Wavefront sensors

One in the absolute measurement mode and two in the reference mode.

Setup for testing of optical components should provide optical conjugation between the component under test and the wavefront sensor with proper scaling. See section our Product Guide for general recommendations and typical measurement schemes.

FrontSurfer is a wavefront analysis and control system based on Shack- Hartmann wavefront sensors and deformable mirrors from OKO Technologies.

The wavefront sensor package includes FrontSurfer software and a measurement head - Hartmann or Shack-Hartmann wavefront sensor. The Hartmann wavefront sensor consist of a precision Hartmann mask and a CMOS (or CCD) camera. In the Shack-Hartmann sensor, the mask is replaced by a microlens array.

In this mode, the wavefront is reconstructed from one intensity pattern captured by the wavefront sensor. Geometric parameters of the Hartmann mask or microlens array are used as a reference. This mode can only be used with a precision Hartmann mask (or microlens array) having complete hexagonal or square structure of subapertures.

Typical configuration of the FrontSurfer wavefront sensor has a precision of about λ/60 PV (for λ=0.63 µm) in the reference mode and about λ/6 PV in the absolute measurement mode. In the reference mode, the precision is mainly limited by the image sensornoise and can be improved by averaging over multiple frames and using a microlens array with larger focal distance. In the absolute measurement mode, the precision is limited by fabrication errors of the microlens array (or Hartmann mask).

In this mode, the wavefront is reconstructed from two intensity patterns captured by the wavefront sensor. The first one (main pattern) is measured in presence of the the aberration to be reconstructed, and the second one (reference pattern) is measured for calibration purposes, i.e., with the aberration removed. In this mode, the microlens array (Hartmann mask) can be neither complete nor regular; one can even use an array with random positioning of sub-apertures.

Typical configuration of the FrontSurfer wavefront sensor has a noise-limited sensitivity of about λ/60 PV (for λ=0.63 μm). The sensitivity can be improved by averaging over multiple frames and using a microlens array with larger focal distance.

Applications include optical shop testing of transmissive and reflective optics, alignment of optical systems, real-time monitoring and active compensation of optical aberrations.

FrontSurfer can be interfaced with any camera or frame grabber, but it requires a special video plugin for FrontSurfer. Plugins for Picasso PCI-2SQM framegrabber from Arvoo, DFG/LC1 framegrabber from Imaging Source, A601f/A602f CMOS digital cameras from Basler, and UI- 2210M/2410M from IDS Imaging are included in the distribution. Front-Surfer manual contains description of the functions that should be included in such a plugin, so that the user can develop his own plugin following these instructions.