Pinhole detection device

A pinhole detection device comprising:

• a light source that emits light to an object to be inspected;
• an optical lens disposed between the light source and the object to be inspected;
• and
• a detection unit that detects light that has been converged by the optical lens and passed through a pinhole in the object to be inspected,
• wherein the detection unit includes an optical fiber that transmits the light that has passed through the pinhole in the object to be inspected,
• wherein when a maximum detectable angle at which the pinhole with respect to an optical axis of the light source is detectable is defined as θ, a maximum angle of incidence of light that can be transmitted by the optical fiber with respect to the optical axis of the light source is in a range of θ+0° to θ+5°
• wherein a first linear Fresnel lens and a second linear Fresnel lens are provided between the light source and the detection unit, the first linear Fresnel lens being disposed nearer to the light source along a longitudinal direction of the light source, the second linear Fresnel lens being disposed nearer to the detection unit than the first linear Fresnel lens along the longitudinal direction of the light source,
• wherein the first linear Fresnel lens refracts light from the light source into parallel light, and
• wherein as viewed in the longitudinal direction of the light source, the second linear Fresnel refracts the parallel light such that a maximum angle of polarization of light refracted by the second linear Fresnel lens is equal to or smaller than a maximum angle of incidence with respect to an end face of the optical fiber.