Nonlinear Optics Senior Project Abstracts
Intensity and Polymer Dependence of Photoinduced Azimuthal Gliding in Azo Dye-Doped Nematic Liquid Crystals
Valerie Basore, 2007
The intensity dependence of azimuthal gliding - and relaxation from that gliding - on sample surfaces was investigated using a method that allowed for the direct measurement of NLC reorientation on the exit surface of the sample. Samples were prepared and oriented in several small ways in order to understand how rubbing of the soft plate of the sample affected gliding, as well as the differences between the intensity dependence on hard and soft polymer surfaces. Rubbing was found to have no effect on the gliding. The hard sample showed a much larger intensity dependence for gliding than did the soft samples, indicating complex dye-polymer interactions. No pattern in sample relaxation was found. Finally, the use of a white light source as a probe beam was shown to cause reorientation via photoisomerization.
Spatial Solitons in Azo Dye-Doped Nematic Liquid Crystals
David Barnes, 2006
The anisotropy, nonlinearlity, and reorientation effects of nematic liquid crystals makes them ideal mediums for the creation of self-confined electro-magnetic waves called solitons. Solitons form channels that can guide secondary signals, providing possible applications in optical circuitry, reconfigurable interconnects, and optical surgery. Azo-dyes have been used to dope nematic liquid crystals, allowing them to reorient at much lower light intensities. Here, the results of an experimental investigation of the formation of solitons in both doped and non-doped nematic liquid crystals have been found to be inconclusive. Further exploration into the formation and propagation of solitons in dye-doped liquid crystals is essential.
LCPCF Bandgaps And Their Properties in the Visual Range
Matthew Geiger, 2006
Liquid Crystals (LC?s) can be infiltrated into a Photonic Crystal Fiber (PCF) in order to create a tunable Bandgap. Because PCF?s allow the transmission of light in the infrared and visual range, it is possible to study the transmission properties of the LCPCF Bandgap in the visual range. Changing the physical properties of the PCF changes its transmission properties and, thus, the Bandgap properties. Furthermore, LCPCF Bandgaps are tunable through various means. By studying the tunability of LCPCF Bandgaps, it is possible to uncover applications for these Bandgaps.
Director Gliding in the Reorientation of Dye-Doped Nematic Liquid Crystals
Vincent Werner, 2006
A procedure was developed to construct special liquid crystal samples. The samples consisted of two glass plates, both of which conducted electricity. One was coated with a polyimide for hard planar alignment, the other with polyethyl-methacrylate to allow for free rotation of the molecules along the surface. Then, a change in absorbance experiment was performed to provide information about the initial reorientation and further gliding of dyed liquid crystals. The initial reorientation plots show a very inconsistent start to the motion that is taken over as the field increases. The molecules were observed to glide to new positions over time in samples made with one hard plate and one soft plate. There was also further movement observed in a sample made with two hard plates.
Surface Effects in Azo Dye-Doped 5CB Nematic Liquid Crystal Cells
Zachary Cataldi, 2005
Pump-probe experiments were conducted on planar aligned 5CB liquid crystal samples doped with DO3, 4MR, 5MR, 6MR and Methyl-red. A He-Ne laser was used as the probe and a doubled Nd:YAG laser with a 4 nanosecond pulse length was used as the pump beam. The optically induced phase shift caused by the pump laser pulse produced a double exponential decay. The excited state during trans-cis isomerization as well as surface effects are responsible for the double exponential decay. The final amplitude that the double exponential decayed to did not behave as expected. It was fit to a constant value but it may also be able to be a linear fit. A decrease in order was also present as the intensity increased. At approximately 120?J this increase in disorder ceased and liquid crystal reorientation began to increase the amount of order in the sample. All reorientation was found to be in plane and no out of plane reorientation was found.
Chaotic Rotations of the Director in Azo Dye-Doped Nematic Liquid Crystals
Greg Schivley, 2004
The behavior of liquid crystals doped with azo dyes when excited by a linearly polarized Ar+ pump is investigated. Of particular interest is a route to chaotic motion of the director previously seen in transparent liquid crystals, known as a gluing bifurcation. A liquid crystal modulator was used to investigate the ellipticity of an initially linearly polarized probe beam after passing through the liquid crystal sample, with the data processed by a LabVIEW program on a PC.
Enhancements, Due to Trace Amounts of Azobenzene Dyes, on the Optical Torque Induced by an Argon Laser on Nematic Liquid Crystals
Michael Hunter, 2003
The birefringent properties of liquid crystals create an optical path length difference between ordinary and extraordinary polarized light. The path length difference for the liquid crystal E70A is studied with .1% doping of the azobenzene dyes DO3, 4MR, 5MR, and 6MR. Azobenzene dyes exhibit isomerization. Therefore the time for relaxation from cis to trans configurations, along with the information about the trans/cis ratios from experimentation on planar aligned liquid crystals, may be combined with information about the retardance from homeotropically aligned liquid crystals. This information is used to find the sign and magnitude of the contribution to the total torque on the system from each dye configuration. A pure E70A liquid crystal sample yielded a phase difference in ordinary and extraordinary polarized light of -.069pi radians; whereas values of .043pi, -.014pi, -.206pi, -.093pi, and .006pi radians were found for values containing various azobenzene dyes. Although this experiment does not study the planar aligned scenario, the magnitude and sign of the retardance gives an indication of how the cis and trans isomers behave differently.
Analysis of One-Way Image Reconstruction via Four-Wave Mixing
Fadey Jabr, 2003
We demonstrate the ability to reconstruct a phase conjugate beam using a BaTiO3:Rh crystal and a one-way imaging via four-wave mixing setup. The phase conjugate beam is reconstructed once it propagates through the distortion. Reconstruction of a phase conjugate beam using a dye-doped nematic liquid crystal is then attempted using the same concepts in the previous experiment. In the liquid crystal experiment, a dc field is externally applied to assist in the molecular reorientation process. Due to time constraints, image reconstruction using a nematic liquid crystal was never achieved. However, phase conjugation has been achieved by others using a nematic liquid crystal, therefore, image reconstruction is also possible.
One-way Image Reconstruction Through Non-Linearly Aberrating Media
Clifford Francis, 2001
With the improvement of laser technology, physical and non-linear optics, developed as a reliable way to explore the complex interactions between light and matter. Recently there has been great interest in using monochromatic laser light to send images through distorting media and reconstruct the image using non-linear optics. It has been demonstrated that by using some consequences of non-linear light interaction such as the photorefractive effect, wave mixing, and various imaging techniques, that the laser light can be reconstructed, even at low intensities. The process termed the photorefractive effect, starts with the type of material you use, specifically materials which are non-linearly polarizable at low intensities. The photorefractive crystal Barium Titanate (BaTiO3) promotes optical phase conjugation in a way that makes image reconstruction possible. J. W. Goodman, K. Singh, and J. Puth, have all established techniques useful to one-way image reconstruction. The ultimate goal of this study was to perform one-way image reconstruction through a non-linearly aberrating nematic liquid crystal sample. By comparing and analyzing two-way and one-way techniques a new optical setup can be demonstrated to be functional using non-linear optics but at low intensities.
Investigation of the Nonlinear Optical Properties of Dyed Nematic Liquid Crystals
Jessica Merlin, 2001
No abstract available.
One-way Imaging via Four-wave Mixing: Analysis and Cleanup of Reconstructed Images
Matthew Moneck, 2000
A method of one-way imaging was demonstrated in which an object and reference wave were co-propagated through a phase distorting medium. Image reconstruction took place via four-wave mixing, and the reconstructed images were analyzed with a beam analyzer. Any remaining image degradation was subsequently analyzed, and an alternative method of one-way imaging was suggested as a means of cleaning up any remaining degradation. The feasibility of image cleanup using the alternative method was examined and presented.
Experimental and Theoretical Investigation into Dyed Nematic Liquid Crystals via Four-Wave Mixing
Audria Stubna, 2000
No abstract available.
An Investigation into the Modeling of the Photrefractive Effect in BaTiO3:Rh via Two-Beam Coupling and the Z-Scan Technique
Christopher Sunderman, 2000
The following is a study of the modeling of BaTiO3:Rh via theoretical analysis and experimental study using two-beam coupling and the Z-scan technique. Using two-beam coupling the gains, response times as a function of twist angle and intensity are investigated for different melt dopant densities of 1600-ppm, 2400-ppm, and 3200-ppm. The results show that the 2400-ppm has lower gain but a faster response time when compared to the two other crystals. Evidence for the three-state model of the photorefractive effect is provided. The Z-scan technique is investigated as a possible method for measuring the nonlinear absorption of BaTiO3.