Cavity-enhanced direct optical frequency comb spectroscopy is a long and intimidating name for what is basically a medical breath test. You see the string words and you might think this is too complicated for you to understand. Spectroscopy is the study of spectra which is the case is the distribution of colored light. A pulsed laser beam was aimed into the cavity which was design to bounce laser light back and forth. By the time the laser light exited the cavity, it would have traveled several kilometers struck every molecule breathed into the cavity. This allowed comparative analysis of the light frequencies that were absorbed and the amounts. From there, the scientist were able to determine the molecules that were originally present in breath and their concentrations.

Think of the method as a way of sorting through the different molecules in human breath and finding traces of chemicals that could indicate disease.