Abstract: We disclose several instrument architectures for the measurement of arbitrary phase retardation on advanced lithography photomasks. These architectures combine traditional interferometric techniques with high-magnification UV microscopy. Features are interrogated using a multitude of phase probes, formed by a imaging a number of variable apertures back-illuminated by phase-coherent beams, onto the surface of the photomask with a given demagnification. The size, spacing, and orientation of the phase probes may be adjusted to suit photomask feature geometries. Means are provided to vary the relative optical phase between the phase probes. These phase probes both reflect from and transmit through the photomask; the stationary, non-localized interference fringes, formed in the regions of phase probe electric field overlap, contain information on the optical path difference between the two probes.

Abstract: A method and apparatus for high-efficiency stimulated Raman Stokes and anti-Stokes scattering is described. A dual-Raman scattering cell configuration is disclosed. A variable pressure of the first Raman cell causes a controllable pressure shift of the Raman-active two-photon transition. The frequency-shifted Stokes radiation generated in the first Raman cell, along with the residual pump laser radiation, is applied to a second Raman cell whose pressure is adjusted to maximize production of the anti-Stokes sidebands. By the steps of applying the first Stokes sideband “injection” signal, and controlling its frequency via the pressure difference of the two Raman cells, and its intensity by appropriate focussing, the process of Raman scattering may be significantly enhanced over the techniques of the prior art. These techniques are of especial interest to the production of intense, coherent, short-wavelength radiation, especially when only a single pump laser frequency is available.

Abstract: This invention greatly improves the quality of images obtained using optical systems illuminated by coherent light. It does so by removing the undesirable psuedo-random variations in the final image due to interference speckle and inhomogeneities in the spatial intensity distribution of the light source. A bundle of light-guiding fibers is interposed between the illumination source and the imaging system. Non-uniform propagation within the fiber bundle creates a psuedo-random phase variation across the illumination beam, which gives rise to a dynamic interference speckle pattern superimposed upon the desired image acquired by the optical system. Rotating the fiber bundle around the axis of propagation, whilst simultaneously integrating the output of the photosensitive detector over a period of time, substantially removes variations due to source inhomogeneities and coherent interference.