An apparatus for optical testing of a sample in the form of a plate-shaped optical element, the apparatus comprising: (a) a rotatable assembly comprising: (i) a general-cylinder having a central hollow including a height axis of said general-cylinder, said hollow sized to receive at least a core area of the sample, (ii) a turntable aligned with said height axis and operable to rotate said rotatable assembly around the height axis of said general-cylinder,, and (iii) a receptacle including said hollow, said receptacle sized to receive at least a portion of the sample, and said receptacle sealed for receiving a quantity of index matching fluid, such that said fluid surrounds and is in contact with at least said core area, and is in contact with said general-cylinder, and (b) an optical arrangement: (i) aligned with said height axis, (ii) including an optical source for providing an optical light beam normal to a circumferential surface area at a first side of said general-cylinder, such that said optical light beam impinges on the core area of the sample, and (iii) including an optical detector for accepting said optical light beam normal to a circumferential surface area at a second side of said general-cylinder after said optical light beam has been transmitted through the core area of the sample or for accepting said optical light beam normal to a circumferential surface area of said general-cylinder after said optical beam has been reflected from the core area of the sample, wherein the general-cylinder is interchangeable and detachably clamped to the turntable; and said sample is coated with a coating, said coating used to manipulate light incident to the sample. (a) a rotatable assembly comprising: (i) a general-cylinder having a central hollow including a height axis of said general-cylinder, said hollow sized to receive at least a core area of the sample, (ii) a turntable aligned with said height axis and operable to rotate said rotatable assembly around the height axis of said general-cylinder,, and (iii) a receptacle including said hollow, said receptacle sized to receive at least a portion of the sample, and said receptacle sealed for receiving a quantity of index matching fluid, such that said fluid surrounds and is in contact with at least said core area, and is in contact with said general-cylinder, and (i) a general-cylinder having a central hollow including a height axis of said general-cylinder, said hollow sized to receive at least a core area of the sample, (ii) a turntable aligned with said height axis and operable to rotate said rotatable assembly around the height axis of said general-cylinder,, and (iii) a receptacle including said hollow, said receptacle sized to receive at least a portion of the sample, and said receptacle sealed for receiving a quantity of index matching fluid, such that said fluid surrounds and is in contact with at least said core area, and is in contact with said general-cylinder, and (b) an optical arrangement: (i) aligned with said height axis, (ii) including an optical source for providing an optical light beam normal to a circumferential surface area at a first side of said general-cylinder, such that said optical light beam impinges on the core area of the sample, and (iii) including an optical detector for accepting said optical light beam normal to a circumferential surface area at a second side of said general-cylinder after said optical light beam has been transmitted through the core area of the sample or for accepting said optical light beam normal to a circumferential surface area of said general-cylinder after said optical beam has been reflected from the core area of the sample, (i) aligned with said height axis, (ii) including an optical source for providing an optical light beam normal to a circumferential surface area at a first side of said general-cylinder, such that said optical light beam impinges on the core area of the sample, and (iii) including an optical detector for accepting said optical light beam normal to a circumferential surface area at a second side of said general-cylinder after said optical light beam has been transmitted through the core area of the sample or for accepting said optical light beam normal to a circumferential surface area of said general-cylinder after said optical beam has been reflected from the core area of the sample, the general-cylinder is interchangeable and detachably clamped to the turntable; and said sample is coated with a coating, said coating used to manipulate light incident to the sample.