Instantaneous Intensity Research Articles

Laser Color Recording Directly on Nine-Inch Color Film

A Laser Color Recorder is described which yields Landsat or similar high-resolution images directly on photographic color film. This development, sponsored by NASA Goddard Space Flight Center, provides the capability for transferring computer-formatted magnetic tape data directly to positive or negative color imagery. Designed to circumvent the current task of reconstructing color images by combining individual (monochrome) color separation negatives, this recorder yields Landsat pictures, directly, with growth potential for the recording of advanced, high-resolution color image sensor data. Three individual laser beams, representing the three primary colors, are modulated separately, then combined precisely to form a single beam of light. This synthesized beam, in which the instantaneous hue and intensity are determined by the modulating signals, is focused on the recording film through a rotating scanning mirror. The entire scanner assembly is translated across the format length to form a raster image directly on the photographic color film.

Instantaneous intensity distribution in a focused laser beam at 063 μm and 106 μm propagating through the atmosphere

Experimental results from investigations of instantaneous intensity distributions in focused laser beams at 0.63 microm and 10.6 microm at a distance of approximately 5 km are presented and discussed. At 0.63 microm the beam pattern is broken into several diffraction-scale spots because focusing is saturated. At 10.6 microm the beam pattern is almost uniform. This is valid for beam dimensions smaller than the correlation length of the amplitude.

High-order multimode radiation statistics of aTEM 00 Q-switched neodymium laser

We interpret our recent experimental results concerning the dependence of the 11-photon Xe ionization rate on the axial-mode number of aQ-switched laser. If one takes the experimental procedure into account, the stochastical quantity of interest is the ratio between the instantaneous intensity and the mean intensity averaged over a round-trip duration. The enhancement factor normalized to the monomode case is the eleventh moment of that over-intensity. The measurements indicate that nearby longitudinal modes are FM-type phase correlated, while distant modes are phase independent. The radiation emitted by our Nd3+ glass laser have not the statistical properties of a pulsed Gaussian field, yet when the spectrum is sufficiently large (several Å) itsk-th-order over-intensity moment has the same valuek! as for a pulsed Gaussian field with a large spectrum.

Effect of beam intensity on target response to high−intensity pulsed CO2 laser radiation

The mechanical response of various classes of opaque materials exposed in air to high−intensity pulsed 10.6−μm−wavelength laser radiation is described. At beam intensities below approximately 107 W/cm2 (pulse durations of 4×10−3 and 3×10−4 sec), the magnitude of the total impulse delivered to the target is found to depend on the nature of the target material. At intensities greater than approximately 108 W/cm2 (pulse duration of 2×10−5 sec), there is negligible difference in the impulse response of different materials. Moreover, at the higher power densities total impulse delivered to a target by a 0.04−cm2 laser beam is found to be proportional to the physical area of the target up to approximately 8 cm2. These results are correlated with the the interrelationships among the instantaneous laser intensity, the instantaneous pressure generated at the target surface, and the observed state of development of the laser plume. Also reported is a survey of the thermal response of aluminum targets to laser irradiation over this range of power densities. These studies reveal that the apparent thermal coupling coefficient of aluminum remains at the cw value of approximately 3% at incident power densities as great as 105 W/cm2. Between 105 and 107 W/cm2, the optical coupling coefficient goes through a maximum of approximately 6%, then drops to a level close to zero at power densities greater than 108 W/cm2.

Rate-distortion functions for nonhomogeneous Poisson processes (Corresp.)

Information rates for nonhomogeneous Poisson counting processes are derived. A source coding theorem is proved and rate-distortion functions are obtained for the reconstruction of the sample functions of the latter sources. Distortion measures which depend upon the magnitude of the error as well as on a temporal weighting function proportional to the instantaneous intensity of the source are assumed. The analysis utilizes recent results concerning information rates for homogeneous Poisson processes and appropriate time-scale transformations, which map the source sample functions into an isometric induced source.

A new method of bone mineral estimation using a conventional x-ray set.

The technique described here uses an unmodified clinical X-ray set, whose output variations in intensity and spectral distribution, due to changes in the voltage in the mains supply, are compensated for by a two-detector system. This employs two scintillation crystals coupled with photodiodes to measure the instantaneous total intensity of two neighbouring beams of X rays, one passing through a reference filter and the other through a limb to be investigated. The equipment has been designed to scan the ulna at a steady speed of 1 cm/sec; furthermore, special techniques have been developed to ensure that the arm is secured in the moving frame, without discomfort to the patient, so that there is negligible positional error. The system enables a spatial resolution of an element of 0·25 mm in width to be obtained. It has been shown that the error of each absorption measurement does not exceed 2 per cent. The results are presented as a plot on X-ray film, which is a suitable form for clinical records, as scans carried out with an interval of time may easily be compared by superposition.

Diffraction and Interference of Partially Coherent Light Traversing Two Superposed Sound Fields

The diffraction and interference of a light wave passing through two superposed sound waves have been studied theoretically on the basis of Huygens' principle. As a result of frequency shifts in every deflected light ray caused by the sound waves, the instantaneous intensity resulting from linear superposition of the deflected light rays consists of the d.c. component as well as the a.c. component as a sum of beating signals among those rays, provided that the coherence time of the light is long enough compared with the period of a beating signal under consideration. A general formula for diffraction is derived and two-beam interference is considered as a special case. The resultant formula illustrates that the complex degree of coherence is modulated, after traversing the sound field, with a form of the Bessel function of zeroth-order which varies with Raman-Nath parameters as well as with the separation of two points on the wavefront of the light. This validity will hold so long as the inclination factors for the deflected light rays in Huygens' principle are regarded to be nearly equivalent. The results for progressive and standing sound waves are described as special cases.

Random Wave-Front Perturbations and Telescopic Star Images

A computational model of random perturbations induced in wavefronts in the entry pupil of telescopes of moderate aperture has been constructed and used to predict the instantaneous distribution of intensity in the perturbed stellar images formed by such telescopes. Parameters of the model have been chosen to give a reasonably life-like imitation of perturbations due to imperfect ‘seeing’; and in order to gain some idea of the adequacy of the model, instantaneous intensity distributions in images of α-Aur have been obtained by computer reduction of observations made at the Cambridge 36-inch telescope using a spectracon electrono-graphic image tube. The model and its predictions are described and compared with the observations.

Time-Dependent Photoelectric Counting Statistics for aQ-Switched Laser Near Threshold

The time-dependent variation of the photoelectric counting probability has been measured for a $Q$-switched single-mode laser, whose steady state is in the neighborhood of the threshold of oscillation. The mean and the variance of the instantaneous light intensity, at various times and for various pump parameters, are derived and found to be in very good agreement with the values predicted by Risken and Vollmer.

Photoelectric Detection with Two-Photon Absorption*

A formula for the photoelectron-counting distribution for a two-photon detector is derived quantum mechanically assuming that the ionising transitions in the atoms of the detector take place through the simultaneous absorption of two photons. It is assumed that the incident light is quasimonochromatic. It is shown that the distribution of the photoelectrons is given by the average of a Poisson distribution, the parameter of the distribution being proportional to the time integral of the square of the instantaneous light intensity. Counting distributions for the thermal (gaussian) light and for some models of laser light are obtained for the limiting case when the counting-time interval T is short compared to the coherence time Tc of the light. An approximate formula for arbitrary time intervals for the counting distribution of thermal light is also proposed.

Detectability of seismomagnetic effect

Recent measurement of seismomagnetic effect by modern magnetometers indicates that very accurate observations should be made to detect a geomagnetic change possibly associated with an earthquake. Even if we use a proton precession magnetometer, which is free from a drift, attention should be drawn to the magnetic field produced by electric currents induced in the earth. Observations in Japan show that instantaneous values of the total geomagnetic field are considerably different for stations only several kilometers distant from one another.It is also made clear that the total intensity values at a station are systematically larger or smaller in some cases than those values at another station. The fact suggests possible use of a weighted difference technique based on a proportional constant to be determined empirically. A standard deviation, amounting to 2γ, for comparison of instantaneous total intensity values between two stations 100–200 km distant from one another in Japan has been achieved by making use of the weighted difference technique for nighttime data.

Pole Figure Integrator

A device, applicable to samples with fiber texture, is used on a diffractometer to average the diffracted x-ray intensities representing values on a pole figure. In the process, the fiber axis is rotated end-over-end continuously at a constant rate through an angle φ which is also the colatitude coordinate of the pole figure. To convert the time average of the intensity to a space average over the pole figure, the instantaneous intensity is multiplied by a factor |sin φ|; this factor is generated by a rotating variable attenuating filter located in the path of the incident beam. When the diffraction angle is varied at a uniform rate during this process, the resulting scan is equivalent to a diffractometer pattern of the sample material with random orientation. By using, in addition, a similar scan made with an attenuating filter generating the function cos2φ|sinφ|, an orientation parameter 〈cos2φ〉 can be easily evaluated for plane normals, crystal axes, and molecular axes.

EFFECT OF MODE BEATING IN LASER-PRODUCED GAS BREAKDOWN

Experiments have been carried out which show that the electrical breakdown of gases by optical frequency radiation is independent of the instantaneous intensity fluctuations arising from the interaction of modes present in laser radiation. Gas breakdown thresholds, determined with a single-mode ruby laser and a phase-locked neodymium laser are in substantial agreement with published threshold data for conventional, multiple-mode laser radiation. It was thus determined that the breakdown threshold does not depend upon short term temporal and spatial fluctuations of the power density.

Clinical Comparison of Xenon-Arc and Laser Photocoagulation of Retinal Lesions

Photocoagulation of the choroid and retina can be produced by the absorption of light energy from either the xenon-arc or the laser photocoagulator. Both coagulator systems deliver light energy in the visible or infrared region of the spectrum, and the ultimate chorioretinal effect is determined by the total amount of light energy absorbed and converted to heat. The major physical difference between the light and laser systems is the type of radiation developed by each method. The ruby laser beam delivers light energy at one wavelength (6943 A) in the deep red region of the visible spectrum. The effect on an ocular tissue is determined by the specific tissue absorption for that wavelength only and by the instantaneous (0.0005 seconds) intensity of the beam. The xenonarc high pressure bulb delivers radiation from all portions of the visible and near infrared spectrum (Fig). This broad spectral energy output is presented to

Scattered Intensities for Random Distributions—Microwave Data and Optical Applications

We compare theory and microwave intensity measurements (5-mm wavelength) on a dynamical model of a compressible gas. The model consists of a slab-region styrofoam container (25cm × 50 cm × 60 cm) whose top and bottom are grids which allowfor the passage of turbulent air streams, but serve to confine light-weight randomly moving spheres (3.45-cm diam, relative index of refraction of 1.016 at 5-mm wavelength). We varied the number (N) of scatterers in the container (fractional volume w in the central region ranging from about 0.03 to 0.3), and made measurements in the forward direction (θ = 0), as well as at off-forward angles in the range θ = 0° to 15°, and θ = 30° to 80°. The essential limitations on the general utility of our data are set by difficulties in relating w to N, and by the supplementary statistical procedures used to reduce our chart records of instantaneous total intensity data into coherent and incoherent components. For most parts of the program, the accord between numerical computations based on theory and our specific measurements is adequate, and the general predictions of theory are satisfactorily substantiated, e.g., that for gaslike distributions of lossless large scatterers the incoherent intensity divided by the departure of the coherent intensity from the forward intensity in the absence of scatterers is practically independent of concentration.

Turbidometric estimations in Mexico city using the Volz sun photometer

Measuring, with the aid of two filters, the instantaneous intensity of the solar radiation in two wave lengths (λB = 0.44 μ, λR = 0.64 μ) by means of a sun photometer designed byVolz, we carried out determinations of the decadic turbidity coefficientB (λ=0.5 μ) and the wave length exponent α of the haze extinction for Mexico City. Observations were made for almost two and a half years (1960 to 1962 period). A seasonal size distribution in both parameters was found. Although the data thus obtained are provenient of a contaminated atmosphere, comparison of our data is made with those found for higher latitudes ofAngstrom, Schuepp andVolz. The height of the homogeneous haze layerHD was calculated showing pronounced variations for a given wind direction. The maximum and minimum values ofB enable us to get, by the first approximation, the aerosol size distribution ofJunge for our latitudes. However, for exceptional very clear days having maximum actinometric intensity of the solar radiation the sensitivity of the microamperimeter in theVolz sun photometer fails.

ELECTRICAL STIMULATION OF EIGHT CRANIAL NERVE.

This is a report concerning the methods by which we have succeeded in stimulating the eighth nerve electrically. To carry out this study certain postulates were made for the purpose of selecting the initial experiment. We first assumed that many patients suffering from congenital and acquired hearing loss harbored a defective or inadequate organ of Corti rather than a functionless auditory nerve. 1 It would follow therefore that we should attempt to develop a method of stimulating the never electrically, in a manner similar to that previously done by Djourno et al. 2 An additional postulate was that the individual nerve fibers of the auditory branch of the eighth nerve are nonspecific. We further assumed that the number of nerve fibers firing simultaneously is a function of the instantaneous sound intensity, that the number of serial firings per second is a function of frequency, and that interpretation of this

Synchrocyclotron 200-Meter Flight Path Neutron Velocity Spectrometer

Our synchrocyclotron neutron time-of-flight spectrometer now uses a 200-m flight path and two 2000-channel analyzers. The many important modifications and improvements described in this paper have been made as a result of operating experience. The present operation uses ∼20 nsec bursts at an instantaneous intensity ∼5×1018 evaporation neutrons per second and a 60-cps repetition rate. The resolution for energies above 1 keV is now limited by the time analyzers which have 100-nsec detection channel widths, giving a resolution of 0.5 nsec/m in the keV region.

A proposed fast-wave photo-electric laser mixer for millimetre-wave generation

A photo-electric cell having the form of a parallel-strip transmission line in which the lower strip is photo-emissive is proposed as a means of generating millimetre waves from two laser beams.The non-emissive strip is maintained at a positive potential with respect to the emissive strip, so that photo electrons are attracted to it. By making the potential as large as possible and the separation of the strips as small as possible the electron transit time is reduced.Two laser beams, differing in frequency by the required millimetric frequency, are directed on to the photo-emissive surface along the strip at almost grazing incidence. Electron emission is proportional to the instantaneous intensity of the two beams together; as this is proportional to the square of the sum of their amplitudes a difference-frequency term (in the millimetric range) appears in the photo-current emitted. As the laser beams travel almost parallel to the strips, the phase velocity of the beams measured along the strips is almost equal to that of a millimetric TEM wave travelling between them. Through the electron-emission process, such a TEM wave is in fact generated, and grows linearly in amplitude with distance along the strips.The theory of the device is worked out, and a numerical example is given.

Metastable Atoms and the Auroral Afterglow of Nitrogen

The auroral afterglow of nitrogen is attributed to N atoms in the high metastable level 6S which in binary collisions with normal N atoms produce excited N2+ ions and with normal N2 molecules excite their spectrum. This hypothesis explains (1) the high energy of the levels emitting light, (2) the dominant instantaneous intensity of the brief duration auroral afterglow, (3) the absence of the N2+ bands in Kaplan's ``blue afterglow,'' and (4) the suppression of the same bands by oxygen impurity.