High-precision wavelength calibration of astronomical spectrographs with laser frequency combs

We describe a possible new technique for precise wavelength calibration of high-resolution astronomical spectrographs using femtosecond-pulsed mode-locked lasers controlled by stable oscillators such as atomic clocks. Such ‘frequency combs’ provide a series of narrow modes which are uniformly spaced according to the laser's pulse repetition rate and whose absolute frequencies are known a priori with relative precision better than 10−12. Simulations of frequency comb spectra show that the photon-limited wavelength calibration precision achievable with existing echelle spectrographs should be ~1 cm s−1 when integrated over a 4000 Å range. Moreover, comb spectra may be used to accurately characterize distortions…

• SA
  Science and Technology Facilities Council