S. P. Heussler

Free-standing THz electromagnetic metamaterials.

Using micromanufactured S-shaped gold strings suspended in free space by means of window-frames, we experimentally demonstrate an electromagnetic meta-material (EM(3)) in which the metallic structures are no longer embedded in matrices or deposited on substrates such that the response is solely determined by the geometrical parameters and the properties of the metal. Two carefully aligned and assembled window-frames form a bi-layer chip that exhibits 2D left-handed pass-bands corresponding to two different magnetic resonant loops in the range of 1.4 to 2.2 THz as characterized by Fourier transform interferometry and numerical simulation. Chips have a comparably large useful area of 56 mm(2). Our results are a step towards providing EM(3) that fulfill the common notions of a material.

All-metal self-supported THz metamaterial--the meta-foil.

Modern metamaterials face functional constraints as they are commonly embedded in or deposited on dielectric materials. We provide a new solution by microfabricating a completely free-standing all-metal self-supported metamaterial. Using upright S-string architecture with the distinctive feature of metallic transverse interconnects, we form a locally stiff, globally flexible space-grid. Infrared Fourier transform interferometry reveals the typical double-peak structure of a magnetically excited left-handed and an electrically excited right-handed pass-band that is maintained under strong bending and heating, and is sensitive to dielectrics. Exploiting UV/X-ray lithography and ultimately plastic moulding, meta-foils can be mass manufactured cost-effectively to serve as optical elements.

Infrared Spectro/Microscopy at SSLS — Edge Effect Source in a Compact Superconducting Storage Ring

Singapore Synchrotron Light Source (SSLS) is commissioning its new beamline for Infrared Spectro/Microscopy (ISMI). The infrared light is extracted from the edge region of dipole D1 of the compact superconducting electron storage ring Helios 2. The nominal source point is located at half the maximum field, i.e., at 2.25 T. The end station comprises both, a medium and a high resolution Fourier transform infrared spectrometer (FTIR), the former featuring an infrared microscope as well as a UHV chamber for catalysis experiments. Synchrotron Radiation Workshop (SRW) calculations and a preliminary experimental evaluation of ISMI show the capability of this beamline to deliver a bright flux of photons in the Far and Mid infrared spectral regions.

THz meta-foil – a platform for practical applications of metamaterials

The meta-foil, an all-metal fully self-supported locally stiff and globally flexible metamaterial, is presented. Its architecture is based on an array of parallel S-strings interconnected by transverse metal rods that are periodically repeated along the strings. For the present samples, this period is about once or twice the length of an S, which is 31 µm. The resonance frequency of the left-handed pass-band is 3.2 THz or somewhat higher depending on geometry. The meta-foil is manufactured by UV or X-ray lithography-based microfabrication. In the end, it may be produced cost-effectively by plastic moulding. The physical function is explained by numerical simulation and equivalent circuit theory. The spectra are measured by Fourier transform infrared spectroscopy. Maximum transmission is achieved at normal incidence with a cosine-square-like decrease with incidence angle. A change of geometrical parameters alters the resonance frequency as expected. The spectra are also rather sensitive to surrounding dielectrics, indicating a sensor capability. As the meta-foil can be bent, a cylindrical hyperlens set-up is discussed as a forthcoming application to sub-wavelength resolution imaging.

Multichannel Fourier-transform interferometry for fast signals

Multichannel Fourier transform interferometry to measure the spectrum of arbitrarily short pulses and of fast time-varying signals was achieved using a micro/nanomanufactured multimirror array. We describe the performance of a demonstrator FTIR that works in the mid-infrared (MIR) range of 700-1400 cm(-1) and reaches a spectral resolution of 10 cm(-1) taking into account apodization. Spectral measurements down to pulse lengths of 319 µs were carried out using a mechanical camera shutter. Arbitrarily short pulses are expected feasible provided the source can deliver enough photons to overcome the noise equivalent number of photons.

Deep X-Ray Lithography in the Fabrication Process of a 3D Diffractive Optical Element

We present first results of the fabrication process of a diffractive optical element (DOE) using deep X‐ray lithography. The DOE forms the core of our proposed fast parallel‐processing infrared Fourier transform interferometer (FPP FTIR) that works without moving parts and may allow instantaneous spectral analysis only limited by detector bandwidth. Design and specifications of the DOE are discussed. A fabrication process including deep X‐ray lithography (DXRL) on stepped substrates is introduced.

Industrial applications of micro/nanofabrication at Singapore Synchrotron Light Source

SSLS (Singapore Synchrotron Light Source) has set up a complete one-stop shop for micro/nanofabrication in the framework of the LIGA process. It is dubbed LiMiNT for Lithography for Micro and Nanotechnology and allows complete prototyping using the integral cycle of the LIGA process for producing micro/nanostructures from mask design/fabrication over X-ray lithography to electroplating in Ni, Cu, or Au, and, finally, hot embossing in a wide variety of plastics as one of the capabilities to cover a wide range of application fields and to go into higher volume production. The process chain also includes plasma cleaning and sputtering as well as substrate preparation processes including metal buffer layers, plating bases, and spin coating, polishing, and dicing. Furthermore, metrology using scanning electron microscopy (SEM), optical profilometry, and optical microscopy is available. LiMiNT is run as a research lab as well as a foundry. In this paper, several industrial applications will be presented, in which LiMiNT functions as a foundry to provide external customers the micro/nano fabrication services. These services include the fabrication of optical or X-ray masks, of micro/nano structures from polymers or from metals and of moulds for hot embossing or injection moulding.

Pulsed and high-speed FTIR spectroscopy

Fourier transform interferometry is commonly performed by means of mechanically scanning interferometers such as a Michelson and characterized by one scanning mirror. This results in severe limitations of the capability of measuring fast signals. To overcome this drawback, we present a multi-channel FTIR spectrometer (MC-FTIR) that is capable of single-shot operation no matter how short the single pulse is, provided it delivers sufficient photons for the signal to exceed the noise. It can capture fast transient signals, limited by the signal-to-noise ratio and data transfer rate of the detector. Our device is based on a micro/nanomanufactured 3D multimirror array (MMA) which allows collecting a whole interferogram simultaneously. MMAs are manufactured by means of a patented multiple moving mask grey-level deep X-ray lithography process. Up to 640 mirror cells, generating optical path differences from 0 to about 1 mm, were achieved so far at optical quality. We have demonstrated sub-millisecond pulses and a theoretical spectral resolution of 10 cm-1 in the mid-IR. The optical system is similar to a Czerny-Turner mount with the MMA replacing the grating and an MCT focal plane array (FPA) capturing the interferogram. Our MC-FTIR enables extension of FTIR-based IR spectroscopy to arbitrarily short pulses and to fast transient signals. As the optical system is small and rugged, the instrument lends itself readily to field applications. Ongoing work is aimed at emerging applications including biomedical, laser-induced breakdown spectroscopy, and spectroscopy of synchrotron radiation.

Free‐space Electromagnetic Metamaterials From The Far Infrared To The Visible

The development of electromagnetic metamaterials by micro/nanomanufacturing at SSLS has led to matrix‐embedded or substrate‐supported rod‐split‐ring‐based samples reaching left‐handed pass‐bands at 216 THz or 1.39 μm and to free‐space S‐string bi‐layer chips at 2.2 THz. Potential applications of metamaterials range from sub‐wavelength resolution imaging over invisibility cloaking to advanced antennae and are relevant to fields including microscopy, lithography, electromagnetic shielding, and telecommunication.

Micro/nanomanufactured THz electromagnetic metamaterials as a base for applications in transportation

Micro/nanomanufactured electromagnetic metamaterials in the THz spectral range may help extending the use of metamaterials in transportation. S-string based THz metamaterials as manufactured by SSLS, in particular, the meta-foil, provide a promising platform for applications. Special emphasis may be given to antennas being conformal or quickly steerable or tunable for inter-traffic communication. Achievements by SSLS in co-operation with MIT and Zhejiang University are discussed and potential applications outlined.