Pulsed Sources for Atomic Fluorescence

Pulsed vs. continuous wave atomic fluorescence spectrometry

“…Sir: It is well known that the ideal experimental setup for atomic fluorescence spectroscopy has to combine the use of a high intensity source of excitation and a low background, highly efficient atomization reservoir. In recent years, several authors have attempted to assemble a fluorescence setup consisting of a pulsed excitation source and a gated detection system (1, 2). Understandably, the aim of this research was twofold: (i) high source radiances could be achieved within a narrow time interval while still maintaining the discharge conditions at a practical level of operation, and (ii) background noise due to the atomizer and detector could be greatly diminished because of the gated operation of the detector.…”

“…Understandably, the aim of this research was twofold: (i) high source radiances could be achieved within a narrow time interval while still maintaining the discharge conditions at a practical level of operation, and (ii) background noise due to the atomizer and detector could be greatly diminished because of the gated operation of the detector. Experimental results (1)(2)(3)(4)(5)(6)(7)(8) were obtained using both continuum as well as line sources, such as xenon arcs and hollow cathode lamps. Moreover, tunable dye lasers, operated with a low duty cycle, have also been investigated because of their unique properties of high peak power, wavelength tunability and narrow spectral bandwidth.…”

“…THEORETICAL EQUATIONS (1,3) Assuming that the total noise in a fluorescence setup is due to atomizer-source-detector shot noise, the gain, G, in signal-to-noise ratio due to source pulsing (po) and detector gating as compared to continuous wave operation (cw) of both source and detector can be expressed as follows: G(po/Cw) = {(^p)peak/(^c)av} {ftp}1'2 (1) in the case of background shot noise limited systems, and G(po/cw) = {(£Xp)peak/(£Xc)av}1/2W1/2 (2) in the case of source-related or -induced shot noise limited systems. Here, ( ) stands for the average spectral irradiance (erg s"1 cm'2 nm"1) of an excitation source operated in the cw mode and (E\p)peak represents the peak spectral irradiance of the pulsed source, characterized by a pulse width ip (s) and a repetition rate / (Hz).…”

External heavy atom effect on detection limits and lifetimes of phosphorescence in time resolved laser excited phosphorimetry

“…Time resolved phosphorimetry was first demonstrated as a means of chemical analysis by Keirs et al (1). They resolved a mixture of acetophenone (rp = 8 ms) and benzophenone (rp = 6 ms) at concentrations in the range of 3 to 10"6 M.…”

“…The expression for the duty factor (4) applied to a dc measurement system. Winefordner (5) has suggested that the independent variability of gate time, tg, delay time, id, and repetition rate, /, of a pulsed source-gated detector along with the spectral shift toward the ultraviolet (6) when using pulsed xenon flashlamps should make such a system optimal for phosphorescence spectrometry.…”