Active focus locking in an optically sectioning microscope utilizing a deformable membrane mirror.

A significant challenge for in vivo imaging is to remove movement artifacts. These movements (typically due to either respiration and cardiac-related movement or surface chemical response) are normally limited to the axial direction, and hence features move in and out of the focal plane. This presents a real problem for high-resolution optically sectioned imaging techniques such as confocal and multiphoton microscopy. To overcome this we have developed an actively locked focus-tracking system based around a deformable membrane mirror. This has a significant advantage over more conventional focus-tracking techniques where the microscope objective is dithered, since the active element is not in direct, or indirect, contact with the sample. To examine the operational limits and to demonstrate possible applications for this form of focus locking, sample oscillation and movement are simulated for two different biological applications. We were able to track focus over a 400 microm range (limited by the range of the piezomounted objective) with a rms precision on the focal depth of 0.31 microm +/- 0.05 microm.

Adaptive optics for enhanced signal in CARS microscopy.

We report the use of adaptive optics with coherent anti-Stokes Raman scattering (CARS) microscopy for label-free deep tissue imaging based on molecular vibrational spectroscopy. The setup employs a deformable membrane mirror and a random search optimization algorithm to improve signal intensity and image quality at large sample depths. We demonstrate the ability to correct for both system and sample-induced aberrations in test samples as well as in muscle tissue in order to enhance the CARS signal. The combined system and sample-induced aberration correction increased the signal by an average factor of approximately 3x for the test samples at a depth of 700 microm and approximately 6x for muscle tissue at a depth of 260 microm. The enhanced signal and higher penetration depth offered by adaptive optics will augment CARS microscopy as an in vivo and in situ biomedical imaging modality.