Chapter 11
Label-Free Super-Resolution Microscopy
by Nonlinear Photo-modulated
Reflectivity
Omer Tzang, Dror Hershkovitz and Ori Cheshnovsky
Abstract Nonlinear photo-modulated reflectivity (NPMR) for far-field, label-free,
super-resolution (SR) microscopy is based on the nonlinear changes in the reflectance
of materials, induced by an ultra-short pump pulse. In NPMR, a modulated train of
pump pulse is focused on the sample that photo-excites temperature and/or chargecarriers changes, spatially distributed inside the diffraction-limited spot. A spatially
overlapping, delayed, and unmodulated train of probe pulse monitors the resulting
nonlinear reflectance changes by the detection of the high harmonics in the probe
reflectance. The resulting point spread function (PSF) of the combined pump and
probe is narrower than the diffraction-limited PSF, and the improvement in resolution
scales like
√
n, where n is the nonlinearity order. NPMR is suitable to characterize
semiconductors and metals in vacuum, ambient and liquid, semi-transparent and
opaque systems. In order to detect weak high-order nonlinearities at the harmonics
of the modulation frequencies, pure sine modulation is required. We have succeeded
in modulating our pump source with harmonic impurity down to 10
−4 . Examples
of resolution enhancement include nanostructured silicon, plasmonic gold surfaces,
and vanadium dioxide (VO 2 ) upon photo-induction of its characteristic insulator-tometal transition. To further reduce the PSF and improve the resolution, it is possible
to couple NPMR to other resolution-enhancement approaches, such as spatial modulation and apodization of the pump beam. Additionally, under specific conditions,
the method can be simplified to use a single-laser pulse. Finally, we show that the
nonlinear response to photo-excitation can be coupled to other SR modalities, such
as Raman scattering and nonlinear photo-acoustic signals.
O. Tzang · D. Hershkovitz · O. Cheshnovsky (B)
School of Chemistry, The Raymond and Beverly Sackler, Faculty of Exact Sciences, Tel Aviv
University, Tel Aviv 6997801, Israel
e-mail: orich@post.tau.ac.il
© Springer Nature Switzerland AG 2019
V. Astratov (ed.), Label-Free Super-Resolution Microscopy,
Biological and Medical Physics, Biomedical Engineering,
https://doi.org/10.1007/978-3-030-21722-8_11
261
Label-Free Super-Resolution Microscopy
by Nonlinear Photo-modulated
Reflectivity
Omer Tzang, Dror Hershkovitz and Ori Cheshnovsky
Abstract Nonlinear photo-modulated reflectivity (NPMR) for far-field, label-free,
super-resolution (SR) microscopy is based on the nonlinear changes in the reflectance
of materials, induced by an ultra-short pump pulse. In NPMR, a modulated train of
pump pulse is focused on the sample that photo-excites temperature and/or chargecarriers changes, spatially distributed inside the diffraction-limited spot. A spatially
overlapping, delayed, and unmodulated train of probe pulse monitors the resulting
nonlinear reflectance changes by the detection of the high harmonics in the probe
reflectance. The resulting point spread function (PSF) of the combined pump and
probe is narrower than the diffraction-limited PSF, and the improvement in resolution
scales like
√
n, where n is the nonlinearity order. NPMR is suitable to characterize
semiconductors and metals in vacuum, ambient and liquid, semi-transparent and
opaque systems. In order to detect weak high-order nonlinearities at the harmonics
of the modulation frequencies, pure sine modulation is required. We have succeeded
in modulating our pump source with harmonic impurity down to 10
−4 . Examples
of resolution enhancement include nanostructured silicon, plasmonic gold surfaces,
and vanadium dioxide (VO 2 ) upon photo-induction of its characteristic insulator-tometal transition. To further reduce the PSF and improve the resolution, it is possible
to couple NPMR to other resolution-enhancement approaches, such as spatial modulation and apodization of the pump beam. Additionally, under specific conditions,
the method can be simplified to use a single-laser pulse. Finally, we show that the
nonlinear response to photo-excitation can be coupled to other SR modalities, such
as Raman scattering and nonlinear photo-acoustic signals.
O. Tzang · D. Hershkovitz · O. Cheshnovsky (B)
School of Chemistry, The Raymond and Beverly Sackler, Faculty of Exact Sciences, Tel Aviv
University, Tel Aviv 6997801, Israel
e-mail: orich@post.tau.ac.il
© Springer Nature Switzerland AG 2019
V. Astratov (ed.), Label-Free Super-Resolution Microscopy,
Biological and Medical Physics, Biomedical Engineering,
https://doi.org/10.1007/978-3-030-21722-8_11
261