Label-Free Saturated Structured Excitation Microscopy

Abstract

Micro-and nanoscale chemical and structural heterogeneities, whether they are intrinsic material properties like grain boundaries or intentionally encoded via nanoscale fabrication techniques, pose a challenge to current material characterization methods. To precisely interrogate the electronic structure of these complex materials systems, spectroscopic techniques with high spatial resolution are required. However, conventional optical microscopies are limited to probe volumes of~200 nm due to the diffraction limit of visible light. While a variety of sub-diffraction-limited techniques have been developed, many rely on fluorescent contrast agents. Herein we describe label-free saturated structured excitation microscopy (LF-SSEM) applicable to nonlinear imaging approaches such as stimulated Raman and pump-probe microscopy. By exploiting the nonlinear sample response of saturated excitation, LF-SSEM provides theoretically limitless resolution enhancement without the need for a photoluminescent sample.

Spatially Resolved Photogenerated Exciton and Charge Transport in Emerging Semiconductors

“…Immediately following diffraction-limited preparation of an exciton population, Penwell et al (37; see also 131) reduce it to a sub 100-nm-diameter population using an annular stimulated emission depletion light pulse (Figure 5f ). The sharp circular population boundary obtained using nonlinear saturation of electronic quenching transitions as a function of patterned illumination intensity (37) [a strategy also explored by Grumstrup and coworkers (132,133) with TA microscopy and King & Granick (134) with electroluminescence] drives radial diffusive expansion that is detected on pico-to nanosecond timescales using a second, time-delayed stimulated emission depletion pulse in combination with time-gated fluorescence detection (135). TRUSTED thus yielded L D = 16 nm in amorphous poly[2,5-di(hexyloxy)cyanoterephthalylidene] with few-nanometer sensitivity.…”