QLS is designed as a planar laser optical measurement technique for the quantification of the mass concentration in mixing flows. It is based on elastically scattered laser light (Mie scattering), where the luminant sources are small scattering particles that have to be added to one of the flow components.
QLS is an amplitude related method, i.e. all signal influencing parameters have to be taken into account and must be corrected in the post processing step by means of digital image processing. The technique furnishes the mass concentration only in the special case of isothermal mixing of identitical gases. Since not all transmission parameters are known in experiments, the scattering signal is devided by the signal at the jet entrance location, yielding a relative mass concentration field with a 100% concentration value at the jet entrance.