How does CRDS compare to ICOS?
CRDS is a completely time-based technique whereas ICOS is inherently an absorption (intensity-based) measurement. To determine the path length, ICOS must use a time-based ringdown measurement at the end of each spectral absorption scan ‚Äî an additional step that is not necessary in CRDS. Intensity-based measurements like ICOS are limited by laser noise and drift. In contrast, the time-based CRDS measurement is actually taken while the laser is off and is therefore not subject to any laser noise or drift. One additional difference unique to Picarro’s CRDS technology is the use of an ultra-precise (~2MHz) wavelength monitor with its ability to actively target the laser to specifically-known wavelengths. In contrast, ICOS does not employ this and in fact, uses laser current to sweep the wavelength of the laser ‚Äî this is inherently nonlinear. These nonlinearities are translated directly into the absorption spectrum measurement and can cause errors in the concentration calculations.
