Journal of Magnetism and Magnetic Materials. Volumes 198-199, 1 June 1999,

Optical Sensors are used in numerous research, and commercial applications today. These sensors are used for quality and process control, medico technologies, metrology, imaging, and remote sensing to mention a few examples. Today there are many types of optical sensors; many based on the use of lasers, imaging systems, and/or fibers. In this article, development of devices to implement the various sensor types and their configuration into sensing elements are presented. Some of the enabling technologies discussed include advances in short pulsed high power lasers, imaging methods, micro and nano-structured optical sensing systems, and THz sensing. This article addresses various sensor types, and include all aspects of optical sensors from the components employed, their configuration through detection schemes and algorithms, and application of sensors.

Optical sensors and their applications

Tip-based nanofabrication (TBN) is a family of emerging nanofabrication techniques that use a nanometer scale tip to fabricate nanostructures. In this review, we first introduce the history of the TBN and the technology development. We then briefly review various TBN techniques that use different physical or chemical mechanisms to fabricate features and discuss some of the state-of-the-art techniques. Subsequently, we focus on those TBN methods that have demonstrated potential to scale up the manufacturing throughput. Finally, we discuss several research directions that are essential for making TBN a scalable nano-manufacturing technology.

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Tip-Based Nanofabrication for Scalable Manufacturing

Large-area (∼8000 mm2) Au nanogap plasmon resonator array substrates manufactured using maskless laser interference lithography (LIL) with high uniformity are presented. The periodically spaced subwavelength nanogap arrays are formed between adjacent nanopyramid (NPy) structures with precisely defined pitch and high length density (∼1 km cm−2), and are ideally suited as scattering sites for surface enhanced Raman scattering (SERS), as well as refractive index sensing. The two-dimensional grid arrangement of NPy structures renders the excitation of the plasmon resonators minimally dependent on the incident polarization. The SERS average enhancement factor (AEF) has been characterized using over 30 000 individual measurements of benzenethiol (BT) chemisorbed on the Au NPy surfaces. From the 1(a1), βCCC + νCS ring mode (1074 cm−1) of BT on surfaces with pitch λg = 200 nm, AEF = 0.8 × 106 and for surfaces with λg = 500 nm, AEF = 0.3 × 107 from over 99% of the imaged spots. Maximum AEFs > 108 have been measured in both cases.

Large-area nanogap plasmon resonator arrays for plasmonics applications

Blazed gratings are of dedicated interest for the monochromatization of synchrotron radiation when a high photon flux is required, such as, for example, in resonant inelastic X-ray scattering experiments or when the use of laminar gratings is excluded due to too high flux densities and expected damage, for example at free-electron laser beamlines. Their availability became a bottleneck since the decommissioning of the grating manufacture facility at Carl Zeiss in Oberkochen. To resolve this situation a new technological laboratory was established at the Helmholtz Zentrum Berlin, including instrumentation from Carl Zeiss. Besides the upgraded ZEISS equipment, an advanced grating production line has been developed, including a new ultra-precise ruling machine, ion etching technology as well as laser interference lithography. While the old ZEISS ruling machine GTM-6 allows ruling for a grating length up to 170 mm, the new GTM-24 will have the capacity for 600 mm (24 inch) gratings with groove densities between 50 lines mm−1 and 1200 lines mm−1. A new ion etching machine with a scanning radiofrequency excited ion beam (HF) source allows gratings to be etched into substrates of up to 500 mm length. For a final at-wavelength characterization, a new reflectometer at a new Optics beamline at the BESSY-II storage ring is under operation. This paper reports on the status of the grating fabrication, the measured quality of fabricated items by ex situ and in situ metrology, and future development goals.

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Gratings for synchrotron and FEL beamlines: a project for the manufacture of ultra-precise gratings at Helmholtz Zentrum Berlin

In this chapter we explain how submicron gratings can be prepared by Laser Interference Lithography (LIL). In this maskless lithography technique, the standing wave pattern that exists at the intersection of two coherent laser beams is used to expose a photosensitive layer. We show how to build the basic setup, with special attention for the optical aspects. The pros and cons of different types of resist as well as the limitations and errors of the setup are discussed. The bottleneck in Laser Interference Lithography is the presence of internal reflection in the photo-resist layer. These reflections can be reduced by the use of antireflection coatings. However the thicknesses of these coatings depends on the angle of exposure and the material property or combination of materials in thin films. We show with some examples how to deal with this issue. Finally we show examples of more complex patterns that can be realized by multiple exposures.

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Laser Interference Lithography

We propose a novel and highly sensitive integrated read-out scheme, capable of detecting sub-nanometre deflections of a cantilever in close proximity to a grated waveguide structure. A very compact and stable sensor element can be realized by monolithically integrating a microcantilever structure with the grated waveguide (GWG), using conventional layer deposition and sacrificial layer etching techniques. The platform integrating a high quality GWG and a low initial bending cantilever has been fabricated and characterized.

https://ris.utwente.nl/ws/files/5394255/Pham,_S._van_IEEE_LEOS_Benelux_Ch_27,28_Nov_08_Pp155-158.pdf

Fabrication of microcantilever-based IO grated waveguide sensors for detection of nano-displacements

A novel mechano-optical sensor based on read-out with a Si3N4 grated waveguide

A proof-of-concept study is reported on fabrication and characterization of a novel and compact integrated mechano-optical sensor based-on a micro-bridge suspended above a Si<inf>3</inf>N<inf>4</inf> grated waveguide.

Potassium double tungstates doped with different rare-earth (RE) ions, have been shown as promising materials to provide high, broadband, stable gain at different wavelengths including ~1 μm (Yb3+), 1.55 μm (Er3+) and ~2 μm (Tm3+). In this paper, the utilization of this material in nanophotonic platforms will be presented. Several plasmonic structures of interest have been theoretically proposed. The integration and fabrication techniques required to produce these devices, namely bonding, thin layer transfer and focused ion beam milling have been developed. This work represents the first step towards the utilization of rare-earth doped double tungstates in nanophotonics.

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Hendricus A.G.M. van Wolferen

Papers

Laser Interference Lithography

Fabrication of microcantilever-based IO grated waveguide sensors for detection of nano-displacements

A novel mechano-optical sensor based on read-out with a Si3N4 grated waveguide

A novel mechano-optical sensor based on read-out with a Si3N4 grated waveguide

Photonic integration and fabrication technologies for on-chip active nano-devices in double tungstate gain materials