Aerodyne Tunable IR Laser Direct Absorption Spectrometer (TILDAS) model QC-TILDAS-CS is a laser spectrometer producing measurements of Ethane dry mole fraction at 1 Hz.

The QC-TILDAS-CS is manufactured by Aerodyne Research Inc. (USA). It measures ethane dry mole fraction in ambient air. Sample air is pumped through a cell into which the single laser beam is directed. The laser beam passes many times across the cell before exiting onto a photodetector. The laser frequency is tuned across an ethane absorption line - the depth of this lines is used to determine the ethane mole fraction.