Atmospheric turbulence can significantly impact the quality of an image by causing distortions during image acquisition. The turbulence can affect the image sharpness and contrast. We will quantify atmospheric impacts on image quality by using standard image quality metrics for measuring image blur (such as the variance of the Laplacian). In this paper we will utilize meteorological and contrast targetboard observations to train machinelearning models. We utilize approximately two years of optical turbulence data and meteorological data along a coastal path to train and test the models. A comparison between various ML algorithms, such as XGBoost (Extreme Gradient Boosting) and LightGBM (Light Gradient Boosting Machine), is performed to determine which best predicts the image quality metrics.
The refractive index structure parameter (Cn2) is of interest because it characterizes turbulence, which affects optical propagation through the atmosphere, including free space optical communications, laser propagation, and imaging. This work seeks to develop a geography-agnostic model that can predict Cn2 and received signal strength index (RSSI), with as few input parameters as possible. This work trains models including the Gaussian process regression, neural network, and bagged decision tree types, and use r-squared and root-mean squared error to compare model performance. Most of the data used to train and test the algorithms is collected in San Diego, a Csa-type climate (hot-summer Mediterranean climate) according to Köppen climate classification. We then demonstrate application of the trained models to a different site with similar climate, using available common input parameters, and quantitatively assess each model's respective efficacy.
Aluminum-doped zinc oxide metamaterial emerged as a promising plasmonic material due to its low optical loss and high conductivity. The Hong-Ou-Mandel effect is a result of two photons interfering on a beam-splitter. The coincidence rate of the detectors will drop to zero when the identical input photons overlap perfectly in time which results in the Hong-Ou-Mandel dip. If the time delay is scanned, the position of the HOM dip can be measured with femtosecond precision. Therefore, this two-photon interference effect has the potential for applications in precision measurement of time delays. Here, we experimentally observed Hong-Ou-Mandel interference for multilayered AZO/ZnO metamaterial. The Hong-Ou-Mandel effect was observed using a biphoton source with a periodically-poled Potassium Titanyl Phosphate crystal and two single photon counting modules monitoring the output from a beam splitter at 810 nm wavelength. The coincidence probability for separable photons, as a function of time delay τ, was fitted using least square method. The multilayered AZO/ZnO sample (carrier concentration 1020 -1021cm-3) on quartz substrate was used for delay. Our measurements show that the extracted time delay τ=25 µm for multilayered AZO/ZnO was about two orders of magnitude larger than expected from the thickness of the sample.
Multilayered Al:ZnO/ZnO metamaterial, a material that exhibits unique optical properties such as hyperbolic dispersion, attracted a high research interest due to its low optical loss and high conductivity. Combination of the optical gain and strong anisotropy for the Al:ZnO/ZnO metamaterial provide novel opportunities to control spontaneous emission. High doping concentrations (1020- 1021 cm-3 ) for Al:ZnO/ZnO require the inclusion the effect of the band filling. While ZnO has a large bandgap of ~3.3 eV, it has been suggested that in Al:ZnO the Burstein-Moss effect results in an increase in bandgap and thus a decrease in emitted wavelength, which may partially explain the suppression of visible photoluminescence and increase in ultraviolet photoluminescence observed in highly doped Al:ZnO. Here, we investigated the interplay between bandgap renormalization and band filling (Burstein-Moss effect). The results of our calculations show that the energy shift due to the Burstein-Moss effect (blue-shift) and bandgap renormalization (redshift) strongly depends on carrier concentration in multilayered Al:ZnO/ZnO. We found that the energy blue-shift due to BursteinMoss compensates the red-shift from the bandgap renormalization when a carrier concentration reaches 1020 cm-3 .
The emission properties of aluminum-doped zinc oxide are numerically investigated. A complete model for photoluminescence, based on the set of rate equations for electron-hole recombination, is used to study the influence of carrier concentration (1017-1020 cm-3 ) on the visible and ultraviolet (UV) emission. The set of coupled rate equations is solved numerically using the fourth order Runge-Kutta technique for various optical pump intensities and pulse durations. The results for low carrier concentration (~1017 cm-3 ) show that at low pump intensity (0.01 mJ/cm2 ) visible emission is dominant in the emission spectrum and, as the pump intensity increases (~1 mJ/cm2 ), the UV emission becomes dominant. The study of ultrafast dynamics shows that for pump pulse durations of less than ~ 1 ns the intensity of the UV emission is an order of magnitude larger compared to the visible intensity for aluminum-doped ZnO samples with carrier concentration ~1018 cm-3 .
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