Laboratory Featured Article

Frequency comb generation at terahertz frequencies by coherent phonon excitation in silicon

M Hase, M Katsuragawa, AM Constantinescu, H Petek - Nature Photonics, doi: 10.1038/nphoton.2012.35

High-order nonlinear light–matter interactions in gases enable the generation of X-ray and attosecond light pulses, metrology and spectroscopy1. Optical nonlinearities in solid-state materials are particularly interesting for combining optical and electronic functions for high-bandwidth information processing2. Third-order nonlinear optical processes in silicon have been used to process optical signals with bandwidths greater than 1 GHz (ref. 2). However, fundamental physical processes for a silicon-based optical modulator in the terahertz bandwidth range have not yet been explored. Here, we demonstrate ultrafast phononic modulation of the optical index of silicon by irradiation with intense few-cycle femtosecond pulses. The anisotropic reflectivity modulation by the resonant Raman susceptibility at the fundamental frequency of the longitudinal optical phonon of silicon (15.6 THz) generates a frequency comb up to seventh order. All-optical >100 THz frequency comb generation is realized by harnessing the coherent atomic motion of the silicon crystalline lattice at its highest mechanical frequency.



Frequency comb observed in the Fourier transform spectrum




Dr. Hrvoje Petek is the Editor-in-Chief of Progress in Surface Science and the co-director of PINSE (Petersen Institute of NanoScience and Engineering).

We are grateful for financial support from the following funding agencies:

Disclaimer: Certain aspects of the website may not work in Internet Explorer. We apologize for the inconvenience.

Double click to see the video if it does not automatically start.