Optics

SILSEF nanopatterning technologies are well suited for use in the optics domain. Indeed, micro-nano structures can be used for various application such as diffraction grating for spectrometer, antireflection patterns, plasmonic effects for bio detection, or light management. SILSEF catalogue of patterns permits the demonstration of principle of a given function. Further development can be made using dedicated patterns.

Antireflective treatment

At SILSEF, antireflective treatments are realized by transferring nanostructures into a substrate or a deposited thin film on its surface. Those structures are based on the so called “moth-eye effect” and acte as an adaptative index layer which simulate a low optic index at the tip of the nanostructures and gradually increases to match the index of the substrate.

This technology allows an effective treatment on a wide spectral band and a large range of incident light angles. The developped processes do not require the use of expensive equipments and can be applied on large surface, plane or curved and on a wide range of materials.

Plasmonic

Two kind of plasmonic effects can be distinguished: unlocalized plasmon resonance and localized plasmon resonance.

In an unlocalized plasmonic based effects, such as Surface Plasmon Resonance (SPR) type used for sensing, the resonance is due to coupling between the incident light and a metallic periodically nanopatterned surface. It produces a broad absorption dip in the reflection spectrum at the resonance wavelength or at the coupling angle. Such response can be exploited in sensors for species detection (gas, molecules…)

In localized plasmonic effects, the electromagnetic field of the incident light is locally enhanced and can thus be used to increase optical coupling (such as SERS based sensors). 

Prism detection and angular analysis
Gold nano-patterns for SERS and LSPR detection devices

Diffraction

A diffraction grating is an optical element having the ability to diffract light by a periodic variation of its profile and / or its index (hologram). The diffraction gratings have the property of deflecting angularly a monochromatic beam as well as angularly separating the wavelengths of a polychromatic beam.

Diffraction gratings have interesting properties for who wants to “manipulate” light. It is possible to separate a monochromatic incident beam into several beams or to angularly separate the different wavelengths of a polychromatic source. It is also possible to play on different grating’s parameters such as the period, the material, the depth to obtain the desired diffraction intensity . 

Diffracting patterns on silicon substrate

Light extraction

In a PET scanner detector, the high refractive index of the scintillator crystal causes a large number of the produced UV-vis photons to remain trapped inside the crystal: therefore up to the 70% of the light produced is not collected by the photodetector. Also, the spatial resolution and the sensitivity of existing PET systems suffer from this low collection efficiency of photons.

SILSEF developed solutions with CERN consisting in:

  • Light extracting layers can be deposited/fabricated on the exit surface of the scintillator crystal in order to increase the number of photons extracted.
  • A possible light extraction layer is a nano-patterned thin film of a material with refractive index higher than the LYSO scintillator (n > 1,8): this diffraction grating is referred to as ‘photonic crystal’ (PhC).

Visit www.napa-technologies.com for further details.