The carrier phase

Steve Cundiff investigates the control of the carrier-envelope phase of ultrashort laser pulses. The carrier-envelope phase is an evolving phase shift between the peak of an ultrashort pulse's envelope function (superimposed on a continuous carrier wave) and the closest peak of that carrier wave. Its control will make it possible to synthesize arbitrary electronic waveforms at optical frequencies. This capability is expected to lead to improvements in signal processing, more precise experiments in extremely nonlinear optics, and, eventually, to the coherent control of quantum processes.

Cundiff and his group use a technique known as "self referencing" to control the carrier-envelope phase evolution, or offset frequency, of a mode-locked laser. Self referencing establishes a direct link between optical and microwave frequencies that can be used to measure optical and microwave frequencies that can be used to measure optical frequencies relative to a radio frequency (rf) source or to generate an rf signal based on an optical frequency standard. The group uses quantum interference instead of optical interference in semiconductors to implement their self-referencing technique as well as to detect and lock the offset frequency.

Mode-locked lasers can deliver high-stability rf references over an optical fiber network. To improve the performance of this process, Cundiff's group is implementing dispersion compensation and optical detection of the timing error between the received signal and the mode-locked laser that functions as a local clock.