We sit down this week with Isaac Trumper to discuss his new work on an instantaneous phase shifting deflectometry system he developed and deployed on an iPhone. His work allows for dynamic metrology of optical surfaces in an extremely low cost form.
Background:
Deflectometry is a specific method used to optically measure a surface shape. The concept is based on a simple principle, if a candle is lit and we hold it at a known position in front of a reflective surface, also at a known position, and then move our eye until we see the candle, we can calculate the slope of the mirror. By doing this for all points on a mirror, we can integrate the surface slopes to arrive at a surface profile. If instead of a candle we upgraded to a screen, we can now display very complex images to illuminate the entire mirror surface at once, allowing us to calculate all the surface slopes without moving our source. A source image used commonly is a sinusoidal pattern, which is phase shifted a number of times. This pattern is presented in the x and y orthogonal directions to obtain x and y slope maps, which allows for the calculation of a complete surface map. One previous limitation to this method is that the screen had to display each phase shifted sinusoid consecutively. This is no longer the case, as Isaac Trumper recently has proven that the phase shifts can be encoded into different color channels, red, green, and blue, of the screen. This allows for three simultaneous phase shifted sinusoids to be presented at once. Additionally, using Fourier transform techniques, Trumper was able to encode the x and y sinusoid patterns simultaneously, allowing for one screen to be showing a total of 3 unique patterns in the x direction, and 3 unique patterns in the y direction; i.e. 6 multiplexed channels at once. This allows for a single display and image capture to entirely capture all the required information to completely solve for the surface profile of your optic under test.
For a complete description of the work done, please see Isaac Trumper’s recent paper, located at http://www.loft.optics.arizona.edu/documents/journal_articles/oe-24-24-27993_DKim.pdf.