A coupled wave analysis is given of the Bragg diffraction of light by thick hologram gratings, which is analogous to Phariseau's treatment of acoustic gratings and to the “dynamical” theory of X-ray diffraction. The theory remains valid for large diffraction efficiencies where the incident wave is strongly depleted. It is applied to transmission holograms and to reflection holograms. Spatial modulations of both the refractive index and the absorption constant are allowed for. The effects of loss in the grating and of slanted fringes are also considered. Algebraic formulas and their numerical evaluations are given for the diffraction efficiencies and the angular and wavelength sensitivities of the various hologram types.

Coupled wave theory for thick hologram gratings

Foundering of mafic lower continental crust into underlying convecting mantle has been proposed as one means to explain the unusually evolved chemical composition of Earth's continental crust, yet direct evidence of this process has been scarce. Here we report that Late Jurassic high-magnesium andesites, dacites and adakites (siliceous lavas with high strontium and low heavy-rare-earth element and yttrium contents) from the North China craton have chemical and petrographic features consistent with their origin as partial melts of eclogite that subsequently interacted with mantle peridotite. Similar features observed in adakites and some Archaean sodium-rich granitoids of the tonalite-trondhjemite-granodiorite series have been interpreted to result from interaction of slab melts with the mantle wedge. Unlike their arc-related counterparts, however, the Chinese magmas carry inherited Archaean zircons and have neodymium and strontium isotopic compositions overlapping those of eclogite xenoliths derived from the lower crust of the North China craton. Such features cannot be produced by crustal assimilation of slab melts, given the high Mg#, nickel and chromium contents of the lavas. We infer that the Chinese lavas derive from ancient mafic lower crust that foundered into the convecting mantle and subsequently melted and interacted with peridotite. We suggest that lower crustal foundering occurred within the North China craton during the Late Jurassic, and thus provides constraints on the timing of lithosphere removal beneath the North China craton.

Recycling lower continental crust in the North China craton

General principles are formulated for the objective reconstruction of a three dimensional object from a set of electron microscope images. These principles are applied to the calculation of a three dimensional density map of the tail of bacteriophage T4.

Reconstruction of Three Dimensional Structures from Electron Micrographs

The supply and accumulation of silica in the marine environment

Two-photon fluorescence microscopy is one of the most important recent inventions in biological imaging. This technology enables noninvasive study of biological specimens in three dimensions with submicrometer resolution. Two-photon excitation of fluorophores results from the simultaneous absorption of two photons. This excitation process has a number of unique advantages, such as reduced specimen photodamage and enhanced penetration depth. It also produces higher-contrast images and is a novel method to trigger localized photochemical reactions. Two-photon microscopy continues to find an increasing number of applications in biology and medicine.

Two-Photon Excitation Fluorescence Microscopy

Fig. 2. A. Instrumental response. B. Excitation spectrum of the 1.93-1L fluorescence of 1I2-atom percent Tm+3 in Er20 3• C. Excitation spectrum of the 1.93-1L fluorescence of 1/2-atom percent Tm+3 in Y203' times as intense as the emission from 1/2% Tm+3 in Y20 3 at 77°K under tungsten excitation. The laser experiments were conducted with a sample approximately 1 cm in length with flat and parallel silvered ends using a fast gold-doped germanium detector. The threshold was less than 3 joules into a I-in. straight xenon flash lamp in close proximity to the liquid nitrogen dewar containing the sample. No laser operation could be obtained from the nearby fluorescent lines at an energy input of 20 joules. The lifetime of the fluorescence is 2.9 msec at 77°K with a build-up time of about 200 f..tsec. Nearthreshold laser emission is observed 50 f..tsec after the 250-f..tsec lamp pulse is over, an effect which is a consequence of this build-up time. CW operation was observed using 500-W quartziodine tungsten lamps as the pumping source. In the configuration used, the liquid nitrogen dewar containing the sample was surrounded by an array of 12 lamps. Threshold was reached with three lamps. The crystals were grown by A. C. Pastor and K. Arita under the direction of R. C. Pastor. We thank D. Roberts for the use of the CW laser housing, C. R. Duncan for technical assistance, and]. Mikiska for the coatings.

Lensless Fourier-Transform Method for Optical Holography

Optical image synthesis (complex amplitude addition and subtraction) by hollographic fourier transformation

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/32013/0000055.pdf;sequence=1

Fourier-transform spectroscopy using holographic imaging without computing and with stationary interferometers

White-light reconstruction of holographic images using the Lippmann-Bragg diffraction effect☆

/pdf/holography-with-spatially-noncoherent-light-3lhtcily7l.pdf

George W. Stroke

Papers

Lensless Fourier-Transform Method for Optical Holography

Optical image synthesis (complex amplitude addition and subtraction) by hollographic fourier transformation

Fourier-transform spectroscopy using holographic imaging without computing and with stationary interferometers

White-light reconstruction of holographic images using the Lippmann-Bragg diffraction effect☆

Holography with spatially noncoherent light