Imaging theory of structured pump-probe microscopy

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.

Three-dimensional wide-field pump-probe structured illumination microscopy

“…It is worthwhile now to compare our work with existing pump-probe SIM publications. Previous works about pump-probe SIM are based on intensity measurement for 2D coherent imaging [22][23][24][25]. Let us call the reconstruction method in those works as the intensity SIM framework and the one that we are suggesting in this paper as the field SIM framework.…”

“…As an alternative method to point scanning, there have been publications to implement wide-field pump-probe microscopy based on coherent anti-Stokes Raman scattering (CARS) [19][20][21]. People have also applied SIM to pump-probe microscopy to increase the lateral resolution in two dimensions in various configurations including point scanning, line scanning and wide-field [22][23][24][25]. In this article, we extend these previous works to three dimensions (3D) in widefield configuration and propose a scheme that is compatible with pump-probe modalities where signal wavelength is not shifted from those of input beams (for example, signal wavelength is anti-Stokes shifted for CARS, but it is not for SRS).…”

Label-Free Saturated Structured Excitation Microscopy

“…The DL spectrum ( I DL (k)) can be understood as the object spectrum ( O(k)) filtered by a triple convolution of the four optical transfer functions (OTFs; H n (k)). A detailed discussion of DL imaging theory can be found elsewhere [11,12].…”

“…The excitation pulse PSF is eliminated from Equation (5), due to the necessary condition that the spatial frequency of the excitation profile falls within the bounds of the optical transfer function of the imaging system. Under conditions where the excitation density scales linearly with the pump power (low fluence), a series of structured images collected with a structured excitation field like that given by Equation (4) can be utilized to reconstruct an image with a factor of two improvement in spatial resolution over the diffraction limit [11,12].…”

“…For example, the principles of stimulated emission depletion [5] have been successfully applied to Stimulated Raman Microscopy (SRM) [7] and to Pump-Probe Microscopy (PPM) [8]. Our research group has leveraged the theoretical basis of Laterally Modulated Excitation Microscopy [6] to develop Structured PPM, which provides a factor of two improvement in spatial resolution without relying on high-intensity saturation or de-excitation phenomena [11,12]. To achieve higher imaging resolution with a structured excitation field, it is necessary to invoke higher order nonlinear light-matter interactions [13,14].…”