaneous application of a magnetic field and two collinear, overlapping laser beams nearly resonant with the $6{}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}-7\mathrm{}{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ and $6{}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}-7\mathrm{}{}_{}{}^2{}_{}{}^{}S_{\frac{1}{2}}^{}{}_{}{}^{}$ transitions, respectively. The effect of the magnetic field is to mix hyperfine levels—atomic polarization effects are negligible. The optical difference-frequency power generated at low magnetic field varies as the square of the magnetic-field component normal to the laser-beam propagation direction.