Traceable calibration of Shack–Hartmann wavefront sensors employing spherical wavefronts

Markus Schake,Gerd Ehret,Ulrich Berg,Johannes Bautsch,Lorenz Wagner,Rainer Tutsch,Johannes Pfund

doi:10.1117/1.oe.59.8.084104

Abstract

Traceable, highly accurate calibration of wavefront sensors such as Shack–Hartmann sensors is a challenging task and an active field of research. We have developed a measurement system for the traceable calibration of wavefront sensors employing spherical wavefronts and a point light source in combination with a three-axis linear stage. We obtain an absolute calibration of sensor errors, including the reference spot position and wavefront gradient-dependent errors for each microlens individually. We discuss the main error influences and present an initial measurement uncertainty budget for the calibration. The calibration can be performed with an expanded measurement uncertainty (95% coverage interval) of better than 5 μrad for the wavefront gradient deviation.

Highlights

Shack–Hartmann wavefront sensors (SHSs)[1] are widely used in different fields that require accurate wavefront sensing
Sensor errors occur due to residual misalignment between the microlens array (MLA) and the image sensor[5] or imperfections such as aberrations of the MLA
3 Measurement Results we present the measurement results of a Shack–Hartmann sensor obtained with the setup described above

Summary

Introduction

Shack–Hartmann wavefront sensors (SHSs)[1] are widely used in different fields that require accurate wavefront sensing. The main problem, in this case, is how to determine the exact absolute distance between the sensor and the fiber tip: an erroneous value of this distance would result in a power error due to the spherical reference wavefront employed. This can be overcome by performing several measurements at different distances between the fiber tip and the sensor and by measuring only the relative movements.[6,7,8] Additional sensor parameters such as the distance between the MLA and the image sensor can be obtained using this approach. Microlens-specific errors that are dependent on the incident wavefront slope cannot be characterized

Methods

Results

Conclusion