Alignment of optical systems using Optocraft SHSLab wavefront sensors
The SHSLab is a powerful and comprehensive wavefront measurement solution from Micro-Epsilon . Developed by Optocraft GmbH , a member of the Micro-Epsilon group of companies since 2018 , SHSLab Shack-Hartmann wavefront sensors are used for applications such as optics testing , optics alignment and laser beam characterisation . Wavefront sensors are used in production and R & D in optics manufacturing , laser industries , astronomy and space applications , as well as by contact- and intra ocular lens manufacturers , including mobile phone optics , microscope and photographic lenses .
A typical application is for the alignment of optical systems , where wavefront guiding facilitates and speeds up the alignment process significantly . The following application describes the alignment of a collimation lens in front of a light source , and the set up of a Kepler telescope . The discussed principle can be applied to many alignment applications , not just the specific example described below .
Alignment of collimating lens and Kepler telescope In the test set up , a fibre-coupled LED is used emitting at 625nm . In the first step , the fibre end and the SHSLab Shack- Hartmann wavefront sensor ( WFS ) are mounted on a rail on an optical table . The WFS detects the spherical wave emitted by the fibre . In this situation , the wavefront curvature radius measured by the WFS is equal to the distance between the fibre end and the micro-lens plane of the WFS . This means it can be used to align the correct axial position of the fibre end .
A collimating lens is placed ( focal length ƒ = 60mm ) in front of the fibre . First , the lens is aligned in the lateral direction by minimising the wavefront tilt α , which is directly related to the lateral misalignment Δx between the lens and the fibre end : Δx = ƒ . tan α . Next , the lens is aligned in the axial direction by minimising the spherical power of the wavefront ( resp . wavefront defocus ). The spherical power Dsp is directly related to the axial misalignment :
Using a relatively simple centering stage for x-y alignment of the collimating lens , the tilt can be reduced to 0.007mrad . By displacing the lens along the rail in the z-direction , the beam can be collimated and a wavefront curvature radius of Rwf ≥ 110m can be achieved ( the achievable collimation is limited by the mechanical components of the setup , not by WFS measurement precision ).
38