Large-aperture electrically tunable lenses with 1ms hysteresis-free response for remote focusing

Project summary The fast millisecond timescale of neuronal activity has posed a difficulty for D volumetric imaging whose speed is limited in part by the axial scan methods currently available The use of electrically tunable lenses ETLs for remote focusing confers speed and vibration reduction advantages over the more traditional sample stage or microscope objective motion but current state of the art ETLs are liquid lenses that still require mechanical movement from a piezo ring with their transition speed limited to ms by mechanical ringing We propose to build and test an ETL based on switchable liquid crystal polarization grating lenses LCPG lenses that can perform remote axial focusing at ms timescale an order of magnitude speed improvement over state of the art axial focusing techniques The LCPG lens is a nonmechanical device and thus has no ringing or hysteresis particularly useful for repeated scans of the same sample location or for superresolution techniques where absolute repeatability in axial position is key The speed of the LCPG lens is not linked to its aperture size and LCPG lenses can be easily made with mm or larger apertures avoiding vignetting by matching or exceeding the back aperture diameters of modern high performance objectives Unlike a piezo liquid ETL a LCPG lens can be made with any custom lens profile including aspherical and can include compensation for aberrations Although the LCPG lens offers discrete rather than continuous focal scanning these devices have andgt efficiency and can be stacked to produce as many focal planes as desired Using mm substrates an stage LCPG lens would be just mm thick but could achieve focal planes The Phase I LCPG lens will have stages and available focal planes with clear aperture and focal plane location tailored for use as a high speed remote focusing lens in a two photon P microscope system Specific aims LCPG lens fabrication Includes fabrication of both LCPG lenses and liquid crystal waveplate switches assembly into a cascaded stack index matching and addition of electrodes LCPG lens characterization Includes benchtop characterization of efficiency at the target wavelength switching speed and Shack Hartmann measurement of wavefront quality compared to the template lens Integration into CW microscope Using one of our existing CW microscope D spatial light modulator systems we will characterize the amount of focal length shift introduced by the LCPG lens along with the D focal spot sizes and aberrations in different focal planes Integration into P microscope We will directly compare the performance of the LCPG lens to the state of the art piezo liquid lens by replacing a piezo liquid ETL with the Phase I lens in a P microscope system used for D neuronal imaging We will gather feedback from this end user system to focus our further development efforts Project narrative To study the brain we need to be able to image the D interaction of neurons at a fast millisecond timescale However current D microscope scans rely on mechanical methods that are about x too slow We will introduce a nonmechanical millisecond timescale D scan method that uses liquid crystal polarization grating LCPG lenses