Abstract
With sub-micron spatial resolution and femtosecond temporal resolution, pump probe microscopy provides a powerful spectroscopic probe of complex electronic environments in bulk and nanoscale materials. However, the electronic structure of many materials systems are governed by compositional and morphological heterogeneities on length scales that lie below the diffraction limit. We have recently demonstrated Structured Pump Probe Microscopy (SPPM), which employs a patterned pump excitation field to provide spectroscopic interrogation of sub-diffraction limited sample volumes. Herein, we develop the imaging theory of SPPM in two dimensions to accompany the previously published experimental methodology. We show that regardless of pump and probe wavelengths, a nearly two-fold reduction in spectroscopic probe volume can be achieved. We also examine the limitations of the approach, with a detailed discussion of ringing in the point spread function that can reduce imaging performance.
Highlights
The electronic structure of complex materials systems is often altered by a variety of localized defects, i.e. compositional and morphological variation, point defects, and grain boundaries [1]
The resolution limit of optical systems is often characterized by the full width at half maximum of the point spread function (PSF), which is restricted by the Abbe limit [14]: fwhmmin
In Panel B, we show the ratio of the structured pump probe microscopy (SPPM) and DL PSFs plotted versus the pump wavelength for a series of probe wavelengths
Summary
The electronic structure of complex materials systems is often altered by a variety of localized defects, i.e. compositional and morphological variation, point defects, and grain boundaries [1]. To enable more precise structure-function correlations in complex materials systems, extensive technique development efforts have been directed toward surpassing the diffraction limit [5,6,7,8,9,10,11,12]. The OTF acts as a low-pass filter, attenuating the high (spatial) frequency information of the imaged object that lies outside the passband. SPPM is theoretically related to Structured Illumination Microscopy (SIM), a fluorescence imaging technique that utilizes a structured excitation field to improve spatial resolution [15,16,17,18]. Structuring the excitation field expands the optical system’s OTF, and improves spatial resolution by nearly a factor of two. The remainder of this manuscript is organized as follows.
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