Specular Reflection Of Light Research Articles

Reflective properties of natural snow: approximate asymptotic theory versus in situ measurements

Results of measurements of the bidirectional reflection function of snow for the solar zenith angle close to 54/spl deg/ are compared with a recently developed snow optical model based on the representation of snow grains as fractal particles. The model has a high accuracy out of the principal plane for the observation zenith angles smaller than 60/spl deg/. However, the accuracy is reduced in the principal plane. Specular light reflection by partially oriented snow plates on the snow surface not accounted for by the model can play a role for measurements in the principal plane. The model discussed can be used for the grain size retrieval using both ground and spaceborne measurements of the snow reflectance. This is supported by a high accuracy of the model in a broad spectral range 545-2120 nm as demonstrated in this work.

Resonance optical spectroscopy of long-period quantum-well structures

Theory of specular light reflection from long-period quantum-well structures taking into account the exciton contribution to dielectric polarization has been developed for an arbitrary relation between the background refractive index in the well, n a, and barrier-material refractive index nb. General expressions for the optical reflection and transmission coefficients for a structure with N equidistant quantum wells are derived with the use of the Green’s function and transfer matrix methods. Normal and oblique light reflectance spectra from II-VI-based heterostructures were found to reveal a bright interference pattern caused by the difference between n a and n b. A comparison of the theory with experiment has yielded the dispersion of n a and n b within a broad wavelength range and the parameters of the quasi-two-dimensional heavyhole exciton (e1-hh1), namely, the resonant frequency and the radiative and nonradiative damping rates. Reflectance spectra from resonant Bragg and quasi-Bragg structures with real exciton parameters are calculated, and the effect on these spectra of the refractive-index difference and the deviation from the Bragg condition is analyzed.

Properties and application of luster pigments

AbstractIn contrast to conventional pigments, which interact with light by absorption and/or diffuse scattering, effect or luster pigments show optical properties that are due to specular reflection of light by aligned flaky particles. Their main property is goniochromaticity, i.e. the change of lightness and/or color hue with the viewing angle of the observer. The paper describes the different type of luster pigments, their optical properties and applications and manufacturing methods.

Light reflection from a naturally optically active birefringent medium

The measurement of natural optical activity by means of specular light reflection can provide an alternative method for spectroscopy of chiral materials that is in some cases (e.g., for thin films and opaque materials) more advantageous than current methods based on light transmission. The Fresnel amplitudes for specular reflection of light from a naturally chiral, birefringent medium are derived on the basis of a theory that takes account of spatial dispersion in both the electric and the magnetic material relations. Previous derivations neglecting the light-induced magnetization result in Fresnel amplitudes that violate the law of energy conservation (Poynting’s theorem). The differential reflection of left- and right-circularly polarized light by chiral uniaxial media is examined as a function of angle incidence and shown to peak near Brewster’s angle. The measurement of the differential circular reflection may possibly be best accomplished by photoelastic modulation of the probe-beam polarization followed by synchronous detection; the experimental prospect for achieving this is discussed.

Experimental configurations using optical phase modulation to measure chiral asymmetries in light specularly reflected from a naturally gyrotropic medium

Chirally asymmetric responses of a gyrotropic medium to left and right circularly polarized light as manifested in specular light reflection are systematically identified and interpreted. Experimental configurations using one or more photoelastic modulators and synchronous detection are described, by means of which the chiral asymmetries should be measurable with a sensitivity comparable with that of light-transmission techniques. Measurement of these chiral asymmetries would (a) provide experimental tests of recently proposed Fresnel scattering amplitudes for isotropic chiral media and (b) open up new spectroscopic possibilities for the investigation of nontransparent gyrotropic media.

Optical properties and structure of drawn polyethyleneterephtalate-polyethylene films

Films made by coextrusion of polyethyleneterephtalate and low density polyethylene exhibit specular reflection of light when stretched. Unlike the behaviour of films made of pure PET, where specular reflection is rare and does occur at extremely high stretching rates only, PET/LDPE films show specular reflection independent of the stretching rate. A film, containing 70% PET and 30% LDPE, prepared by coextrusion of the two components, has been investigated by scanning electron microscopy, light microscopy and by measuring the optical properties with a spectrophotometer. The (unstretched) „as prepared“ sample has been compared with a sample stretched to λ=4. The optical measurements show as a result of the stretching a strong decrease of the transmittance and an increase of the remittance. While there is no drastic change of the dispersion (which is only slight), the increase of the refractive index indicates some straininduced crystallization. The scanning electron micrographs show long, needlelike voids and indicate a fractionation of the two components as a result of the stretching. This fractionation has been investigated by heating the samples up under the light microscope: while the stretched sample shows a separation of the components, the unstretched sample does not.

Scanning techniques in grey-scale ultrasonography.

In the past two years the technological basis of ultrasonic diagnosis has developed rapidly in the direction of grey-scale imaging. Hitherto ultrasonic imaging has been directed primarily at twodimensional display of the relatively large ultrasonic echoes that are returned by major organ interfaces: the new development aims at displaying, in addition, the relatively weak echoes that arise from the fine structure of tissues themselves. Such a technique results in the visualization of the consistency of the organ rather than its mere outline. This permits differential diagnosis of diffuse pathologies which are recognized by the specific pattern produced by each pathological process. Thus, in liver for example, the appearances of fatty infiltration, cirrhosis, diffuse lymphocytic infiltration, malignant infiltration, chronic inflammatory changes and viral hepatitis may be separately differentiated. There is an important practical implication of this new approach, which arises from the process by which the echoes are caused. Echoes from major organ interfaces, such as the fetal skull, appear to result from a process akin to specular reflection of light and are thus seen most efficiently where the ultrasonic beam strikes the interface at normal incidence, and it is this concept that has given rise to the technique of “compound scanning”, in which an attempt is made to angle the transducer so as to find the maximum echo (Donald, McVicar and Brown, 1958).

Studies of adsorbed states at the electrode/electrolyte interface by specular reflection of light

The reflection of light from an electrode surface was investigated using a multiple-reflection and a single-reflection cell. The single-reflection studies were combined with a modulation of the reflectivity of the interface. The potential drop across the electrolytic double layer was modulated. The electro-reflection technique enables one to investigate the adsorbed layer without interference by light absorption in the electrolyte. Results are reported for the adsorption of methylene blue on a platinum electrode.

Reflection of Light from Filmed Rough Surface: Determination of Film Thickness and rms Roughness

The specular reflection of light from non-conducting slightly random surfaces which are uniformly or partially filmed, is investigated in a statistical manner. The film is assumed to be thin, transparent and uniform in thickness. Two possible methods for determining its thickness d, rms roughness σ and, if necessary, refractive index are introduced. One method uses the minima of specular reflectance curves near the Brewster angle and the other uses the reflectance values directly. The latter can apply only up to σ/λ=0.025, where λ is wavelength, owing to the effect of diffuse reflection. The former is almost free from this effect, does not require the absolute value of reflectance and enables one to discriminate whether the surface is filmed uniformly or partially.

Colors Produced by Reflection at Grazing Incidence from Rough Surfaces*

Using a precision spectrometer with a photomultiplier attached to its telescope, the specular reflection of light from various rough surfaces was measured at angles of incidence in the region 80° to 89°. Seven interference filters were used to isolate spectral bands covering the visible spectrum. From the measured values of reflectance the chromaticity of the specularly reflected light was computed, assuming CIE source “A” for the incident light. It was found that at all angles the resulting colors lay in a narrow region near the Planckian locus, being more reddish than the incident light. The maximum redness was found at an angle where the specular reflectance had already become small. It is shown to be likely that if the specularly reflected light could be isolated the surface would form an accurate means of reducing color temperature.