Applications ranging from atomic clocks to medical diagnostics and calibrating astronomy instruments require laser light at various controlled frequencies. That requires frequency combs, which measure different colors of light.
Now frequency combs are getting smaller and easier to manufacture thanks to techniques developed by physicists at the National Institute of Standards and Technology (Boulder, Colo. ). The scientists say they can make the core of a miniature quartz glass frequency comb in one minute, as opposed to hours, days or even weeks for conventional techniques.
According to this news release, the technique involves laser machining of a quartz rod (see image above) to create smooth disks within which light can circulate. The size and shape of this resonator cavity is chosen by users—its diameter can be varied from about 0.2 to 8 mm, the release says, and its thickness and curvature can be shaped as well. After machining, the researchers use a low-power infrared laser to pump light into the quartz, creating a comb with a Q factor—a measure of the length of time light circulates inside the cavity without leaking out—equal to or better than that of cavities made by other methods.
“We make a resonator in one minute, and one minute after that we are making a frequency comb,” NIST researcher Scott Papp says in the release. NIST says equipment for the process costs about $10,000, compared to at least $1 million for a microfabrication system that must be used in a cleanroom.
According to the release, NIST researchers have been making compact frequency combs for several years. “By confining light in a small space, the optical cavity—which, confusingly enough, is solid—enhances optical intensity and interactions,” the release explains. “The comb itself is the light, which starts out as a single color or frequency that through optical processes is transformed to a set of additional shades, each sharply defined and equally spaced on the spectrum. A typical NIST microcomb might have 300 ‘teeth,’ or ticks on the ruler, each a slightly different color.”
NIST says a key advantage of microcombs is the ability to vary the spacing between the teeth for a variety of applications. Researchers plan to apply for a patent on the machining technique, which could be applied to a variety of other glassy materials.