Pinhole arrays and spatial filters are used for spatial filtering and act as virtual point light sources in many optical systems. In this case, a pinhole (pinhole aperture) limits the NA (divergence) and blocks larger angles. In laser applications, for example, adjusting the aperture diameter will hide (spatially filter) higher laser modes in order to improve the beam properties such as the focus.
Nipkow discs are used in confocal microscopy. As part of the lighting system, they are also found in fluorescence microscopy and material testing. The elements feature pinholes, which are arranged in a ‘Nipkow pattern’ on a planar substrate. IMT ensures that there are no defects during the microstructuring of the black chrome coating. This is because even the smallest of defects in the size of a pinhole diameter will lead to streaking in the confocal image, thereby rendering the disc unusable.
In the traditional Hartmann test, a pinhole array is positioned in front of the optical system to be investigated. The corresponding 2D point cloud is depicted by the system on a CCD camera. As the pinhole distances on the substrate and the resulting point distances on the CCD are known, it is possible to determine aberrations introduced by the optical system. Shack-Hartmann wavefront sensors use microlenses instead of pinhole arrays. They are generally used in the characterisation of optical systems and in adaptive optics. In ophthalmology, the eyes are measured with a wavefront sensor before laser treatment (LASIK), allowing the areas to be treated to be defined.
Customers rely on the ‘Made by IMT’ quality both for Hartmann plates and for the microstructuring of supplied microlens arrays, onto which a metal coating needs to be applied in order to avoid interfering light.