ABSTRACT
Stable Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 7.5 The Dynamical Hole in the Initial State Wavefunction:
Compression Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 7.5.1 Phenomenological Observation of a Depletion Hole,
a Momentum Kick, and a Compression Effect . . . . . . . . . . . . . . . . . . . . 276 7.5.2 Analysis of the Momentum Transfer with Partially Integrated
Mass Current and Population. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 7.5.3 Advantage of the Compression Effect for Photoassociation
with a Second Pulse. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 7.5.4 Redistribution of Population in the Lower State
after a Photoassociation Pulse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 7.5.4.1 Redistribution in the a3Σ+u State in the Case of Cesium
Photoassociation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 7.5.4.2 Correlated Pairs of Hot Atoms . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
7.6 Beyond the Impulsive or Adiabatic Approximations: New Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 7.6.1 Controlling the Compression Effect with a Nonimpulsive
Pulse Inducing Many Rabi Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 7.6.2 Nonadiabatic Broadband Pulse: Excitation at Large Distances. . . 284
7.6.2.1 Large Transfer of Population Outside the PAWindow. . 284 7.6.2.2 Thermal Average . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284
7.7 Conclusion and Prospects for the Near Future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
The formation of ultracold molecules in the lowest rovibrational level of the ground electronic state is presently a subject of intense investigation. By ultracold, we mean molecules at a temperature well below 1mK.As discussed in Chapters 5 and 6 of the present book byW. Stwalley and colleagues, and by Paul Julienne, the photoassociation (PA) route [1,2] is a very efficient one. Whereas laser cooling techniques cannot directly be applied tomolecules, it is possible to start from an assembly of laser-cooled atoms, and then make cold molecules in an excited electronic state by photoassociating atom pairs. For that purpose, most experiments use a cw laser red-detuned, relative to the atomic resonance line, to a frequency coinciding with the transition to a loosely bound vibrational level of the dimer. Being in an excited electronic state, the photoassociated molecule is short-lived, and a second step is necessary to form a stable molecule, hereafter named the stabilization step. When it decays by spontaneous emission, the molecule may either break apart again into a pair of cold atoms, or reach various vibrational levels of the ground electronic state (or of the lowest triplet state in the case of alkali dimers) [3-5]. In the latter case stable molecules are indeed formed, and schemes to increase their formation rate depend very much upon details in their spectroscopy (such as the existence of long-range wells in the potential curves of the excited state, or of resonant coupling between two excited channels [6,7]). Therefore, the molecular spectroscopy foundation of the field reveals itself as essential.
