noise-immune

The system can be sped up or made more noise-immune by using a PID controller.

There is, however, one technique that so far has succeeded in making full use of the cavity by combining locked CEAS with FMS so as to circumvent both of these problems, and that is Noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS).

Although the requirements for the performance of the lock are less stringent than for other direct cw-CEAS techniques (due to the noise-immune principle), the laser frequency still has to be kept locked within the cavity mode during signal acquisition, i.e. it should follow the mode while the cavity is scanned, including a possible wavelength modulation.