الفهرس 
acknowledgmentOnly 14 pages are availabe for public view
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Abstract
A great deal of information about atomic or molecular excited states are based on traditional spectroscopic observations. For diatomic molecules, their absorption and emission spectra were very often limited by Doppler broadening until the years 1950. Some important prameters such as Lande factor, hyperfine structure constants, life times, ... etc, could be obtained using the classical spectroscopy only with very sophisticated experiments but with a poor accuracy.
Over a long period, the optical spectroscopy possibilities have been limi- ted by the resolving power of the used dispersive devices. As examples, the
prism spectrometer has a resolution of about R 104, the diffraction grating R10as for the Fabry-Perot interferometer, its resolution can reach 106.
Using resolution values of some 103, the alkaline doublet lines were dis- covered with a resolution of 10, one could observe the hyperfine structure for some atomic and molecular spectra. With increase of the resolution, for example up to 5 x 105, one can reach the Doppler width due to the thermal molecule motion, which seems to be an upper physical limit to the analysis of spectral lines. This resolution value R 106 has the same order of magnitude as c/v ratio [i.e. light velocity atomic or molecular thermal velocity] in a gas. The Doppler width for optical lines in a gas is about 106 times the line frequency.
Hence, conventional spectroscopy, has not increas aed the resolving power beyond 106 since the Doppler broadening prevents any hyperfine structure study. The only atoms which were studied by conventional spectroscopy in the presence of the Doppler broadening are those whose spectra consist of isolated lines.
The use of lasers, especially tunable dye lasers, changed drastically the above situation. It is possible now to realise a selective excitation of rota- tion vibration levels of molecular electronic states, that means to excite one given level. That opens the field of spectroscopic and metrologic applications. In the sub-Doppler domain one can use different techniques.