A dual-beam source of actinic light for photosynthesis research

The role of optics in research at ames research center

Photooptical processes and optical measuring techniques play an important role in many research programs at NASA's Ames Research Center. Its programs in aerodynamics, in space sciences, and in life sciences are often critically dependent on the experimental data and the theoretical insight provided by optics. The expanding role of optics during Ames' history is described. An extensive bibliography of research reports is provided-including reports of basic work in aerodynamics, space sciences, and life sciences which have relied heavily on optics; reports of research being done from a flying observatory; and reports describing developments in optical technology.

Paramagnetic Unit in Spinach Subchloroplast Particles: Estimation of Size

A pulsed ruby laser (wavelength, 694.3 nanometers) was used to measure the dependence on light intensity of light-induced electron paramagnetic resonance (ERR) signal 1 for short flashes of uniform duration (400 microseconds). Approximately 10(18) photons per square centimeter per flash from the unattenuated beam were available to the sample of subchloroplast "system 1" particles from spinach. The experimental dependence of the EPR signal height plotted as a function of the total number of incident photons per flash was exponential. From measurement of the slope at a very low relative photon flux and the saturated EPR signal amplitude, the value for the cross section or "effective size" of the light-induced paramagnetic unit, sigma(EPR), was found to be 300 x 10(-17) square centimeter. This result is compared with a measured optical absorption cross section, sigma(694nm), of 2.5 x 10(-17) square centimeter, for the identical sample at the laser wavelength. The hundredfold difference in size supports the thesis that the paramagnetic state is a property of an aggregate of chlorophyll molecules of the same general size as the photosynthetic unit.