We present a technique that involves tailoring the angular spectrum in optical microscopy of
silicon integrated circuits, with a solid immersion lens. Spatial light modulation to select only
supercritical light at the substrate/dielectric interface, yields only evanescent and scattered light
in the interconnect layers. We demonstrated the technique in optical excitation microscopy of
65nm silicon-on-insulator circuits, which enabled localization of a fault during microprocessor
development. Acquiring images with and without angular spectrum tailoring allowed
longitudinal localization of the electrical response to optical excitation. Lateral registration of
electrical response and confocal reflection images to the circuit layout was also significantly
In this work, we demonstrate how a polarization switching technique can be used to create multiple fiber ends, and allow the radiation to pass twice through each amplifying section for more efficient energy extraction. The technique uses a polarizing beam splitter combined with polarization switching in each arm of the cavity to define a ring-like cavity with multiple gain sections that can be end pumped. Polarization-maintaining double-clad rare-earth-doped fiber with slightly multi-mode core was used as the gain sections. A laser system based on the in-cavity polarization switching design has been demonstrated with maximum measured 62% slope efficiency and close to 30W output. The relatively low output power is only limited by the available pump sources.
High energy laser systems, both pulsd and CW, have become of significant interst in the recent past. To achieve higher powers in a laser system, it is often necessary to consider means by which individual lasers can be made coherent with one another. This can be achieved through the use of a master oscillator concept, which can have problems with overall stability, or by monitoring the phases of each individual laser and using feedback technique that can be used to combine individual pumped fiber gain sources into a cavity with a single output and a single set of longitudinal modes. We discuss the advantages of end pumping of double clad fiber lasers and speculate on means by which an all-glass double clad fiber laser may be developed.
We demonstrate a through the substrate, numerical aperture increasing lens (NAIL) technique for high-resolution inspection of silicon devices. We experimentally demonstrate a resolution of 0.2 micrometers , with the ultimate diffraction limit of 0.14 micrometers . Absorption limits inspection in silicon to wavelengths greater than 1 micrometers , placing an ultimate limit of 0.5 micrometers resolution on standard subsurface microscopy techniques. Our numerical aperture increasing lens reduces this limit to 0.14 micrometers , a significant improvement for device visual inspection (patent pending). The NAIL technique yields a resolution improvement over standard optical microscopy of at least a factor of n, the refractive index of the substrate material, and up to a factor of n 2. In silicon, this constitutes a resolution improvement between 3.6 and 13. This is accomplished by increasing the numerical aperture of the imaging system, without introducing any spherical aberration to the collected light. A specialized lens made of the same material as the substrate is placed on the back surface of the substrate. The convex surface of this lens is spherical with a radius of curvature, R. The vertical thickness of the lens, D, should be selected according to D equals $ (1 + 1/n)-X and the substrate thickness X.