Investigation Of MWIR Radiance Calibration Based On Parametric Down-conversion

The calibration of high precision infrared radiance belongs to the radiometry, and has been one of basic technique in the radiometric calibration field. Primary standard and transfer chain of standard are needed by the conventional methods in infrared radiometric calibration.In this paper, a new method of radiance calibration based on the parametric down-conversion is introduced. This new type of calibration mode does not depend on external primary standard and standard transfe chain, both of which two points also limits the accuracy of traditional calibration method. What’s more, radiance measurement made with this new method based on the parametric down-conversion is realized by the measurement of the average number of photons per mode, which doesn’t need any knowledge of geometrical factor such as the solid angle and the acreage of the source, decreasing the possible uncertainty sources. From this point of view, this new method has higher accuracy compared with the traditional calibration method.Based on the investigation of the application of parametric down-conversion in the metrology as well as its present development, the system of middle infrared radiance calibration was established. A high power CW laser at 532nm was used to pump a PPLN nonlinear crystal, producing correlated photons pairs at wavelengths of VIS-IR (631nm and 3390nm). According to the characteristics of nonlinear crystal, satisfied the quasi-phase matching (QPM) manner and the propagation direction of IR-VIS correlated photons keep the same as the pump beam. In the output light path, the signal down-conversion photons are separated from the residual pump laser and IR laser by using a dichroic mirror to reflect the visible photons to another direction vertical its original propagation, a cut off filter and an interference passband filter were used to attenuate the pump beam and other background light. On both the spontaneous down-conversion and stimulated down-conversion the signal phontons average number of photons per mode can be measured, and the radiance of the middle infrared radiance source(OPO 3390nm) can be calculated. In the experiment the power of the pump power and the source of infrared radiation were 17mW and 1.48mW, the experimental results and the estimated results are in the same order of magnitude by using the traditional method, and the relative standard deviation of two methods is 4.22%.The results showed that relative combined uncertainties of a OPO laser at 3390nm was better than 1.18%. Calculate water bath blackbody temperature of five points of radial values use this theory, and Planck formula will inversion the actual temperature, the deviation of the inversion temperature compared with the preset temperature was 5.17%.The two experimental results proved the feasibility of radiance calibration of the infrared radiation by detecting the photon counting in the visible band. The results of the study were expected to be used in the field of high precision calibration of infrared band based on stimulated parametric down-conversion and infrared OPO laser and other fields.