Because laser power density changes over the life of a gas fill, it is sometimes necessary to perform power density stabilization. In this scheme, the beam passes through a fixed area aperture and onto the detector. As the power density of the beam drops due to beam area growth, the total energy passing through the aperture is reduced.
Power density stabilization system
A motorized variable attenuator, employing angle-tuned, high-reflection, coated beam splitters, adjusts the power density. Power density adjustment occurs because the optical transmission of the attenuator elements varies with the incident angle.
By using a servo control system, constant power through the aperture can be maintained by continuous attenuator adjustment. Using a beam splitter that reflects a small percentage of the beam onto the detector, you can perform active stabilization during parts processing. This scheme is typically used in high-precision applications where power density stability is more important than beam transmission efficiency.