Showing papers on "Light field published in 1972"

Absorption and Emission of Evanescent Photons

Abstract: Experiments have been carried out to investigate the excitation of molecules by evanescent light, and the emission of evanescent light in the fluorescence of excited molecules. It is confirmed that the absorption proceeds at a rate proportional to the second-order (normally ordered) product of the complex field amplitude, whether the light field is homogeneous or evanescent, and that the emission process follows a reciprocity principle.

Photon-Count Distributions and Irradiance Fluctuations of a Log-Normally Distributed Light Field*

Abstract: We discuss some experimental results concerning the statistical properties of a light beam scattered by a rotating ground glass with large surface inhomogeneities (average size 20 μm), when the illuminated area of the scattering surface contains only a few scattering centers. Photon-count distribution measurements indicate that, to a high degree of accuracy, the field amplitude of the scattered light fluctuates as a log-normal variate. The irradiance correlation function is a gaussian function of time with a half-width at half-height that varies inversely with the angular speed of the ground glass but is largely independent of the angle of scattering. Identical functional dependence was previously found, using a ground glass with much smaller surface inhomogeneities (average size 1 μm). Finally, we report some experimental tests of a recent calculation by Mitchell concerning what has been defined as the permanence of the log-normal distribution. We find that, even when the detecting surface of the photomultiplier is illuminated by several coherence areas of the scattered field during a single counting interval, the field-amplitude distribution remains log-normal to an excellent approximation.

Optical scanning apparatus

Abstract: An object to be studied or analyzed is flooded with light from a laser. The light field transmitted from the object, which might for example be a transparency or a vibrating surface, is received by a photodetector. Another portion of the laser light or radiation is deflected throughout a scanning pattern and also caused to fall upon the photodetector. An optical system included in the reference beam path brings the reference beam to a focus (either real or virtual image) at a selected distance from the active surface of the photodetector. As a result, the electric signals developed by the photodetector represent a cross-section of the light field, transmitted from the object, located a distance from the photodetector surface which is the same as the distance therefrom to the focus of the scanned reference beam. Different cross-sections of the signal field from the object may be displayed merely by modifying the optical system. Depending on the manner in which the electric signals are processed, they may be caused to represent either a direct image or a hologram of the cross-section being visualized. By using the electric signals to drive a television-type monitor, a real-time display is reproduced.

Some aspects of the axially symmetric submarine daylight field

Abstract: A set of differential equations is derived to relate the light field and its derivative to the inherent optical properties of sea water (volume-scattering function and beam-attenuation coefficient) when the light field is axially symmetric From these equations, the volume-scattering function and the beam-attenuation coefficient can be calculated if the light field and its derivative with depth are known The equations are then used to provide an alternate proof for the asymptotic light field hypothesis The shape of the asymptotic light field is derived as a function of the inherent optical properties and the asymptotic decay constant It is finally shown that if the shape of the asymptotic light field and the asymptotic decay constant are known, the inherent optical properties can be calculated

VII Quantum Detection Theory

Abstract: Publisher Summary This chapter focuses on the quantum detection theory. It provides an outline of the detection theory appropriate for classical physics and shows the way it is modified to take the laws of quantum mechanics into account. The chapter also proposes a model of an ideal quantum receiver and discusses it analysis to determine the detectabilities of both coherent laser light and incoherent natural light. A telescope is used not only to discover a star, but to measure its location and radiant power, and a spectrometer measures the wavelengths and radiant fluxes of spectral lines. A laser radar determines the distance to a target by measuring the time elapsed until the arrival of a reflected coherent light pulse. Each of these instruments can be regarded as estimating certain parameters of the light field at its aperture and its results are liable to error because of the random nature of that field, subject to quantum fluctuations and corrupted by background light. As the primary field becomes weaker, error increases. The chapter also shows the way the attendant limitations on the measuring power of an optical instrument can be evaluated.

Measurement of the light-field amplitude-correlation function through joint photon-count distributions.

Abstract: When an amplitude-stabilized He-Ne laser beam is scattered by a rotating ground glass with small surface inhomogeneities, the probability density of the instantaneous scattered-wave amplitude is Gaussian. In this paper, we suggest the use of the joint photon-count probability distribution to measure the absolute value of the electric-field amplitude-correlation function for random Gaussian light fields, and report the results of an experiment in which the Gaussian field is produced by scattering a light beam through a rotating ground glass. This procedure offers an alternative to other conventional methods, such as self-beating spectroscopy and irradiance-correlation techniques. The correlation time of the scattered-field amplitude in the present experiment has been measured with an accuracy of approximately 0.8%.

Alignment of light-localized beam and radiographic x-ray beam.

Abstract: A method of checking the alignment of the light field with the x-ray field on variable-aperture radiographic collimators is described. Of 133 collimators tested by this method, 12% failed to meet the alignment requirements recommended by the NCRP.

Spatial Filtering Considerations in Bragg Diffraction Imaging

Abstract: Many of the techniques and effects observed in images from systems using Bragg diffraction imaging can be explained using concepts of optical spatial filtering. This is possible because the Bragg diffraction phenomenom can be thought of as an interaction of a plane-wave of light with a plane-wave of sound to produce a plane-wave of diffracted light. Changing the incident light causes a change in the diffracted light. Hence, the input light field of the imaging system plays an analogous role to the filter transparency of an optical spatial filtering system. The plane-wave components of the diffracted light that form the image of the sound field can be selectively changed by modification of the incident light field. When the imaging method is analyzed as a plane-wave: plane-wave interaction, simple explanations can be given for such diverse effects as the observed astigmatic resolution, the dependence of the resolution on the semi-apex angle of the incident light wedge, dark field imaging, and reflection imaging.