PerspectiveUltrafast Optics

Electro-optic combs rise above the noise

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Science  28 Sep 2018:
Vol. 361, Issue 6409, pp. 1316
DOI: 10.1126/science.aau7507

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Lasers typically emit light at one frequency, but some are engineered to emit light at a set of evenly spaced optical frequencies that maintain a stable phase relation, as if a myriad of lasers were radiating in unison. Most of these laser frequency combs are based on mode-locked lasers that deliver ultrashort light pulses in a repetitive manner. This approach has found use in attosecond physics, optical clocks, molecular spectroscopy, and the generation of ultrastable microwaves (1). Before the advent of the mode-locked frequency comb (2, 3), the electro-optic modulation method (4) was a popular technique for measuring frequency differences between lasers (5). On page 1358 of this issue, Carlson et al. (6) report that electro-optic modulation of light can be used to create an ultrafast laser source for the generation of frequency combs. The “comeback” of this method is part of a larger set of efforts exploring alternative techniques for creating frequency combs to enable new applications and facilitate their operation outside the laboratory (7).