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In this Letter, continuum thermodynamic and phase field approaches (PFAs) predicted internal stress-induced reduction in melting temperature for laser-irradiated heating of a nanolayer. Internal stresses appear due to thermal strain under constrained conditions and completely relax during melting, producing an additional thermodynamic driving force for melting. Thermodynamic melting temperature for Al reduces from 933.67 K for a stress-free condition down to 898.1 K for uniaxial strain and to 920.8 K for plane strain. Our PFA simulations demonstrated barrierless surface-induced melt nucleation below these temperatures and propagation of two solid-melt interfaces toward each other at the temperatures very close to the corresponding predicted thermodynamic equilibrium temperatures for the heating rate Q≤1.51×1010K/s. At higher heating rates, kinetic superheating competes with a reduction in melting temperature and melting under uniaxial strain occurs at 902.1 K for Q = 1.51 × 1011 K/s and 936.9 K for Q = 1.46 × 1012 K/s.

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An advanced continuum model for nanoscale melting and kinetic superheating of an aluminum nanolayer irradiated by a picosecond laser is formulated. Barrierless nucleation of surface premelting and melting occurs, followed by a propagation of two solid-melt interfaces toward each other and their collision. For a slow heating rate of Q = 0.015 K ps(-1) melting occurs at the equilibrium melting temperature under uniaxial strain conditions T = 898.1 K (i.e., below equilibrium melting temperature Teq = 933.67 K) and corresponding biaxial stresses, which relax during melting. For a high heating rate of Q = 0.99-84 K ps(-1), melting occurs significantly above Teq. Surprisingly, an increase in heating rate leads to temperature reduction at the 3 nm wide moving interfaces due to fast absorption of the heat of fusion. A significant, rapid temperature drop (100-500 K, even below melting temperature) at the very end of melting is revealed, which is caused by the collision of two finite-width interfaces and accelerated melting in about the 5 nm zone. For Q = 25-84 K ps(-1), standing elastic stress waves are observed in a solid with nodal points at the moving solid-melt interfaces, which, however, do not have a profound effect on melting time or temperatures. When surface melting is suppressed, barrierless bulk melting occurs in the entire sample, and elastodynamic effects are more important. Good correspondence with published, experimentally-determined melting time is found for a broad range of heating rates. Similar approaches can be applied to study various phase transformations in different materials and nanostructures under high heating rates.

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Levoy and Hanrahan to capture all the rays in free space. [2] The reconstruction of depth refocusing was demonstrated by Isaksen et al. in 2000. [3] However, LF imaging schemes are critically susceptible to a low imaging resolution. For reconstructed LF images, the resolution substantially reduces compared with conventional 2D imaging system images. For LF imaging, the resolution of the reconstructed image is inherently limited by the number of elemental lenses. Based on the Nyquist sampling theorem, [11] the spatial density of the MLA should be increased to obtain an LF image exhibiting improved spatial resolution. Due to the increase in the elemental lens density resulting from the adoption of passive MLAs, however, the angular sampling resolution of LF imaging is unavoidably affected under the condition of an image sensor with a fixed pixel density, since the ray direction sampling decreases for the case of an elemental lens of reduced aperture. So far, several reconstruction schemes have attempted to ameliorate the spatial resolution of the reconstructed images without deteriorating the angular resolution. Deconvolution algorithms [12,13] and wavefront coding techniques [14-16] were developed to reconstruct 3D depth images featuring an enhanced spatial resolution. Yet, the corresponding resolution uniformity is unacceptable for the reconstruction depth information while the resolution is diffraction limited. Other studies focused on enhancing the spatial resolution of LF images by capitalizing on laterally shifted MLAs. Jang and Javidi proposed a resolution-enhanced integral photography system drawing upon a synchronously moving MLA. [17] Lim et al. proposed resolution-enhanced LF microscopy utilizing a moving MLA driven by an electrically controlled piezo-actuator. [18] Due to the presence of the moving MLA translated by an electromechanical system, however, operation is hardly stable requiring additional transducer modules. As a result, the LF imaging system unavoidably becomes bulky, being slow in capturing elemental image arrays. In the meantime, the metasurface, depending on a subwavelength array of optical antennas, has emerged as a prominent planar optical platform in the visible regime, that can flexibly manipulate the phase profile. [19-29] In particular, the metasurface is capable of individually imparting an arbitrary phase to each orthogonal linear polarization. [30-32] Polarization-tuned multifunctional metasurface devices including beam deflectors, [33-35] metalenses, [36-39] waveplates, [40-42] and multi-image metaholograms [43-46] have been introduced. There The light-field (LF) imaging technique can obtain the light intensity and directional ray distribution information by utilizing a microlens array (MLA). Based on the recoded 3D information, full-parallax or depth-slice images can be reconstructed. Due to the limited ray sampling rate of the MLA, however, conventional LF imaging schemes are fatally susceptible to a trade-off between the spatial and angular resolution. To mitigate this issue...

A novel directional backlight system based on volume-holographic optical elements (VHOEs) is demonstrated for time-sequential autostereoscopic three-dimensional (3-D) flat-panel displays. Here, VHOEs are employed to control the direction of light for a time-multiplexed display for each of the left and the right view. Those VHOEs are fabricated by recording interference patterns between collimated reference beams and diverging object beams for each of the left and right eyes on the volume holographic recording material. For this, self-developing photopolymer films (Bayfol® HX) were used, since those simplify the manufacturing process of VHOEs substantially. Here, the directional lights are similar to the collimated reference beams that were used to record the VHOEs and create two diffracted beams similar to the object beams used for recording the VHOEs. Then, those diffracted beams read the left and right images alternately shown on the LCD panel and form two converging viewing zones in front of the user's eyes. By this he can perceive the 3-D image. Theoretical predictions and experimental results are presented and the performance of the developed prototype is shown.