Optical scanning microscope

Abstract

Abstract A scanning optical microscope causes a collimated light beam to impinge on a Bragg cell. A high frequency signal applied to another surface of the Bragg cell modulates the impinging light beam. The output of the Bragg cell comprises two waves: a portion of the impinging light beam which passes directly through the cell or diffraction grating, and a second deflected output beam whose frequency is shifted by the frequency of the applied signal. By modifying the frequency of the applied frequency signal, the deflected beam may be scanned across the surface, while the reference beam remains in place and serves as a phase reference. By detecting the two beams reflected from the surface on a single photodetector, shifts in phase and amplitude of the deflected beam can be determined. To provide further isolation of the system from external vibration, a second input light beam is applied to the diffraction grating, the input of this second beam being in a plane which is essentially perpendicular to the direction of the scanned output beam. This input beam, after passing through the diffraction grating, will provide two further beams which impinge on the surface. These two beams, which are to serve as reference beams, should be focused on a known flat surface; alternatively, the size of these beams may be expanded so their size is very large relative to any surface feature to be detected; or as a further alternative, they may be reflected from a known stable reference surface. In either event, the surface reflection of these beams is detected at a separate photodetector; upon mixing with the scan beam, the reference can be used to detect any changes in phase and amplitude, while cancelling out variations due to changes in frequency of the modulating optical wave.

Inventors

• 👤 Roger L. Jungerman
• 👤 Gordon S. Kino

Bibliographic Details