Friday, March 4, 2011
Toward Synthesis of Arbitrary Optical Waveforms: At the heart of the approach of Chan et al. is molecular modulation (2–7). This technique, pioneered by Harris's group at Stanford University, uses the excitation of vibrational and rotational transitions of molecules to modulate laser light at very high frequencies. Using the fundamental vibrational transition in molecular hydrogen, Chan et al. generated five spectral components ranging in wavelength from 2406 nm (infrared) to 481 nm (orange). The frequency difference between adjacent spectral components is 125 terahertz (THz), which is the vibrational frequency of hydrogen. By adjusting the phase and amplitude of each spectral component, they synthesized trains of square, sawtooth, and other waveform pulses (typically with a width of a few femtoseconds). Although the current experiment uses only five spectral components, future improvements on the technique may result in the generation of thousands of spectral components covering the full optical region of the spectrum.