text: A variety of signals can be obtained by NICE-OHMS. First, due to the presence of high intensity counter-propagating beams in the cavity, both Doppler-broadened and Doppler-free signals can be obtained. The former have the advantage of being present at high intracavity pressures, which is suitable when atmospheric pressure samples are analyzed, whereas the latter provide narrow frequency features, which is of importance for frequency standard applications, but also opens up possibilities for interference-free detection. Second, due to the use of FMS, both absorption and dispersion signals can be detected (or a combination thereof). Third, to reduce the influence of low frequency noise, wavelength modulation (wm) can additionally be applied, which implies that the technique can be operated in either fm or wm mode.
  The mode of operation to be preferred depends on the particular application of the technique and on the prevailing experimental conditions, mainly the type of noise or background signal that limits the detectability.