Radiation imagery chemistry: process – composition – or product th – Holographic process – composition – or product
Reexamination Certificate
2000-06-01
2003-05-06
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Holographic process, composition, or product
C430S002000, C430S394000, C359S001000, C359S003000, C359S004000, C359S006000, C359S024000, C356S370000
Reexamination Certificate
active
06558851
ABSTRACT:
FIELD OF INVENTION
This invention relates to the photo-sensitive thermoplastic top-layer of a media for registration of optical holograms in the holographic interferometry technique and devices. Certain compositions and novel compounds for the photo-sensitive thermoplastic media are disclosed. Such layers are often referred to as amorphous molecular semiconductor (AMS) films.
BACKGROUND
Optical holographic interferometry technique is well suited for non-destructive testing of internal defects in blocks and units of machines and devices, welded seams, as well as measuring stresses of an object during the object's work load and residual stresses caused by technological processes of welding, forging, soldering etc. These applications are useful for fields such as offshore oil industry, shipping industry, process industry, air industry, and all types of constructions where strength is vital or fatigue may cause a problem.
In simple terms, the principle of non-destructive testing by holographic interferometry technique can be described as follows: First a hologram of an investigating area of the object is made. Then the object is exposed to a weak load in order to create stresses in the investigation area of the object. Further, the illumination of the registering medium containing the developed holographic image of the investigating area of the object with the reference beam, and illumination of the same area exposed to the load with the object beam are performed simultaneously. This occurs in such a way, that two light waves will be simultaneously behind the recording medium. One of which is created by illuminating the recording medium (containing the developed image) by the reference beam and which corresponds to the light wave scattered from the object during illumination by the object beam before loading, and the other corresponds to the light wave scattered by the studied object exposed to the load. As a result of the interference between these two light waves, an interferogram of the studied area is formed, and interference fringes localised on the object can be observed. An abnormal behaviour of the interference fringes gives evidence of the presence of a defect. One can estimate the size of the defect from the size of the region where the abnormal interference fringes are observed. Residual stresses are revealed and evaluated in a similar manner. The only difference is that in this case, a release of stresses in the investigation spot are performed instead of loading the object by drilling a small and shallow hole.
The recording of a hologram will typically be performed as follows: In the case when the registering medium consists of three layers: a glass substrate (first layer), a transparent electric conducting layer (second layer), and an AMS-film (third layer). First, the surface of the AMS-film is charged with positive ions by corona discharge. Then the hologram of the investigating area of the object is formed on the charged AMS-film surface. For this aim, the laser beam is divided by a splitter in two parts, one of them (let us denote it as reference beam) is directed to the charged surface of the AMS-film; and another one (denoted as object beam) is directed to the investigating area of the object in such way that having reflected from this area, it is directed to the charged surface of the AMS-film as well. The reference and the object beams are interfered and form the holographic image of the studied object, i.e. the spatial light intensity distribution on the charged surface of the AMS-film. The carrying spatial frequency of this distribution is determined by the angle between the reference and the object beams on the charged surface of the AMS-film, and the spatial frequency band is determined by the angle size of the investigated area of the object. Free electrons and holes are photo-generated in the AMS-film due to the light of the holographic image and the strong electric field (due to the film charging). The electrons migrate to the positively charged surface and neutralise the positive ions, and the holes migrate in the opposite direction are removed from the bulk film by passing into the transparent electro-conducting sub-layer. The latent electrostatic image of the hologram is formed on the charged surface of the AMS-film during the exposure time (the time when the charged surface of the AMS-film is exposed to the holographic light pattern). The latent image is the surface charge distribution and is proportional to the light intensities of the hologram image, but phase shifted by 180°. The variable spatial components of the charge density on the charged film surface results in appearance of the variable normal and tangential forces applied to the surface of the AMS-film. In other words, the latent image of a hologram can be considered as distribution of normal and tangential forces applied to the film surface. The electrostatic image is developed by heating the AMS-film up to the temperature of its transition into the viscous-flow state by means of passing an electric current pulse through the conducting tin dioxide sub-layer. When this takes place, the normal and tangential forces of the latent electrostatic image deform the AMS-film surface and the latent electrostatic image is transferred into a geometrical relief of the surface, which spatial distribution corresponds to the spatial light intensity distribution in hologram image. The heating of the AMS-film terminates at the end of the current pulse, and the geometrical relief becomes fixed. The created geometrical relief is a developed holographic image of the investigated object. When the registering medium with developed holographic image is illuminated by the reference beam, the holographic image of the investigated object is restored due to the diffraction of the beam by the geometrical relief of the surface.
STATE OF THE ART
As mentioned, this invention relates to a holographic registering medium based on amorphous molecular semiconductor films (AMS-films). Such a holographic medium is typically a flat piece made up of three transparent layers; a lower supporting layer made of glass, an intermediate layer of an electric conducting substance, and a top layer consisting of a thermoplastic photo-sensitive AMS-film. The intermediate layer is employed as an electric heat element for heating the top layer during the developing process, while the top layer is serving as the registering film.
Photo-sensitive AMS-films must possess at least four properties in order to be able to register holographic images. The film must be thermoplastic, it must provide physically separate transport bands both for holes and electrons, and it must provide centres for photo-generation of electron-hole pairs. The thermoplastic property is often ensured by employing a thermoplastic substrate which has good film forming properties as the film forming basis (let us denote this substrate as substance P). The transport bands for holes is provided by adding a substance which has good donor properties (substance D) and the transport bands for electrons is provided by adding a substance that has good acceptor properties (substance A). The centres for photo-generation is in conventional AMS-films provided by charge-transfer-complexes or exciplexes (these terms will be defined later). The centres for photo-generation of electron-hole pairs will be denoted as substance F.
Let us take a more detailed look of how the light intensity distribution above the film surface is transferred into an electrostatic image: When a light quantum is absorbed by a F-substance in the AMS-film it becomes excited, which results in a probability that a hole may escape from the F-molecule to a D-molecule and an electron may escape to an A-molecule. If this takes place, a Coulombically bonded electron-hole pair is created. Further, there is a probability that due to the influence of the applied high electric field, charge carriers of the electron-hole pair will not return back to the F-molecule, but would instead dissociate into free charge carriers (f
Davidenko Nikolay Aleksandorvich
Fjeldstad Irina Evgenievna
Fjeldstad John Petter
Kostenko Leonid Ivanovich
Kuvshinsky Nikolay Georgievich
Angebranndt Martin
Birch & Stewart Kolasch & Birch, LLP
Holo Tech A.S.
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