May 11, 2007, Santa Clara, CA--An ultrafast laser introduced by Coherent, the Micra-CEP, generates carrier-envelope-phase (CEP) stabilized ultrafast laser pulses. The system combines Coherent's broadband ultrafast Micra laser with a CEP detection module and fast-feedback electronics. By active feedback control of the laser, the CEP stabilizer locks the phase velocity of the oscillating light field to the group velocity of the pulse envelope. Thus for ultrashort pulses consisting of only a few optical cycles, the peak of the oscillating electric field can be maximized under the pulse envelope.
Carrier-envelope phase stabilization has been used in research lasers for years and has made its way into the commercial world. A laser pulse consists of the oscillating light field imposed on the pulse shape; for long pulses of dozens of optical cycles or longer, the phase of the field relative to the carrier envelope (the pulse shape) is utterly unimportant. But for shorter pulses, getting the peak of the electric-field oscillation centered at the maximum of the pulse envelope results in a higher peak amplitude for that one oscillation, in effect resulting in a more powerful pulse at that point--without having to boost the power of the associated laser hardware.
At the heart of the CEP module is a nonlinear interferometer; this unit uses a photonic-crystal fiber to generate an octave-spanning optical spectrum. The red end of this spectrum is frequency-doubled and combined with the green end of this same broad spectrum. The resultant beat frequency is sensed by a fast photodetector that provides the CEP feedback signal. After suitable processing, this signal is then used to control a fast cavity-mirror actuator inside the Micra laser to control the carrier phase. Uses of the Micra-CEP include attosecond research, high-harmonic generation, optical clocks, and coherent control, says Coherent.