| 摘要 |
<p>Optical metrology apparatus, specifically a laser probe (1) , includes a frame (10) comprised of a material selected to have a predetermined coefficient of thermal expansion. A beamsplitter (36) is coupled to the frame for generating a sample beam optical path (D) and a reference beam optical path (C). The beamsplitter is optically coupled to an optical fiber (12) that delivers radiation to and conveys radiation from the frame. A piezoelectric stack (48) has an excitation signal coupled thereto and includes a mirror (26) for phase modulating the reference beam optical path length in response to the excitation signal. The laser probe includes a first strain gauge (58) that is coupled to the piezoelectric stack and a second strain gauge (60) that is coupled to the frame. A closed loop control system (A1, A2, A3, A4, VR) varies the excitation signal in accordance with the detected strains so as to maintain the reference beam optical path length in a predetermined relationship to a path length of the sample beam optical path. This athermalizes the probe, in that any expansion or contraction of the frame is matched by the piezoelectric stack, yielding a net zero change in the non-common beam path lengths. The apparatus includes an optical fiber support (14) that is rotatably coupled to the frame for positioning the optical fiber at a desired angular position. <IMAGE></p> |
