Improvement of signal-to-noise ratio of a subterahertz spectrometer using a continuous-wave multimode laser diode by single-mode fiber optics

The signal-to-noise ratio of the subterahertz spectroscopic system proposed previously, which uses a continuous-wave multimode laser diode and photoconductive antennas, is improved significantly by adopting single-mode fiber optics. The noise estimated from the transmittance measurement of a Si wafer is reduced to about 1/6 of that obtained by the previous system. The improvement is based on the reduction of the random phase distribution of laser modes with various mode patterns, resulting in the increase of the continuous components in the spectrum. (C) 2004 American Institute of Physics.