| Atomic line filters have been suggested to be attractive in areas of Doppler velocimetry, resonance fluorescence detection, and resonance ionization detection. They are based on the resonant absorption of photons by an atomic vapor, and allow all other radiation to pass. This allows the detection of very low levels of light superimposed on a large optical background. Several elements have been studied for use as atomic line filters, such as the alkali metals, alkaline earths, and thallium. As previously recognized, thallium is especially attractive since the 535.046 nm metastable transition overlaps with the second harmonic output of an Nd:La2Be2O 5 (BEL) laser (1070 nm). This makes thallium ideal for certain applications as an atomic line filter.; Recently a see-through hollow cathode lamp, or galvatron (Hamamatsu), was made commercially available. The galvatron geometry is unique compared to traditional hollow cathode lamps since the cathode and cell are oriented in a T-shape, with the cathode bored completely through to allow the propagation of a light source through the cathode. This allows multi-step excitation of the atomic vapor, not easily accomplished with a traditional hollow cathode lamp.; The advantages that a galvatron offers over conventional atomic reservoirs make it an attractive candidate for the application as an atomic line filter; however, little spectroscopic data have been found in the literature. For this reason, Doppler temperatures, number densities, quantum efficiencies, and lifetimes have been determined in order to characterize this atomic reservoir as a potential atomic line filter. These parameters are determined by use of various spectroscopic techniques which include emission, absorption, time-resolved fluorescence, and time-resolved laser-induced saturated fluorescence spectroscopy. From these measurements, it has been demonstrated that a galvatron is an attractive atomic reservoir for applications as an atomic line filter. The spectral resolution of this atomic line filter was found to be superior to that of a traditional hollow cathode lamp and electrodeless discharge lamp. A desired number density can be rapidly produced by applying the appropriate current and can be reproduced from one experiment to the next. In addition, the quantum efficiency of this system was found to be limited only by the competing radiative pathways of the particular energy level arrangement which allows it to be a very efficient detector. This system has the potential to be simple, compact, and portable which makes it an ideal atomic line filter. |
