The optical power calibrator was built for use with the THIAX emissive detector array during its development. This is a detector of pure thermal radiation from the surface of a black body or a source of stratospheric ozone, allowing calibration of the differential gain of active- and passive-sample detectors of the array. The calibration technique is based on the materials and geometric factors characteristic of the active sample be it a fix-position black body or an ozone source. The calibrator can also be used to measure the absolute response of the array as a function of wavelength. Data for a range of temperatures, pressures, and window positions for a multi-window passive-sample detector performing this measurement are presented. This is compared with a similar measurement obtained using a double-beam grating spectro-radiometer, and the results are excellent. The same measurement is obtained using a total-black-body optical radiometer developed to support THIAX.
Mechanical anisotropic Fabry-Perot interferometry (FAI) is a direct optical technique for high accuracy generation of high-quality spectral interference fringes. The fringe quality is determined by the angle of the optical system relative to the incident radiation. Departures from the ideal situation cause first- or second-order aberrations. One of the most important parameter determining the maximum resolution of the interferometer is the acceptance angle: it is the minimum angle between the optical axis of the instrument and the incident radiation. As a rule of thumb for FAI, the acceptance angle (in radians) has to be less than 1·10-3 times the wavelength of the system. Modification of the instrument geometry can reduce the accepted angle, but a more efficient approach for maximum resolution can be achieved with the selection of radiation with minimum spatial directions or a suitable modulation of the optical path length. Here we describe a different approach that allows the achieved fringe visibility to be limited to a minimum independent of the wavelength: the groove profile is periodically updated in the Fourier domain, effectively “limiting” the working angular range of the instrument. d2c66b5586