arXiv subjects

Sisira Suresh

Publications and source records attributed to Sisira Suresh.

2 recordsLinked to original sources

arXiv2024

Hyperspectral acquisition with ScanImage at the single pixel level: Application to time domain coherent Raman imaging

We present a comprehensive strategy and its practical implementation using the commercial ScanImage software platform to perform hyperspectral point scanning microscopy when a fast time dependent signal varies at each pixel level. In the proposed acquisition scheme the scan along the X axis is slowed down while the data acquisition is maintained at high pace to enable the rapid acquisition of the time dependent signal at each pixel level. The ScanImage generated raw 2D images have a very asymmetric aspect ratio between X and Y, the X axis encoding both for space and time acquisition. The results are X axis macro-pixel where the associated time depend signal is sampled therefore providing an hyperspectral information. We exemplified the proposed hyperspectral scheme in the context of time domain coherent Raman imaging where a pump pulse impulsively excites molecular vibrations that are subsequently probed by a time delayed probe pulse. In this case the time dependent signal is a fast acousto-optics delay line that can scan a delay of 4.5ps in 25$μ$s, at each pixel level. We this acquisition scheme we demonstrate ultra-fast hyperspectral vibrational imaging in the low frequency range [10$cm^{-1}$, 150 $cm^{-1}$] over a 500 $μm$ field of view in 14ms (7 frames/s). The proposed acquisition scheme can be readily extended to other applications requiring to acquired a fast evolving signal at each pixel level.

physics.optics↗

arXiv2021

Enhanced Nonlinear Optical Responses of Layered Epsilon-Near-Zero Metamaterials at Visible Frequencies

Optical materials with vanishing dielectric permittivity, known as epsilon-near-zero (ENZ) materials, have been shown to possess enhanced nonlinear optical responses in their ENZ region. These strong nonlinear optical properties have been firmly established in homogeneous materials; however, it is as of yet unclear whether metamaterials with effective optical parameters can exhibit a similar enhancement. Here, we probe an optical ENZ metamaterial composed of a subwavelength periodic stack of alternating Ag and SiO$_2$ layers and measure a nonlinear refractive index $n_2 = (1.2 \pm 0.1) \times 10^{-12}$ m$^2$/W and nonlinear absorption coefficient $β= (-1.5 \pm 0.2) \times 10^{-5}$ m/W at its effective zero-permittivity wavelength. The measured $n_2$ is $10^7$ times larger than $n_2$ of fused silica and four times larger than that the $n_2$ of silver. We observe that the nonlinear enhancement in $n_2$ scales as $1/(n_0 \mathrm{Re}[n_0])$, where $n_0$ is the linear effective refractive index. As opposed to homogeneous ENZ materials, whose optical properties are dictated by their intrinsic material properties and hence are not widely tunable, the zero-permittivity wavelength of the demonstrated metamaterials may be chosen to lie anywhere within the visible spectrum by selecting the right thicknesses of the sub-wavelength layers. Consequently, our results offer the promise of a means to design metamaterials with large nonlinearities for applications in nanophotonics at any specified optical wavelength.

physics.optics↗