Detection of trace concentrations of elements by intra-cavity frequency- dispersion laser atomic spectroscopy

A new method of analytical laser spectroscopy is suggested. It is based on transformation of resonance linear dispersion of absorbing atoms inside the cavity of a two-mode laser with homogeneous super-broad gain profile into mode beats frequency variation. The detection sensitivity with respect to absorption in the probing volume as high as 1010 Hz cm−1 has been achieved. This value is in excellent agreement with the theoretical prediction. A sensitivity of about 1012 Hz (gml)−1 has been demonstrated in experiments with aqueous sodium standards. The experimentally achieved limit of detection of approximately 10 ngml−1 was limited by the purity of the distilled water. It has been estimated by extrapolation that a limit of detection of the order of 0.1–1.0 pgml−1 can be achieved when using ultrapure water and registering beats frequency shifts of the order of 1 Hz. The method is shown to be independent of intensity and stationary lasing time.