How does WS-CRDS compare to ICOS?
WS-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 — an additional step that is not necessary in WS-CRDS. Intensity-based measurements like ICOS are limited by laser noise and drift. In contrast, the time-based WS-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 WS-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 — this is inherently nonlinear. These nonlinearities are translated directly into the absorption spectrum measurement and can cause errors in the concentration calculatio
