Paper 3.15: N. Bloembergen, Y.H. Zou and L.J. Rothberg, “Collision-induced Hanle resonances of kilohertz width in phase-conjugate four-wave light mixing,” Phys. Rev. Lett. 54, 186–188, 1985.

Two new associates continued the experimental investigations in sodium vapor with variable inert buffer gas pressure, concentrating on the low frequency resonance corresponding to a raman-type resonance between two Zeeman-sublevels of the electronic ground state and the polarization characteristics of a raman-type transition with vanishing Stokes shift between two degenerate Zeeman levels. The latter effect may be considered as a collision-induced Hanle-effect resonance and is the subject of this communication. Previously, two detailed papers on collision-induced resonances between non-degenerate hyperfine and Zeeman sublevels had been published, “High-resolution studies of collision-induced population grating resonances in optical four-wave mixing in sodium vapor,” (N. Bloembergen and L.J. Rothberg, Phys. Rev. A30, 2327–2338, 1984) and “High resolution four-wave light-mixing studies of collision-induced coherence in Na vapor,” (N. Bloembergen and L.J. Rothberg, Phys. Rev. A30, 820–830, 1984). Lewis Rotheberg obtained his Ph.D. degree from Harvard University on the basis of this work. He joined the AT&T Bell Telephone Laboratories, where he works on femtosecond biophysical processes.

Ying-hua Zou, a professor of physics at Peking University in Beijing, China, joined our group as a visiting scholar under an exchange program between the American Physical Society and the Chinese Ministry of Education. He continued the detailed study of the collision-induced Hanle resonances. They were written up in a full-length paper, “Collision-enhanced four-wave light mixing in Na vapor,” (N. Bloembergen and Y.H. Zou, Phys. Rev. A33, 1730–1742, 1986). We visited Y.H. Zou and his wife twice in our travels to China in 1989 and 1994, respectively. I visited his laboratory at the university, and we were also guests in his modest apartment, where the hospitality was inversely proportional to the physical space. In 1994, Professor Zou was our host companion on a five day trip up and down the gorges of the Yang-tse river. He was almost as surprised as we were by the contrast in living conditions between the burgeoning metropolis Beijing and the towns in interior China.