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Self-starting harmonic frequency comb generation with a THz repetition rate in a quantum cascade laser is demonstrated. The mode spacing uniformity is verified to within 5 × 10−12 parts of the central frequency. The findings extend the range of applications of quantum cascade laser frequency combs.
By engineering photosensitive proteins and tweaking the classical properties of light, it should be possible to tune the response of a cell equipped with photoreceptors. But would these cells be able to sense the subtle quantum properties of light?