Optical diffraction effect

Fig. 4 and Fig. 5 show the surface morphologies aftm photo-ablation of PMMA/pyrene, and CMS, CMS/pyrene respectively. In these figures a copper-mesh mask was used in contact with the polymer films for the gena-atkm of sharp etch patterns. For PMMA/pyrene films, in the low pyrene concentration range, the etched surface is quite rough with dendritic and needle-like structures as well as solidified droplets on the bottom of the irradiated areas present although the edges of the etched features are reasonably sharp (Fig. 4a). When the laser fiuence is increased, the etched surface becomes cleaner and more smooth. At a high pyrene concentration, clean and sharp etch patterns can be obtained at a relatively low fiuence, e.g., at a = 1.04 x 10 cm and F = 0.3 J/cm as shown in Fig. 4b. In most cases, periodic structures are observed near the edges of the wire mask, which most likely result from the optical diffraction effect of the wires.

The resolution of the resist patterning is a function of the resist contrast and the optical diffraction effects produced by the mask aligner. For a description of Fraunhofer and Fresnel diffraction effects which limit resolution as a function of the optical modulation transfer function of the mask aligner, see Campbell [12] and Mack [13], In general, a shorter wavelength is key to achieve smaller feature sizes, for example, deep UV is able to generate features in... 

This expression is the main tool used in describing diffraction effects associated with Fourier optics. Holographic techniques and effects can, likewise, be approached similarly by describing first the plane wave case which can then be generalized to address more complex distribution problems by using the same superposition principle. 

Due to diffraction effects of micron-sized mirrors in a regular array, commonly used techniques for surface characterization based on interferometry are inefficient. To overcome the diffraction effects we have developed a novel surface characterization method with an incoherent light source, based on the Foucault s knife-edge test (Zamkotsian and Dohlen, 1999). Since Leon Foucault introduced the knife-edge test in the last century (Foucault, 1859), it has been widely used for testing optical surfaces (see Ch. 3). The test offers a simple way of obtaining easily understandable, qualitative information of the surface shape. 

The IR microscopy sampling technique is the ultimate sampling technique since only one particle is required for analysis. Due to the restrictions of diffraction effects, typically, the particles of interest must be greater in size than 10 x 10 /xm. Once the sample of interest is placed upon an IR optical window,... 

In many cases, the profile a spectroscopist sees is just the instrumental profile, but not the profile emitted by the source. In the simplest case (geometric optics, matched slits), this is a triangular slit function, but diffraction effects by beam limiting apertures, lens (or mirror) aberrations, poor alignment of the spectroscopic apparatus, etc., do often significantly modify the triangular function, especially if high resolution is employed. 

The optical microscope is one of the most basic instruments for particle sizing and is applicable to a typical size range of 0.8 /xm to 150 /xm. The lower limit is a result of the diffraction effects on the particle image as observed in a microscope. The limit of resolution of an optical microscope can be estimated by (Yamate and Stockham, 1977)... 

An ultraviolet-laser based thermo-optical absorbance detector for micrometer capillaries was used by Qi et al. [76] to monitor the separation of a mixture of 13 phenylthiohydantoin-amino acids. A modulated pump laser beam periodically illuminated the capillary at a point near its end. Complex deflection and diffraction effects occur at the capillary-solution interface. Perturbation of the refractive index at this interface changes the intensity of the probe beam that is measured using a small photodiode. 

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