2.7～3.0μm波段高反镜反射率测量研究OACSTPCD

The highly reflective(HR)mirrors with high-performance are widely employed in mid-infrared(mid-IR)laser systems.The manufacturing of mid-IR HR mirrors with high reflectivity requires techniques to precisely measure their high reflectivity.In this paper,a continuous-wave cavity ring-down(CRD)experimental apparatus in the 2.7-3.0 μm spectral range is established based on a quantum-cascade laser for high reflectivity measurement.By precisely optimizing the laser wavelength within the reflection band of the mid-IR HR mirrors,analyzing the influence of water vapor absorption on the ring-down time and reflectivity measurements,and comparing the reflectivity results measured under ambient air in clean-room laboratory and under nitrogen purging,the accurate measurement of high reflectivity is achieved at the 2.7-3.0 μm spectral band with an absolute reflectivity measurement accuracy of below 2×10-5 for about 99.95%reflectivity.The experimental results demonstrate that by setting the laser wavelength precisely to 2.9 μm and employing equal lengths of initial and test ring-down cavities(RDC)to avoid the influence of water vapor's absorption lines,the reflectivity measurement for the 2.7-3.0 μm spectral band can be performed under normal clean-room laboratory air,without the need of nitrogen purging.