Two dimensional random access multiphoton spatial frequency modulated imaging with at-focus pulse characterization and compression

Abstract

First, we present a newly developed two photon excitation time resolved photoluminescence (2PE-TRPL) microscopy system of high spatial and temporal resolution, capable of detailed 3D analysis for PL emission intensity and minority carrier lifetime. Initial data shows PL intensity, lifetime, and diffusion length imaging in polycrystalline CdTe and indicates variations of diffusion coefficient and bulk lifetime in a polycrystalline CdTe sample. Second, a nonlinear imaging platform is demonstrated with the following novel advances. First, it includes the first implementation of a spectral phase and amplitude reconstruction and compensation (SPARC) platform within a nonlinear microscopy platform. Notably, SPARC is a both second-order compensation system AND provides a means of characterizing the pulse temporal amplitude and spectral phase directly at the microscope focus, allowing for a true characterization of light exposure conditions experienced by the specimen at the image plane. For the first time, to our knowledge, we provide characterization of each of the multi-foci within a random access platform, measured directly at focus. We also provide a Bootstraps error analysis of the pulse retrieval algorithm. We've also demonstrated the utility of the SPARC platform both as a pulse compressor and characterization means. Second, we have shown that spatial frequency modulation imaging (SPIFI), a technique which enables single element detection for extended excitation sources within scattering media, can be extended into two-dimensions with essentially the same mask design used for the original light sheet systems. Here we make use of a spatial light modulator (SLM) in conjunction with SPIFI to create multiple foci at arbitrary points within the image plane, each tagged with a distinct temporal modulation frequency. This enables multifocal imaging within a random-access environment, with 1D detection where the spatial positions are demultiplexed with simple frequency domain processing and provides a pathway towards the enhanced resolution capability of SPIFI in two dimensions for the first time.