Grating for optical measurements, an assembly for measurements of one or more optical parameters of a medium and a method of using the assembly

A grating for optical measurements comprising:

• a base plate extending in a plane in two spatial directions;
• a plural number q of periodic patterns, each with a surface and space periodic wave optical mask and each with a different interval frequency;
• wherein the periodic patterns are arranged adjacent each other in the base plate;
• a plural number n of first periodic patterns, each with a surface and space periodic wave optical mask of the same interval frequency;
• a plural number m of second periodic patterns, each with a surface and space periodic wave optical mask of the same second interval frequency;
• wherein the second periodic pattern is arranged adjacent each other in the base plate with a second phase shift (ps2) between the masks of adjacent second periodic patterns;
• wherein the first periodic pattern is arranged adjacent each other in the base plate with a first phase shift (ps1) between the masks of adjacent first periodic patterns;
• and
• wherein a block of second periodic patterns is arranged adjacent a block of first periodic patterns and wherein the first interval frequency is different from the second interval frequency.