Wavefront Sensing

A wavefront is a surface of constant phase in a propagating beam. So for a collimated beam, this would be a flat cross-section, while if you passed that beam through a lens you would then have a spherical wavefront. Being able to measure a wavefront has many uses. For an adaptive optics system, knowing the wavefront allows you to create a feedback loop to update the deformable mirror and correct the beam. For experiments measuring the wavefront of a beam passed through flow in a wind tunnel gives insight into the density field of the fluid and allows you to see structures like vorticies of a shear layer connecting by. 

Much of the work done in the Aero-Optics lab is to develop and improve wavefront sensing devices and techniques.

Ultra high speed analog wavefront sensor

We developed, built, and tested an analog wavefront sensor that allows us to measure wavefronts on the order of Megahertz. Fast wavefront measurement is especially important for adaptive optics systems where the rule of thumb is that you need to be able to measure 100x your desired correction rate in order to be able to make accurate corrections. For an aircraft in cruise at Mach 0.8 you may see structures moving by at a rate of kilohertz, in which case you would have to measure on the order of Megahertz! As you go faster this requirement only increases.  An analog sensor allows us to skip over much of the processing involved in camera based sensors and thus get higher speeds. We are continuing to work to develop this sensor to push the limits of wavefront sensing.

Other unconventional wavefront sensing

Converging-diverging sensor

Shock-tolerant wavefront reconstruction