Healybriggs8407

We propose a version of the supporting quadric method for calculating a refractive optical element with two working surfaces for collimated beam shaping. Using optimal mass transportation theory and generalized Voronoi cells, we show that the proposed method can be regarded as a gradient method of maximizing a concave function, which is a discrete analogue of the Lagrange functional in the corresponding mass transportation problem. It is demonstrated that any maximum of this function provides a solution to the problem of collimated beam shaping. Therefore, the proposed method does not suffer from "trapping" at a local extremum, which is typical for gradient methods. We present design examples of refractive optical elements illustrating high performance of the method.Multiband terahertz (THz) detectors have attractive prospects in the areas of THz sensing and imaging. This paper presents a monolithic resonant CMOS fully integrated triple-band THz thermal detector that is composed of a compact loop antenna and an optimized proportional to absolute temperature (PTAT) sensor, leading to an uncooled, compact, low-cost, easy-integration, and mass-production multiband detector. The principles of operation, theoretical calculation, and experimental validation are demonstrated in detail. Calculated responsivities are 34.9 V/W, 51.6 V/W, and 47.6 V/W at the operation frequencies of 0.91 THz, 2.58 THz, and 4.3 THz, respectively, for the natural atmospheric windows. Relatively better experimental results are obtained at 0.91 THz and 2.58 THz due to the scarcity of THz sources, showing maximum responsivities of 29.2 V/W and 46.5 V/W with minimum NEPs of 1.57 µW/Hz0.5 and 1.26 µW/Hz0.5, respectively. The presented triple-band thermal detector has the natural scalability to focal plane arrays, providing great potential for multiband THz sensing and imaging systems.Mid-infrared imaging detectors are essential tools for many applications because they can visualize the objects in the dark via thermal radiation. However, these detectors have to pair with separate spectral and polarization filters to select the target spectral bands and polarization states, resulting in complicated and bulky imaging systems. One way to mitigate the need for separate spectral filters and polarizers is to use metamaterial absorbers, which are arrays of optical resonators with sub-wavelength dimensions and spacing, to tailor the responses of the detector pixels. Here we report an intelligent program based on the genetic algorithm that automates the design and optimization of a metal-insulator-metal based metamaterial absorber with multi-sized nanostrip antennas as the top layer. The program starts from a randomly generated pattern of the top antenna layer, and it iteratively approaches the optimized designs of two polarization selective MIM absorbers with wideband high absorption in the specified 3-5 (MWIR) band and 8-12 µm (LWIR) band. The measured absorption spectra of the two optimized designs agree well with the simulated results. The influences of the incident angle of light, the finite size of detector pixels, and the air gap between the neighboring pixels on the spectral absorption are numerically evaluated.We present a large-area perfect blackbody sheet, which would offer a planar standard radiator for high-precision thermal imager calibration. Polydimethylsiloxane (PDMS) sheets with nano-precision surface micro-cavity structures achieve both ultra-low reflectance (ultra-high emissivity close to unity) over the thermal infrared wavelengths and high durability to mechanical contact. The investigation on the geometrical parameters of the conical micro-cavities, that is, radii and aspect ratios (ratio of height to radius), confirmed that the PDMS blackbody sheet with a micro-cavity radius of ∼6 µm and an aspect ratio of ∼4 exhibits the optimum hemispherical reflectance of less than 0.002 (emissivity of higher than 0.998) at the thermal infrared wavelengths (6-15 µm). Furthermore, the large-area PDMS blackbody sheet of 100 mm × 80 mm maintained an excellent in-plane uniformity of the emissivity. This unprecedented large-area perfect blackbody conforms to the International Electrotechnical Commission (IEC) standard recommendation regarding thermal imager calibration for fever screening in terms of the emissivity performance.Quantum key distribution (QKD) can help two distant peers to share secret key bits, whose security is guaranteed by the law of physics. In practice, the secret key rate of a QKD protocol is always lowered with the increasing of channel distance, which severely limits the applications of QKD. Recently, twin-field (TF) QKD has been proposed and intensively studied, since it can beat the rate-distance limit and greatly increase the achievable distance of QKD. Remarkalebly, K. Maeda et. al. proposed a simple finite-key analysis for TF-QKD based on operator dominance condition. Although they showed that their method is sufficient to beat the rate-distance limit, their operator dominance condition is not general, i.e. it can be only applied in three decoy states scenarios, which implies that its key rate cannot be increased by introducing more decoy states, and also cannot reach the asymptotic bound even in case of preparing infinite decoy states and optical pulses. Here, to bridge this gap, we propose an improved finite-key analysis of TF-QKD through devising new operator dominance condition. We show that by adding the number of decoy states, the secret key rate can be furtherly improved and approach the asymptotic bound. MEK activation Our theory can be directly used in TF-QKD experiment to obtain higher secret key rate. Our results can be directly used in experiments to obtain higher key rates.As an analog of optical laser, phonon laser has potential applications in various areas. We study a type of phonon laser implemented by two coupled micro-cavities, one of which carries optical gain medium. The phonon laser operation is under a blue detuned external drive leading to dynamical instability. The saturation of the optical gain is considered, and its induced nonlinearity results in more complicated behaviors in stimulated phonon emission. To deal with such complex dynamics, we apply a composite numerical approach, in addition to a previously used dynamical approach, to the time evolution of the system. The workable phonon laser operation is found to be achievable by choosing the proper system parameters. Moreover, low threshold for the phonon laser operation is possible with the suitable coupling between the cavities and an optimum damping rate in one cavity.