High resolution spectroscopy with novel nonlinear devices

Summary form only given. Efficient frequency mixing in new non-linear materials, like periodically-poled (PP) crystals, is actually opening new spectral windows to high resolution spectroscopy. This provides additional degrees of freedom for an appropriate selection of the transitions to investigate. Difference frequency generation of radiation in PP-LiNbO/sub 3/, at a wavelength tunable around 4.3 /spl mu/m, has proven to be an extremely sensitive tool for CO/sub 2/ detection and has recently taken to the first demonstration of saturated-absorption spectroscopy of molecular transitions at powers as low as 10 /spl mu/W. Special care has been devoted to reduction of excess noise of the source to approach the quantum limit. A systematic study has also been performed in order to have a full control on far-field beam shapes. For this purpose, a numerical routine has been implemented, that calculates the three-dimensional evolution of the complex field, generated in the periodically-poled material. We are presently taking advantage of the peculiar features of this source to make a more stringent experimental test of the symmetrization postulate for bosons and we report our new experimental results. Frequency doubling fiber-amplified radiation from a diode laser at 1083 nm, using a PP-KTP crystal, is providing a very stable grid of frequency references by using saturated I/sub 2/ lines around 541 nm. The 1.2 THz wide tunability of this green source can allow to substantially extend and improve the database for a metrologically important molecule, like iodine. Moreover, we are presently exploiting the high stability of these I/sub 2/ references for precision spectroscopy in a beam of metastable helium, at 1083 nm and for improving the determination of the fine structure constant.