Observation of backward high-harmonic emission from solids.

We experimentally demonstrate backward emission of high-harmonics of a near-infrared laser from MgO and Si crystals in the direction of specular reflection. We show that the variation of the high-harmonic power with the angle of incidence can be predicted with nonlinear reflection coefficients derived originally for perturbative nonlinearities. A comparison of transmission and reflection geometries suggests that backward-propagating high-harmonics are an excellent reference to study nonlinear propagation of intense light in solids. Backward emission will enable phase matching of the high-harmonic beam and the integration of the functionalities of extended gas-phase high-harmonic beamlines into a single optical element. The potential to achieve phase matching paves the way to solid-state based high-harmonic sources with higher flux than the best transmission-based sources, where high-harmonics are strongly absorbed by the crystal itself.

Off-axis phase-matched terahertz emission from two-color laser-induced plasma filaments.

We observe off-axis phase-matched terahertz generation in long air-plasma filaments produced by femtosecond two-color laser focusing. Here, phase matching naturally occurs due to off-axis constructive interference between locally generated terahertz waves, and this determines the far-field terahertz radiation profiles and yields. For a filament longer than the characteristic two-color dephasing length, it emits conical terahertz radiation in the off-axis direction, peaked at 4-7° depending on the radiation frequencies. The total terahertz yield continuously increases with the filament length, well beyond the dephasing length. The phase-matching condition observed here provides a simple method for scalable terahertz generation in elongated plasmas.

Two-dimensional plasma current and optimized terahertz generation in two-color photoionization.

Two-dimensional (2-D) transverse photocurrent generation is studied and applied to control and optimize terahertz energy and polarization in two-color, laser-produced air filaments. A full control of terahertz output is demonstrated and explained in the context of 2-D photocurrent model.

Effect of IOP elevation on matrix metalloproteinase-2 in rabbit anterior chamber.

To investigate changes in the level of matrix metalloproteinase-2 (MMP-2) in the anterior chamber of rabbit with intraocular pressure (IOP) elevation. The IOP was elevated with scleral encircling in 12 rabbits. In the control group (4 rabbits), IOP was not changed after scleral encircling, and in group 1 (4 rabbits) and 2 (4 rabbits), IOP was elevated about 10 and 20 mmHg respectively after scleral encircling. At 2 days after scleral encircling, aqueous sampling was performed and levels of MMP-2 were checked by Western blots and gelatin zymograms. The greater the IOP elevation, the more MMP-2 expression in the anterior chamber by Western blots and gelatin zymograms. The increase in MMP-2 expression in response to IOP elevation may have important implications for the IOP feedback control mechanism.

The effective concentration and exposure time of mitomycin-C for the inhibition of lens epithelial cell proliferation in rabbit eyes.

The proliferation of residual lens epithelial cells following cataract surgery is assumed to be a major cause of posterior capsular opacification. To assess the efficacy of mitomycin-C in preventing posterior capsular opacification, we determined the effective concentration and exposure time of mitomycin-C in inhibiting rabbit lens epithelial cell proliferation. The fourth-passaged rabbit lens epithelial cells were maintained for one day and then exposed to mitomycin-C for 1, 2, 3, and 5 minutes, respectively. There were 9 different plating concentrations of mitomycin-C with two-fold serial dilution. The maintenance of the phenotypic properties of lens epithelial cells was confirmed by continuous transcription of lambda-crystalline mRNA determined by reverse transcription-polymerase chain reaction and the polymorphism of the restriction fragment. Cell proliferation was assayed with 3H-thymidine incorporation into DNA. The fourth-passaged cells maintained the expression of lambda-crystalline mRNA, suggesting that they are phenotypically authentic lens epithelial cells. The effective concentrations and exposure time of mitomycin-C were 0.1 mg/ml for 1 minute and 2 minutes, and 0.025 mg/ml for 2 minutes. By these results, we postulated that mitomycin-C at relatively short incubation times could be clinically used for prevention of posterior capsular opacification after cataract surgery.