Optical phase-noise dynamics of Titanium:sapphire optical frequency combs

Stabilized optical frequency combs (OFC) can have remarkable levels of coherence across their broad spectral bandwidth. We study the scaling of the optical noise across hundreds of nanometers of optical spectra. We measure the residual phase noise between two OFC's (having offset frequencies $f^{(1)}_0 $ and $f^{(2)}_0$) referenced to a common cavity-stabilized narrow linewidth CW laser. Their relative offset frequency $ \Delta f_0 = f^{(2)}_0 - f^{(1)}_0 $, which appears across their entire spectra, provides a convenient measure of the phase noise. By comparing $\Delta f_0$ at different spectral regions, we demonstrate that the observed scaling of the residual phase noise is in very good agreement with the noise predicted from the standard frequency comb equation.