Illumination Dose Research Articles

On the Theory of the Reconstruction of a Weak Phase-amplitude Object from its Images, Especially in Electron Microscopy

In this paper we study the statistical properties of the reconstructed object wavefunction of a weak phase-amplitude object from two low-dose image intensity distributions. The images are obtained by successively illuminating the object coherently by plane quasi-monochromatic waves which make different angles with the optical axis. The case is discussed for isoplanatic conditions and one lateral dimension. Explicit expressions of the mean and variance of the reconstructed wavefunction are presented in terms of the illumination dose. The low spatial frequencies which were hardly retrievable in the method based on two defocused images obtained under axial illumination are accessible in this approach.

Process Parameter Control in Optical Lithography

Today in projection lithography the loss in useful resolution stems primarily from the problem of process control. Unavoidable variations in process parameters produce either unacceptable variations in resist linewidth, or result in “unresolved” features-lines missing or spaces not cleared. In this paper simulation is used to perform quantitative studies on the sensitivity of critical dimensions of positive resist profiles with respect to variations in resist thickness T, illumination dose and development time tdev. A modified version of the simulation program SAMPLE was used.1) The results obtained show that: 1) In most cases exposure and development time trade off with little effect on linewidth control; 2) Greater linewidth control may be achieved at the expense of minimum linewidth; 3) The use of post-exposure bake generally improves linewidth control, and, significantly, resolution on aluminum substrates with steps; 4) Linewidth control and practical resolution are drastically increased by planarization and elimination of reflections; a combination of both techniques can extend lithography to the sub-micron regime.

Illumination-dose dependence of persistent photoconductivity ofn-GaAs epitaxial layers

The dependence of persistent photoconductivity on illumination dose is studied forn-type GaAs epitaxial layers on Cr-doped semi-insulating GaAs substrates. Mobility and electron number, but not necessarily density, are enhanced by illumination. The logarithmic dependence of the persistent electron number on illumination dose is explained with a macroscopic potential barrier between layer and substrate, with holes being trapped in the substrate. The mobility enhancement is attributed to screening of ionized impurities by the photogenerated electrons.

Kinetics of Activation of Nicotinamide Adenine Dinucleotide Kinase by Phytochrome—Far Red-absorbing Form

The effects of exogenous redox cofactors and purine analogues on the activation of the NAD kinase by Pfr were examined. Addition of phenazine methosulfate, flavin mononucleotide, or methylene blue increased the activation of NAD kinase by red light in a partially purified preparation of phytochrome. Phenazine methosulfate and flavin mononucleotide do not absorb light in the red or far red region, so they do not act as light receptors in this activation. Thus they probably intervene in electron transfer between phytochrome and NAD kinase. Addition of kinetin with these compounds increased photopotentiation further. In the presence of phenazine methosulfate and kinetin, the activation of NAD kinase by red light was counteracted by illumination with far red light immediately after red light.The relation between the dose of illumination with red light and the degree of activation of NAD kinase was measured. Illumination for 5 minutes with 800 ergs cm(-2) sec(-1) of red light was sufficient to obtain maximal activation. In the dark, the activated state of NAD kinase was maintained for about 10 min and then rapidly lost. The time of preservation of the activated state was greatly shortened by illumination with far red light, indicating the participation of phytochrome.

Variability of photodynamic killing in Escherichia coli and avoidance of variability with agar.

Photodynamic killing of Escherichia coli in acridine orange is influenced by the composition of the containing vessel, and after high kill the variance between replicate suspensions is greater than attributable solely to sampling and plating. Addition of agar minimizes both phenomena, but a higher illumination dose is required to produce the same degree of killing.

Analysis of photoenzymatic repair of UV lesions in DNA by single light flashes: III. Comparison of the repair effects at various temperatures between +37° and −196°

UV-irradiated transforming DNA of Haemophilus influenzae can be repaired in vitro in the presence of yeast photoreactivating enzyme (PRE) by an intense light flash of about 1 msec duration. Such a flash repaires a fraction > 0.9 of enzyme-complexed photorepairable lesions at all temperatures between +37° and −40°, but only a fraction of about 0.25 or 0.1 at −78° or −196° respectively. A similar decline below −40° is observed for photoenzymatic repair (PR) of E. coli B s−1 cells and for PR of transforming DNA by continuous illumination with white light. The decreased effects at low temperatures result neither from damage to the reaction mixture by freezing or by the illumination itself, nor do they result from dissociation of the PRE-substrate complexes in the dark. The drastic reduction in the extent of PR is observed already below −2° if the photolytic reaction is limited by using a less intense light flash. These results are best explained by assuming that the relative repair efficiency of incident photons drops substantially below −2°, but this is not noticed with a very intense flash, where the number of incident photons is excessive. It remains open whether the decreasing repair efficiency with decreasing temperature reflects reduced absorbance or a reduced quantum yield of the absorbed photons. Increased PR effects at −78° and −196° can be obtained by sequential flashes or by increased periods of illumination with white light, but the kinetics indicate the presence of 2 or more fractions of PRE-substrate complexes, differing in their probabilities of being repaired. At low temperature as well as at room temperature flashes photolyse a majority of the complexes more efficiently than equivalent doses of continuous illumination, suggesting an enhancement of PR by absorption of 2 or more photons within a limited time interval.

Observations on photodynamic inactivation of vaccinia virus and its effect on immunogenicity.

Photoinactivation of vaccinia virus sensitized by methylene blue had parameters similar to those observed with other viruses. Thus inactivation proceeded exponentially to completion, was irreversible, independent of temperature and the intensity of illumination. Inactivation was dependent on the dose of illumination and the concentrations of both methylene blue and hydrogen ions. The effects of pH appeared to be primarily concerned with the tenacity of dye-virus binding. Inactivation was inhibited by small amounts of nucleic acid but not by their bases or pentoses. Inactivation was only affected by the presence of extraneous protein in relatively high concentration: it was not affected by the enzymes catalase or peroxidase. Attempts to obtain direct chemical evidence of the participation of viral nucleic acid in photoinactivation were unsuccessful.Recombination experiments strongly indicated the involvement of viral protein in photoinactivation. Immunogenicity was not impaired since good responses of neutralizing antibody were obtained in rabbits immunized with vaccines photoinactivated over a wide range of exposure times.