Albert Rose

The sensitivity performance of the human eye on an absolute scale.

An absolute scale of performance is set up in terms of the performance of an ideal picture pickup device, that is, one limited only by random fluctuations in the primary photo process. Only one parameter, the quantum efficiency of the primary photo process, locates position on this scale. The characteristic equation for the performance of an ideal device has the form BC2α2=constantwhere B is the luminance of the scene, and C and α are respectively the threshold contrast and angular size of a test object in the scene. This ideal type of performance is shown to be satisfied by a simple experimental television pickup arrangement. By means of the arrangement, two parameters, storage time of the eye and threshold signal-to-noise ratio are determined to be 0.2 seconds and five respectively. Published data on the performance of the eye are compared with ideal performance. In the ranges of B(10−6 to 102 footlamberts), C(2 to 100 percent) and α(2′ to 100′), the performance of the eye may be matched by an ideal device having a quantum efficiency of 5 percent at low lights and 0.5 percent at high lights. This is of considerable technical importance in simplifying the analysis of problems involving comparisons of the performance of the eye and man-made devices. To the extent that independent measurements of the quantum efficiency of the eye confirm the values (0.5 percent to 5.0 percent), the performance of the eye is limited by fluctuations in the primary photo process. To the same extent, other mechanisms for describing the eye that do not take these fluctuations into account are ruled out. It is argued that the phenomenon of dark adaptation can be ascribed only in small part to the primary photo-process and must be mainly controlled by a variable gain mechanism located between the primary photo-process and the nerve fibers carrying pulses to the brain.

Performance of Photoconductors

All semi-conductors and insulators are photoconductors. The characteristic parameter of a photoconductor is the life time of a free carrier. The photo-electron current is equal to the product of absorbed photon current and the ratio of life time to transit time of a free carrier. This relation holds as well for the commonly known types of barriers as for uniform photoconductors. The photo-electron current may range from a small fraction of the photon current to many powers of ten greater than the photon current depending on the ratio of life time to transit time. There is good evidence for life times in different photoconductors extending from 10-12 seconds to values approaching a second. The life times of free electrons and free holes are in general independent of each other and markedly different. Only at sufficiently high excitation rates for which the free carrier densities exceed the densities of bound states do the electron and hole life times necessarily become equal. The usual termination of the life time of a free carrier is by recombination with a deep lying bound state in the forbidden zone. These recombination processes are structure sensitive, complex, and generally not amenable to exact solution. A useful insight can be gained by dividing the bound states into deep-lying states, called ground states, that govern the rates of recombination and thereby the free carrier densities; and shallow lying bound states, called traps, that are responsible for observed response times exceeding the carrier life times.

Comparative Anatomy of Models for Double Injection of Electrons and Holes into Solids

The several models for double injection of electrons and holes into solids are shown to fall into three groups: field‐dominated, diffusion‐dominated, and hybrid models. The current‐voltage relation for the field‐dominated models can be written out of hand, within a factor of two, using the criterion: ambipolar drift transit time of free pairs=lifetime of free pairs. Current‐voltage dependencies J ∝ Vn, with n ranging from 1.5 to 3, depend on whether the material is insulating or semiconducting and the recombination monomolecular or bimolecular. In the diffusion‐dominated models the current increases indefinitely while the voltage across the body of the sample remains constant at a value 2kT/e exp (L/2LD), where L and LD are the sample length and diffusion length, respectively. In the hybrid models, a field‐dominated current in one part of the sample is matched to a diffusion‐dominated current in the remainder of the sample. For all of the models reviewed, solutions for the current‐voltage relations are ob...

Quantum and noise limitations of the visual process.

A set of photographs is presented that gives a direct measure of the quantum limitations of the visual process at low illuminations.

Photovoltaic Effect Derived from the Carnot Cycle

An expression for the maximum power derivable from any photovoltaic device is developed in terms of the incident light intensity measured in units of black body radiation. The expression shows the linear dependence of photovoltage on light intensity at low light levels, the logarithmic dependence at intermediate light levels and the saturation at high light levels. The analysis is used to resolve a paradox proposed by W. Shockley.

X‐Ray Noise Observation Using a Photoconductive Pickup Tube

A television pickup tube arrangement using a Vidicon for the direct recording of x‐ray images is described. The transmitted x‐ray picture shows noise characteristics that are clearly those of the absorbed x‐ray photons. The internal conversion gain (number of carriers generated per absorbed x‐ray photon) is estimated by two independent methods, one of which is based on a measurement of x‐ray noise. Both methods give a gain of about 500 for a 100 kv x‐ray photon. The agreement between the two methods is evidence for the validity of the simple electron‐multiplier model for the noise current in the photoconductive selenium target. The appearance of x‐ray noise means that all the information contained in the absorbed fraction of the x‐ray beam is being transmitted. Thirty pictures per second are transmitted when irradiating the Vidicon with a 5 ma, 100 kv x‐ray beam at a distance of two feet. Wires of one mil diameter were clearly observable.

Coherent motion and stereopsis in dynamic visual noise.

Abstract Dynamic visual noise that is binocularly viewed with one eye shaded by a neutral density filter is perceived as having coherent lateral motion and stereoscopic depth. Typically, the incoherent stimulus is transformed into a pair of oppositely drifting sheets, one apparently recessed, the other protruded with respect to the plane of the display. Experimental results which characterize the spatial and temporal properties of this effect are presented. We explain this phenomenon as a global processing version of an apparent motion Pulfrich effect.

A Mechanical Model for the Motion of Electrons in a Magnetic Field

A mechanical model in the form of a gyroscope may be made to simulate the path of an electron in a uniform magnetic field acted upon by transverse electric fields. In using the model, one employs the following substitutions: The uniform magnetic field is replaced by the spin velocity of the gyroscope, the electric fields are replaced by magnetic fields which give the same field configuration, and the electron is replaced by one pole of a permanent magnet mounted on the axis of the gyroscope. The spin velocity may be arbitrarily chosen for convenient observation. Then, depending upon the value of the spin velocity, the dimensions of the gyroscope, the strength of the permanent magnet and the scale factor used in setting up the model, the strength of the magnetic field in the model is adjusted to correspond to the strength of the electric field in the actual case. The path described by the magnetic pole, under these conditions, corresponds to the actual path of the electron. Since the error involved in iden...