Patent ID: 7605371

Claim:
A terahertz spectrometer comprising: (a) two units of femtosecond laser means each having a laser repetition rate (mode-locked frequency) different from each other; (b) mode-locked frequency controlling means for controlling the two units of femtosecond laser means at the same time independently each such that the mode-locked frequency of each of the two units of femtosecond laser means is stabilized and the difference in the mode-locked frequencies is held at a predetermined fixed value; (c) terahertz wave radiating means for emitting a terahertz electromagnetic pulse by using output light of one femtosecond laser as excitation light and by using a photoconductivity switch or a nonlinear optical crystal; (d) terahertz wave optical system means for irradiating a sample for spectroscopy with a terahertz electromagnetic pulse emitted from the terahertz wave radiating means and further guiding the terahertz electromagnetic pulse influenced by the sample; (e) terahertz wave detecting means for detecting an temporal waveform of electric field of the terahertz electromagnetic pulse by using output light of the other femtosecond laser as probe pulse light, by making incident the terahertz electromagnetic pulse and probe pulse light, and by using a photoconductive switch or an electro-optical sampling method; (f) trigger signal generating means for generating a time origin signal by extracting a part of the output light of the two units of the femtosecond laser means; and (g) signal waveform measuring means by detecting in synchronization a signal waveform of the terahertz electromagnetic pulse, by amplifying the weak electric signal outputted from the terahertz wave detecting means and by using as a time origin signal the signal outputted from the trigger signal generating means.