Apparatus having a multiple angle transparent rotating element for measuring the thickness of transparent objects

An apparatus configured as a Michelson interferometer for measuring thickness of a transparent object, comprising:

• a radiation source for generating radiation having short coherence length;
• a measuring arm having the object arranged at a first end thereof;
• a reference arm having a reflector arranged at a first end thereof;
• an observation arm having a radiation detector arranged at a first end thereof;
• a coupling unit, coupling said radiation source and second ends of said measuring, reference, and observation arms, for dividing the radiation from said source into said measuring arm and said reference arm and for combining radiation reflected by the object and the reflector, by interference and coupling, into said observation arm;
• and
• a path length variation element arranged between the object and said coupling unit along said measuring arm, said path length variation element being optically transparent for the radiation, being rotatable about a rotational axis thereof, having at least four side walls and having an axis of symmetry identical with the rotational axis,
• the rotational axis of said path length variation element being arranged perpendicular to a propagation direction of the radiation incident on said path length variation element from said coupling unit, the incident radiation being reflected at least twice at inner side walls of said path length variation element.

An apparatus configured as a Michelson interferometer for measuring thickness of a transparent object, comprising:

• a radiation source for generating radiation having short coherence length;
• a measuring arm having the object arranged at a first end thereof;
• a reference arm having a reflector arranged at a first end thereof;
• an observation arm having a radiation detector arranged at a first end thereof;
• a coupling unit, coupling said radiation source and second ends of said measuring, reference, and observation arms, for dividing the radiation from said source into said measuring arm and said reference arm and for combining radiation reflected by the object and the reflector, by interference and coupling, into said observation arm;
• and
• first and second path length variation elements optically transparent for the radiation, being rotatable about respective rotational axes thereof, each having at least four side walls and each having an axis of symmetry identical with the respective rotational axis,
• said first path length variation element being arranged between the reflector and said coupling unit along said reference arm and said second path length variation element being arranged between said object and said coupling unit along said measuring arm,
• the rotational axes of said path length variation elements being arranged perpendicular to a propagation direction of the radiation incident on said path length variation elements from said coupling unit, the incident radiation being reflected at least twice at inner side walls of said path length variation elements,
• the rotational axes of said path length variation elements being contrary.