Viii. Quantum Electronics I. Precision Measurements of Atomic Level Splitting and Level Shifts in Intense Optical Fields National Science Foundation (grant Phy77-07156)

We have performed high precision measurements of level splitting and level shifts of an excited atomic state in the presence of an intense optical field. Such measurements are important to the understanding of the details of atom-field interaction and in the development of high precision optical clocks. The level we studied is an isolated 2 single magnetic sublevel 3 P3/2 (F= 3, 2m F = 3) in sodium when subjected to a strong laser field coupling this level and the 3 '1/2 (F = 2, mF = 2) level in the ground state. Doppler and collisional broadening were eliminated by employing atomic beam techniques. The experimental arrangement has a highly collimated sodium atomic beam prepared in one magnetic sublevel mF = 2 in the 3 S1/ (F= 2) ground state. The prepared sodium atoms are subjected simultaneously to two collinear but counterpropagating laser fields, aligned perpendicular to the atomic beam. One laser field at 5890 A, the driving field, is circularly polarized and fixed in frequency either on-resonance or off-resonance with 3 2S/2 (F = 2)-3 2 P 3 /2 (F = 3) transition. Since the light is circularly polarized, the only allowed Am = +1 transition is to the m F = 3 sublevel in the excited 3 P3/2 (F = 3) state. The second laser field at 5688 A is tunable and is used to probe the 2 2 3 P 3 /2 (F = 3, m F = 3) sublevel by inducing transitions to a higher level 4 D 5/2 (F =4, mF =4). The fluorescence from the 4 D 5/2 (F =4) state to the 3 P3/ 2 (F = 3) state is detected and used as a measure of probe field absorption. With a'weak on-resonance driving field and a weak probe field, the observed linewidth of the probed transition was very close to the natural width (3. 3 MHz) of the 4 2D5/2 (F = 4) upper level even though the natural width of the 3 2 P3/2 (F = 3) lower level is 10 MHz. The measured line shape was compared directly with a theoretical line shape