US 6,552,806 B1 · Automated minimization of optical path difference and reference mirror focus in white-light interference microscope objective

Abstract

Average fringe contrast is determined by PSI measurements at each step of relatively large translations of the reference optics and mirror of a white-light Linnik interference objective and the resulting data are used to minimize the OPD between the reference and test beam paths of the instrument. Utilizing the same algorithms used in the art to perform conventional vertical scanning interferometry, the position of minimum OPD is determined by finding the position of maximum average fringe contrast. Furthermore, by automating the system with a precise translation mechanism, operator-to-operator variations are completely eliminated and the precision of the process of OPD minimization is greatly improved. In another embodiment of the invention, the optimal focal position of the reference mirror is found at the same time by calculating the average lateral variation of fringe contrast as a function of OPD and focal position. The optimal OPD and focal position correspond to the maximum average lateral variation of fringe contrast in the resulting three-dimensional space.

Claims25

Dependent claims

A method for minimizing the optical path difference between a test beam path and a reference beam path produced in an interference microscope objective having a reference-arm assembly that comprises a reference lens and a reference mirror, and having first scanning means for carrying out interference measurements of a test surface, the method comprising the following steps:

(a) providing second scanning means for translating the reference-arm assembly along said reference beam path;
(b) translating the reference-arm assembly through a plurality of positions along the reference beam path using said second scanning means;
(c) measuring a fringe modulation at predetermined locations corresponding to said plurality of positions along the reference beam path;
(d) determining a location of the reference-arm assembly along the reference beam path corresponding to an optimal fringe modulation;
and
(e) fixing said optimal-fringe-modulation location of the reference-arm assembly such that interferometric measurements of the test surface may be carried out by varying the optical path difference therefrom.

3 more elements

A method for minimizing the optical path difference between a test beam path and a reference beam path produced in an interference microscope objective having a reference-arm assembly that comprises a reference lens and a reference mirror, and for contemporaneously optimizing the focal position of the reference mirror, wherein the objective comprises first scanning means for carrying out interference measurements of a test surface, the method comprising the following steps:

(a) providing second scanning means for translating the reference-arm assembly in an OPD dimension along said reference beam path;
(b) providing third scanning means for translating the reference mirror with respect to the reference lens in a focal-distance dimension along said reference beam path;
(c) measuring a fringe modulation at predetermined locations corresponding to a plurality of OPD and focal-distance positions obtained using said second and third scanning means;
(d) calculating a lateral variation of fringe modulation for each of said predetermined locations;
(e) determining an optimal OPD position and an optimal focal-distance position corresponding to an optimal lateral variation of fringe modulation;
and
(f) fixing the OPD and focal-distance positions at said optimal OPD and focal-distance positions such that interferometric measurements of the test surface may be carried out by varying the OPD therefrom.

4 more elements

An apparatus for minimizing the optical path difference between a test beam path and a reference beam path produced in an interference microscope objective having a reference-arm assembly that comprises a reference lens and a reference mirror, and for contemporaneously optimizing the focal position of the reference mirror, the apparatus having first scanning means for carrying out interference measurements of a test surface, comprising:

second scanning means for translating the reference-arm assembly in an OPD dimension along said reference beam path;
third scanning means for translating the reference mirror with respect to the reference lens in a focal-distance dimension along said reference beam path;
means for measuring a fringe modulation at predetermined locations corresponding to a plurality of OPD and focal-distance positions obtained using said second and third scanning means;
means for calculating a lateral variation of fringe modulation for each of said predetermined locations;
means for determining an optimal OPD and focal-distance position corresponding to an optimal lateral variation of fringe modulation;
and
means for fixing the OPD and focal-distance positions at said optimal OPD and focal-distance positions such that interferometric measurements of the test surface may be carried out by varying the OPD therefrom.

4 more elements

Dependencies are inferred from the claim text.

Automated minimization of optical path difference and reference mirror focus in white-light interference microscope objective

Life of this patent

Automated minimization of optical path difference and reference mirror focus in white-light interference microscope objective

Life of this patent

Abstract

Claims25