The terahertz spectral regime, ranging from about 0.1-15 THz, is one of the least explored yet most technologically transformative spectral regions. One current challenge is to develop efficient and compact terahertz emitters/detectors with a broadband and gapless spectrum that can be tailored for various pump photon energies. Here we demonstrate efficient single-cycle broadband THz generation, ranging from about 0.1-4 THz, from a thin layer of split-ring resonators with few tens of nanometers thickness by pumping at the telecommunications wavelength of 1.5 mm (200 THz). The terahertz emission arises from exciting the magnetic-dipole resonance of the split-ring resonators and quickly decreases under off-resonance pumping. This, together with pump polarization dependence and power scaling of the terahertz emission, identifies the role of optically induced nonlinear currents in split-ring resonators. We also reveal a giant sheet nonlinear susceptibility B10 À 16 m 2 V À 1 that far exceeds thin films and bulk non-centrosymmetric materials.

Optical experiments on second-harmonic generation from split-ring-resonator square arrays show a nonmonotonic dependence of the conversion efficiency on the lattice constant. This finding is interpreted in terms of a competition between dilution effects and linewidth or near-field changes due to interactions among the individual elements in the array.

We present experiments on second-harmonic generation from arrays of magnetic split-ring resonators and arrays of complementary split-ring resonators. In both cases, the fundamental resonance is excited by the incident femtosecond laser pulses under normal incidence, leading to comparably strong second-harmonic signals. These findings are discussed in terms of Babinet's principle and in terms of a recently developed microscopic classical theory that leads to good agreement regarding the relative and the absolute nonlinear signal strengths. The hydrodynamic convective contribution is found to be the dominant source of secondharmonic generation-in contrast to a previous assignment [Science 313, 502 (2006) Photonic metamaterials are an emerging class of tailored composite effective materials that can provide interesting optical properties such as, e.g., magnetism at elevated frequencies [1][2][3] or an enhanced nonlinear optical response [1,[4][5][6][7][8][9][10]. Indeed, in a series of recent experiments [6-8], we have observed second-harmonic generation (SHG) from planar arrays of gold split-ring resonators (SRRs) exhibiting a pronounced magnetic-dipole response. In essence, a SRR is an almost closed loop of a metal wire that can be viewed as a subwavelength electromagnet in which the incident light field induces a circulating oscillating electrical current, leading to a local magnetic field (magnetic-dipole moment) perpendicular to the SRR plane. It has been found [7,8] that arrays of gold "T"s show SHG that is 2 orders of magnitude smaller than that of the gold SRR arrays-despite the facts that the "T"s also exhibit a resonance at the incident fundamental laser frequency and that they are also known to exhibit pronounced local field enhancements.In this Letter, we aim at further clarifying the underlying mechanism. First, we present new experimental results on complementary split-ring resonators (CSRRs), i.e., SRRs in which the metal in the sample plane is replaced by air and vice versa. According to the generalized Babinet's principle [11,12], magnetic and electric fields are interchanged with respect to SRR (precisely, E ជ ͑r ជ , t͒ ↔ −c 0 B ជ ͑r ជ , t͒). Hence, the magnetic-dipole moment of the SRR turns into an electric-dipole moment of the CSRR, allowing us to investigate whether the magnetic-dipole moment is crucial for efficient SHG. Second, we compare these experimental results with numerical calculations based on a recently developed microscopic classical theory of the metal-based metamaterial optical nonlinearities [13].The samples for our experiments are fabricated by standard electron-beam lithography, electron-beam evaporation of the 25 nm thick gold layer onto a glass substrate coated with a 5 nm thin film of indium tin oxide (ITO), and subsequent lift-off. Details can be found in [14]. The SRR and the CSRR arrays have been fabricated on two different glass substrates, however, with closely similar processing steps. The footprint of each array is 100 m ϫ 100 m. Electron micrographs of representativ...

Reliable sample delivery is essential to biological imaging using X-ray Free Electron Lasers (XFELs). Continuous injection using the Gas Dynamic Virtual Nozzle (GDVN) has proven valuable, particularly for time-resolved studies. However, many important aspects of GDVN functionality have yet to be thoroughly understood and/or refined due to fabrication limitations. We report the application of 2-photon polymerization as a form of high-resolution 3D printing to fabricate high-fidelity GDVNs with submicron resolution. This technique allows rapid prototyping of a wide range of different types of nozzles from standard CAD drawings and optimization of crucial dimensions for optimal performance. Three nozzles were tested with pure water to determine general nozzle performance and reproducibility, with nearly reproducible off-axis jetting being the result. X-ray tomography and index matching were successfully used to evaluate the interior nozzle structures and identify the cause of off-axis jetting. Subsequent refinements to fabrication resulted in straight jetting. A performance test of printed nozzles at an XFEL provided high quality femtosecond diffraction patterns.

We demonstrate metamaterial metal-based bolometers, which take advantage of resonant absorption in that a spectral and/or polarization filter can be built into the bolometer. Our proof-of-principle gold-nanostructure-based devices operate around 1.5 \mum wavelength and exhibit room-temperature time constants of about 134 \mus. The ultimate detectivity is limited by Johnson noise, enabling room-temperature detection of 1 nW light levels within 1 Hz bandwidth. Graded bolometer arrays might allow for integrated spectrometers with several octaves bandwidth without the need for gratings or prisms and for integrated polarization analysis without external polarization optics