Holographic Exposure Device

A capability to fashion interference gratings in different forms and materials is furnished by the holographic exposure device.  The gratings are formed by holographic illumination of a photoresist-covered substrate by interference of two coherent beams of light at an angle.  This is the same technique that is used to write the gratings in distributed feedback diode lasers and distributed Bragg reflector diode lasers. Both beams come from a 458 nm Argon-Ion laser with one of the beams illuminating the substrate at an oblique angle and a turning mirror used to form the other interfering beam at the same angle to the perpendicular to the substrate.

For some applications, a grating-pattern in the photoresist is the preferred realization, so the grating is exposed and the photoresist developed, which completes processing of the grating.  In other applications, the grating is in the glass substrate.  After the photoresist has been developed, the substrate is etched by ion milling to transfer the photoresist pattern to the substrate.  After chemical removal of the photoresist, the substrate is ready for use as a grating (Figure 1).