Method and apparatus including in-resonator imaging lens for improving resolution of a resonator-enhanced optical system

An optical system for detecting features of a surface of interest, said system comprising:

• an illumination subsystem for producing an illumination beam;
• a detection subsystem for detecting a beam reflected from said surface of interest;
• and
• a resonator positioned in an optical path between said surface under observation and said illumination subsystem for increasing an effective resolution of said detection subsystem, said resonator comprising
• multiple reflective surfaces, including at least said surface of interest and at least one other reflective surface for sustaining multiple internal reflections in a cavity formed between said reflective surfaces, and
• an imaging lens positioned at a predetermined position along an optical path between said at least one other reflective surface and said surface of interest and having a predetermined focal length such that a first region on said at least one other reflective surface is imaged onto a second region on said surface of interest.