Acceleration of sub-relativistic electrons with an evanescent optical wave at a planar interface.

We report on a theoretical and experimental study of the energy transfer between an optical evanescent wave, propagating in vacuum along the planar boundary of a dielectric material, and a beam of sub-relativistic electrons. The evanescent wave is excited via total internal reflection in the dielectric by an infrared (λ = 2 µm) femtosecond laser pulse. By matching the electron propagation velocity to the phase velocity of the evanescent wave, energy modulation of the electron beam is achieved. A maximum energy gain of 800 eV is observed, corresponding to the absorption of more than 1000 photons by one electron. The maximum observed acceleration gradient is 19 ± 2 MeV/m. The striking advantage of this scheme is that a structuring of the acceleration element's surface is not required, enabling the use of materials with high laser damage thresholds that are difficult to nano-structure, such as SiC, Al2O3 or CaF2.

siRNA silencing of keratinocyte-specific GFP expression in a transgenic mouse skin model.

Small interfering RNAs (siRNAs) can be designed to specifically and potently target and silence a mutant allele, with little or no effect on the corresponding wild-type allele expression, presenting an opportunity for therapeutic intervention. Although several siRNAs have entered clinical trials, the development of siRNA therapeutics as a new drug class will require the development of improved delivery technologies. In this study, a reporter mouse model (transgenic click beetle luciferase/humanized monster green fluorescent protein) was developed to enable the study of siRNA delivery to skin; in this transgenic mouse, green fluorescent protein reporter gene expression is confined to the epidermis. Intradermal injection of siRNAs targeting the reporter gene resulted in marked reduction of green fluorescent protein expression in the localized treatment areas as measured by histology, real-time quantitative polymerase chain reaction and intravital imaging using a dual-axes confocal fluorescence microscope. These results indicate that this transgenic mouse skin model, coupled with in vivo imaging, will be useful for development of efficient and 'patient-friendly' siRNA delivery techniques and should facilitate the translation of siRNA-based therapeutics to the clinic for treatment of skin disorders.

Deformable grating optical modulator.

A new type of light modulator, the deformable grating modulator, based on electrically controlling the amplitude of a micromachined phase grating is described. Mechanical motion of one quarter of a wavelength is sufficient for switching in this device. The small mechanical motion allows the use of structures with high mechanical resonance frequencies. We have developed a deformable grating modulator with a bandwidth of 1.8 MHz and a switching voltage of 3.2 V and have demonstrated modulation with 16 dB of contrast. Smaller devices with bandwidths of as much as 6.1 MHz and predicted switching voltages of less than 10 V were also fabricated.