The new JILA "frequency comb spectroscopy" technique uses infrared laser light in many different colors, or frequencies, to identify trace levels of different molecules at the same time. The animation shows one (blue) water molecule entering the cavity in which laser light is stored, absorbing some of the light, and leaving a "signature" of the absorbed light in the blue trace across the spectrum in the foreground. Each stripe in the spectrum represents a different color. Then a (green) ammonia molecule enters the cavity and absorbs light at different characteristic frequencies, as indicated in the green trace below. Then two molecules of each type enter the cavity simultaneously, and both the blue and green traces cross the spectrum at the same time, but cutting deeper than before, indicating the presence of twice as many molecules.
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