Development of detectors and calibration methods for spectral irradiance and radiometric temperature measurements

Abstract

The research work, described in this thesis, has been carried out at the Metrology Research Institute of Helsinki University of Technology between 2000 and 2005. The research focused on the development of new detectors, calibration methods and their applications in optical radiometry.

A new photodetector, which is based on three GaAsP Schottky-barrier photodiodes, has been introduced. The spectral properties of the GaAsP trap detector have been studied in the wavelength range between 200 nm and 600 nm. Spectral reflectance of a single windowless GaAsP photodiode, measured with high-accuracy gonioreflectometer, has been presented. Based on these measurements, the internal quantum efficiencies for both the single photodiode and the trap detector have been calculated.

A novel scanning method for characterization of filter radiometers, which uses a wavelength tuneable Ti:Sapphire laser source, has been described. High accuracy calibration of filter radiometers at 900 nm has been conducted. The results have been compared to the spectral irradiance responsivities measured with the more conventional monochromator-based method.

Both the laser-based method and the monochromator-based method have been used for characterization of the detectors for radiometric measurements of the thermodynamic temperatures of several blackbodies in irradiance mode. Four filter radiometers with central wavelengths between 600 nm and 900 nm have been used. The measured temperatures include the freezing temperature of silver and copper, which are defined by the International Temperature Scale of 1990.