Collision-induced Hanle resonances of kilohertz width in phase conjugate four-wave light mixing.

Hanle resonances for coherent four-wave mixing in the ground state of Na are reported, whose intensity increases and whose linewidth decreases with increasing inert buffer gas pressure. In 10 millitorr Na vapor with four atmospheres of argon, resonances of less than 35 milligauss FWHM width are observed. The high resolution permits direct observation of the fundamental homogeneous broadening mechanisms for the Zeeman coherences responsible for four-wave mixing.