Researchers studied the possibility of holographic recording in the absence of mutual coherence of wave beams, or pulses, so that they were not consistent in time and space. As a rule, a holographic recording of an object is created on the basis of a mutual increase or manifestation of the amplitude of two or more coherent waves when they are superimposed on each other. The same study proved that wave-beam coherence is optional. The investigated approach opens up new possibilities for obtaining information with extremely accurate temporal correspondence in interferometric and holographic experiments. Letters to JETP and on the page of Optika Express magazine. Research Fund of the Russian Science Foundation. The best works on optical holography and interferometry named after Yu.I. Ostrovsky.
Holography is a special technology for photographing. This was made possible thanks to two properties of light waves — diffraction (waviness of obstacles and inhomogeneities) and interference (redistribution of light intensity when several waves are superimposed). The usual hologram works as follows. The light beam emitted by the laser expands and is divided into two parts. One of them (reference beam) falls on a photographic plate, is reflected from the subject. Both pulses must be coherent, therefore, there must be a condition for the consistency of wave processes in time and space. During holographic recording, coherent reference and subject beams are added onto a photographic plate, forming an interference pattern. Where there is a maximum frequency, the emulsion is illuminated more strongly, where the minima are weaker. If you kill an object and illuminate a photographic plate at which the result of interference is recorded, that is, only in the form of a beam, then an impulse will arise that will have a copy of the beam, the reflected effect.
If the object moves, it becomes possible to use short pulses of light. This eliminates the fuzziness of the object. In holography, the movement of an object propagates the interference pattern, which leads to the disappearance of the beam-copy of the object. However, the area of overlap and interference of the rays. It is interesting to use completely short pulses for holographic recording when recording very fast processes, but it is almost impossible to form them using the interference pattern.
To date, tremendous progress has been made in generating the limits of short light pulses. They are actively used to study and control the dynamics of ultrafast processes in matter. Today it is possible to receive light pulses of ultrashort (attosecond) duration. The ways of obtaining unipolar and subcycle pulses, in which there is only half the period of oscillations of the light wave, are already being discussed. It is proposed to use such pulses, scientists have resolved the contradiction that exists in conventional interferometry and holography. This should be monochromatic light, which should have a constant constant frequency, amplitude and phase. Quick changes are needed to create a hologram. This is proof that the pulse duration is not obvious, since scientists are moving away from direct intersections of light beams in a recording medium (they do not intersect in the medium at the same moment). High monochromaticity, which is necessary for recording holograms. It will be a very short impulse. Moreover, the shorter it is, the more accurate is its action.
“We showed that it is possible to carry out a holographic recording of information about an object even without coherence between the reference and subject beams, even using radiation from different sources. Such recording can be carried out using pulses of sub-cycle or unipolar radiation when a resonant medium with a long phase memory time is used as the recording medium, “says Rostislav Arkhipov, Head of Research, Ph.D. in Physics and Mathematics, Senior Lecturer, St. Petersburg State University. — In this case, the interference pattern of the subcycle or unipolar pulse reflected from the object with the medium polarization wave created by the same short pulse is recorded in the medium. Coherence is ensured by a polarization wave, which, when interacting with the radiation reflected from the object, will induce a population lattice of the energy levels of the medium in the medium. This lattice will repeat the pattern of interference in a similar holographic process with a monochromatic source with a wavelength equal to the wavelength of the resonant transition in the medium. ”
Holographic technologies play an important role in human life. For example, you can record information on the entire volume of material from all angles and thereby increase the capacity of storage devices, manipulate large arrays of particles at small distances (light holographic tweezers used by scientists). Also, holograms are on banknotes, credit cards, company packaging. The reproduction of such structures is extremely complex, which complicates the fake and protects consumers from low-quality goods.