Shaded Ring Filter

Nanoscribe's shaded ring filters (SRFs) are specially designed in order to achieve a maximal resolution in three dimensions. The axial resolution is increased by more than 28% with respect to operation without this special optic.
We push resolution to its limits: In combination with a high numerical aperture oil immersion objective with NA=1.4, 100x magnification, the SRF reveals its ultimate strength. Using the SRF in the recommended configuration reduces the ellipticity of the volume pixel (‘voxel’) by > 28%. This is essential if you plan to work at the physical boundaries of photolithography. An increased resolution in the axial direction is one key element to success at the scientific frontier – e.g., in the field of three-dimensional metamaterials or photonic crystals.
 

Figure 1: Point spread function (PSF) in the focal volume. The false color plot shows isointensity-areas with increasing intensities from blue to red. The vertical axis depicts the axial position relative to the focus (nm), the horizontal axis the lateral position relative to the focus. The left image shows the PSF without the use of a SRF, the right image the result achieved with a SRF, where the axial elongation is reduced by >28%.

Data Sheet in Brief:

The use of a SRF has following impact on the performance of a laser lithography system:

• Reduction of the ellipticity of the point spread function along the axial direction by > 28%
• The spatial filtering of the transmittance leads to an effective reduction of the laser intensity by a factor of approximately 5.5
• Necessary demands for the achievement of these specifications (along the laser beam path):
  - Oil immersion objective, NA=1.4, 100x magnification
  - Glass cover slip, 170 μm thickness
  - Suitable photoresist
  Please ask us for details and recommendations for your specific application.

Figure 2: Voxels for a specific isointensity surface. These voxels determine the basic building blocks out of which 3D structures are built up. The threshold between an insufficient and sufficient cross linking density determines the surface of the voxel in the photoresist and is determined by the PSF and the chemical response of the photoresist. After exposure to laser light and development in a developer bath the selectivity of the solvent will lead to the formation of the voxel as the basic building block.
 

Physical Principle:

The shaded ring filter consists of concentric metal rings with reduced transmittance on a glass substrate. When focusing into a photosensitive material, the spatial components of the light will contribute with different intensities. When properly designed, this leads to an improved axial resolution.

SRF Package:

The SRF package includes following components:

• Shaded ring filter
• Installation package, including mounts and installation instruction