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Transition of refractive index contrast in course of grating growth.

Sabel T, Zschocher M - Sci Rep (2013)

Bottom Line: We found two steps of growth, separated by a depletion of the light diffraction.Hence the grating formation mechanisms can be qualified as competing effects regarding the contribution to the refractive index change.We investigate the influence of the preparation and exposure procedure on the transition and consider the usability for integrated wave guide functions.

View Article: PubMed Central - PubMed

Affiliation: Institute for Optics and Atomic Physics, now at Chemical Department, Technische Universität Berlin, Strasse des 17 Juni 135, Berlin, Germany. tina@physik.tuberlin.de

ABSTRACT
Studies on the dynamics of holographic pattern formation in photosensitive polymers, gaining deeper insight into the specific material transformations, are essential for improvements in holographic recording as well as in integrated optics. Here we investigate the kinetics of volume hologram formation in an organic cationic ring-opening polymerization system. The time evolution of the grating strength and the grating phase is presented. We found two steps of growth, separated by a depletion of the light diffraction. Capable to explore this growing behavior, a transition-theory of the refractive index contrast is established. Accordingly the growth curves appear to be ruled by the interplay of polymerization and diffusion. Hence the grating formation mechanisms can be qualified as competing effects regarding the contribution to the refractive index change. We investigate the influence of the preparation and exposure procedure on the transition and consider the usability for integrated wave guide functions.

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Grating phase shift.The time evolution of the grating phase during grating growth corroborates a transition of the refractive index contrast between the first and the second step of growth.
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f3: Grating phase shift.The time evolution of the grating phase during grating growth corroborates a transition of the refractive index contrast between the first and the second step of growth.

Mentions: Figure 3 shows the grating phase and the corresponding growth curve on a logarithmic dimensionless time scale. The growth curve in Fig. 3 corresponds to an exposure time of 15 seconds and tT = 7500 s. The phase shift is clearly visible from Fig. 3, as well as the coincidence with the depletion time tT. Theoretically it is expected to find the grating phase shift sharply located at the transition point (τ = 1). As apparent from Fig. 3 deviations are caused under real conditions. The grating phase shift in Fig. 3 is located between τ = 0.5 and τ = 2. The fact that the grating phase shift spreads over a period around τ = 1 appears plausible under the assumption that the transition does not happen simultaneously all over the probe beam diameter, according to a dependence on the recording intensity. The grating phase shift measurement corroborates the Δn-transition theory: an initial, light induced, positive change of the refractive index is gradually converted to a negative one, triggered by diffusion of low index species. While the phase shift of 180 degree shows the inversion of the lattice planes (see Fig. 2, line 3–5).


Transition of refractive index contrast in course of grating growth.

Sabel T, Zschocher M - Sci Rep (2013)

Grating phase shift.The time evolution of the grating phase during grating growth corroborates a transition of the refractive index contrast between the first and the second step of growth.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3757355&req=5

f3: Grating phase shift.The time evolution of the grating phase during grating growth corroborates a transition of the refractive index contrast between the first and the second step of growth.
Mentions: Figure 3 shows the grating phase and the corresponding growth curve on a logarithmic dimensionless time scale. The growth curve in Fig. 3 corresponds to an exposure time of 15 seconds and tT = 7500 s. The phase shift is clearly visible from Fig. 3, as well as the coincidence with the depletion time tT. Theoretically it is expected to find the grating phase shift sharply located at the transition point (τ = 1). As apparent from Fig. 3 deviations are caused under real conditions. The grating phase shift in Fig. 3 is located between τ = 0.5 and τ = 2. The fact that the grating phase shift spreads over a period around τ = 1 appears plausible under the assumption that the transition does not happen simultaneously all over the probe beam diameter, according to a dependence on the recording intensity. The grating phase shift measurement corroborates the Δn-transition theory: an initial, light induced, positive change of the refractive index is gradually converted to a negative one, triggered by diffusion of low index species. While the phase shift of 180 degree shows the inversion of the lattice planes (see Fig. 2, line 3–5).

Bottom Line: We found two steps of growth, separated by a depletion of the light diffraction.Hence the grating formation mechanisms can be qualified as competing effects regarding the contribution to the refractive index change.We investigate the influence of the preparation and exposure procedure on the transition and consider the usability for integrated wave guide functions.

View Article: PubMed Central - PubMed

Affiliation: Institute for Optics and Atomic Physics, now at Chemical Department, Technische Universität Berlin, Strasse des 17 Juni 135, Berlin, Germany. tina@physik.tuberlin.de

ABSTRACT
Studies on the dynamics of holographic pattern formation in photosensitive polymers, gaining deeper insight into the specific material transformations, are essential for improvements in holographic recording as well as in integrated optics. Here we investigate the kinetics of volume hologram formation in an organic cationic ring-opening polymerization system. The time evolution of the grating strength and the grating phase is presented. We found two steps of growth, separated by a depletion of the light diffraction. Capable to explore this growing behavior, a transition-theory of the refractive index contrast is established. Accordingly the growth curves appear to be ruled by the interplay of polymerization and diffusion. Hence the grating formation mechanisms can be qualified as competing effects regarding the contribution to the refractive index change. We investigate the influence of the preparation and exposure procedure on the transition and consider the usability for integrated wave guide functions.

Show MeSH
Related in: MedlinePlus