| Research Abstract |
We have developed new methods of laser spectroscopy with high resolution and high sensitivity, the principles of which are considerably different from any other methods developed so far. In present methods, the characteristics of a free-running diode laser is used, i.e.very stable output power (amplitude) and large frequency (phase) noise causing the broadening of the spectral line. The phenomena used are based on the nonlinear interaction of atoms with such a laser field. It was found that such a laser field has more degree of freedom than a monochromatic laser field, so that it carries more information of atoms and molecules to be studied. The first method proposed and studied can be realized by a simple system, where a diode laser beam is applied to the sample and the temporal variation of the transmitted light intensity is detected. Frequency-analyzing the detected intensity fluctuation, we have found that the power spectrum includes simultaneously high resolution atomic spectra, such as the Zeeman and hyperfine spectra in both the ground and excited states, which are in a very wide frequency range from 100 kHz to more than 1 GHz. The second type proposed here is the isotope-selective spectroscopy, which enables us to observe the absorption spectra of a particular isotope from the mixed gaseous sample. The isotope selection is made by detecting a Zeeman frequency component of a particular isotope, as the laser frequency is scanned through the absorption lines of of various isotopes. Above methods of laser spectroscopy is useful particularly for the atoms in a particular circumstances. As such atoms, we have made the first studies on the neutral atoms in a superfluid helium, and also on the gaseous atoms existing in the vicinity of the surface of solids.
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