Magnification of conic mirror reflectometers.

Conic mirror reflectometers are used to measure the diffuse reflectance and total integrated scatter of surfaces. In spite of the long history of using conic mirrors for these purposes, the maximum magnification of the three primary types of conic mirror (hemisphere, hemiellipsoid, and dual paraboloid) had not been compared quantitatively. To our knowledge, an exact magnification formula has not been published for any of the three primary conic mirrors. The maximum magnification is needed for proper sizing of detectors and radiation sources used with reflectometers. Exact analytical expressions for the maximum magnification of a Coblentz hemisphere, a hemiellipsoid, and a dual-paraboloid mirror system are derived and compared.

Improved integrating-sphere throughput with a lens and nonimaging concentrator.

A reflectometer design utilizing an integrating sphere with a lens and nonimaging concentrator is described. Compared with previous designs where a collimator was used to restrict the detector field of view, the concentrator-lens combination significantly increases the throughput of the reflectometer. A procedure for designing lens-concentrators is given along with the results of parametric studies. The measured angular response of a lens-concentrator system is compared with ray-trace predictions and with the response of an ideal system.

Integrating sphere designs with isotropic throughput.

An ideal diffuse reflectometer can be defined as a reflectometer with a throughput which is independent of the angle of reflected radiation, as measured at the sample. For integrating spheres, effects related to the detector's field of view (FOV), the beam port, and internal baffles can result in a throughput which is nonisotropic. This paper analyzes these three sources of nonideal behavior and suggests three sphere designs using nonimaging concentrators which minimize FOV related errors. A technique for measuring the error due to the beam port is also discussed as well as ways of minimizing perturbations caused by baffles.

Reflectometer design using nonimaging optics.

A new type of two-stage reflectometer is proposed for the measurement of directional hemispherical reflectance. The proposed reflectometer consists of a primary collecting mirror coupled to a secondary mirror chosen to eliminate the Fresnel variation of the detector (or source) response. The secondary mirror shape needed is an inverted nonimaging compound parabolic concentrator (CPC). For direct mode operation, the detector is placed at the larger CPC aperture. Ray tracing of a CPC/ellipsoid reflectometer indicates that the throughput is high and isotropic. Design trade-offs and two-stage reflectometers employing a hemisphere and dual paraboloid primary are also discussed.