Wavefront Sensors Information
Wavefront sensors measure the aberrations of an optical wavefront. They are common in adaptive optics systems, lens testing, and ophthalmology. A wavefront is the collection of points having the same phase belonging to a propagating wave. A wavefront with no faults or aberrations will be a flat surface, while a distorted wavefront will have a curved surface.
The primary function of a wavefront sensor is to provide is to measurements of abnormalities in an optical wavefront, and provide real time feedback to adaptive optical systems. These sensors rely on Shack-Hartmann or Quadriwave lateral shearing interferometetry technology to complete these tasks.
Shack-Hartmann wavefront sensors consist of an array of lenses called lenslets. These lenslets all have the same focal length and focuses a wavefront and onto a photon sensor. The photon sensor is usually a CCD sensor but can also be a CMOS or quad cell. Based on where the wavefront is focused on the sensor and how far it is away from a normal focal spot, a wavefront can be approximated to determine whether it is normal or distorted.
Quadriwave lateral shearing interferometer sensors make use of a diffractive grating that will cause four replicas of the incident beam to form and propagate. After a short distance, the four new beams will create an interference pattern incident on a CCD photo sensor. Quadiwave lateral shearing can offer higher resolution than Shack-Hartmann sensors.
The following specifications determine the functionality of a wavefront sensor.
Wavelength: The wavelength range that the sensor is compatible with. This is an important consideration based on what type of electromagnetic radiation the sensor is exposed to, such as UV spectrum, visible spectrum, or infrared spectrum.
Aperture size: The aperture size are the dimensions of the window that the electromagnetic wave passes through to reach the lenslets and sensor.
Focal length: Focal length is for Shack-Hartmann sensors that use arrays of lenslets that all have the same focal length to focus the incident wavefront into spots.
Acquisition rate: The acquisition rate is how many frames or pictures of the wavefront the sensor can capture in a second. The units are frames per second (fps).