LIGHT-INDUCED EJECTION OF ALKALI-EARTH ATOMS FROM POLYMER SURFACES: PRELIMINARY RESULTS ON CALCIUM

摘要

Laser-induced fluorescence (LIF) of Calcium atoms at room temperature has been observed in a polydimethylsiloxane coated cell when their walls are illuminated with visible light. Ca atomic density in the gas phase, monitored by the LIF, is much higher than the normal room-temperature vapor pressure of Calcium. In the past years the Photon-Stimulated Desorption (PSD) was observed for several alkali metals that are adsorbed to solid films of PDMS polymers. High yields of photodesorbed atoms (and molecules in the case of Sodium) can be induced by weak visible light, at room temperature and below, and the desorption is characterized by a frequency threshold and by a dependence of the yield on light frequency that behaves functionally in a way similar to that of the photoelectric effect in metals. From the experimental data, the plots of the square root of the fluorescence intensity as a function both of the frequency and of the power of the non-resonant ejecting beam are drawn. As for the alkali metals PSD, the Calcium photo-ejection is characterized by a frequency threshold, which lies in the visible region at about 18500 cm~(-1). However, a power threshold is observed in Calcium atoms photo-ejection, whereas the desorption of alkali atoms from the polymer is easily induced with very weak radiation intensity. The threshold intensity becomes lower when the photo-ejecting light wavelength decreases, ranging from 240 tO 140 mW in the 532 ― 488 nm frequency interval of the ejecting radiation.