Optical frequency combs for those hairy physics problems

Laboratory precision laser spectroscopy has experienced a major advance with the development of optical frequency combs generated by pulsed femtosecond lasers. These lasers emit a broad spectrum (several hundred nanometers in the visible and near infra-red) of equally-spaced ”comb” lines with almost uniform intensity. The precise spectral and temporal qualities of these combs have applications in optical clocks based on atomic references, femtosecond stability timing distribution systems, tests of quantum mechanics and fundamental physical constants, astrophysical spectrograph calibration, high harmonic generation or soft x-ray generation, and atomic and molecular spectroscopy to name only a few. They caught my attention as a possible wavelength reference source for Fabry-Perot interferometers measuring Doppler shifts from mesospheric emissions that enables measurements of wind fields at these altitudes (100 to 300 km). I'll talk about why a wavelength reference is needed for these wind measurements, describe how the frequency combs are produced, and discuss whether using combs is a viable and (more importantly) practical technique for producing a wavelength reference.