Invited:
LABEL-FREE FAR-FIELD SUPER RESOLUTION MICROSCOPY USING NONLINEAR PHOTO-MODULATED REFLECTIVITY

Far-field super-resolution (SR) microscopy has developed to be an important tool in life sciences. However, it relies on, and therefore is limited by the ability to control the fluorescence of label molecules or nanoparticles.

We introduce a new far field label-free SR methodology that is based on the nonlinear response of the reflectance to photo-modulation [1-3]. It relies on the ability to photo-excite a temperature and/or charge-carriers spatial distribution inside the diffraction limited spot by an ultra-short pump pulse. In Nonlinear photo-modulated Reflectivity (NPMR) an overlapping delayed probe pulse monitors reflectance changes. Spatial resolution within the diffraction limited spot is enhanced due to nonlinearities in photo-modulated properties of the matter. NPMR is measured by recording the high harmonics of the probe laser reflectance, photo-modulated by the pump laser.

Examples of resolution enhancement due to nonlinearities (lateral and vertical) will be presented: The change of thermo-reflectance of VO₂ upon its characteristic insulator-to-metal transition at ~340K, the heating process of a nanostructured silicon or gold surfaces, and the nonlinear response of photo-modulated Raman spectra. Super-resolution down to 85nm is demonstrated with a probe laser of 800nm wavelength. Some aditional modalities of NPMR will be discussed.

NPMR is suitable to characterize semiconductors and metals in vacuum, ambient, and liquid, semi-transparent and opaque systems, ultrathin and thick samples alike.

[1] O. Tzang, A. Pevzner, R.E. Marvel, R.F. Haglund, O. Cheshnovsky, "Super-Resolution in Label-Free Photomodulated Reflectivity" Nano Letters, 15, 1362 (2015).

[2] O. Tzang, O. Cheshnovsky, "New modes in label-free super resolution based on photo-modulated reflectivity" Optics Express, 23, 20926 (2015).

[3] O. Tzang, O. Azoury D. Cheshnovsky, "Super resolution methodology based on temperature dependent Raman scattering, Optics Express, 23, 17929 (2015).