Make Absolute Measurements
The VN optical design for making absolute reflectance measurements means much smaller losses than competing VW designs because it requires only one bounce off the sample surface, rather than two. This makes it the ideal solution for measuring low reflectance surfaces such as anti-reflective coatings (AR coatings) and small mirrors or coated samples.
Featuring a near normal 10 degree angle of incidence, the VN accessory can be used for absolute measurements of anti-reflective coatings, multilayer coatings, multilayer dielectric coatings, thin films and laser mirrors. Each mirrored optical surface of the VN accessory is over-coated with magnesium fluoride for enhanced performance in the UV region and maximum reflectivity for the lifetime of the accessory.
Eliminate Reflectance Standards
Unlike relative designs, the Evolution VN does not require an expensive calibrated specular standard to obtain absolute measurements. Removing the need for a calibrated standard also means that your data are not subject to the stated uncertainties in the standard data. There is no worry over potential damage to the standard or semi-annual expense and/or downtime to have the standard re-calibrated.
The VN accessory data is absolute because the optical paths and components are identical between the reference and sample scans except for the presence of the test reflector in the N-position for the sample scan.
Analyze Small Samples
With the Evolution VN accessory, light bounces off the sample surface once, allowing smaller samples to be measured. Any sample greater than 10mm in diameter can be measured. The single bounce design of the VN means you can easily measure many different areas of a larger sample to test the homogeneous nature of your sample surface.
High Performance for Low Reflectance Samples
The measurement accuracy of low reflectance samples such as anti-reflective coatings or solar cell overlays can be limited by the VW design of absolute SRA offered by some other manufacturers. Two bounces on the surface of the anti-reflective coating using the VW design mean that the beam is attenuated twice. A coating with a reflectance of 0.1% thus returns energy equivalent to a transmittance of 0.0001%T (an absorbance of 6A) to the detector. This is beyond the measurement range for many spectrophotometers. The VN design of the Thermo Scientific accessory means that 0.1%R reads as 0.1%R (equivalent to an absorbance of 3A) which is well within the linear range of the Evolution 300.
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