Recent advances in the science and technology of THz waves show promise for a wide variety of important applications in material inspection, imaging, and biomedical science amongst others. However, this promise is impeded by the lack of sufficiently functional THz emitters. Here, we introduce broadband THz emitters based on Pancharatnam-Berry phase nonlinear metasurfaces, which exhibit unique optical functionalities. Using these new emitters, we experimentally demonstrate tunable linear polarization of broadband single cycle THz pulses, the splitting of spin states and THz frequencies in the spatial domain, and the generation of few-cycle pulses with temporal polarization dispersion. Finally, we apply the ability of spin control of THz waves to demonstrate circular dichroism spectroscopy of amino acids. Altogether, we achieve nanoscale and all-optical control over the phase and polarization states of the emitted THz waves.
The transverse electromagnetic waves are major information and energy carriers. In 1996, Hellwarth and Nouchi theoretically identified a radically different, non-transverse type of electromagnetic pulses of toroidal topology. These pulses, which are propagating counterparts of localized toroidal dipole excitations in matter and exhibit unique electromagnetic wave properties, have never been observed before. Here, we report the generation and characterization of such optical and terahertz Toroidal Light Pulses (TLPs), launched from tailored nanostructured metasurfaces comprising toroidal emitters. This achievement paves the way for experimental studies of energy and information transfer with TLPs, their space-time "entanglement", and their light-matter interactions involving anapoles, localized space-time entangled excitations, skyrmions, and toroidal qubits that are of growing interest for the fundamental science of light and applications.
We
report the realization of broadband THz plasmonic metagrating
emitters for simultaneous beam steering and all-optical linear polarization
control. Two types of metagratings are designed and experimentally
demonstrated. First, the plasmonic meta-atoms are arranged in a metagrating
with a binary phase modulation which results in the nonlinear generation
of THz waves to the ±1 diffraction orders, with complete suppression
of the zeroth order. Complete tunability of the diffracted THz linear
polarization direction is demonstrated through simple rotation of
the pump polarization. Then, the concept of lateral phase shift is
introduced into the design of the metagratings using interlaced phase
gradients. By controlling the spatial shift of the submetagrating,
we are able to continuously control the linear polarization states
of the generated THz waves. This method results in a higher nonlinear
diffraction efficiency relative to binary phase modulation. These
functional THz metagratings show exciting promise to meet the challenges
associated with the current diverse array of applications utilizing
THz technology.
Laser beam shaping can play a crucial role in improving many laser processes, especially in selective laser patterning of thin films for display devices and solar cells. Typical Gaussian spatial energy distributions can increase damage to the substrate and lead to large crater edge ridges, which are sub-optimal for typical industrial thin film processes. We report on the design, fabrication, and testing of reflective silicon diffractive optics developed for spatial beam shaping at a wavelength of 355 nm. The application of the elements for laser-selective removal of 20 nm indium tin oxide thin films on glass substrates is demonstrated. The design of the phase profile is first generated using the numerical method of computer-generated holography. The phase profiles are realized on a silicon substrate using a novel two-step fabrication technique consisting of a calibrated focused ion beam and an inductively coupled plasma etch. This results in truly grey-scale, blazed diffractive optics, which were analyzed using white light interferometry and atomic force microscopy. Using the diffractive elements with 355 nm nanosecond pulses shows excellent focused spot profiles with a good reproduction of the intended design with a first-order off-axis diffractive efficiency of approximately 80% at a 45 deg angle of incidence.
Fallout contamination deposited on the roof of a structure is, in many cases, the source of the primary radiation component of the total dose obtained at any point within the structure. Experiments have been performed in which the doses from a souice of radiation present on a roof were measured in many locations within a multi-story building. This report presenis the results of these experiments for roof ancG floor mass thicknesses of 48.6 and 97. 2 psf. Comparisons of the experimentally measured gamma doses with those determined theoretically have been shown throughout this report. Agreement between experiment and theory has, in general, been found to be good. ii FOREWORD This report presents results of an experimental evaluation of radiation attenuatioti and distribution caused by simulated fallout from the roof of a multi-story structure with floors of varying mass thicknesses. The experiment was performed during the period August 1965-1966 by the CONESCO Division of Flow Corporation at the Protective Structures Development Center (PSDC), Fort Belvoir, Virginia. This work was conducted for the Office of Civil Defense through the PSDC, Joint Civil Defense Support Group (JCDSG), Office of the Chief of Engineers, and was accomplished under Subtask 1117A Contract DA-18-050-ENG-3407, Work Order No. OCD-PS-65-17 and Contract DACA 31-67-C-0018, Work Order No. (OCD) DAHC 20-67-W-01l 1,
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