FAR-INFRARED FREQUENCY-MODULATION BY OPTICALLY INDUCED GRATINGS IN SILICON

Frequency modulation of 119 μm (2.5 THz) H2O laser radiation by optically induced gratings in Si is reported. The gratings were excited using two diode-pumped, frequency-tunable Nd:YAG lasers. Frequency shifts up to 15 MHz were generated. With 26 mW effective optical exitation power a maximal efficiency of 1.5×10-3 was achieved, with a 3 dB roll-off frequency of 35 kHz for the Si wafer used in the experiment. Results of numerical model calculations are presented, which show that efficiencies in the 10% region should be achievable with moderate optical excitation power. It is pointed out that the principle of optically induced gratings offers a promising tool to transfer frequency modulation from the near-infrared to the far-infrared spectral range.