Advances in thin film coating technology have made it possible to produce reflectors with very little energy loss over specific wavelength ranges. These low loss mirrors have a major application in laser cavity ring down (CRD) instrumentation. With reflectance at nearly 100% they can also be used as calibration aids in the process of standard mirror certification. The figure below shows the low loss mirrors used in calibrations by the Optical Reference Laboratory.
The calibration process uses a relative reflectance technique:
- Establish an instrument baseline (autozero) using a calibrated standard mirror in the sample beam.
- Scan the low loss mirrors relative to this baseline.
- Multiply the spectra from these scans times the known spectrum of the calibrated standard.
This should produce spectra similar to those in the figure. If the peaks of the resulting spectra are within +/- 0.1% of the 100% line (+/- 0.2% in the UV), the accuracy of the standard mirror is supported. Mirrors of unknown reflectivity may be scanned in the same sampling sequence as part of their calibration process. Please contact Optical Reference Laboratory for further details.