The Walsworth Group

Laser Combs for Astrophysics

We have developed a new technique using laser frequency combs for improving the precision and stability of wavelength calibration of astrophysical spectrographs by up to two orders of magnitude. This "astro-comb" will provide a key advance in the resolution of changes in astrophysical Doppler shifts and redshifts, and thus may allow the discovery of Earth-like planets and new measurements of astrophysical dynamics relevant to cosmology.

For example, both of the two main techniques to find exoplanets rely on the planet's very small effect on its star. The radial velocity technique measures the star's "wobble" (and hence Doppler shift) due to the planet's gravitational pull as it circles; while the transit technique measures the dimming of a star's light as a planet passes in front of it. With current technology, both of these techniques can identify relatively large planets that have a noticeable effect on their star. Smaller, rocky planets, like Earth and Mars, are too small to be detected by current techniques.

The astro-comb uses a mode-locked femtosecond laser and Fabry-Perot filtering cavity, linked to an atomic clock, to provide a precise and stable wavelength standard well-suited to astrophysical spectrographs and against which light from a star can be measured.

Recent Posters (click to download)


Broadband dispersion-free optical cavities based on zero group delay dispersion mirror sets. pdf icon
L.J. Chen, G. Chang, C.H Li, A.J. Benedick, D.F. Philips, R.L. Walsworth and F.X. Kärtner,
Optics Express,18 23294 (2010).

A laser frequency comb that enables radial velocity measurements with a precision of 1 cm s-1. pdf icon
C.-H. Li, A.J. Benedick, P. Fendel, A.G. Glenday, F.X. Kartner, D.F. Phillips,
D. Sasselov, A. Szentgyorgyi and R.L. Walsworth
Nature 452, 610-612 (2008) 0804.0955

With a coarse-tooth comb pdf icon
G. Walker,
Nature, 452, 538 (April 3, 2008).

Easy ways to other Earths pdf icon
E. Hand,
Nature, 452, 514 (April 3, 2008).

Laser precision added to searchfor new Earths pdf icon
A. Powell,
Harvard website (April 2, 2008).