Patent ID: 8704154

Claim:
A non-contact probe comprising: an emitting element that radiates light; a light receiving element that receives the light radiated from the emitting element, the non-contact probe detecting an object without contact based on the light received by the light receiving element; and an optical filter that covers an optical path to the light receiving element, the optical filter comprising a transmission band in which a light included in a first wavelength range of the light radiated from the emitting element is transmitted and a blocking band in which light included in a second wavelength range outside of the first wavelength range is blocked, wherein the optical filter has a spectral linewidth of a spectral characteristic that is set to be broader than a spectra linewidth of a spectral characteristic of the emitting element and narrower than a spectral linewidth of a spectral characteristic of the light receiving element, wherein the optical filter comprises a light-incident surface and a light radiation surface parallel to each other, the light-incident surface and the light radiation surface being disposed to be inclined to a plane orthogonal to an optical axis of the light receiving element, and a distance t between the light-incident surface and the light radiation surface of the optical filter is designed to satisfy a relation of formulae below when an angle between the optical axis of the light receiving element and a normal line of the light-incident surface is denoted by I, a refractive index of the optical filter is denoted by n, and a distance from the optical axis of the light receiving element to the farthest point in which the light receiving element receives light is denoted by d: t<d ·cos( r )/sin(1 −r ); r=a sin(sin( i )/ n ).