  A tapered semiconductor amplifier is injection seeded by a femtosecond
optical frequency comb at 780 nm from a mode-locked Ti:sapphire laser. Energy
gains over 17 dB (12 dB) are obtained for 1 mW (20 mW) of average input power
when the input pulses are stretched into the picosecond range. A spectral
window of supercontinuum light generated in a photonic fiber has also been
amplified. Interferometric measurements show sub-hertz linewidths for a
heterodyne beat between the input and amplified comb components, yielding no
detectable phase-noise degradation under amplification. These amplifiers can be
used to boost the infrared power in f-to-2f interferometers used to determine
the carrier-to-envelope offset frequency, with clear advantages for
stabilization of octave-spanning femtosecond lasers and other supercontinuum
light sources with very limited power in the infrared.
