Polaroid Sheets Research Articles

Chiral Crystallization of Ethylenediamine Sulfate

Optimized conditions for the chiral crystallization of ethylenediamine sulfate, which can serve as an ideal undergraduate experiment, are described. Large, flat, colorless crystals of ethylenediamine sulfate are obtained in an undisturbed evaporation dish within a period of approximately five to seven days. The crystals are ideal for polarimetry studies and observation using Polaroid sheets. Students become familiar with polarizing filters and how they can be used to distinguish between dextrorotatory and levorotatory crystals. Of 100 randomly sampled crystals, 47 crystals showed a (+)-rotation, while 53 crystals showed a (-)-rotation. The absolute value of the average optical rotation of the 100 crystals was found to be 158/mm ± 2 for the D line of sodium. The relative direction of rotation of polarized light was also determined by simply observing the change in optical rotatory dispersion of the crystals placed between two Polaroid sheets as one of the sheets was rotated clockwise or counter clockwise.

Cometary Polarimetry

AbstractComets are known to have a high (2-10 percent) polarization, caused mainly due to dust scattering and resonance fluorescence emission. Since near earth comets are generally bright (integrated visual magnitudes of 10 or even brighter) and as they show high polarization near earth-sun location, one can try to perform imaging polarimetry of such objects with small (40 cm or even smaller) telescopes. By using a dichroic polaroid sheet either in front of the telescope tube or before the imaging detector at the Cassegrain plane, one can record cometary images with a good signal to noise ratio. By rotating the dichroic sheet in three discrete steps and then reducing the corresponding three comet images to a single image, one can determine the linear polarization value at each pixel location on the image. The error in polarization will typically be the inverse of the ‘signal to noise ratio’. Such polarization images of a comet help us to determine its dust properties and also to look for possible dust jet activities. This type of work is possible with small telescopes and minor instruments.

Light polarization experiments with a diode laser pointer

Polarized light has many uses: glare reduction, stress analysis, microscope image enhancement, thin-film characterization, astronomy, saccharimetry, and atomic spectroscopy. Here we discuss introductory polarized light measurements in which a diode laser pointer replaces the more frequently used polarized He-Ne laser. A diode laser has been used in introductory optics experiments, and in a more advanced polarization-reflection experiment. Its strong collimated beam is completely polarized and, being free of infrared radiation, it permits Polaroid sheets to be used successfully with semiconductor detectors.

Measurement of the absorption of light by polaroid sheet

Measurement of the absorption of light by polaroid sheet

Threshold light modulator for analog-to-digital image conversion

A threshold light modulator with an internal singular optical feedback is proposed. It consists of a photoconductor and an electrooptic medium between which are located a semitransparent mirror, a biaxial crystal film, and a Polaroid sheet. The proposed modulator is an optical analog of a Schmitt trigger and it can be used to quantize images setting an arbitrarily selected threshold level. In addition, it can function as a parallel digital optical adder. A theoretical analysis is made of the dynamic properties of the threshold modulator, taking into account the real characteristics of its component layers such as the dark current of the photoconductor, the residual transmission of the Polaroid sheet, etc.

Induction of orientation of bacterial cellulose microfibrils by a novel terpenoid from Acetobacter xylinum.

1. The bacterium Acetobacter xylinum produces extracellular cellulose microfibrils that form a pellicle in the medium enmeshing the bacterial cells. These microfibrils may show some localized alignment, which can be seen as birefringence when the culture is viewed between crossed Polaroid sheets. 2. An increase in birefringence can be induced by the addition of small amounts of certain classes of lipids, particularly sterols, to the cultures. 3. A crude lipid extract from Acetobacter cells induced greatly increased birefringence when added to fresh cultures of this organism. 4. When the bacterial lipids were fractionated, most of the activity was recovered in a complex, polar lipid. The lipid is secreted into the medium during growth and is unstable. The non-saponifiable portion of this lipid is shown to be a 1:1 mixture of a saturated and a monounsaturated C(35) tetrahydroxy terpene with a hopane ring system in the accompanying paper by Förster et al. (1973). The saturated molecule is referred to as tetrahydroxybacteriohopane. 5. Tetrahydroxybacteriohopane is itself capable of inducing birefringence in cultures as is 22-hydroxyhopane, which was also isolated from the non-saponifiable fraction of the total lipids. 6. The mechanism of induction of birefringence (orientation of microfibrils) is not known. This is unlikely to be a specific effect, since all the above compounds are active (intact lipid, tetrahydroxybacteriohopane, 22-hydroxyhopane), as are other classes of lipid. It is suggested, however, that a common mechanism may be involved and that similar compounds may be concerned with control of microfibril alignment in the cells of higher plants.

Resonance Raman spectra of conjugated polyvinylenes in dichroic polarizing sheets (polaroid KN-42)

Resonance Raman (RR) spectra of the aligned polyvinylene chromophores in KN-42 Polaroid sheets have been laser excited at 4880, 5309, 5682 and 6471 Å, and the polarization of the scattered light was determined with the following results: 1) the diagonal scattering tensor elements α zz in the direction of maximum absorption is ≈10 times larger than any other α ij ; 2) the polyvinylenes give rise to a pair of intense Raman bands corresponding to CC and CC stretching, the lineshapes of which depend on the wavelength of excitation. This dependence indicates that the two observed bands consist of at least two components each, and that the components differ in their excitation profiles. The effects are discussed in terms of the distribution in length of the conjugated segments in the sample.

A simple method for determining principal-stress directions in embedded-polariscope models

A disadvantage of the embedded-polariscope method is the inability to observe isoclinics because the embedded Polaroid sheets are fixed within the model. Perforating the embedded active layer with an array of small-diameter holes allows observation of stress trajectories in the layer from the isochromatic patterns. Further, it is shown that the full-field fringes are little disturbed by the presence of the small perforations. The techniques of model fabrication are described, as well as an extension of the method to reveal bending-stress trajectories in plates loaded out of plane.

The 'Chromatic Abstractoscope': An Application of Polarized Light

Both of us are physicists at the University of Chile where we developed an interest in devices capable of producing results with physical phenomena comparable to the works of abstract painters. This interest led to a rather exciting experience which we would like to communicate in this note: An open air exhibition of the visual arts (Feria de Artes Plasticas) was held in Santiago, in a park along the river Mapocho, in December 1960. This annual exhibition is an important event in Santiago, and, as scientists with an interest in the fine arts, we decided that it would be a good occasion for showing to the public some form of expression that might constitute a bridge between science and art. We thought that the colours obtained through the interference of polarized light by birefringent crystals would provide a good example. In polarized light the transverse vibrations are restricted to certain special directions; for instance, in plane polarized light they are all in one plane. A polarizing material, such as Polaroid sheet, has the property of transmitting only those transverse light vibrations that are vibrating in a certain plane. A birefringent material splits a wave of light into two waves that propagate through the material with different velocities, thus giving rise to interference effects which when polarized light is used produce colours. Both of us had on many occasions demonstrated this well-known effect to our students of physics and crystallography; their reaction made us think the general public might also enjoy seeing it. When discussing the programme and technical details of our 'show', we decided that in addition to demonstrating experiments of crystal growth by means of polarized light, we would also replace the crystals with colourless cellophane sheet (another birefringent material). When pieces of cellophane that have been folded and crushed into various

A bonded polariscope for three-dimensional photoviscoelastic studies

A method of incorporating an internally bonded polariscope into a transparent model has been developed for use with viscoelastic materials. The newly developed technique serves to isolate one or more planes in a three-dimensional model so that a threedimensional photoviscoelastic analysis can be performed. The model may be subjected to a variety of loadings at room temperature, and only the photomechanical effects in the isolated plane will be observable. In the experimental program, a viscoelastic cement was developed whose mechanical properties matched those of a chosen model material. The cement was used to bond the polarizing sheet into the model. The restraining effect of the stiff elastic Polaroid sheet was reduced by cutting a gridwork of slits into this material. Tests performed on simple disk models and on star-grain rocket models containing bonded-polariscope elements showed structural continuity through the cemented joint. The fringe pattern observed through the bonded polariscope in star-grain models was the same as that observed using a conventional polariscope. On the basis of the favorable test results, the newly developed technique was judged acceptable.

Crystal Fabric Studies on Emmons Glacier Mount Rainier, Washington

Optical orientations of 1,725 ice crystals were determined at eleven locations on the Emmons Glacier by means of a 6-inch universal stage mounted between crossed polaroid sheets. The crystals were 0.2–6 inches across and from three to forty were included in each 4½ × 6-inch thin-section. Down-valley glacier movements of 3.4–9.2 inches per day were recorded at four of the higher locations, and another three were in ice believed to be essentially stagnant. The optic axes at most locations, when plotted on a Schmidt equal-area projection, form consistent patterns featuring four strong maxima at the corners of diamond-shaped quadrangles. Concentrations as high as 26 per cent in 1 per cent of the area were recorded. The angular separation of opposite corners of the diamond-shaped quadrangles average 84° and 52°, respectively. The pattern in stagnant ice is the same and as strong as the pattern in moving ice. Poles to shear planes and clear ice bands in the glacier at the locations studied fall near the centers of the diamonds. If this pattern is controlled by gliding within the ice crystals, it suggests the possibility of glide planes in ice crystals other than the well-known basal glide plane.