Volume 94, Issue 10, 15 November 2003
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
94(2003); http://dx.doi.org/10.1063/1.1621725View Description Hide Description
The time dependent birefringence of polymer-based electro-opticmaterials is investigated using ellipsometry. We show that the birefringence after switching off the poling field does not depend only on the induced refractive index, but also on how that level was reached. The role of the poling voltage and poling time is discussed in turn-on and turn-off experiments and an original curve-fit function is introduced. We also propose a schematic model of the polymer dynamics in the system, which is consistent with complementary dielectricmeasurements.
94(2003); http://dx.doi.org/10.1063/1.1622770View Description Hide Description
Future large space-based telescopesystems require precise optical surface quality and wave-front stability. One source of noise for very large precise optical systems is ambient thermal energy which induces statistical fluctuations in the strain energy state of the structure. We broadly model such optical systems as bending energy dominated or membrane in-plane energy dominated and derive analytical expressions for the governing parameters that determine noise magnitude. It is shown that for bending-based systemsthermal noise increases as aperture is increased and as bending stiffness is decreased, while for membrane mirror systems it is the in-plane pretension level that determines the noise magnitude. The analysis is extended to numerical finite element techniques to illustrate the effects on very general large damped structures where we address the form of equivalent thermal loading density required in modeling such distributed structures. Calculations show that temporal rms deformation noise on the order of a picometer or less can be expected for apertures up to about 10 m and therefore is probably not significant. For lightweight precision aperturesystems greater than 10 m, thermal noise may need to be considered in the design.
Coupling effects for counterpropagating light beams in lithium niobate crystals studied by grating translation technique for extremely high external electric fields94(2003); http://dx.doi.org/10.1063/1.1619569View Description Hide Description
The grating translation technique (GTT), which employs a momentary shift of light fringes during holographic recording, is a powerful tool for characterization of nonlinear materials. Earlier, it was used in the transmission geometry. We formulate the main relations of GTT for the reflection case. These allow us to determine in situ the real and imaginary parts of the coupling strength and to detect the formation of refractive-index and absorption gratings. We apply GTT to determine the photorefractive characteristics of two-wave coupling in -cut iron-doped lithium niobate crystals for an extremely small grating spacing and extremely large externally applied electric fields (up to 650 kV/cm). Stabilization of the light fringes, crucially important in the reflection geometry, has been achieved with the use of an electronic feedback loop. We prove that the feedback introduces a frequency detuning between the light beams and modifies strongly the nonlinear response.