A new optical setup for increasing the intensity of atomic fluorescence flame spectrometry is presented. The arrangement consists of two concave spherical mirrors and an elliposidal mirror whose primary focus is located at the flame position, and secondary at the entrance slit of the monochromator. Approximately 10 times gain in the measured intensities was obtained. The system is also useful for flame emission work, for which about five times gain was observed. With a low background flame such as the air–H<sub>2</sub> for the N<sub>2</sub>–H<sub>2</sub> diffusion flame and 400 μ slits, calcium can be detected at the level of 0.005 μg/ml. Moreover, the observed thermally assisted anti-Stokes fluorescence of In and Ga can be of analytical importance since the detection limits with a total consumption burner and the air–H<sub>2</sub> flame were found to be 0.015 and 0.02 μg/ml, respectively. Detection limits in atomic fluorescence for Cr, Tl, In, and Fe are also presented.
P. Benetti, N. Omenetto, and G. Rossi, "A New Optical System for Flame Spectroscopy with Special Reference to Thermally Assisted Anti-Stokes Fluorescence Applications," Appl. Spectrosc. 25, 57-60 (1971)