Spectroscope

A spectroscope comprising:

• an incident slit;
• a collimator lens type optical system that makes the light rays passing through the incident slit parallel light rays;
• a diffraction grating that receives the parallel light rays and, according to a wavelength, outputs the light rays at different angles;
• a condenser lens type optical system that condenses the output light from the diffraction grating;
• and
• a two-dimensional light-receiving detector having a two-dimensional light-receiving surface that detects the light rays that have been condensed by the condenser lens type optical system;
• wherein
• the collimator lens type optical system and the condenser lens type optical system are disposed so that an angle 2γ defined between an optical axis of the collimator lens type optical system and an optical axis of the condenser lens type optical system may be acute;
• the condenser lens type optical system is disposed so that a distance between itself and the diffraction grating may be shorter than a distance between the collimator lens type optical system and the diffraction grating;
• the diffraction grating is a reflection type diffraction grating, whereby a setting is made so that a normal line vector at a central point of the reflection surface may be directed, from a bisector of the angle defined between the optical axis of the collimator lens type optical system and the optical axis of the condenser lens type optical system, toward a side where the collimator lens type optical system is disposed;
• and
• the light rays passing through the incident slit are dispersed by the diffraction grating to cause a dispersion light image of the slit to be imaged on the light-receiving surface of the two-dimensional detector to spectrally measure respective points along a direction of the slit.