Coherent control of predissociation of the Rb dimer in 8times10-3Torr of Rb vapor is achieved with chirped femtosecond laser pulses. The preferred dissociation channels for different values of pulse chirp are found experimentally.
We have studied the effects of chirped femtosecond laser pulses on the formation of ultracold molecules in a Rb magneto-optical trap. We have found that application of chirped femtosecond pulses suppressed the formation of (85)Rb and (87)Rb(2) a(3)sigma(+)(u) molecules in contrast to comparable nonchirped pulses, cw illumination, and background formation rates. Variation of the amount of chirp indicated that this suppression is coherent in nature, suggesting that coherent control is likely to be useful for manipulating the dynamics of ultracold quantum molecular gases.
We explore the control of the Landau-Zener (LZ) transition in NaI predissociation with low-intensity linearly and quadratically chirped femtosecond far-infrared laser pulses by solving the coupled time-dependent Schrödinger equations. We find that the LZ transition between the excited state and the ground state can be enhanced or be suppressed using a well-delayed control pulse with a proper linear or quadratic chirp. With instantaneously controlling the energy gap, the resonant population inversion induced by Rabi oscillation can facilitate or prohibit the molecular population transfer in the avoided-crossing region. This work provides a deep understanding of coherent control of LZ transition in molecular reaction with chirped femtosecond laser pulses.
We demonstrate coherent control of bond making, a milestone on the way to coherent control of photoinduced bimolecular chemical reactions. In strong-field multiphoton femtosecond photoassociation experiments, we find the yield of detected magnesium dimer molecules to be enhanced for positively chirped pulses and suppressed for negatively chirped pulses. Our ab initio model shows that control is achieved by purification combined with chirp-dependent Raman transitions. Experimental closed-loop phase optimization using a learning algorithm yields an improved pulse that utilizes vibrational coherent dynamics in addition to chirp-dependent Raman transitions. Our results show that coherent control of binary photoreactions is feasible even under thermal conditions.