Nanoscale amplification of non-linear processes in solid-state devices opens novel applications in nano-electronics, nano-medicine or high energy conversion for example. Coupling few nano-joules laser energy at a nanometer scale for strong field physics is demonstrated. We report enhancement of high harmonic generation in nano-structured semiconductors using nanoscale amplification of a mid-infrared laser in the sample rather than using large laser amplifier systems. Field amplification is achieved through light confinement in nano-structured semiconductor 3D waveguides. The high harmonic nano-converter consists of an array of zinc-oxide nanocones. They exhibit a large amplification volume, 6 orders of magnitude larger than previously reported [1] and avoid melting observed in metallic plasmonic structures. The amplification of high harmonics is observed by coupling only 5-10 nano-joules of a 3.2 µm high repetition-rate OPCPA laser at the entrance of each nanocone. Harmonic amplification (factor 30) depends on the laser energy input, wavelength and nanocone geometry [2].
[1] Vampa et al., Nat. Phys. 13, 659–662 (2017).
[2] Franz et al., arXiv:1709.09153 [physics.optics] (2017)
Diagnosis improvement by means of metal nanoparticles possibilities is studied. Set of experiments to reveal their presence in deeper layers of multilayered biological tissue on optical properties is performed. Spectra in the optical range were collected on several distances, from several thicknesses of the first layer. Results are being discussed.
Determining the optical properties of biological tissues in vivo from spectral intensity measurements performed at their surface is still a challenge. Based on spectroscopic data acquired, the aim is to solve an inverse problem, where the optical parameter values of a forward model are to be estimated through optimization procedure of some cost function. In many cases it is an ill-posed problem because of small numbers of measures, errors on experimental data, nature of a forward model output data, which may be affected by statistical noise in the case of Monte Carlo (MC) simulation or approximated values for short inter-fibre distances (for Diffusion Equation Approximation (DEA)). In case of optical biopsy, spatially resolved diffuse reflectance spectroscopy is one simple technique that uses various excitation-toemission fibre distances to probe tissue in depths. The aim of the present contribution is to study the characteristics of some classically used cost function, optimization methods (Levenberg-Marquardt algorithm) and how it is reaching global minimum when using MC and/or DEA approaches. Several methods of smoothing filters and fitting were tested on the reflectance curves, I(r), gathered from MC simulations. It was obtained that smoothing the initial data with local regression weighted second degree polynomial and then fitting the data with double exponential decay function decreases the probability of the inverse algorithm to converge to local minima close to the initial point of first guess.
Brain glial tumors have peculiar features of the perifocal region extension, characterized by its indistinct area, which
complicates determination of the borders for tissue resection. In the present study filter-reduced back-scattered laser light
signals, compared to the data from mathematical modeling, were used for description of the brain white matter. The
simulations of the scattered light distributions were performed in a Monte Carlo program using scattering and absorption
parameters of the different grades of the brain glial tumors. The parameters were obtained by the Mie calculations for
three main types of scatterers: myelinated axon fibers, cell nuclei and mitochondria. It was revealed that diffuse-reflected
light, measured at the perifocal areas of the glial brain tumors, shows a significant difference relative to the signal,
measured at the normal tissue, which signifies the possibility to provide diagnostically useful information on the tissue
state, and to determine the borders of the tumor, thus to reduce the recurrence appearance. Differences in the values of
ratios of diffuse reflectance from active growth parts of tumors and normal white matter can be useful for determination
of the degree of tumor progress during the spectroscopic analysis.
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