Online broadband monitoring for high precision optical coatings
For many demanding applications, dielectric optical coatings are specified and manufactured to meet strict reflectivity values, sometimes at multiple wavelengths or over a broad band. In order to achieve such precision, the coating layer thickness must be determined and met.
Typically, there are three methods of monitoring this; measuring a witness sample, monitoring the behaviour of a quartz crystal, or simply using a timer. These methods are not sufficient to meet the growing demands on today’s laser optics.
LASER COMPONENTS now relies on online broadband monitoring, whereby a diode spectrometer is used to monitor the visible spectrum during the coating process. An empty hole in the substrate holder lets through unfiltered light from the BBM lamp, and an area without a hole gives a dark current.
These reference values are compared with the incoming signal through a reference window, allowing the current layer thickness to be determined with an absolute accuracy of ±0.5nm.
Broadband monitoring is used in LASER COMPONENTS’ IAD and IBS coatings.
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