Correcting for spherical aberration in multiphoton microscopy using a two-dimensional spatial light modulator

Abstract

In the past few decades, there has been an explosion of construction techniques for microscopy systems. These systems can include various types of lasers, including solid state and more recently, fiber lasers. There are many advantages to a fiber laser, including portability, small size, ease of alignment, and low maintenance. In particular, this report details the construction of a 1 um, 150 fs, all-normal-dispersion (ANDi) fiber laser that is used for microscopic imaging. In conjunction with the fiber laser, I constructed a two-photon excitation fluorescence (TPEF) microscope that can be used for sub-1-m-resolution images of scattering media. The key driving specimen for this system is biological systems, but the laser-microscope system can be used to image any scattering media, including high-index materials used in solar cells (for example, CdTe, which has an index of 2.8 at 1150 nm [1]). After construction of the laser-microscope system, we developed a system using a two-dimensional spatial light modulator (SLM) to correct for spherical aberration that arises at the image plane. To do this, we created a phase mask that induced a variable quartic phase on the spatial profile of the excitation beam. The SLM system has been tested on a TPEF microscope using specimen scanning techniques. Additionally, I designed and constructed a theta microscope to try to improve axial resolution (~4 um from a Yb:KGW laser through a 0.65 NA objective) to match its lateral resolution (1 um) by interfering the foci from two different microscope objectives.