Integrating sphere

Abstract: We reevaluate the absolute fluorescence and phosphorescence quantum yields of standard solutions by using a novel instrument developed for measuring the absolute emission quantum yields of solutions. The instrument consists of an integrating sphere equipped with a monochromatized Xe arc lamp as the light source and a multichannel spectrometer. By using a back-thinned CCD (BT-CCD) as the detector, the sensitivity for spectral detection in both the short and long wavelength regions is greatly improved compared with that of an optical detection system that uses a conventional photodetector. Using this instrument, we reevaluate the absolute fluorescence quantum yields (Φf) of some commonly used fluorescence standard solutions by taking into account the effect of reabsorption/reemission. The value of Φf for 5 × 10−3 M quinine bisulfate in 1 N H2SO4 is measured to be 0.52, which is in good agreement with the value (0.508) obtained by Melhuish by using a modified Vavilov method. In contrast, the value of Φf for 1.0 × 10−5 M quinine bisulfate in 1 N H2SO4, which is one of the most commonly used standards in quantum yield measurements based on the relative method, is measured to be 0.60. This value is significantly larger than Melhuish’s value (0.546), which was estimated by extrapolating the value of Φf for 5 × 10−3 M quinine bisulfate solution to infinite dilution using the self-quenching constant. The fluorescence quantum yield of 9,10-diphenylanthracene in cyclohexane is measured to be 0.97. This system can also be used to determine the phosphorescence quantum yields (Φp) of metal complexes that emit phosphorescence in the near-infrared region: the values of Φp for [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) are estimated to be 0.063 in water and 0.095 in acetonitrile under deaerated conditions at 298 K, while that in aerated water, which is frequently used as a luminescent reference in biological studies, is reevaluated to be 0.040.

Abstract: The absorption and transport scattering coefficients of caucasian and negroid dermis, subdermal fat and muscle have been measured for all wavelengths between 620 and 1000 nm. Samples of tissue 2 mm thick were measured ex vivo to determine their reflectance and transmittance. A Monte Carlo model of the measurement system and light transport in tissue was then used to recover the optical coefficients. The sample reflectance and transmittance were measured using a single integrating sphere 'comparison' method. This has the advantage over conventional double-sphere techniques in that no corrections are required for sphere properties, and so measurements sufficiently accurate to recover the absorption coefficient reliably could be made. The optical properties of caucasian dermis were found to be approximately twice those of the underlying fat layer. At 633 nm, the mean optical properties over 12 samples were 0.033 mm(-1) and 0.013 mm(-1) for absorption coefficient and 2.73 mm(-1) and 1.26 mm(-1) for transport scattering coefficient for caucasian dermis and the underlying fat layer respectively. The transport scattering coefficient for all biological samples showed a monotonic decrease with increasing wavelength. The method was calibrated using solid tissue phantoms and by comparison with a temporally resolved technique.

Abstract: In this paper we present the absorption coefficient mu(a) and the isotropic scattering coefficient mu(s)(') for 22 human skin samples measured using a double integrating sphere apparatus in the wavelength range of 1000-2200 nm These in vitro results show that values for mua) follow 70% of the absorption coefficient of water and values for mu(s)(') range from 3 to 16 cm(-1) From the measured optical properties, it was found that a 2% Intralipid solution provides a suitable skin tissue phantom

Abstract: The optical absorption and scattering coefficients have been determined for specimens of normal and diseased human breast tissues over the range of wavelengths from 500 to 1100 nm. Total attenuation coefficients were measured for thin slices of tissue cut on a microtome. The diffuse reflectance and transmittance were measured for 1.0 mm thick samples of these tissues, using standard integrating sphere techniques. Monte Carlo simulations were performed to derive the scattering and absorption coefficients, as well as the mean cosine of the scattering angle. The results indicate that scatter exceeds absorption by at least two orders of magnitude. Absorption is most significant at wavelengths below 600 nm. The scattering coefficients lie in the range 30-90 mm-1 at 500 nm, and fall smoothly with increasing wavelength to between 10 and 50 mm-1 at 1100 nm. The scattering coefficient for adipose tissue differs, in that it is invariant with wavelength over this spectral range. For all tissues examined, the scattered light is highly forward peaked, with the mean cosine of the scattering angle in the range 0.945-0.985. Systematic differences between the optical properties of some tissue types are demonstrated.