US 2008/0165355 A1Published application

High-Resolution High-Speed Terahertz Spectrometer

AssigneeOsaka University

InventorsTakeshi Yasui, Tsutomu Araki, Eisuke Saneyoshi

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Abstract

A high-resolution high-speed terahertz spectrometry for measuring a terahertz frequency spectrum at high speed with a laser mode-locking frequency which is the theoretical limitation frequency resolution of the terahertz time-domain spectroscopy. The mode-locking frequencies of two femtosecond laser light sources are controlled so that they are stabilized at high degree and the difference between the mode-locking frequencies is constant. The output of the laser light sources are used as a pumping light for generating terahertz pulses and a probe pulse light for terahertz detection. Since the time delay timings of the terahertz pulses and the probe pulse light the pulse periods of which are slightly different from each other shift from each other and the difference increases. Therefore, the temporally expanded terahertz pulses are measured by high-speed sampling without using any mechanical stage for time delay scanning. Part of the laser beams are extracted and time origin signals are generated by trigger signal generating means and used as trigger signals. Consequently the influence of the timing jitter can be eliminated. The terahertz electric field time waveform measured by high-speed sampling with the measurement time window of the pulse period is subjected to time-scale conversion and Fourier transform. Therefore, a terahertz frequency spectrum can be measured with high resolution of the theoretical limitation frequency resolution (=mode-locking frequency) and at high speed.

Claims7

Dependent claims

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.

5 more elements

Dependencies are inferred from the claim text.