Holographic transmission bandpass filter

摘要

A narrow bandwidth bandpass filter having high transmission efficiency for the passband and excellent out-of-band attenuation employs a transmission holographic grating sandwiched between the oblique faces of a pair of right angle glass prisms. An incoming laser beam to be filtered is incident normal to one of the prism faces so as to intersect the holographic grating at about 45 DEG . The grating frequency is such as to diffract light of the transmission wavelength through substantially 90 DEG so that it exits the cube formed by the two prisms from the right angle face of the second prism. The out-of-band wavelengths of the incident beam are either transmitted unaffected through the grating or diffracted at a different angle than the light of the transmission wavelength. A spatial filter comprising a mask with a central aperture is supported a spaced distance from the output face of the cube so that diffracted light of the transmission wavelength passes through the aperture and the unwanted wavelengths, which are diffracted at different angles than the transmission wavelength, are blocked by the mask.