<title>Scatter Measurements On LAK9 And SF1 Glasses At 0.915 µm</title>

Abstract

Scatter measurements on LAK9 and SF1 glasses at 0.915 pmWilliam L. Wolfe, John E. Hubbs and Frederick O. BartellOptical Sciences Center, University of Arizona, Tucson, AZ 85721AbstractMeasurements of two refractive samples were made at 0.915 pm of the BRDF to angles asclose as 3° from specular. The data fit a one -dimensional power spectrum using vectorelectromagnetic theory. The autocorrelation length and its error were estimated and fromthese a most probable value and upper bound of the BRDF at 1° from specular were determined.IntroductionThe reflected scatter from transmitting optical elements is sometimes of importance inthe reduction of stray light through an optical system. We had occasion to make such mea-surements for the Perkin -Elmer Corporation for one of their instruments. The results con-cerning the smoothness of the samples are interesting, but we find the implications concern-ing theory and technique to be more exciting.Statement of the problemBriefly stated, the problem was to measure the bidirectional reflectance distributionfunction (BRDF) at the diode wavelength (0.915 pm) and within about 1° of the speculardirection. The problems would surely be that of getting undue influence from the instrumen-tal scatter itself. The problems of replacing one of our standard lasers' with the diodeseemed to be relatively easy.The instrument profileThe background scatter of our instrument near the specular direction results from thescattering of the primary mirror. The diode laser flux is collected by a lens, shownthrough a pinhole for cleanup and collimated. The collimated beam passes through a chopperand attenuators and reaches an off -axis parabola. This element again focuses the beamthrough a pinhole and onto an F /40 sphere of about 3 in. diameter. The focal point of thesphere is at the detector assembly. The geometry of the mirror, the sample and the detec-tor are shown in Fig. 1. The mirror is labeled M; it is at a distance L from the sample,which is designated S. The detector D is at a distance R from the center of the sample,about which it rotates as a center. The angle 8 is the scatter angle. This geometry isshown for the transmission case, but it applies equally well for an unfolded reflection