Control of thickness of Fabry-Perot etalon - uses detection of peak light transmission of etalon when source coincides with Newton ring

摘要

The Fabry-Perot standard thickness control system forms a quasi point image at infinity from a light source. This image describes a geometric figure whose form is such that it cuts the localised Newtons ring system at infinity associated with the standard. The zone of the standard whose thickness is to be controlled is illuminated by the light source at infinity. The light transmitted by the standard is detected. A peak intensity is detected when the source coincides with a Newton ring. From a knowledge of the instants of peak appearance one can calculate the fractional excess of the standard in the zone. This fractional excess is compared with a reference. An error signal is produced which is proportional to any difference. This error signal is applied to a control system which controls the thickness of the standard in the zone.