  Photonic-chip based TIRF illumination has been used to demonstrate several
on-chip optical nanoscopy methods. The sample is illuminated by the evanescent
field generated by the electromagnetic wave modes guided inside the optical
waveguide. In addition to the photokinetics of the fluorophores, the waveguide
modes can be further exploited for introducing controlled intensity
fluctuations for exploitation by techniques such as super-resolution optical
fluctuation imaging (SOFI). However, the problem of non-uniform illumination
pattern generated by the modes contribute to artifacts in the reconstructed
image. To alleviate this problem, we propose to perform Haar wavelet kernel
(HAWK) analysis on the original image stack prior to the application of (SOFI).
HAWK produces a computational image stack with higher spatio-temporal sparsity
than the original stack. In the case of multimoded non-uniform illumination
patterns, HAWK processing bre aks the mode pattern while introducing
spatio-temporal sparsity, thereby differentially affecting the non-uniformity
of the illumination. Consequently, this assists nanoscopy methods such as SOFI
to better support super-resolution, which is otherwise compromised due to
spatial correlation of the mode patterns in the raw image. Furthermore,
applying HAWK prior to SOFI alleviates the problem of artifacts due to
non-uniform illumination without degrading temporal resolution. Our
experimental results demonstrate resolution enhancement as well as reduction in
artifacts through the combination of HAWK and SOFI.
