Polarization control of attosecond pulses using bi-chromatic elliptically polarized laser

We study the high harmonic generation (HHG) using elliptically polarized two-color driving fields. The HHG via bi-chromatic counter-rotating laser fields is a promising source of circularly polarized ultrashort XUV radiation at the attosecond time scale. The ellipticity or the polarization of the attosecond pulses can be tweaked by modifying the emitted harmonics' ellipticity, which can be controlled by varying the driver fields. A simple setup is used to control the polarization of the driving fields, which eventually changes the ellipticity of the attosecond pulses. A well-defined scaling for the ellipticity of the attosecond pulse as a function of the rotation angle of the quarter-wave plate is also deduced by solving the time-dependent Schr\"odinger equation (TDSE) in two dimensions. The scaling can further be explored to obtain the attosecond pulses of the desired degree of polarization, ranging from linear to elliptical to circular polarization.

A Theoretical Study for Designing Optical Multilayer Films Using NdF3/ ThF4

An idea of a colored glaze is presented in this study to hide and dispose all the obstacles of using solar systems as facades integrated with buildings. This aim is achieved by designing multilayer optical interference filters by using Mat lab program . Appropriate dielectric materials, namely NdF3 of high refractive index (nH =1.6) and ThF4 of low refractive index (nL =1.5143) were employed. Quarter wave thicknesses of high (H) and low (L) refractive index were deposited on a microscopic slide substrate with n=1.513 and 550 nm design wavelength (l°). Two optical models were designed, which are Air//HL//glass and Air//LH//glass, for even numbers of layers (2-32 layers). The challenge in this study is to find the most efficient design which has lower solar reflectance (Rsol.) and higher solar transmittance (Tsol.) to raise the efficiency of the solar systems and, in parallel, obtain the colored reflection to achieve the esthetic appearance of the buildings integrated with the solar system facades. The Tsol. value was high (94-95 %), whereas the Rsol. was very low (4-5 %). Hence, the efficiency of the solar system was increased. The two optical models exhibited green color reflectance in the visible region. The first design, i.e. Air/HL/glass, showed higher values of Rvis. and the merit factor (M) than the second model, resulting in a higher potential of coloration. The first design requires fewer materials and layers, thus, it is more cost-effective as compared to the second one.

Real-time Selective Harmonic Minimization using a Hybrid Analog/Digital Computing Method

We present a hybrid analog/digital computing circuit to solve a selective harmonic minimization problem. The approach leverages favorable attributes of digital and analog controllers to yield a fast and scalable optimization solver. A digital microcontroller programs the cost function and other user-defined inputs to the optimization. Voltages in the circuit represent switching angles in the optimization problem. In steady state, the voltages converge to Karush–Kuhn–Tucker (KKT) points of the problem. We present a specific realization of the computing circuit that solves for eight independent switching angles for a quarter-wave symmetric PWM driven two-level single-phase inverter. Seven undesired harmonics are minimized while retaining control over the modulation index. The proposed computing circuit is verified with simulations and a PCB hardware implementation. The experimental results demonstrate that the proposed circuit can converge to the optimal solution in less than 5.0 ms, which is substantially faster than existing methods and facilitates real-time implementation. Moreover, the steady-state power consumption of the PCB implementation is approximately 750 mW, which is also significantly lower than published methods for comparable applications. The computing circuit is utilized to generate the PWM for a 2 kW single-phase inverter, which validates its feasibility in practical applications.

Real-time Selective Harmonic Minimization using a Hybrid Analog/Digital Computing Method

We present a hybrid analog/digital computing circuit to solve a selective harmonic minimization problem. The approach leverages favorable attributes of digital and analog controllers to yield a fast and scalable optimization solver. A digital microcontroller programs the cost function and other user-defined inputs to the optimization. Voltages in the circuit represent switching angles in the optimization problem. In steady state, the voltages converge to Karush–Kuhn–Tucker (KKT) points of the problem. We present a specific realization of the computing circuit that solves for eight independent switching angles for a quarter-wave symmetric PWM driven two-level single-phase inverter. Seven undesired harmonics are minimized while retaining control over the modulation index. The proposed computing circuit is verified with simulations and a PCB hardware implementation. The experimental results demonstrate that the proposed circuit can converge to the optimal solution in less than 5.0 ms, which is substantially faster than existing methods and facilitates real-time implementation. Moreover, the steady-state power consumption of the PCB implementation is approximately 750 mW, which is also significantly lower than published methods for comparable applications. The computing circuit is utilized to generate the PWM for a 2 kW single-phase inverter, which validates its feasibility in practical applications.

Polariton condensation in an organic microcavity utilising a hybrid metal-DBR mirror

We have developed a simplified approach to fabricate high-reflectivity mirrors suitable for applications in a strongly-coupled organic-semiconductor microcavity. Such mirrors are based on a small number of quarter-wave dielectric pairs deposited on top of a thick silver film that combine high reflectivity and broad reflectivity bandwidth. Using this approach, we construct a microcavity containing the molecular dye BODIPY-Br in which the bottom cavity mirror is composed of a silver layer coated by a SiO2 and a Nb2O5 film, and show that this cavity undergoes polariton condensation at a similar threshold to that of a control cavity whose bottom mirror consists of ten quarter-wave dielectric pairs. We observe, however, that the roughness of the hybrid mirror—caused by limited adhesion between the silver and the dielectric pair—apparently prevents complete collapse of the population to the ground polariton state above the condensation threshold.