Gj. Fiechtner et al., QUANTITATIVE CONCENTRATION MEASUREMENTS OF ATOMIC SODIUM IN AN ATMOSPHERIC HYDROCARBON FLAME WITH ASYNCHRONOUS OPTICAL-SAMPLING, Applied optics, 34(6), 1995, pp. 1117-1126
We report the development of a pump-probe instrument that uses a high-
repetition-rate (82-MHz) picosecond laser. To maximize laser power and
to minimize jitter between the pump- and the probe-pulse trains, we c
hoose the asynchronous optical sampling (ASOPS) configuration. Verific
ation of the method is obtained through concentration measurements of
atomic sodium in an atmospheric methane-air flame. For the first time
to our knowledge, ASOPS measurements are made on a quantitative basis.
This is accomplished by calibration of the sodium concentration with
atomic absorption spectroscopy. ASOPS measurements are taken at a rate
of 155.7 kHZ With only 128 averages, resulting in a corresponding det
ection limit of 5 x 10(9) cm(-3). The quenching-rate coefficient is ob
tained in a single measurement with a variation of ASOPS, which we cal
l dual-beam ASOPS. The value of this coefficient is in excellent agree
ment with literature values for the present flame conditions. Based on
our quantitative results for detection of atomic sodium, a detection
limit of 2 x 10(17) cm(-3) is predicted for the Q(1) (9) line of A (2)
Sigma(+) (v = 0)-X(2)II (v = 0) hydroxyl at 2000 K; Although this val
ue is too large for practical flame studies, a number of improvements
that should lower the ASOPS detection limit are suggested.