Ellipsoidal mirror reflectometer

Abstract

A new e llip soidal mirror re Aec to me te r is d esc rib ed, in whi c h radi a nt Au x from a n infrared mo noc hro lll a t (>I-is fo c use d on a specimen placed a t th e firs t foca l po int of th e ell ip so id a nd a th e rm o pil e d e tec tor is pla cet! at th e seco nd. Errors assoc iat ed with a n gul ar a nd a rea l variation s in se ns iti vity of th e det ector a nd wi th aberra ti o ns in th e opt ics we re largely e limin a te d thro ugh use of a s ma ll ave ragin g s ph e re pl aced ove r th e d e tector. Losses ca used by th e presc nce of th e e nt ra nee ho le in th c el lipsoidal m ir ror a nd frolll mirror abso rption we re e va lu a ted both th eoreti ca ll y a nd ex pe rim e nt a ll y. Co rrecti o ns for th ese losses pe rmitt ed abso lute re Acc ta nce to be o btain ed for bo th d iffu se and parti a ll y diffu se re Aec tin g s pecim e ns. In additi on, th e uniqu e op ti cs of th e e lli pso id a l mirro r provid e more ve rsa tilit y th an is ava il able in Ilrcv iou s re Hec to me te rs. Thi s ve rsa tilit y in c lu d es th e ab ilit y to acc ura te ly meas ure direc ti o na l-he mi s p he ri ca l, s pec ul ar, nons llec ular , and direc ti o na l-a nnul a r co ne re Aec tan ce. An a nal ys is of the acc uracy of th e in s trum e nt indi ca tes th a t an acc uracy of be tt e r th a n one pe r ce nt is poss ibl e fo r a ll e ng in ee rin g materia ls. Th e li se of th e s ulfur ave rag in g s ph e re a lso allowed the cons tru c ti o n of a s impl e acc u ra te s pec ul a r re Aec tome te r for ca li bration of th e mirror re fe re nce stand a rd s use d in th ese meas urement s.Key Words : Avera gin g sp heres, bidirect ional re fl ec t ali ce, diffu se re fl ec tance , e llipso ida l re Aee to me te r, infrared, infra re d det ec tors , re Hec tan ce . re Aee tollle te r, s pat ia l se ns itivit y, s pec tral refle c ta nce, spee ular re Aec tanc e.

A rotating cylinder method for measuring normal spectral emittance of ceramic oxide specimens from 1200 to 1600 K

“…In fact, it does not eve n exte nd down ward to roo m temperature as in di cated by th e c urves plotted in fi g ure 19. Th e roo m-tempe rature (300 O K) points we re compute d from reflectance me asure ments made with an e llipsoidal r e fl ec to me ter that meas ures a bs olu te re fl ec tance of sp ecime ns irrespective of whe ther they are spec ular, diffuse, or only partially diffu se in their refl ection behavior [24]. The s peci me ns were prepare d with the same mate rials and processing use d for the c ylinders.…”

A Laser Source Integrating Sphere for the Measurement of Directional, Hemispherical Reflectance at High Temperatures

“…An accuracy of 1% or better had been obtained previously with an ellipsoidal mirror reflectometer [ 4], but this involved quite an, elaborate correction pro- °' theoretical analysis, this integrating sphere reflectometer is capable of measuring high temperature reflectance of any material to better than 1%.…”

Flux averaging devices for the infrared.

“…This last approach is being Investigated at this time by Mitchell Finkel.1/ (d) Present Use of the Averaging Sphere in the Infrared . The author (2) has successfully used the sulfur-coated averaging sphere to improve the accuracy of the elipsoidal mirror reflectometer and to construct a simple, but acciirate, multiple-reflection, infrared, specular reflectometer. In both cases, an Increased accuracy accompanied a decrease in the required precision of optical alignment.…”

“…M. Finkel2/ has found the large area InSb detector to be similarly spatially sensitive. Thus, it is apparent that if a large area detector is to be used to accurately compare a small area beam with a large area beam (2), or to compare two beams of similar size (but smaller than the detector), it will be necessajry to use some flux averaging device. Flgvires 6 and 7 illustrate that the angular sen3itivity3/ of a ten-Junction thermopile (appendix A) is such that to accurately compare beams incident on the detector from different directions, with different solid angles, or with marginal rays exceeding an angle of 25°from the normal to the sensitive area of the detector, it will be necessary to use an averaging -device with the detector.…”

“…The reason that the change of R/Rq varies with wavelength is that the reflectance of sulfur varies with wavelength. With low sphere wall reflectance (i.e., long wavelengths for sulfur), the flux from the first reflection is a major portion of the flux in the sphere; and if the detector views even a very small amount of this flux (which is the case for large images on the spheref wall), there is a significant increase in detector response (2). This error can be eliminated by increasing the thickness of the shield shoTrfn in figure 18j however, this will reduce the efficiency of the sphere, which is intolerable, because the system is already energy limited in the 7-10 micron region when a thermopile detector is used.…”