Increasing requirements for the accuracy of infrared radiation measurements require the use of tuneable laser radiation to calibrate IR radiation detectors. In the development of appropriate laser systems, PTB applies a combination of latest laser technology and non-linear optics. This set-up has demonstrated the very efficient generation of pulsed IR radiation which is tuneable in the wavelength range from 0.7 µm to 2 µm.
To an increasing extent measurement procedures exploiting IR radiation are not only used in telecommunications, but also in industrial process control and monitoring, in medical diagnostics, climatology, for the exploration of raw materials as well as in global and local environmental protection. Commensurately, the accuracy requirements for calibrations are increasing as well. In the medium term it will no longer be possible to meet these requirements with mono-chromatized thermal IR radiation of low spectral intensity. Laser radiation will be required which has so far been available only for single wavelengths or narrowly limited wavelength ranges.
Within the scope of a project promoted by the Federal Ministry of Economics and Labour (BMWA), PTB has therefore started to develop laser systems to generate tuneable monochromatic radiation over the entire IR range up to 10 µm wavelengths. In this project, the first important success has now been achieved: the prototype of a signal-resonant optical parametric oscillator (OPO) allowed tuneable radiation in the near infrared from 700 nm to 980 nm and from 1080 nm to 2000 nm to be generated with a conversion efficiency of approximately 20 %. Pump light source for the OPO was a pulsed Yb:YAG disk laser with frequency doubling developed in cooperation with Spectra-Physics GmbH. A procedure has been developed at PTB which enables longitudinal single-mode operation of this laser and a patent application has been filed.
This unique combination of latest laser technology and non-linear optics provides the basis to generate monochromatic infrared radiation up to 10 µm as aspired. In the next step it is to be demonstrated that the procedure can also generate continuous IR radiation with a continuously (cw-) pump laser.