High powers need high purities: The current development of high-power lasers calls for better quality assessment of optical materials for high-power applications and sensitive methods.

Photothermal methods like common-path interferometry (PCI) are used to measure and secure the performance and quality of optical materials and coatings. PCI is based on a pump-probe-technique: A strong continuous-wave (cw) pump beam is focused into the sample, heating it locally due to light absorption. The resulting local change of the refractive index causes refraction and diffraction effects on the crossing probe beam.

 Tunable pump lasers provide new measurement options

Traditionally, high-sensitivity absorption measurements are performed at the fixed wavelengths of high-power lasers, since these are the most relevant ones for such optical components. Fraunhofer IPM goes one step further by combining PCI with in-house developed cw optical parametric oscillators (OPO) as pump lasers. This way, absorption spectra of materials and components to cover large wavelength ranges can be provided.

 Your benefits

Combining high sensitivity and tunable pump sources results in two benefits:
Utilizing the tunability of the OPOs by Fraunhofer IPM, medium-strength absorption features present in the sample, e.g. OH absorption in fused silica, may be recorded with the PCI spectrometer and used for an absolute calibration of the absorption measurement if “new” materials are to be analyzed.

In material and technology development, recording the absorption spectra may assist to identify process-related impurities which limit the performance of the material.  

Fraunhofer IPM offers absorption measurements as a service as well as turn-key systems tailored to the customers needs.