Wavelength modulation background correction

All of the flicker noises can be effectively eliminated by the use of double-beam optics in conjunction with a background correction system such as Zeeman splitting or a well-aligned (or wavelength-modulated) continuum source. Thus the ultimate limiting noise in atomic absorption is source shot noise, which can be reduced (relative to total source intensity or I, ) by increasing the source intensity, up to the point of optical saturation. 

The possibility of modulating the emitted wavelength of DLs at GHz frequencies by the modulation of the diode current allows one to reduce the low-frequency (flicker) noise in the baseline, which again improves the detection limit. Emission wavelength modulation also permits to correct for unspecific background absorption, thereby improving the selectivity of the technique. 

Background correction by wavelength-modulation is not widely used, but seems to have considerable potential for simultaneous multi-element AAS with continuum sources. Alternatively, high-resolution echelle gratings may be used that can detect both the elemental line and the background at the same time. 

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