Wavefront sensorless adaptive optics temporal focusing-based multiphoton microscopy.

Temporal profile distortions reduce excitation efficiency and image quality in temporal focusing-based multiphoton microscopy. In order to compensate the distortions, a wavefront sensorless adaptive optics system (AOS) was integrated into the microscope. The feedback control signal of the AOS was acquired from local image intensity maximization via a hill-climbing algorithm. The control signal was then utilized to drive a deformable mirror in such a way as to eliminate the distortions. With the AOS correction, not only is the axial excitation symmetrically refocused, but the axial resolution with full two-photon excited fluorescence (TPEF) intensity is also maintained. Hence, the contrast of the TPEF image of a R6G-doped PMMA thin film is enhanced along with a 3.7-fold increase in intensity. Furthermore, the TPEF image quality of 1µm fluorescent beads sealed in agarose gel at different depths is improved.

Easily implementable field programmable gate array-based adaptive optics system with state-space multichannel control.

In this paper, an easily implementable adaptive optics system (AOS) based on a real-time field programmable gate array (FPGA) platform with state-space multichannel control programmed by LabVIEW has been developed, and also integrated into a laser focusing system successfully. To meet the requirements of simple programming configuration and easy integration with other devices, the FPGA-based AOS introduces a standard operation procedure including AOS identification, computation, and operation. The overall system with a 32-channel driving signal for a deformable mirror (DM) as input and a Zernike polynomial via a lab-made Shack-Hartmann wavefront sensor (SHWS) as output is optimally identified to construct a multichannel state-space model off-line. In real-time operation, the FPGA platform first calculates the Zernike polynomial of the optical wavefront measured from the SHWS as the feedback signal. Then, a state-space multichannel controller according to the feedback signal and the identified model is designed and implemented in the FPGA to drive the DM for phase distortion compensation. The current FPGA-based AOS is capable of suppressing low-frequency thermal disturbances with a steady-state phase error of less than 0.1 π within less than 10 time steps when the control loop is operated at a frequency of 30 Hz.