Kostkowski, Appl. Opt. 5, No. 12, p. 1959 Mar. 4-6, 1964, pp. 141-145 (NASA SP-55, 1965 Further refinement of this value cannot be expected to affect the results of future radiometric work. 3-217The 6-220The New Cavity DetectorThe nearest approach to a spectrally "flat" detector is the new cavity or "blackbody" The first possibility mentioned above, namely, the failure of the blackness to be independent of wavelength, has been partially checked in a few instances. The specularly reflected component has been found small by several investigators,'^'" but the determination of the total scattered radiation from such blacks has not been previously undertaken in the vacuum ultraviolet. The energy loss due to photoejected electrons had apparently been overlooked previous to the initiation of the present study, although it is well known that most surfaces exhibit a marked increase in photoelectric yield when the photon energy exceeds 9-10 eV.''^' ' The present studies were conducted using a particu- Th« ordinate is the ratio of the scattered intensity at angle e to the incident beam intensity.C. ResultsThe samples of gold-black measured in these experiments were prepared by a thermopile manufacturer (C. Reeder) and are typical of the blacks used on thermopiles for the far ultraviolet. As a preliminary check of the scatter-measuring apparatus, a highly polished sample of silica was studied.The angular distribution of the reflected beam from the sample closely followed the distribution of the direct beam, thus indicating that the highly polished flat did not scatter appreciably at X584 A, and that the measuring apparatus was not recording unwanted scatteredlight signals. the thinner of the two gold-black samples (presumably identical to that used on the thermopile tested in Sees. Ill and IV). In Fig. 2, two scans are shown, the difference between them being a 90°rotation of the scattering sample about the incident beam axis. The difference between the two curves indicates some anisotropy in the angular scattering by the gold-black. Also shown in Fig. 2 The specular component of the reflectively scattered radiation was absent in the heavier gold-black-on-gold sample tested, as can be seen in Fig. 3, where the distributions are plotted for the same three wavelengths in the far ultraviolet. It can be seen that the scattering loss increases slightly with decreasing wavelength which may reflect the changing ratio of wavelength-toparticle size of the gold-black. The integrated total scattering for this heavier black was 2.1% at X584 A, 2.0% at X1025 A, and 1.9% at X1216 A.These same two samples of gold-black-on-gold were tested for total scattering in the visible and near infrared spectral regions using an integrating sphere and an appropriate spectrophotometer.The thin sample showed a total scatter of 1.6-3.1 (±0.5)% and the thicker sample 1.5-2.9 (±0.5)% over the region 0.4 m to 2.2 IX.Thus, while reflective scattering is a nonnegligible loss for thermopile blacks, it would seem that the similarity of thi...
Ultra-short pulsed lasers are known for their ability to precisely machine materials including human hard and soft tissues while minimizing the amount of thermal energy deposited to the surroundings. Non-thermal ablation produced by ultra-short pulsed lasers in the femtosecond to picosecond range is very effective for dental applications. As shown in Figure 1, most decay occurs in the dentin, which is found between the outer surface (enamel) and the inner region containing the nerve endings (pulp) [1]. Caries removal and the preparation of cavities in dentistry are primarily performed by the use of mechanical drills. The current techniques are invasive and cause patient discomfort. Due to the vibrations of the drills it is necessary to use local anesthetic for the majority of dental procedures. A continuous water spray is used in conjunction with the drills to balance the temperature rise produced by mechanical vibrations. Drills are somewhat limited in precision causing a large amount of healthy tooth to be lost during any restoration process. Replacing a multitude of mechanical tools with one non-invasive, accurate and painless laser treatment will be a huge advancement to the current dental techniques.
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