Laser Spectroscopy in Molecular Beams

For many years molecular beams were mainly employed for scattering experiments. The combination of new spectroscopic methods with molecular beam techniques has brought about a wealth of new information on the structure of atoms and molecules, on details of collision processes, and on fundamentals of quantum optics and the interaction of light with matter. 

There are several aspects of laser spectroscopy performed with molecular beams that have contributed to the success of these combined techniques. First, the spectral resolution of absorption and fluorescence spectra can be increased by using collimated molecular beams with reduced transverse velocity components (Sect. 4.1). Second, the internal cooling of molecules during the adiabatic expansion of supersonic beams compresses their population distribution into the lowest vibrational-rotational levels. This greatly reduces the number of absorbing levels and results in a drastic simplification of the absorption spectrum (Sect. 4.2). 

The low translational temperature achieved in supersonic beams allows the generation and observation of loosely bound van der Waals complexes and clusters (Sect. 4.3). The collision-free conditions in molecular beams after their expansion into a vacuum chamber facilitates saturation of absorbing levels, since no collisions refill a level depleted by optical pumping. This makes Doppler-free saturation spectroscopy feasible even at low cw laser intensities (Sect. 4.4). 

New techniques of high-resolution laser spectroscopy in beams of positive or negative ions have been developed. These techniques are discussed in Sects. 4.5 and 4.6. 

Several examples illustrate the advantages of molecular beams for spectroscopic investigation. The wide, new field of laser spectroscopy of collision processes in crossed molecular beams is discussed in Chap. 8. 

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Laser Spectroscopy in Molecular Beams turbomolecular pump laser beam... 

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