Peter R. Fontana

Multidetector intensity interferometers

The intensity fluctuations of incoherent radiation are used to determine the position of sources with respect to a detector system. For electromagnetic radiation the system uses square‐law detectors and for acoustic waves the detector output is squared before being processed. The theory is developed for n detectors and the results are applied to two‐, three‐, and four‐detector arrangements. The two‐detector intensity inteferometer measures the square of the first‐order correlation function and can determine the angular size of a source. The three‐detector intensity interferometer yields two coordinates of the location of a source, and a modified version involving only one detector functions as a Fourier transform spectrometer. It measures the first‐order correlation function and thus can be used to obtain the spectrum of the source. The four‐detector intensity interferometer can simultaneously determine the three‐dimensional coordinates of several sources. The operation of several acoustic multidetector i...

Resonance Radiation from Interacting Atoms

The frequency distribution of resonant radiation emitted by a system of two identical interacting atoms is calculated. The separation between the atoms is assumed to be much larger than the size of their charge distributions. Initially one atom is excited while the second one is in the ground state. The two atoms are coupled through the radiation field and the electrostatic interaction. For not too large internuclear separations the line shape of the emitted radiation exhibits two distinct peaks, and the general features are identical with the result obtained from resonance fluorescence scattering. In the decay process, however, there is equal probability of scattering through the symmetric and antisymmetric states, and thus the peak heights of the emitted radiation are different from the ones in the resonance fluorescent case. For large internuclear separations the two peaks merge into the one characteristic of the line shape of a single isolated atom.

Effects of Atomic Interactions on the Absorption and Emission of Radiation

The processes of absorption and emission of radiation by a system of two interacting atoms is investigated. Separation between the atoms is assumed to be much larger than the atomic diameter, and interactions considered are those between the individual atoms and the radiation field and the electrostatic interaction between the atoms. Calculations include those for the time‐dependent probability amplitude of the intermediate and final states as well as that of the emission line shape. The line shape of the emitted radiation consists of two peaks whose amplitude, separation, and half‐width are functions of both the internuclear separation R of the atoms and the energy difference of the excited states of the two atoms. For a large energy difference, the peaks are distinct; for small energy differences, the peaks are distinct at smaller separations, but merge toward the line shape characteristic of a single, isolated atom as R increases.

Optical spectrum of strongly coupled dressed atomic states

A strong radio-frequency field couples two excited atomic states which also interact with the virtual radiation field. The radio-frequency field dresses the atomic states and the virtual radiation field causes them to decay spontaneously. The spectrum of the emitted radiation is calculated by Fourier transforming the differential equations for the amplitudes. The solutions are given in terms of recurrence relationships which can be evaluated to any desired accuracy. The optical radiation field acts as a probe on the dressed atomic states. The spectrum shows all the radio-frequency induced resonances. The frequencies of the states and the Bloch-Siegert shifts of the multi-photon resonances can be deduced from this spectrum.

Crossing and anticrossing signals from Li7

The intensity of scattered radiation from the 22P state in Li7 is calculated as a function of a static external magnetic field. The hyperfine levels of theJ=3/2,Mj=−3/2 andJ=1/2,Mj=−1/2 states cross or anticross near 4780 gauss. The intensity depends on the directions and polarizations of the incident and scattered beams. The peak of the derivative of the corresponding experimental values are 4783.8±0.2 gauss and 4779.8±0.9 gauss, respectively. The theoretical width of the anticrossing signal is 36 gauss which compares well with the experimental result of 35.72±0.36 gauss.