High Incident Light Intensities Research Articles

High light-level blooming in the silicon vidicon

Blooming occurs in silicon-vidicon targets because more hole-electron pairs are created at a given point by the incident light signal than can be removed by the action of the scanning electron beam. The excess carriers move laterally in the target through diffusion and, as a result, the blooming has the following properties- 1) the Slope of the blooming curve on semilog paper does not depend on the size of the incident light spot, i.e., at a given overload intensity, all circular spot sizes add the same excess amount to their radii; 2) the radius of a bloomed spot increases linearly with the log of the incident intensity; 3) the Slope of the blooming curve does not depend on beam current; however, the intensity at which the blooming begins does depend directly on the beam current. At very high incident-light intensities, a dramatic increase in the blooming is observed. This can be attributed to diffusion under conditions where the minority carrier level has become equal to the majority carrier level.

Evidence for Two Photoreactions and Possible Involvement of Phytochrome in Light-dependent Stomatal Opening

Leaves of the xantha mutant of Helianthus annuus have a higher rate of transpiration and a lower diffusive resistance in the light than in the dark. Stomates of this nonphotosynthetic mutant open in the light and close in the dark.Comparative studies of tobacco, xantha mutant, and wild-type sunflower stomatal opening over a range of light intensities in isolated portions of the spectrum reveal two patterns of response: (a) a low intensity opening in the green and far red characterized by partial opening, absence of a threshold, and saturation of the response at low light intensities; (b) a high intensity response in the blue characterized by a threshold (intensities greater than 100 microwatts per square centimeter needed for opening) and a linear opening response at higher incident light intensities. In xantha mutant stomates only the low intensity system appears to be operational, while both low and high intensity systems are present in the wild-type sunflower and tobacco.Red light has an inhibiting effect on stomatal opening in both mutant and wild-type sunflowers. They require prior exposure to far red for opening to occur in red light. This redfar red antagonism suggests the involvement of phytochrome.