Lens metrology: How to measure a double-sided thick aspherical lens optically?

In lens metrology, how do people measure a double-sided thick aspherical lens optically? By "optically" I mean for example, using wavefront sensing, interferometry or the interferogram methods.

I searched a little but only found mirror surfaces measurement.

To me, the difficulty is, there are two sides to be measured, but we only get one "accumulated phase" from our measurement. For example, from Shack-Hartmann wavefront sensors we only get one single phase for the lens, but we need the surfaces from both sides. It is mixed.

So is it possible to do double-side lenses metrology optically?

• Is the lens assumed to be mirror-symmetric? That could allow the normal approach to work. – probably_someone May 1 '18 at 0:29
• @probably_someone Unfortunately not. The lens assumes to be a freeform, an asymmetric one. And could you hint more on the "normal approach"? – WDC May 1 '18 at 0:32
• What do you want to measure? Do you want to know the curvature of each surface? – S. McGrew May 1 '18 at 0:39
• There are probably several different ways to do that, but I would do it by measuring the wavefront of a collimated beam reflected off the front surface, then measure the wavefront of a collimated beam reflected off the back surface. One surface at a time makes it MUCH simpler. – S. McGrew May 1 '18 at 0:42
• Don't know if there is a straightforward way to measure the curvature of both surfaces by sending a beam all the way through the lens. Possibly it could be done by using several different incident beams (e.g., collimated, diverging, and converging by known amounts), measuring the resulting wavefront for each, and solving the parallel equations made by plugging in the wavefront values to a thick-lens equation. It could be a messy calculation. – S. McGrew May 1 '18 at 0:57