Analysis of Optical Surface and Coating Properties

Our Services

Light scattering caused by imperfections of optical components can critically affect the performance of optical systems. Even high-quality optical components exhibit some level of light scattering leading to optical losses, image degradation, and straylight. Detailed knowledge of the scattering properties is therefore essential for quality control and performance predictions.

While Total Scattering (TS) provides a simple number for the scattering loss of an optical component, Angle Resolved Scattering (ARS/Bidirectional Scattering Distribution Function (BSDF)) provides more detailed information about the angular distribution of the scattered light. It is therefore a powerful tool for analyzing the scattering origins with applications for a variety of optical components - from polished and coated surfaces to nano- and microstructures or diffraction gratings.

Depending on the final application and the characteristics of the sample to be analyzed, measuring light scattering can be a challenging task and requires careful considerations and planning. We have over 30 years of experience in performing high-quality scattered light measurements in various scenarios, enabling the quantification and modeling of scattered light in a broad spectral range - from DUV to visible and IR.

Fraunhofer IOF is specialized in analyzing various optical problems, finding the right measurement strategy to balance gain of information and effort, performing high-quality light scattering measurements, and interpreting the results to support your development.

We offer:

• Perform high-quality light scattering measurements
• Determination of total scattering losses, identification of inhomogeneities, anisotropies, etc.
• Model light scattering of surfaces, layers and optical materials based on the analysis of surface roughness and vice versa
• Link light scattering properties to surface imperfections (roughness, defects, sub-surface damage, etc.), manufacturing processes, optical and coating design, and functional properties (wetting, laser stability, etc.)
• Development of customer-specific measurement systems for your characterization tasks

Parameters:

• ARS or BSDF according to ISO 19986 or SEMI/ASTM1392
• TS according to ISO 13696
• Reflectance, transmittance, diffraction efficiency
• Wavelengths from DUV (193 nm) to IR (10.6 µm)
• Highest sensitivity, high dynamic range (BSDF < 10-8 sr^-1 in VIS/NIR)

Customized Light Scattering Measurement Systems
In addition to measurements with our in-house developed laboratory systems, we offer the development of customized measuring systems and compact sensors that can be used on your premises and even directly in production processes.

Across many application areas - from laser material processing to quantum technology and space travel - new developments require lower and lower light absorption in optical components. We address your demands for absolute absorption measurements in optical materials and thin films over a wide wavelength range from the deep UV to the infrared. Our LID (laser induced deflection) technique uniquely combines photothermal measurements with electrical calibration for reliable absolute absorption data.

We offer:

• Customized measurement services for direct determination and analysis of absorption in various optical materials and coatings
• Customized measurement system developments for your application

Parameters:

• Highest sensitivity (sub ppm level)
• Reliable absolute calibration
• Adapted measurement concepts for different sample geometries
• No laser/wavelength restrictions (pulsed and cw light sources, DUV-IR spectral range)
• Bulk materials / layers / fibers

​ With our specially developed measurement concepts, we can tackle challenges that are difficult to solve with other approaches, such as the sensitive measurement of materials with low photothermal responses and the analysis  of non-transparent materials in the visible range.

Optical performance is a key quality feature for optical components and coatings. Understanding the underlying optical parameters and constants (R, T, n, k, etc.) is therefore crucial for development and optimization. From broadband anti-reflective properties to ultra-high reflective laser mirrors each application highlights distinct challenges that demand customized metrology solutions. With our broad portfolio of measurement and analysis methods, we select the optimum approach and adapt the measurement program to your specific needs:

• We use spectrophotometers to determine reflection and transmission properties over a broad wavelength range. The VN-accessories specially developed at Fraunhofer IOF allow reflectance and transmittance measurements with an identical measuring spot on the sample.
• For extremely low-loss mirrors with a reflectance of more than 99.9%, which can no longer be achieved with standard reflectance measurements such as spectrophotometry, we use cavity ring-down (CRD) technology. This enables highly accurate reflectance measurements of 99.99% or even 99.999%.
• Using ellipsometry, optical layer constants such as the refractive index n, absorption coefficient k, layer thickness or phase shift can be determined spectrally or spatially resolved.

We offer:

• Customized measurement and analysis services (spectral R/T measurements, highly sensitive reflectance measurements, determination of optical constants, layer thickness, thermal and vacuum shift, phase shift)
• Development of VN-accessories for spectrophotometry (e.g. for the GPOB from Perkin Elmer for angles of incidence of 6° and 45°)
• Development of customized CRD measurement systems

Parameters:
Spectrophotometry

• Absolute R/T measurement  at variable angles of incidence (T: 0° - 89°, R: 5.1° - 85°), spectral range 200-2500 nm
• Measurements on curved and small surfaces with the microspectrometer (measuring spot 17-70 µm)
• FTIR spectrophotometry with an extended measuring range in the IR (spectral range 1.3 - 25 µm)

Cavity Ring Down

• Reflectance values > 99.999 %
• Measurements on samples up to 2" in size at perpendicular incidence and/or 10° - 45°
• Wavelength range: 355 - 1550 nm

Ellipsometry

• Measurement at variable angles in the spectral range 200-2500 nm
• Imaging ellipsometry in the spectral range 360 nm - 1000 nm, lateral resolution < 1 µm