March 2015
Spotlight Summary by Ilya Shadrivov
Optical diffraction properties of multimicrogratings
Diffraction gratings are known to most of us from school, and they fascinate everyone with the colorful rainbows they can produce. Researchers in the United States used recent advances in nano-fabrication as well as a clever design to engineer “super” diffraction gratings that can actually make our life safer.
A diffraction grating is a periodically structured surface, and interference of the waves reflected by or transmitted through the grating produces interesting patterns that can give us some information about the underlying periodic structure or about the incident light. Diffraction gratings are used in spectrometers, pulse compressors and other light manipulating and analyzing devices. The phenomenon of diffraction is common to waves of different natures and of different scales; for example, it is used in crystallography, where the crystalline structure of solids is studied by observing the diffraction of X-rays. Diffraction itself depends on the type of periodicity, including the period of the structural elements, and their reflective or transmissive properties. Diffraction is strongly wavelength-dependent. That is why we see white light split into a rainbow after passing through a grating. The symmetry of the grating defines the pattern of the diffracted light. For example, simple linear grating made of parallel stripes produces diffraction with the spots along the line that is perpendicular to the stripes of the grating. A hexagonal pattern produces diffraction along three crossing lines which are at 120 degrees with respect to each other.
The authors of this work used nano-fabrication techniques to make a “multi-micrograting”. Imagine a structure that is made of small linear gratings which are cut into hexagonal patches and placed together in a honeycomb lattice at various angles. The process involves some state-of-the-art fabrication that can create large area structures with 1μm feature sizes. The diffraction pattern produced by this structure is quite remarkable. It has contributions due to the several periodicities in the structure: linear gratings, hexagonal pattern, and oblique crystalline structure of hexagonal cells with different orientation of the linear patterns. The diffraction pattern has fine features which are produced due to the larger physical periodicity in the grating, while larger features in the pattern are produced by the finest linear gratings.
While other applications of these gratings are yet to be demonstrated, it is quite fascinating that they can be used as stress sensors. Imagine that one were to put such a grating on an airplane structure under high stress areas. If the structure is wearing out, the accumulated deformation of the materials will transfer to the diffraction grating, which will become distorted. Since the diffraction pattern depends strongly on the size of the grating components, an inspection with a relatively simple camera setup will reveal the scale of the deformation. This would allow for non-invasive diagnostics of crucial structural elements of airplanes and other devices that can actually pinpoint the strength of deformations in different directions.
You must log in to add comments.
A diffraction grating is a periodically structured surface, and interference of the waves reflected by or transmitted through the grating produces interesting patterns that can give us some information about the underlying periodic structure or about the incident light. Diffraction gratings are used in spectrometers, pulse compressors and other light manipulating and analyzing devices. The phenomenon of diffraction is common to waves of different natures and of different scales; for example, it is used in crystallography, where the crystalline structure of solids is studied by observing the diffraction of X-rays. Diffraction itself depends on the type of periodicity, including the period of the structural elements, and their reflective or transmissive properties. Diffraction is strongly wavelength-dependent. That is why we see white light split into a rainbow after passing through a grating. The symmetry of the grating defines the pattern of the diffracted light. For example, simple linear grating made of parallel stripes produces diffraction with the spots along the line that is perpendicular to the stripes of the grating. A hexagonal pattern produces diffraction along three crossing lines which are at 120 degrees with respect to each other.
The authors of this work used nano-fabrication techniques to make a “multi-micrograting”. Imagine a structure that is made of small linear gratings which are cut into hexagonal patches and placed together in a honeycomb lattice at various angles. The process involves some state-of-the-art fabrication that can create large area structures with 1μm feature sizes. The diffraction pattern produced by this structure is quite remarkable. It has contributions due to the several periodicities in the structure: linear gratings, hexagonal pattern, and oblique crystalline structure of hexagonal cells with different orientation of the linear patterns. The diffraction pattern has fine features which are produced due to the larger physical periodicity in the grating, while larger features in the pattern are produced by the finest linear gratings.
While other applications of these gratings are yet to be demonstrated, it is quite fascinating that they can be used as stress sensors. Imagine that one were to put such a grating on an airplane structure under high stress areas. If the structure is wearing out, the accumulated deformation of the materials will transfer to the diffraction grating, which will become distorted. Since the diffraction pattern depends strongly on the size of the grating components, an inspection with a relatively simple camera setup will reveal the scale of the deformation. This would allow for non-invasive diagnostics of crucial structural elements of airplanes and other devices that can actually pinpoint the strength of deformations in different directions.
Add Comment
You must log in to add comments.
Article Information
Optical diffraction properties of multimicrogratings
Christian A. Rothenbach, Ivan I. Kravchenko, and Mool C. Gupta
Appl. Opt. 54(7) 1808-1818 (2015) View: Abstract | HTML | PDF