Optics

Generation and application of energetic, broadband terahertz pulses (bandwidth ~0.1-50 THz) is an active and contemporary area of research. The main thrust is toward the development of efficient sources with minimum complexities-a true table-top setup. In this work, we demonstrate the generation of terahertz radiation via ultrashort pulse induced filamentation in liquids-a counterintuitive observation due to their large absorption coefficient in the terahertz regime. The generated terahertz energy is more than an order of magnitude higher than that obtained from the two-color filamentation of air (the most standard table-top technique). Such high terahertz energies would generate electric fields of the order of MV cm-1, which opens the doors for various nonlinear terahertz spectroscopic applications. The counterintuitive phenomenon has been explained via the solution of nonlinear pulse propagation equation in the liquid medium.

Ultrafast pump-probe reflectometry and Doppler spectrometry of a supercritical density plasma layer excited by 1017–1018 W/cm2 intensity, 30 fs, and 800 nm laser pulses reveal the interplay of laser intensity contrast and inward shock wave strength. The inward shock wave velocity increases with an increase in laser intensity contrast. This trend is supported by simulations as well as by a separate independent experiment employing an external prepulse to control the inward motion of the shock wave. This kind of cost-effective control of shock wave strength using femtosecond pulses could open up new applications in medicine, science, and engineering.

We report upon the picosecond plasma dynamics at the rear surface of a thin aluminium foil (of either 5.5 μm or 12 μm thickness) excited by high contrast (picosecond intensity contrast of 10−10), 800 nm, femtosecond pulses at an intensity of 3 × 1019 W/cm2. We employ ultrafast pump-probe reflectometry using a second harmonic probe (400 nm) interacting with the rear surface of the target. A rise in the probe reflectivity 30 ps after the pump pulse interaction reveals the breakout of a shock wave at the target rear surface which reflects the 400 nm probe pulse. Simulations using the ZEPHYROS hybrid particle-in-cell code were performed to understand the heating of the target under the influence of the high intensity laser pulse, and the temperature profile was then passed to the radiation-hydrodynamic simulation code HYADES in order to model the shock wave propagation in the target. A good agreement was found between the calculations and experimental results.

The choice of the optimal orientation of the solar panels is by far one of the most important issues in the practical application of solar installations. The use of phase changing materials (PCMs) is an efficient approach of storing solar thermal energy. Because PCMs are isothermal in nature, they provide better density energy storage and the capacity to function across a wide temperature range. Unfortunately, this feature is very rare on various solar power panels; however, ignoring it can reduce the performance of the panels to unacceptable levels. The fact is that the angle of incidence of rays on the surface greatly affects the reflection coefficient and, consequently, the role of unacceptable solar energy. In this paper, a smart energy harvesting model was proposed. In the case of glass, when the angle of incidence varies vertically from its surface to 30, the reflection coefficient is practically unchanged and slightly less than 5%, i.e., more than 95% of the radiation goes in...

The technological equipment geometry control has a significant impact on the overall quality and performance of the product in many manufacturing processes such as multi-position assembly and stamping as well as on productivity and production costs. One of the most promising means of technology equipment geometry control in the digital economy condition is a laser tracker. The robotic incremental sheet forming process assumes the necessary flexibility and profitability due to a very flexible tool chain. In this case, the trajectory of the universal tool is set using a processing program determined by the product geometry. The technological equipment geometry control of the robotic complex for incremental sheet forming was carried out in 2 stages. At the first stage, the measurements were carried out manually in the absolute range measuring system mode. At the second stage, a dynamic measurement of the blank plane displacement was carried out automatically in the interferometer mode ...

Semakin pesatnya perkembangan teknologi informasi masa kini, para pengembang aplikasi khususnya aplikasi yang berbasis web dalam membangun ataupun mengembangkan aplikasi masih menggunakan pemrograman php konvensional. Karena kehadiran teknologi framework khususnya framework yii, banyak pengembang aplikasi yang masih menggunakan php kovensional sedikit demi sedikit beralih ke cara yang menggunakan teknologi framework (yii). Namun tidak semua pengembang php konvensional beralih ke teknologi framework, para pengembang masih beranggapan php konvensional masih lebih baik dari pada menggunnakan teknologi framework (yii). Pengembangan atau dibangunnya dua aplikasi yang menggunakan php konvensional dan menggunakan framework yii, untuk di analisis dengan metode analisis perbandingan efisiensi dan analisis perbandingan performa, dimana analisis perbandingan efisiensi guna di dapatkannya efisiensi pembuatan aplikasi, serta analisis perbandingan performa untuk mencari seberapa kuat dan cepat pe...

Laser induced breakdown plasmas are ``dirty'' events yielding a mixture of ionized species, electrons, and non-ionized matter of various size. Molecular emissions have been detected in excited nanosecond plasmas microseconds after the ablation event. However, with these ...

Telah diaplikasikan serat optik sebagai sensor kekentalan oli Mesran SAE 20W-50 berbasis perubahan temperatur dengan metode back scattering yang memanfaatkan perubahan intensitas cahaya. Rancangan sistem sensor serat optik terdiri dari sumber cahaya yang berasal dari laser dioda (λ = 650 nm), serat optik FD-620-10, fotodetektor OPT 101. Sampel yang digunakan adalah oli Mesran SAE 20W-50. Berkas cahaya dari laser dioda yang ditransmisikan melalui serat optik transmitter akan dihamburkan oleh permukaan oli dan diteruskan kembali melalui serat optik receiver menuju fotodetektor. Pengujian sistem sensor serat optik dilakukan pada dua kondisi, yaitu saat oli dipanaskan pada temperatur 30 oC hingga 100 oC dan saat oli didinginkan pada temperatur 100 oC hingga kembali 30 oC dengan interval yang diberikan adalah 5 oC. Nilai tegangan keluaran tertinggi didapatkan pada temperatur 100 oC, yaitu 0,168 V (saat dipanaskan) dan 0,171 V (saat didinginkan). Nilai tegangan keluaran terendah didapatka...

Grating-based x-ray differential phase contrast imaging (DPCI) often uses a phase stepping procedure to acquire data that enables the extraction of phase information. This method prolongs the time needed for data acquisition by several times compared with conventional x-ray absorption image acquisitions. A novel analyzer grating design was developed in this work to eliminate the additional data acquisition time needed to perform phase stepping in DPCI. The new analyzer grating was fabricated such that the linear grating structures are shifted from one detector row to the next; the amount of the lateral shift was equal to a fraction of the x-ray diffraction fringe pattern. The x-ray data from several neighboring detector rows were then combined to extract differential phase information. Initial experimental results have demonstrated that the new analyzer grating enables accurate DPCI signal acquisition from a single x-ray exposure like conventional x-ray absorption imaging.

Los estados electrónicos confinados en un punto cuántico de GaAs, de forma piramidal y cónica, se han investigado a través del enfoque cuasi analítico válido para ángulos pequeños y el método exacto de elementos finitos para incluir todos los ángulos y alturas. Se han reportado los resultados de la energía de confinamiento en función de la forma y el tamaño de ambas estructuras y finalmente se han comparado los valores aproximados con los exactos provenientes del método de elementos finitos.

We report that equidistant 1D arrays of thin-film lithium niobate nano-waveguides generically support topological edge states. Unlike conventional coupled-waveguide topological systems, the topological properties of these arrays are dictated by the interplay between intra- and inter-modal couplings of two families of guided modes with different parities. Exploiting two modes within the same waveguide to design a topological invariant allows us to decrease the system size by a factor of two and substantially simplify the structure. We present two example geometries where topological edge states of different types (based on either quasi-TE or quasi-TM modes) can be observed within a wide range of wavelengths and array spacings.

We investigate the interaction between high frequency surface acoustic waves and periodic microstructured patterns that form phononic crystals. The experimental method combines an optical pump-probe setup with interferometric detection and provides picosecond temporal and micron spatial resolutions. Surface acoustic waves with frequency components up to 1.3 GHz are imaged in real-time propagating over the periodic metamaterial. We used a DRIE (deep reactive ion etching) process to fabricate 2D air-silicon phononic crystals in the form of a square lattice. We present real-time animations of surface acoustic waves scattered by the phononic crystals. In particular we describe the frequency and angular dependence of the surface acoustic wave reflection from a 2D phononic crystal boundary. Fourier analysis allows us to reveal details of the acoustic band structure including gaps. The presence of such phononic band gaps enables us to visualize surface acoustic waves in waveguides, cavitie...

Phononic crystals are periodic composite materials exhibiting amazing wave propagation properties. In many works, complete band gaps are being looked for, i.e. the materials constituting the phononic crystal and its lattice arrangement are chosen such that propagation for all waves within a prescribed frequency range is forbidden. In other studies, the phononic crystal is considered a metamaterial, the anisotropic spatial dispersion of which can be tuned, and in which negative refraction can even be observed under certain circumstances. Such effects are usually considered in the sub-diffraction regime, i.e. below some critical onset frequency. In this work, we specifically examine phononic crystals in the diffraction regime. Indeed, the boundaries of a finite size phononic crystal embedded in a host propagation medium can be viewed as diffraction gratings, as we show. We will specifically consider two cases: two-dimensional phononic crystals composed of steel rods in water, and two-...