For the first time in vivo retinal imaging has been performed with a new compact, low noise Yb-based ASE source operating in the 1 microm range (NP Photonics, lambdac = 1040 nm, Deltalambda = 50 nm, Pout = 30 mW) at the dispersion minimum of water with ~7 microm axial resolution. OCT tomograms acquired at 800 nm are compared to those achieved at 1040 nm showing about 200 microm deeper penetration into the choroid below the retinal pigment epithelium. Retinal OCT at longer wavelengths significantly improves the visualization of the retinal pigment epithelium/choriocapillaris/choroids interface and superficial choroidal layers as well as reduces the scattering through turbid media and therefore might provide a better diagnosis tool for early stages of retinal pathologies such as age related macular degeneration which is accompanied by choroidal neovascularization, i.e., extensive growth of new blood vessels in the choroid and retina.
We report the first systematic study of the frequency dependence of optical nonlinearities of bulk GaAs at room temperature. In contrast to the previous understanding, band filling and plasma screening of Coulomb enhancement of continuum states are found to be the dominant contributions to the dispersive optical nonlinearities under quasi steady-state excitations. The partly phenomenological semiconductor plasma theory is in good agreement with the experimental data.
We report the observation of spin relaxation of excitons in zero-dimensional semiconductor nanostructures. The spin relaxation is measured in InGaAs quantum disks by using a polarization dependent time-resolved photoluminescence method. The spin relaxation time in a zero-dimensional quantum disk is as long as 0.9 ns at 4 K, which is almost twice as long as the radiative recombination lifetime and is considerably longer than that in quantum wells. The temperature dependence of the spin relaxation time suggests the importance of exciton–acoustic phonon interaction.
Mid-infrared sources are a key enabling technology for various applications such as remote chemical sensing, defense communications and countermeasures, and bio-photonic diagnostics and therapeutics. Conventional mid-IR sources include optical parametric amplifiers, quantum cascade lasers, synchrotron and free electron lasers. An all-fiber approach to generate a high power, single mode beam with extremely wide (1µm-5µm) and simultaneous wavelength coverage has significant advantages in terms of reliability (no moving parts or alignment), room temperature operation, size, weight, and power efficiency. Here, we report single mode, high power extended wavelength coverage (1µm to 5µm) supercontinuum generation using a tellurite-based dispersion managed nonlinear fiber and an all-fiber based short pulse (20 ps), single mode pump source. We have developed this mid IR supercontinuum source based on highly purified solid-core tellurite glass fibers that are waveguide engineered for dispersion-zero matching with Tm-doped pulsed fiber laser pumps. The conversion efficiency from 1922nm pump to mid IR (2μm-5μm) supercontinuum is greater than 30%, and approaching 60% for the full spectrum. We have achieved > 1.2W covering from 1μm to 5μm with 2W of pump. In particular, the wavelength region above 4μm has been difficult to cover with supercontinuum sources based on ZBLAN or chalcogenide fibers. In contrast to that, our nonlinear tellurite fibers have a wider transparency window free of unwanted absorption, and are highly suited for extending the long wavelength emission above 4μm. We achieve spectral power density at 4.1μm already exceeding 0.2mW/nm and with potential for higher by scaling of pump power.
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