Plasmon resonance in nanostructured metals is in essence collective oscillation of free electrons, which is driven by optical electric fields and oscillates at nearly the same frequency as the excitation photons. This is the basic physics for the currently extensively interested topics in optical metamaterials, optical switching, and logic optical “circuits” with potential applications in optical communication and optical computation. We present here an interference effect between photons and plasmon electrons, which is observed as multi-cycle beat-oscillation. The beat frequency is in the range of 3~4 THz, which is equal to the difference between optical frequency of the photons and oscillation frequency of the plasmon electrons. Such beat oscillation evolves in a time scale of more than 1 ps, which is much longer than the optical pulse length, implying interaction between photons and pure damping plasmon-electrons. The discovered mechanisms might be important for exploring new approaches for THz generation.

Senescence-associated receptor-like kinase (SARK) family members in Arabidopsis, soybean, and rice are known to be positive regulators of leaf senescence. In the meantime, SARKs are extensively involved in stress response. However, their function and underlying molecular mechanism in stress responses in moss are not well known. Here, we investigated functional roles of SARK isolated from Physcomitrella patens (PpSARK) in salt stress response and senescence. PpSARK transcripts significantly accumulated under NaCl and abscisic acid (ABA) treatments, with higher expression in the moss gametophyte stage. Insertional gain-of-function mutants of PpSARK (PpSARKg) were more tolerant to salt stress and ABA than wild type (WT), whereas senescence of mutants was delayed during the protonema stage. Expression of stress-responsive genes in the ABA related pathway, such as PpABI3, PpABI5, PpPP2C, and PpLEA were significantly higher in PpSARKg and WT under salt stress conditions, suggesting that PpSARK might positively regulate salt tolerance via an ABA-related pathway. Endogenous ABA contents also increased 3-fold under salt stress conditions. These results indicate that PpSARK functions as a positive regulator in salt stress responses, while possibly functioning as a negative regulator in senescence in moss.

Half-wave plates were introduced into an interference-lithography scheme consisting of three fibers that were arranged into a rectangular triangle. Such a flexible and compact geometry allows convenient tuning of the polarizations of both the UV laser source and each branch arm. This not only enables optimization of the contrast of the produced photonic structures with expected square lattices, but also multiplies the nano-patterning functions of a fixed design of fiber-based interference lithography. The patterns of the photonic structures can be thus tuned simply by rotating a half-wave plate.

Flexible interference lithography using fibers as laser beam splitting and delivering system is demonstrated. A laser beam at 325 nm is used as the ultraviolet light source. Fiber bundles consisting of two, three, or four optical fibers have been utilized for the fabrication of two-dimensional photonic structures with different lattice configurations and different periods. The effective area of the fabricated waveguide grating structures is in the scale of centimeters in diameter with excellent homogeneity, which has much space for further improvement. This flexible interference lithography technique enables simple, compact, and efficient fabrication of photonic structures.