Abstract: A detection apparatus includes four sets of transmitter and receiver wherein the transmitters are on a first sliding member of a frame and the receivers are on a second sliding member of the frame; and drives for moving the first and second sliding members back and forth. During the movements of the first and second sliding members, each transmitter emits laser beam toward the receiver of the same set by passing through a space above a photoresist-coated optical glass by 100 ?m, no signal is generated at the receiver if the laser beam is not blocked, and a signal is generated at the receiver if the laser beam is blocked by at least one of a plurality of particles on the photoresist-coated optical glass.

Abstract: A detection apparatus includes four sets of transmitter and receiver wherein the transmitters are on a first sliding member of a frame and the receivers are on a second sliding member of the frame; and drives for moving the first and second sliding members back and forth. During the movements of the first and second sliding members, each transmitter emits laser beam toward the receiver of the same set by passing through a space above a photoresist-coated optical glass by 100 ?m, no signal is generated at the receiver if the laser beam is not blocked, and a signal is generated at the receiver if the laser beam is blocked by at least one of a plurality of particles on the photoresist-coated optical glass.