An infrared imaging apparatus having thin film spatial filters in a stacked array to filter and collate light generated internally by the infrared imaging apparatus such that the light generated impacts a detection area of the imaging apparatus at or near a critical angle. The index of refraction of the detection area being subject to change when irradiated with infrared light such that the amount of light generated internally and reflected to a light detector attached to the imaging apparatus varies with the intensity of the irradiating infrared light.