Precise wavelength tuning of a dye laser using an active diffractive optical element

In this work, an active, reflecting diffraction grating was developed and characterized. A grating was holographically imposed onto the surface of a ceramic which could be deformed via the transverse, inverse piezoelectric effect, thus allowing active fine tuning of the grating constant. The tuning characteristics of this novel optical element were studied and the results compared with the linear theory of the piezoelectric effect. To demonstrate its applicability, the grating was installed in a dye laser and used to effect precise tuning of the output wavelength of the laser within a range of 220 pm. The possibility of quasi-static to high frequency operation of the system will allow this element to find use in a wide variety of applications.     

Solid-state characterization of the structure and deformation behavior of water-soluble hydroxypropylcellulose

A modus operandi is developed for determining the molecular structure of hydroxypropylcellulose (HPC), and characterizing, in quantitative terms, the morphological changes occurring when a water-cast film of the polymer is deformed. This involves the application of the following eleven different physical measurements: wide-angle x-ray diffraction, differential scanning calorimetry, density, melt rheometry, infrared spectroscopy, refractive index, birefringence, sonic modulus, small-angle light scattering, optical and electron microscopy. In addition, a computer was utilized as a mathematical diffractometer. Morphologically, water-cast HPC was observed to have structure at all levels, from the molecular to the supermolecular. The HPC molecule has a backbone of anhydroglucose units twisted into an irregular 3₁ helix. Intramolecular hydrogen bonding of the poly(propylene oxide) side chains leads to a stiff, rodlike molecule. The molecules are packed into microfibrillar crystallites 470 Å long and 34 Å in diameter. The microfibrils in turn, associate into supermolecular rodlike structures. The structural rearrangements that occur at each morphological level during deformation of HPC film are quantitatively examined and described.     

Quantitative characterization of deformation in polypropylene fibers

A modus operandi is developed for characterizing, in quantitative morphological terms, the structural changes occurring during the preparation (spinning, drawing, and heat setting) and testing (tensile modulus) of isotactic polypropylene fiber. This involves the application of the following eight different physical techniques: wide-angle x-ray diffraction, birefringence, density, sonic modulus, small-angle x-ray diffraction, dark-field microscopy, small-angle light scattering, and tensile modulus. Structural changes on several organizational levels, the spherulitic, the interlamellar, and the molecular, are determined in this manner and related to the processes involved.     

Small-angle light scattering from optically anisotropic spheres and disks. Theory and experimental verification

The small-angle light scattering (SALS) theory for optically anisotropic spheres and disks is examined in depth. An error is found in the existing sphere equations. The correct form of the equations is identified and then experimentally verified for dilute starch suspensions. Increased concentrations and solid films of starch granules are used to identify the effect of concentration on the scattering envelope. Spherulitic films of isotactic polypropylene, isotactic polystyrene, nylon 610, PET, and nylon 66 are then used to examine different aspects of the SALS theory. Experimental observations are found to agree with the predictions of the correct SALS equations. Disk theory is interrogated and correlated with predictions for spheres. It is found that the predicted patterns from spheres and disks are very similar under identical optical conditions, in contradiction to earlier predictions. A method is developed for identifying the optical sign of spherulites too small to be seen in the optical microscope. This study constitutes a comprehensive examination of SALS theory and includes many other aspects of the phenomena. A catalogue of theoretical V_v SALS patterns from spheres and disks is also included.     

Small-angle light scattering and crystallization processes in solid polymer films

Information, not previously measurable, about the internal crystallization processes occurring within spherulitic films can now be obtained by combining refractive index, birefringence, and small-angle light-scattering measurements. The surroundings of a spherulite in a solid film are composed of both the adjacent spherulites and their interstices (boundaries), and it is shown that different crystallization processes can occur in each of these regions. Upon annealing a quenched isotactic polypropylene film, the rate of crystallization within the interstices of the space-filling spherulites is observed to be greater than the rate of crystallization within the spherulites themselves.     

Quantitative characterization of the optical properties of absorbing polymer films: Comparative investigation of the internal reflection intensity analysis method

Nondestructive, three‐dimensional refractive‐index measurements are used for the determination of both the crystallinity and orientation in thin polymer films. The prism wave‐guide coupler is particularly suited for three‐dimensional isotropic and anisotropic thin‐film studies because of the quantitative character of the information obtained and the ease of data acquisition. It has been limited, however, to determining only the refractive index of transparent or weakly absorbing thin‐film samples. On the basis of thin‐film optics, this study develops a new internal reflection intensity analysis (IRIA) method, which uses the intensity information rather than the conventional mode angle values to acquire both the refractive index and the extinction coefficient over a range of transparent to highly absorbing polymer films. Therefore, the IRIA method overcomes the limitations of this prism wave‐guide coupler technique, which can only measure the refractive index of a weakly absorbing sample. With a Metricon PC‐2010 as the skeletal framework, a prototype instrument has been developed to apply and test the IRIA method. A study comparing both the refractive index and extinction coefficient obtained with ellipsometry, ultraviolet–visible/near‐infrared reflectometry, and IRIA for solvent blue 59 dyed polystyrene films confirms that the IRIA method is effective for obtaining the three‐dimensional refractive indices and extinction coefficients of polymer films. In addition, the refractive index and extinction coefficient spectrum (400–800 nm) of solvent blue 59 have been determined with the effective media theory. Furthermore, the three‐dimensional complex refractive indices of highly absorbing black electrical tape, inaccessible to other optical measurement because of its surface character, has been determined by the IRIA method. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 842–855, 2003     

The distribution and conformation of very long-chain plant wax components in a lipid bilayer

Plant wax contains long-chain alkanes and related components which are transported to the surface of the plant by specialized ABC transporter proteins. Here, we determine the distribution and conformation of three wax components, nonacosane, nonacosan-15-one, and nonacosan-15-ol, using unbiased and umbrella sampling molecular dynamics simulations. The molecules all partitioned to the center of the bilayer, with a free-energy difference of -70 kJ/mol between bulk water and the center of the bilayer for the alkane and -55 kJ/mol for the two more-polar molecules. All of the wax molecules were highly mobile in the bilayer, freely moving between opposite leaflets on a time scale of a few nanoseconds. Nonacosan-15-one and nonacosan-15-ol folded double to expose their hydrophilic group to the solvent, whereas nonacosane alternated between orientations spanning the full bilayer and orientations in the center of the bilayer.