Far-Infrared Light Source and Far-Infrared Spectrometer

Abstract

The present invention provides a far-infrared light source capable of reducing the shift in the location irradiated with far-infrared light even when the frequency of the far-infrared light changes. A far-infrared light source according to the present invention is configured so that the variation in the emission angle of far-infrared light in a nonlinear optical crystal when the frequency of the far-infrared light changes is substantially offset by the variation in the refractive angle of the far-infrared light at the interface between the nonlinear optical crystal and a prism when the frequency of the far-infrared light changes

1 . A far-infrared light source for far-infrared light emission comprising:
 a first light source emitting a first laser light being a pulse laser;   a second light source emitting a second laser light and capable of changing the wavelength of the second laser light in a range from a first laser light wavelength to a second laser light wavelength;   a nonlinear optical crystal generating a far-infrared light by permitting the incidence of the first laser light and the second laser light;   a prism attached to a side plane of the nonlinear optical crystal and receiving and emitting the far-infrared light generated by the nonlinear optical crystal; and   a stage for adjusting the angle of the nonlinear optical crystal to an incidence angle of the first laser light, wherein   when the second laser light has the first laser light wavelength, the nonlinear optical crystal emits a first far-infrared light having a first far-infrared wavelength and a first angle to an incidence angle of the second laser light, and when the second laser light has the second laser light wavelength, the nonlinear optical crystal emits a second far-infrared light having a second far-infrared light wavelength and a second angle to the incidence angle of the second laser light, the second angle different from the first angle,   when the far-infrared light has the first far-infrared light wavelength, the nonlinear optical crystal has a first refractive index for the far-infrared light, and when the far-infrared light has the second far-infrared light wavelength, the nonlinear optical crystal has a second refractive index for the far-infrared light, the second refractive index different from the first refractive index,   the nonlinear optical crystal has a configuration where a difference between a third angle and a fourth angle coincides with a difference between the first angle and the second angle, the third angle formed by the first far-infrared light in the nonlinear optical crystal with respect to an interface between the nonlinear optical crystal and the prism when the first far-infrared light travels through the prism at a predetermined angle, and the fourth angle formed by the second far-infrared light in the nonlinear optical crystal with respect to the interface when the second far-infrared light travels through the prism at the predetermined angle, and   the stage has a mechanism of adjusting an angle at which the nonlinear optical crystal is oriented in order to reduce a difference between an angle of the far-infrared light with respect to the interface and an angle of the far-infrared light with respect to the incidence angle of the first laser light or the incidence angle of the second laser light.   
     
     
         2 . The far-infrared light source according to  claim 1 , further comprising an optical system for adjusting an incidence angle at which the second laser light is incident on an entering surface of the nonlinear optical crystal, wherein
 the entering surface has an angle to avoid the first laser light reflected by the entering surface from returning to the optical system, and   an exiting surface of the nonlinear optical crystal for the first laser light has an angle to avoid the first laser light reflected by the exiting surface from returning to the optical system.   
     
     
         3 . The far-infrared light source according to  claim 2 , wherein
 the optical system comprises:   a light deflector for deflecting the second laser light; and   an imaging optical element for imaging the second laser light deflected by the light deflector on the entering surface.   
     
     
         4 . The far-infrared light source according to  claim 1 , further comprising an optical system for irradiating an entering surface of the nonlinear optical crystal with the second laser light, wherein
 the entering surface has an angle to avoid the first laser light reflected by the entering surface from returning to the optical system, and   an exiting surface of the nonlinear optical crystal for the first laser light has an angle to avoid the first laser light reflected by the exiting surface from returning to the optical system.   
     
     
         5 . A far-infrared spectrometer comprising:
 the far-infrared light source according to  claim 1 ;   an illumination optical system for irradiating a sample with the far-infrared light emitted from the far-infrared light source;   a far-infrared light imaging optical system for imaging the far-infrared light transmitted through the sample or reflected by the sample; and   a second nonlinear optical crystal for converting the far-infrared light imaged by the far-infrared imaging optical system to a near-infrared light.   
     
     
         6 . The far-infrared spectrometer according to  claim 5 , the far-infrared light source is configured so that an emission angle of the far-infrared light is changed when its frequency is changed, and
 the illumination optical system corrects an irradiation position of far-infrared light on sample when the angle of the far-infrared light emitted from the far-infrared light source is changed.   
     
     
         7 . The far-infrared spectrometer according to  claim 6 , wherein
 the illumination optical system comprises an angle variable mirror capable of adjusting the angle of a reflection plane to reflect the far-infrared light, and   the angle variable mirror corrects the irradiation position of the far-infrared light on the sample by adjusting the angle of a reflection plane reflecting the far-infrared light.   
     
     
         8 . The far-infrared spectrometer according to  claim 7 , wherein
 the illumination optical system comprises:   a cylindrical lens for collecting the far-infrared light emitted from the far-infrared light source; and   a slit disposed in vicinity of a back focal plane of the cylindrical lens and blocking some of the frequency components of the far-infrared light that is not needed to be applied onto the sample.