Laser etched gratings on polymer layers for alignment of liquid crystals

Newsome, C. J.; O’Neill, Mary; Farley, Robert J.; Bryan‐Brown, G. P.

doi:10.1063/1.121281

Cited by 78 publications

(43 citation statements)

References 12 publications

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“…Gratings having micron to submicron periodicity have other important applications in optoelectronic devices (e.g., Bragg-type filters) [347] and for alignment of liquid crystals [348]. The standard technique for the fabrication of these gratings is the irradiation of a photoresist followed by various development and dry etching processes [349].…”

Section: Introductionmentioning

confidence: 99%

Laser Application of Polymers

Lippert

2004

Polymers and Light

148

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Laser ablation of polymers has been studied with designed materials to evaluate the mechanism of ablation and the role of photochemically active groups on the ablation process, and to test possible applications of laser ablation and designed polymers. The incorporation of photochemically active groups lowers the threshold of ablation and allows high-quality structuring without contamination and modification of the remaining surface. The decomposition of the active chromophore takes place during the excitation pulse of the laser and gaseous products are ejected with supersonic velocity. Time-of-flight mass spectrometry reveals that a metastable species is among the products, suggesting that excited electronic states are involved in the ablation process. Experiments with a reference material, i.e., polyimide, for which a photothermal ablation mechanism has been suggested, exhibited pronounced differences. These results strongly suggest that, in case of designed polymers which contain photochemically active groups, a photochemical part in the ablation mechanism cannot be neglected. Various potential applications for laser ablation and the special photopolymers were evaluated and it became clear that the potential of laser ablation and specially designed material is in the field of microstructuring. Laser ablation can be used to fabricate three-dimensional elements, e.g., microoptical elements.Keywords Laser ablation · Ablation mechanism · Photopolymers · Polyimide · Spectroscopy This was not always true, of course. For many years, the laser was viewed as "an answer in search of a question". That is, it was seen as an elegant device, but one with no real useful application outside of fundamental scientific research. In the last two to three decades however, numerous laser applications have moved from the laboratory to the industrial workplace or the commercial market. Lasers are unique energy sources characterized by their spectral purity, spatial and temporal coherence, and high average peak intensity. Each of these characteristics has led to applications that take advantage of these qualities: -Spatial coherence: e.g., remote sensing, range finding and many holographic techniques. -Spectral purity: e.g., atmospheric monitoring based on high-resolution spectroscopies. -and of course the many other applications in communication and storage, e.g., CDs.All of these high-tech applications have come to define everyday life in the late twentieth century. One property of lasers, however, that of high intensity, did not immediately lead to "delicate" applications but rather to those requiring "brute force". That is, the laser was used in applications for removing material or heating. The first realistic applications involved cutting, drilling, and welding, and the laser was little more advanced than a saw, a drill, or a torch. In a humorous vein A.L. Schawlow proposed and demonstrated the first "laser eraser" in 1965 [4], using the different absorptivities of paper and ink to remove the ink without damaging the und...

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Section: Introductionmentioning

confidence: 99%

Laser Application of Polymers

Lippert

2004

Polymers and Light

148

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“…It is known from literature that relief structures can induce LC alignment 4 and this effect can be used to construct TN LCD cells by writing these relief structures using a laser. 9 However, these patterns were formed by ablation, using a pulsed high energy laser, while in this article we report on laser writing in the melting regime at intensities below the ablation threshold and no material is removed from the substrate.…”

Section: Introductionmentioning

confidence: 99%

Influence of laser writing of polyimides on the alignment of liquid crystals

Versteeg

Bastiaansen

Broer

2002

Journal of Applied Physics

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The influence of direct laser writing in polyimides on the alignment of organic liquid crystals was investigated. Laser writing was performed below the ablation threshold, which resulted in local melting of the polyimide. A surface relief structure was obtained as a result of the fast heating and cooling cycle during laser writing. No alignment of organic liquid crystals in the vicinity of the surface relief structure was observed as a direct result of the laser writing process. However, it appeared to be possible to wipe out the alignment originating from the rubbing process. This property proved to be useful to generate complex patterns in twisted nematic liquid crystal cells with locally uniaxial alignment. The contrast between the nonpatterned and patterned areas ranged between 40 and 50, which illustrates that the earlier described phenomena are potentially useful in, for instance, personalized security features.

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“…18,19 Spatial director distribution in the LC cell depends strongly on director boundary conditions at the cell substrates, in particular, director pre-tilt angle and anchoring energy at the substrates. A series of methods have been developed to control the director boundary conditions, for example, irradiating alignment layers with ion beams, 20 doping the LC cells with nanoparticles, 21 or forming polymer structures on a substrate surface via electrostatic force 22,23 or UV light field. [24][25][26] In this present paper, we speculate that the photorefractive space-charge field may control the anchoring of the LC director at the cell substrates, and therefore affect the grating formation.…”

Section: Introductionmentioning

confidence: 99%

Two beam energy exchange in hybrid liquid crystal cells with photorefractive field controlled boundary conditions

et al. 2016

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We develop a theory describing energy gain when two light beams intersect in a hybrid nematic liquid crystal (LC) cell with photorefractive crystalline substrates. A periodic space-charge field induced by interfering light beams in the photorefractive substrates penetrates into the LC layer and reorients the director. We account for two main mechanisms of the LC director reorientation: the interaction of the photorefractive field with the LC flexopolarization and the director easy axis at the cell boundaries. It is shown that the resulting director grating is a sum of two in-phase gratings: the flexoelectric effect driven grating and the boundary-driven grating. Each light beam diffracts from the induced gratings leading to an energy exchange between beams. We evaluate the signal beam gain coefficient and analyze its dependence on the director anchoring energy and the magnitude of the director easy axis modulation.

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Laser etched gratings on polymer layers for alignment of liquid crystals

Cited by 78 publications

References 12 publications

Laser Application of Polymers

Laser Application of Polymers

Influence of laser writing of polyimides on the alignment of liquid crystals

Two beam energy exchange in hybrid liquid crystal cells with photorefractive field controlled boundary conditions

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