We have carried out a picosecond fluorescence study of holo- and apoazurins of Pseudomonas aeruginosa (azurin Pae), Alcaligenes faecilis (azurin Afe), and Alcaligenes denitrificans (azurin Ade). Azurin Pae contains a single, buried tryptophyl residue; azurin Afe, a single surface tryptophyl residue; and azurin Ade, tryptophyl residues in both environments. From anisotropy measurements we conclude that the interiors of azurins Pae and Ade are not mobile enough to enable motion of the indole ring on a nanosecond time scale. The exposed tryptophans in azurins Afe and Ade show considerable mobility on a few hundred picosecond time scale. The quenching of tryptophan fluorescence observed in the holoproteins is interpreted in terms of electron transfer from excited-state tryptophan to Cu(II). The observed rates are near the maximum predicted by Marcus theory for the separation of donor and acceptor. The involvement of protein matrix and donor mobility for electron transfer is discussed. The two single-tryptophan-containing proteins enable the more complex fluorescence behavior of the two tryptophans of azurin Ade to be understood. The single-exponential fluorescence decay observed for azurin Pae and the nonexponential fluorescence decay observed for azurin Afe are discussed in terms of current models for tryptophan photophysics.

The luminescence of purines and their corresponding nucleosides and nucleotides has been studied at 77°K for different states of ionization and for some alterations of tautomeric forms. To a first approximation, the excitation spectra always coincided with the absorption spectra. Furthermore the emission profiles were independent of the exciting wavelength and, except for the protonated forms of guanine and its derivatives, phosphorescence always consisted of a single exponential decay. The naturally occurring pyrimidines, uracil, thymine, and cytosine, fluoresced over a wide pH range but only phosphoresced at high pH where they have lost a proton. From a study of methylated pyrimidines it was shown that the lactim forms fluoresced at 300°K and phosphoresced at neutral pH at 77°K. In these two respects they differed from the natural pyrimidines and support the commonly accepted lactam structures for the natural pyrimidines. The purines, adenine and guanine, and their derivatives fluoresced and phosphoresced in neutral and basic solutions at 77°K. Upon protonation at pH∼4 the emission of AMP was completely quenched, adenosine had its phosphorescence considerably reduced, while the luminescence of adenine was essentially unchanged. The quantum yields, luminescence spectra, and phosphorescence decay times were measured for all the compounds.

We describe a holographic microscope with a spatial resolution approaching the diffraction limit. The instrument uses a tiny drop of glycerol as a lens to create the spherically diverging reference illumination necessary for Fourier-transform holography. Measurement of the point-spread function, which is obtained by imaging a knife edge in dark-field illumination, indicates a transverse resolution of 1.4 microm with wavelength lambda = 514.5 nm. Longitudinal resolution is obtained from the holograms by the numerical equivalent of optical sectioning. We describe the method of reconstruction and demonstrate the microscope's capability with selected biological specimens. The instrument offers two unique capabilities: (1) it can collect three-dimensional information in a single pulse of light, avoiding specimen damage and bleaching; and (2) it can record three-dimensional motion pictures from a series of light pulses. The conceptual design is applicable to a broad range of wavelengths and we discuss extension to the x-ray regime.

Robust stability is a chief characteristic of relativistic͞charge-displacement self-channeling. Theoretical analysis of the dynamics of this stability (i) reveals a leading role for the eigenmodes in the development of stable channels, (ii) suggests a technique using a simple longitudinal gradient in the electron density to extend the zone of stability into the high electron density͞high power density regime, (iii) indicates that a situation approaching unconditional stability can be achieved, (iv) demonstrates the efficacy of the stable dynamics in trapping severely perturbed beams in single uniform channels, and (v) predicts that Ϸ10 4 critical powers can be trapped in a single stable channel. The scaling of the maximum power density with the propagating wavelength is shown to be proportional to ؊4 for a given propagating power and a fixed ratio of the electron plasma density to the critical plasma density. An estimate of the maximum power density that can be achieved in these channels with a power of Ϸ2 TW at a UV (248 nm) wavelength gives a value of Ϸ10 ), a range that can approach Ϸ100 W͞atom. These conditions provide new possibilities for the production and regulation of many highly energetic physical processes, including hard x-ray generation, the initiation of nuclear reactions, particle acceleration, and the fast ignition of fusion targets. The key to the production of these exceptional conditions is the stable compression of the spatial distribution of powerful (P 0 Ϸ 1 TW-1 PW) pulses of radiation into very narrow plasma channels. Specifically, a complex mechanism, which is triggered by pulses whose power exceeds a critical value P cr and involves both relativistic electron motions and the relative spatial separation of the electron and ion densities caused by the radiation pressure of the intense wave, produces the conditions necessary for channel formation. In brief (1), the ponderomotive radial displacement of the electrons and the contrasting inertial confinement of the ions cooperate to produce the two chief characteristics of the channels. They are (i) the refractive self-focusing action of the displaced electrons, which confines the propagating radiation, and (ii) the high spatial stability of the channels, the feature produced by the immobile electrostatic spine formed by the fixed ions. These narrow channels, which typically have a diameter of a few microns, represent an example of a new, largely unexplored class of strongly nonequilibrium excited matter that combines a very high energy density with a well-ordered structure.The existence of dynamic stability is essential for the control of high power density plasmas. Of particular importance are the physical limits of stable behavior and the corresponding implications on the maximum achievable power density. The overall result of this study is that exceptionally robust stability is a chief characteristic of the relativistic͞charge-displacement self-channeling mechanism. Specifically, the six key findings are: (i) the discovery of the ...