Far-infrared spectroscopy device

A far-infrared spectroscopy device comprising:

• a variable wavelength far-infrared light source that generates first far-infrared light;
• an illumination optical system that irradiates a sample with the first far-infrared light;
• a nonlinear optical crystal for detection that converts second far-infrared light from the sample into near-infrared light by using pump light;
• and
• a far-infrared light imaging optical system that images the sample on the nonlinear optical crystal for detection, wherein
• the variable wavelength far-infrared light source includes two beams of laser light of different wavelengths and a nonlinear optical crystal for generation of far-infrared light,
• the variable wavelength far-infrared light source generating far-infrared light by difference frequency generation or parametric generation, by irradiating the two beams of laser light onto the nonlinear optical crystal for generation of far-infrared light,
• the illumination optical system is an anamorphic imaging optical system that forms an image of a linear far-infrared-light-emitting region of the variable wavelength far-infrared light source on the sample,
• the illumination optical system is constructed by a first, a second and a third cylindrical lenses arranged in this order, and
• the second cylindrical lens has its cylindrical axis parallel to a plane defined by the optical axis of the illumination optical system and the linear far-infrared-light-emitting region of the variable wavelength far-infrared light source,
• the first and the third cylindrical lenses have their cylindrical axes vertical to that of the second cylindrical lens and form an afocal imaging optical system, and
• an irradiation position of the first far-infrared light on the sample does not depend on a wavelength of the first far-infrared light.