ELSD is an acronym for Evaporative Light Scattering Detector. It is used as a quasi-universal detector for HPLC.
The first step is the nebulization of the column effluents with a dry gas as you have mentioned. If the column effluents contain any non-volatile analyte, then those will form minute particles. The mintue particles become suspended in the gas stream and form an aerosol. The gas stream is made to pass through a focused light beam (usually a diode laser) which is perpendicular to the flow direction.
If aersol is present, the light will be scattered, and can be detected/analysed by a detector photodiode which is placed perpendicular to both the light beam and flow direction.
There is a nice picture that I got from this site:
Reference- Analytical Chemistry, G. D. Christian, P. K. Dasgupta, K. A. Schug, 7th ed., Wiley, 2013