China
Africa
Explore chapters and articles related to this topic
Vibrational Spectroscopy
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Peter Fredericks, Llewellyn Rintoul, John Coates
Placement of the sample is important. A choice for sample position is indicated in Figure 7.2. In light dispersion instruments, the sample is normally placed before the monochromator or polychromator (spectrograph). This is essentially to maximize the collection of the low levels of radiation that results after dispersion, and to minimize interference from unwanted, stray sources of radiation. Stray light is one of the main sources of photometric error in this type of instrumentation. One negative influence of placing the sample between the source and the analyzer is that the full impact of the radiation from the source is focused on the sample. This may cause localized heating if the sample is kept in the beam for an extended period. Not only might this cause unwanted thermally induced changes in the sample (decomposition, evaporation, or changes in morphology), but it can also lead to photometric errors, in particular at longer wavelengths, as a result of energy re-radiation effects. This error manifests itself on strong absorption bands, where the sample emits radiation at exactly the same wavelengths as the absorptions, which is observed as a reduction of the measured band intensity.
Illuminators for Microlithography
Published in Fred M. Dickey, Scott C. Holswade, David L. Shealy, Laser Beam Shaping Applications, 2018
The quadrapole is the optimum for the printing of dense features in two orthogonal directions, known as Manhattan geometries. Both the dipole and quadrapole enhance DOF for features at certain orientations and degrade DOF at others. An annular illumination profile has no symmetry preference and allows more of the illumination pupil to be used. The advantage of using more of the pupil is that greater power can be delivered without allowing high irradiance values on the optics near the aperture stop. Maintaining uniform irradiance becomes more difficult for the illuminator as the area of the pupil is decreased.20 This is discussed further in the section on uniformizers. Conventional illumination, unlike off-axis illumination, tends to have more of the zero-order light not participating in image formation. This light contributes to background and stray light or flares in the image formation. This can be deduced by comparing the pupil diagrams of Figure 1.5 and Figure 1.9. Off-axis illumination can also reduce or increase the influences of aberration in the projection lens (Figure 1.11).21,22
Illuminators for Microlithography
Published in Fred M. Dickey, Todd E. Lizotte, Laser Beam Shaping Applications, 2017
The quadrapole is the optimal illumination for the printing of dense features in two orthogonal directions, known as Manhattan geometries. For features that are not orthogonally aligned to the dipole or quadrapole, the DOF is actually degraded. An annular illumination pupil has no orientation preference and allows more of the illumination pupil to be used. Maintaining uniform irradiance becomes more difficult for the illuminator as the area of the pupil is decreased.29 This is discussed further in Section 2.3.3. Conventional illumination, unlike off-axis illumination, tends to have more of the zero-order light not participating in image formation (Figure 2.12). This light contributes to background and stray light or flare in the image formation. Off-axis illumination can also reduce or increase the influences of aberration in the projection lens.30,31
Design and implementation of CCD image-based DNA chip scanner with automatic focus calibration
Published in Systems Science & Control Engineering, 2019
Furthermore, there are still some future improvements. Firstly, the stray light in the optical path can be further reduced by using a material that absorbs light more easily or by using a professional light absorbing paint on the inner surface of the optical path structure. In the future, miniature motor and gear can be used to calibrate the focal length to improve the accuracy of calibration. Finally, we will enable the LED light intensity and temperature of the scanner to be controlled automatically to further increase its flexibility and degree of automation. It can further improve the performance of the instrument by using advanced image processing technology (Zeng et al., 2017; Zeng et al., 2018).