A frequency comb is a special type of laser that emits light consisting of many equally spaced frequencies, resembling the evenly spaced teeth of a comb when plotted in the frequency domain.
Key Features:
- Generated using mode-locked lasers that produce a train of ultrashort pulses.
- The Fourier transform of this pulsed output reveals a spectrum of sharp, discrete frequencies with regular spacing.
- Each “tooth” of the comb corresponds to a specific, well-defined optical frequency.
Why They’re Important:
Frequency combs serve as optical rulers, enabling precise comparison between unknown optical frequencies and known microwave or radio frequencies. This makes them crucial in:
- Atomic clocks and timekeeping
- Spectroscopy (for identifying chemical compositions)
- Astronomical measurements (e.g., detecting exoplanets via Doppler shifts)
- Metrology and fundamental physics experiments
Their precision has revolutionized optical frequency measurement, earning part of the 2005 Nobel Prize in Physics.