Device and method for carrying out spatially directed detection of an electroencephalogram

A process for making a blazed periodic profile in a photoresist layer comprising the steps of;

• taking a first layer of photoresist material which will react to radiation of a first wavelength and which has deposited on it a second layer of photoresist material which will react to radiation of a second wavelength wherein the first photoresist material is substantially insoluble in the second solvent and wherein the layer of second photoresist material is substantially opaque to the radiation of the first wavelength;
• exposing the layer of second photoresist material to a pattern of radiation of the second wavelength;
• treating the layer of second photoresist material with the second solvent so as to develop a first periodic profile;
• exposing the layer of first photoresist material to radiation of the first wavelength through the first periodic profile;
• treating the layer of first photoresist material with the first solvent so as to develop a second periodic profile,
• wherein the step of exposing the layer of first photoresist material to radiation of the first wavelength through the first periodic profile is performed with the radiation being directed toward the first layer at an angle away from the normal to the first photo-resist material.