优点: Water is the most important molecule on earth. Without water, there would be no life possible on this planet. However, in some 'applications' the amount of water vapor needs to be exactly measured. In the Hitran database, many transitions can be found, and there are several strong absorption lines the 1390nm regime, for example. Some of these strong line at 1388nm are shown in the figure, detected with a simple water vapor absorption experiment.