Light-sensitive Material Research Articles

Some Aspects of a Free-Radical Photographic System

Afree-radical photographic process, P-4, is examined. Thi process employs a substituted bipyridylium salt as the lightsensitive material and physical development to amplify the primary image.Monochromatic sensitometry has been used to calculate the quantum exposure scale and to produce conventional D-Iog E curves.The latent-image stability is investigated for storage periods off rom 30min to 14days.The influence of the compositions of the nucleation bath and physical developer is investigated.Conditions are illustrated which yield an improved response compared with those previously published.

Studies on Light-sensitive Material of Organic Titanium Compound (IV)

Studies on Light-sensitive Material of Organic Titanium Compound (IV)

Influence of the information carrier nonlinearity on the density of information recorded in optical memories

An analysis is made of the influence of the information carrier nonlinearity on the density of information recorded in a discrete manner in optical memories. It is shown that the use of nonlinear and threshold light-sensitive materials as information carriers can increase the recording density and the signal/noise ratio in the reproduction of the recorded information. It is reported that information can be recorded at a density of 108 bit/cm2 by helium-neon laser radiation in a nonlinear light-sensitive material based on a chalcogenide glass.

Studies on Light-sensitive Material of Organic Titanium Compound (III)

Studies on Light-sensitive Material of Organic Titanium Compound (III)

Studies on Light-sensitive Material of Organic Titanium Compounds (I)

Studies on Light-sensitive Material of Organic Titanium Compounds (I)

Volume holography of transient optical fields

It is shown that interaction between an optical signal and a special nonmonochromatic reference wave with a bulk light-sensitive material can be used to record information on the spatial and temporal characteristics of the signal. Illumination of a hologram obtained in this way with a special reconstructing wave produces a three-dimensional time-dependent image of the original object. The amount of information which can be recorded in this way is calculated.

Charles Edward Kenneth Mees, 1882-1960

Photography was about sixty years old at the end of the last century. Although it was intended to be used for recording portraits and scenes, the possibility of using it as a recording medium for science was also realized from the start, and through the years it became more and more relied upon as a way of making records for observation and measurement. It was not until towards the end of the century, however, that studies were started on what is now known as ‘the theory of the photographic process,’ which embraces the relationship between the photograph and the thing photographed. Until then the scientific world had shown little interest in the science of photography as distinguished from its practice. The science of photography deals with the physics and chemistry of lightsensitive substances, especially of silver compounds. It is concerned with the nature of the light-sensitive material, the changes occurring when it is exposed to light, the chemical actions involved when a developer is applied to bring out the image, the structure of the developed image, the faithfulness of reproduction of the brightness scale of the original subject, and so on. The first worth-while study of the sensitivity of photographic materials, and the formulation of the rules by which the developed image is related to the original subject, were published by Ferdinand Hurter and V. G. Driffield in 1890. Their investigations, described in the Journal of the Society of Chemical Industry , rested in oblivion for some time. At the end of the century, however, two young students became interested in the subject, eventually found the Hurter and Driffield paper, realized its significance, and very substantially broadened its subject matter.

Dependence of the Sensitivity of Unsensitized Photographic Emulsions upon Temperature*

The change in spectral sensitivity of unsensitized photographic emulsions with temperature and its connection with light-absorption are investigated.In the first part, the influence of temperature upon the shape of the spectral-sensitivity curves is considered and graphs are given showing the ratio of the sensitivities at −195°C and room temperature and the ratio of the sensitivities at +50°C and room temperature as a function of wave-length. For pure silver bromide emulsions, these curves show a minimum at about 470 mµ and a maximum at about 500 mµ. For emulsions containing chloride or iodide, the curve shape is somewhat changed but not in its essential features.In the second part, the absolute change of spectral sensitivity with temperature is discussed. The sensitivity of the basic light-sensitive material, silver bromide, is found to be comparatively little temperature-dependent. The large drop in sensitivity, on lowering the temperature, which is found in commercial emulsions, is due to the chemical sensitization becoming less effective.In the third part, a tentative explanation is given for the results of the first part. It is assumed that the maximum of the sensitivity-ratio curves at 500 mµ is due to a different temperature-dependence in the light-absorption of the silver bromide and that of the reaction product of the chemical sensitizer with the emulsion (probably silver sulfide) which, in this region, acts as an optical sensitizer. Measurements of the spectral light-absorption of a pure silver bromide emulsion show that the decrease in sensitivity with temperature of this emulsion at 400 mµ is, at least in the main, due to decreased light-absorption and only to a smaller extent to a genuine decrease in light-sensitivity.It is concluded from the experimental results that there exist two kinds of sensitivity specks: one kind being numerous and consisting of shallow traps, which are mainly responsible for the sensitivity of chemically non-sensitized grains and for that of the interior of chemically sensitized grains; the other kind being few in number and consisting of deep traps, which are responsible for the surface sensitivity of chemically sensitized grains.

RECENT ADVANCES IN OUR KNOWLEDGE OF THE PHOTOGRAPHIC PROCESS*

While many materials are sensitive to light and can be used for making photographs, the present art of photography is based upon one specific process: The light-sensitive material is silver bromide in the form of extremely small crystals held in a layer of gelatin. These crystals are very sensitive to light when the reaction to light is made manifest by the process of development, that is, by the treatment of the exposed material with a solution of a suitable reducing agent. After exposure to light, the crystals are very much more easily reduced to metallic silver than when they have not been exposed, and as a result of this difference, the effect of exposure becomes visible as an image composed of metallic silver. Significant advances have been made in recent years in the study of the structure of the light-sensitive materials and of the factors which produce in the silver bromide crystals sensitivity so great that very small amounts of light are sufficient to make them developable ; in the study of the action of light itself and of the change which occurs in the exposed crystals ; and in the study of the development reaction by which the exposed crystals are reduced to metallic silver.

RECENT ADVANCES IN OUR KNOWLEDGE OF THE PHOTOGRAPHIC PROCESS

While many materials are sensitive to light and can be used for making photographs, the present art of photography is based upon one specific process: The light-sensitive material is silver bromide in the form of extremely small crystals held in a layer of gelatin. These crystals are very sensitive to light when the reaction to light is made manifest by the process of development, that is, by the treatment of the exposed material with a solution of a suitable reducing agent. After exposure to light, the crystals are very much more easily reduced to metallic silver than when they have not been exposed, and as a result of this difference, the effect of exposure becomes visible as an image composed of metallic silver. Significant advances have been made in recent years in the study of the structure of the light-sensitive materials and of the factors which produce in the silver bromide crystals sensitivity so great that very small amounts of light are sufficient to make them developable ; in the study of the action of light itself and of the change which occurs in the exposed crystals ; and in the study of the development reaction by which the exposed crystals are reduced to metallic silver.

DARK ADAPTATION AND THE DARK GROWTH RESPONSE OF PHYCOMYCES

Light-adapted sporangiophores of the fungus Phycomyces respond to sudden darkening by a temporary decrease in the rate of elongation, after a latent period of several minutes. The reaction time of this "dark growth" response is compound like that of the "light growth" response. It is, moreover, shorter the more intense the previous illumination. The rate of dark adaptation following adaptation to a very large range of light intensities is found to be proportional to the logarithm of the preceding light intensity. It is shown that a constant amount of dark adaptation takes place before the response occurs. On the assumption that changes in the rate of growth reflect changes in the concentration of a substance which at constant light intensity is in equilibrium with a light-sensitive material, possible equations for such a photostationary state are examined. The most reasonable formulation requires that the partial velocity of the "light" reaction be taken proportional to log I instead of to I directly.