#### Adaptive optics in a multiphoton microscope

The following movie shows the correction of a DM-induced aberration in a second-harmonic microscope using model-based wavefront sensorless adaptive optics.

The images refer to a 2D section approximately 33 µm deep inside collagen fibre extracted from rat tail. At sample time $$k = 0$$, the DM introduces a phase aberration with $$N$$ aberration modes. Between sample time $$k = 1$$ and sample time $$k = 8$$ inclusive, $$N + 1$$ trial aberrations are applied and the corresponding values of an image quality metric $$\tilde{y}$$ are measured. Starting from sample time $$k = 9$$, the aberration correction is applied.

To correct the aberration, the least-squares estimate of the (unknown) aberration is computed using the measurements of the image quality metric $$\tilde{y}$$. This involves solving a non-convex optimisation problem. Further details are found in the following paper (pdf).

T. van Werkhoven designed and implemented the second-harmonic microscope. Dr. Hoa Truong prepared the specimen. The experiment was performed in the Molecular Biophysics department in Utrecht, in collaboration with the Leiden Observatory.