RESUMO
Recently developed alignment techniques for liquid crystals enable the definition of arbitrary alignment patterns. We present a method to determine these two-dimensional spatial alignment distributions as well as the retardation of thin nematic liquid crystal films. The method is based on quantifying the influence of the birefringence of such a film on light with known input polarization by measuring the Stokes parameters of light. We show that we are able to distinguish arbitrary alignment patterns unambiguously. In addition, we demonstrate the ability to evaluate the homogeneity of the alignment as well as the thickness or birefringence of the film.
RESUMO
Lasing and self-frequency doubling are achieved in a millimeter-sized laser-active whispering-gallery resonator made of neodymium-doped lithium niobate. A low-cost 808-nm laser diode without external frequency stabilization is sufficient to pump the neodymium ions. Laser oscillation around 1.08 µm drives a frequency-doubling process within the same cavity providing green light. The electrical-optical efficiency of the system reaches up to 2×10-4. To the best of our knowledge, this is the first demonstration of combining lasing and χ(2) frequency conversion in a single high-Q whispering-gallery resonator. This approach is general and can be applied to other materials and other nonlinear optical processes.