The development of solid-state physics and advances in solid-state technology have made it possible to manufacture stable photodetectors suitable for use in infrared on-board optical-electronic equipment. Successes in these fields of knowledge have made it possible to create in recent years, rulers and matrices of receivers with a high density of sensitive elements.
Use of computer ROMs
To form the output signal of the equipment it is necessary to measure in turn the electrical signals coming from each element of the line. It is possible to say that it is necessary to provide serial connection of electric conductors from separate elements to the general output.
By means of such "polling" of sensitive sites located in a row, the electric signal corresponding to one line of the image is generated. The process of switching electric circuits of sensitive elements in the equipment is carried out by a special electronic switch of serial action. As a result, the ruler of receivers provides the line scanned image electronically, instead of mechanically.
The latest, most promising infrared equipment increasingly uses solid-state circuits that provide signal reception and processing from a ruler or matrix in one device. The first two short messages of the group of American researchers about this new idea in the field of solid-state physics and about its experimental check appeared in 1970. Charge-coupled devices - this is the name of this class of devices - attracted a great deal of interest and over the years after their invention have found the most widespread use in imaging devices in computer technology, in information display devices.
From the side of physics...
From the point of view of physics, charge-coupled devices are interesting because the electrical signal in them is not a current or voltage, but an electric charge. A charge-coupled device is a line of electrodes on an insulating basis applied to the surface of a thin wafer of a semiconductor. Usually, under the metal underneath the metal electrodes, there is an insulating layer of SiO 2 oxide, and SiO 2 is used as a semiconductor material. The result is a sandwich: metal - oxide - semiconductor.
In devices with a charge-coupled device, it is possible to influence the position of the energy level through the insulator, moving it down from the horizontal line in the places where the electrodes are located, by applying voltage to metal electrodes. As a result, on the border of the Si - SiO 2 section, the energy diagram will be not a flat, but a hilly surface, on which the troughs will be located under the electrodes, to which the voltage is applied.
For the sake of clarity, the troughs of this relief on the energy diagram are represented as a pit with a flat bottom and vertical walls. The higher the voltage at the electrode, the deeper the pit under the electrode at the location. When the photon hits a radiation-sensitive Si and creates an electron-hole pair, the electron flows into the nearest potential pit. At the further irradiation of the sample, electrons will accumulate and remain in the corresponding potential pits.
For the totality of electrons captured by the potential pit, physicists have also invented a figurative name, which has become generally accepted - the "charge pack". Such charge packs, according to the mechanism described above, will appear on the surface of the semiconductor.
Using Earth's satellite systems to determine the distance to the stars
Determining the distances to the bodies of the solar system is based on the measurement of their horizontal parallaxes. Parallaxes determined by the parallaxes of the luminous displacement are called trigonometric parallaxes.
The direct method of determining the distance to the stars is to measure their annual parallaxes. However, parallaxes can only be found for the nearest stars in this way. Indeed, the limiting angles that can be measured by axonometric methods are about 0 ¢ ¢,01.
The essence of this method is based on the fact that the farther the stars are, the less visible movements caused by their actual movements in space are. Parallaxes defined in this way are called average.
If the distance between the radiating body of the observer changes, the velocity of their relative motion has a component along the beam of vision, called the radial velocity. For linear spectra, radial velocities can be measured based on the Doppler effect of shifting the spectral lines by a value proportional to the radial velocity, regardless of the remoteness of the radiation source. In this case, if the distance increases (the radial velocity is positive), then the lines shift to the red side, and otherwise - to the blue side.
The Doppler effect plays an extremely important role in astrophysics because it allows us to judge the movements of celestial bodies and their rotation based on the measurement of the position of the spectral lines.