RU2406188C1 - Device for directed transmission of microwaves - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: device has a generator of ultra-short laser pulses, a system for forming a tubular laser beam, an adaptive mirror with a control unit and emitter of the transmitted microwaves. Said generator of ultra-short laser pulses also has a system for multiplying frequency of the generated laser radiation, a system for forming a pulse train of said laser radiation having multiplied frequency, excimer laser amplifiers and a system for entering the transmitted microwaves into space. The space is bounded by the wall of the tubular laser beam created during operation of the device, and said system for forming the tubular laser beam is in form of telescopes consisting of spherical or parabolic and conical optical elements. The adaptive mirror is mounted after the excimer laser amplifiers in front of the system for forming the tubular laser beam, and directly after the said system for forming the tubular laser beam there is beam splitter with a wave front detector connected to control unit of the said adaptive mirror.

EFFECT: high accuracy and intensity during radiation transmission, high selectivity towards localisation of receivers of transmitted radiation, and increased distance and time for possible transmission of radiation.

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Description

The invention relates to techniques for microwave radiation (EMF) and can be used in systems for transmitting information and transporting pulses of EMP, in particular to ensure high accuracy when choosing the direction of these transmission and transport and selectivity in relation to the location of receivers of transmitted information and transported pulses EMP and increasing their intensity at microwave receivers.

Known devices for the directional transportation of microwave EMP [1], based on the use of various directional antennas. The disadvantages of these devices are, as a rule, insufficiently high accuracy when choosing the direction of the indicated transmission and transportation, insufficient selectivity with respect to the localization of transmitting information receivers and transported electromagnetic radiation pulses, and insufficiently high intensity of transmitted microwave radiation at microwave signal receivers. It is also known a device [2] for the directional transportation of microwave EMP, containing a titanium-sapphire generator of ultrashort laser pulses, a system for generating a tubular laser beam based on an adaptive mirror with a control unit, and a transmitter for transmitting microwave EMP placed directly at the output of this forming system. The disadvantages of this device are the insufficiently large distance by which microwave signals can be transported, which reaches only tens of centimeters, and the insufficiently long transport time, which reaches only 10 ns.

The aim of the present invention is to remedy these disadvantages and increase the specified distance and the specified time.

This goal is achieved in this invention due to the fact that in the known device for the directional transportation of microwave electromagnetic radiation, including an ultrashort laser pulse generator, a tube laser beam forming system, an adaptive mirror with a control unit and a transmitter of transmitted microwave electromagnetic radiation, said laser pulse generator further comprises a system for multiplying the frequency of the generated laser radiation, a system for generating a train of pulses of said laser radiation of a multiplied frequency, excimer laser amplifiers and a system for introducing transmitted microwave radiation into the space of a tubular laser beam, the device of which the device is intended to be formed, and the specified system for forming a tubular laser beam is telescopes consisting of spherical or parabolic and conical optical elements, and This adaptive mirror is installed after the excimer laser amplifiers in front of the system for the formation of a tubular laser beam, and Just after this formation system, a beam divider is installed with a wavefront sensor connected to the control unit of the indicated adaptive mirror, and also because the generator is a titanium-sapphire generator of ultrashort laser pulses, the frequency multiplication system is a frequency tripler, indicated the train formation system is a system of two plane parallel translucent mirrors, excimer amplifiers are krypton-fluorine laser amplifiers pumped by an electron beam, the tube laser beam-forming system consists of telescopes from two spherical and two conical lenses, and the input system is a microwave radiation mode transformer, a horn microwave emitter located outside the inner space of the tube laser beam, for the formation of which it is intended the proposed device and a metal rotary microwave mirror placed inside the specified internal space.

Figure 1 shows a diagram of the proposed device, where

1 - generator of ultrashort laser pulses;

2 - frequency multiplication system;

3 - a system for the formation of a train of ultrashort laser pulses;

4 - excimer laser amplifiers;

5 - adaptive deformable mirror with a control unit;

6 - a system for forming a tubular laser beam;

7 - formed tubular laser beam;

8 - beam splitter and wavefront sensor;

9 - generator of transmitted microwave EMP;

10 is a system for introducing microwave EMP into a tubular laser beam.

Figure 2 shows a system 6 of the formation of a tubular laser beam, where

11 - a laser beam of circular cross section;

12 - lens telescope;

13 - a telescope of two axicons;

7 - a tubular laser beam.

Figure 3 shows a system 10 for introducing microwave EMP into a tubular laser beam, where

9 - generator of transmitted microwave EMP;

14 - mod transformer;

15 - horn antenna microwave emitter;

16 - metal rotary microwave mirror;

7 - a tubular laser beam;

17 - microwave radiation inside the plasma waveguide.

The proposed device operates as follows. The specified generator 1 ultrashort laser pulses (Figure 1), for example titanium-sapphire, produces a sequence of laser pulses with a duration of several tens of fs, with a repetition frequency of several Hz, with an pulse energy of several mJ and with a wavelength of about 744 nm. Further, the indicated sequence of laser pulses enters the frequency multiplication system 2 (Fig. 1), for example, a frequency tripler (third harmonic generator) built on the basis of nonlinear crystals, which converts each pulse of the indicated sequence into an ultraviolet (UV) pulse with a wavelength of about 248 nm The transition from infrared laser pulses generated by the indicated generator 1 of ultrashort laser pulses to UV pulses obtained using frequency multiplication system 2 allows more efficient ionization of the air when creating a tubular plasma waveguide due to the higher energy of the UV quantum and large effective cross sections of ionization processes for UV quanta. Further, these pulses enter the system 3 of the formation of a train of ultrashort laser pulses (Fig. 1), which is, for example, an optical resonator of two parallel translucent mirrors, with such a distance between the mirrors that the double pass time of the laser pulse between them is several ns. At each reflection from the output mirror, part of the energy of the laser pulse goes outside the resonator, thus forming a train of ultrashort laser pulses that follow each other after the indicated double pass time of the laser pulse, and the intensity of which gradually decreases from pulse to pulse. The use of these trains instead of single ultrashort laser pulses makes it possible to increase the duration of the plasma waveguide and, consequently, the duration of the transportation of microwave radiation. The pulse repetition period is chosen shorter than the lifetime of a free electron in air, which is about 5 ns [3]. These ultrashort laser pulse trains are amplified in excimer laser amplifiers 4 (FIG. 1), for example, electron-beam pumped krypton-fluorine amplifiers that operate at a wavelength of 248 nm. The recovery time of the inverse population in such amplifiers 4 is about 2 ns, which makes it possible to amplify the indicated trains of ultrashort laser pulses to peak powers of the order of tens of TW in each pulse of the indicated train, which was experimentally shown by the authors. The pump duration of such amplifiers 4 is determined by a pulsed high-voltage power source and is, as a rule, hundreds of ns, which allows amplification of trains of ultrashort laser pulses of corresponding durations.

After excimer laser amplifiers 4, an adaptive deformable mirror 5 is installed (Figure 1), which serves to correct the phase distortions of the beam. Having passed through excimer laser amplifiers 4 and reflected from the indicated adaptive mirror 5, the train of amplified pulses enters the system 6 for forming a tubular laser beam (Figure 1), which is, for example, a system from a lens telescope 12 (at least two spherical or parabolic optical elements, such as lenses) and a telescope 13, consisting of at least two axicons (conical optical elements, such as lenses) (Figure 2). The lens telescope 12 reduces the radius of the beam emerging from the excimer amplifiers to a value corresponding to the wall thickness of the formed tubular beam, and the telescope 13 of the axicons forms a tubular laser beam 7. The wall thickness of the tubular laser beam 7 is determined by the radius of the beam formed by the lens telescope 12, its the diameter is the distance between the axicons, and its divergence angle is the ratio of the angles at the axicon vertices. When using the adaptive mirror 5, a beam divider 8 is further installed, which is, for example, a transparent plane-parallel plate that diverts a small part of the beam to a wavefront sensor capable of measuring the phase distortions of the beam. An electronic signal from the wavefront sensor enters the adaptive mirror control unit 5, in which the deformation of the adaptive mirror necessary to correct the measured phase distortions of the beam is calculated from it, and the corresponding signal is sent to the adaptive mirror 5 itself, which is deformed accordingly. This makes it possible, by the time the next train of ultrashort pulses arrives, to correct the aberrations of the optical elements, to reduce the beam divergence inherent in the laser, and as a result to obtain a tubular beam that can propagate over long distances, preserving its cross-sectional shape.

The indicated scheme for the formation of a tubular laser beam 7 was experimentally tested by the authors. As calculations show, the peak power of laser radiation in the wall of such a tubular beam 7 is many times higher than critical [3], which leads to filamentation of laser radiation, i.e. the beam breaks up into many filament filaments, in which, as shown in the literature and the authors, an effective two-quantum ionization of air occurs. The distance between the individual filaments is much less than the wavelength of the channeled microwave radiation [2], which allows us to consider such a wall as a continuous plasma layer with averaged conductivity and permittivity. The authors' calculations show that with a waveguide diameter much larger than the wavelength of the microwave radiation and a wall thickness of the order of the wavelength, such a waveguide can transport microwave radiation traveling at small angles to the axis of the waveguide, even at electron concentrations in the walls of about 10 ¹² -10 ¹³ cm ^-3 , which is much smaller than in the known device [2]. It was calculated that the attenuation length of microwave radiation in such a waveguide is of the order of hundreds of meters, which significantly exceeds the device parameters [2]. The effect of transportation of microwave radiation in such a plasma waveguide is experimentally confirmed by the authors.

The microwave radiation generator (Fig. 1) is a powerful microwave radiation source, such as a vircator, or a low-power microwave radiation source, such as a magnetron or klystron, and the microwave radiation input system in a tubular laser beam (Fig. 3) is, for example, a segment waveguide, transformer 14 modes [1] and a metal rotary mirror 16 for microwave waves, installed inside the space bounded by the walls of the tubular laser beam, which is formed during operation of the proposed device. The mode transformer 14 converts the microwave field mode generated by the microwave generator 9 into a mode optimal for transportation in the created plasma waveguide. The authors calculated that the lower modes of a circular dielectric or metal waveguide, for example, the H ₁₁ mode of a circular metal waveguide [1], are closest to the eigenmodes of the plasma waveguide, which propagate in it with the smallest attenuation. The propagation effect of certain modes of microwave radiation in the specified plasma waveguide with relatively low attenuation is based on the smallness of the angles at which the microwave wave falls on the wall of the specified waveguide (sliding angles), as a result of which the microwave wave is effectively reflected from the wall. All components of the microwave wave incident on the wall at large angles (modes with a large transverse component of the wave vector) pass through it into free space or are absorbed in the wall and are not supported by the waveguide. The use of a transformer 14 modes, which gives one of these modes at the output, which propagate efficiently in the specified waveguide, makes it possible to increase the efficiency of using the power of the microwave generator 9, and thus increase the power density of the microwave radiation at the receiver. Microwave radiation after exiting the horn antenna 15 passes through the wall of the plasma waveguide (Figure 3), however, as the authors show, the reflection of microwave power from it is small. The low reflection is due to the low electron density in the wall and the fact that microwave radiation is incident on it at angles close to the normal, and a sufficiently effective reflection of microwave radiation from a plasma layer with the indicated low density is possible only at very small (moving) angles of incidence, which used in the implementation of this device. Absorption of microwave power in the specified plasma layer is also small due to its small thickness and low density.

The distance over which microwave radiation is transported in the specified plasma waveguide is about hundreds of meters, and the power density at the receiver is 10 or more times the power density when microwave radiation propagates in free space. Also, the specified plasma waveguide can significantly improve the selectivity with respect to the location of the microwave receivers compared with the propagation in free space, and the duration of the transportation of microwave radiation increases to a scale of the order of 1 μs.

An example implementation of the proposed device

The proposed device is implemented, for example, as follows: a titanium-sapphire laser model MPA (Avesta Project Ltd.) generates laser pulses with a duration of about 50 fs, with a repetition frequency of about 10 Hz, with an pulse energy of about 10 mJ and with a wavelength of about 744 nm, which are fed to the frequency tripler, which is a third harmonic generator of the ATsG800 model (Avesta Project Ltd.), which converts these pulses into pulses with a wavelength of 248 nm. These pulses enter the optical resonator, which is a system of two plane parallel mirrors spaced 30 cm apart and having a transparency of 20%, as a result, each of these pulses is repeatedly reflected from the mirrors, while its transit time between the mirrors is 1 ns. At each reflection from the output mirror, part of the pulse energy goes outside the resonator, thus forming a train of ultrashort laser pulses that follow each other after 2 ns, the intensity of which gradually decreases from pulse to pulse. The trains of ultrashort laser pulses thus formed are sequentially amplified in two krypton-fluorine laser amplifiers with apertures of 10 × 10 cm ² and 30 × 30 cm ² and a length of 1 m, pumped by electron beams with a pulse duration of 100 ns and a repetition rate of 10 Hz. The amplifier is a rectangular chamber filled with a mixture of argon, krypton and fluorine at a total pressure of 1.5 atm. Optical windows are placed at the ends of the chamber, and the electron beam is introduced through a vacuum-tight foil that separates the chamber from the electron accelerators. Gas cooling occurs due to its forced circulation through the heat exchanger. Pulse trains pass through amplifiers twice, reflected from deaf mirrors at the ends of amplifiers, as a result of which an output energy density of 10 mJ / cm ² for one ultrashort laser pulse and 500 mJ for a train of 50 ultrashort laser pulses corresponding to a pump pulse is achieved about 100 ns. The total energy of laser radiation in one train is about 500 J. The power supply system of electronic accelerators is based on high-voltage pulse generators providing a pump energy of 1 kJ in the first amplifier and 10 kJ in the second with an efficiency of converting pump energy into laser energy of 5% [4] . These generators contain capacitive storage and switching units and compress the stored energy over time using a magnetic element operating in key mode, followed by exacerbation due to interruption of the current by the diodes.

A diaphragm is installed behind the krypton-fluorine amplifiers, which converts a 30 × 30 cm square laser beam into a 30 cm round beam. An adaptive mirror 5 with a diameter of 35 cm is located behind the diaphragm, equipped with a control unit that calculates the required deformations from signals from the wavefront sensor and generates appropriate control electrical signals.

Having passed through excimer laser amplifiers 4 and reflected from the adaptive mirror 5, the train of amplified pulses enters the system 6 for forming a tubular laser beam, which is a system of a lens telescope 12 and a telescope 13 consisting of two axicons (conical lenses). The lens telescope 12 consists of a positive lens with a diameter of 35 cm with a focal length of 10 m and a negative lens with a diameter of 3.5 cm and a focal length of 1 m located at a distance of 9 m and reduces the radius of the beam emerging from excimer amplifiers 4 to 1.5 cm that determines the wall thickness of the tubular laser beam. The axicon telescope 13 consists of an axicon with a diameter of 3.5 cm with an apex angle of 9 ° and an axicon with a diameter of 35 cm and an angle of apex of 9 °, the distance between axicons is 205 cm, which ensures a radius of a tubular laser beam of 30 cm. A telescope 13 of axicons has a beam splitter 8, which is a plane-parallel plate that diverts part of the energy to a wavefront sensor, the signal from which is used to correct phase distortions in subsequent pulse trains.

The tubular laser beam 7 thus formed ionizes the air along the propagation path and creates a hollow plasma waveguide of circular cross section with a free electron density of the order of 10 ¹³ cm ^-3 , which is accumulated due to the action of a train of ultrashort laser pulses. Microwave radiation is directed to the specified plasma waveguide using an input system, which is a pulsed magnetron that generates microwave pulses with a wavelength of 8 mm, with a peak power of 20 kW and a duration of 100 ns, a transformer 14 modes of microwave radiation, forming the H ₁₁ round metal mode a waveguide, a horn antenna emitter 15, and a rotary metal microwave mirror 16 placed inside said plasma waveguide.

The distance over which microwave radiation is transported in the indicated plasma waveguide is about 1 km, the power density at the receiver is about 10 times higher than the power density during the propagation of microwave radiation in free space, and the duration of microwave radiation transport is about 100 ns.

The results obtained significantly exceed the results obtained when using the prototype device and thus confirm the operability of the proposed device and the achievement of goals.

Literature

1. X. Meinke, F.V. Gundlach. "Radio technical reference book", t.1, State Energy Publishing House, M., L., 1961.

2. M. Chateauneuf, S. Payeur, J. Dubois, J.-C. Kieffer. "Microwave guiding in air by a cylindrical filament array waveguide", Appl. Phys. Letts., V. 92, paper 091104 (2008).

3. N. Khan, N. Mariun, I. Arts, J. Yeak. "Laser-triggered lightning discharge", New J. of Phys., V.4, pp. 61.1-61.20 (2002).

4. M.S. Myers, J.D. Sethian, J.L. J.iuliani, R. Lehmbrg, P. Kepple, M. F. Wolford, F. Hegeler, M. Friedman, T. C. Jones, S.B.Swanekamp, D. Weidenheimer, D.Rose. "Repetitively pulsed, high energy KrF lasers for inertial fusion energy", Nucl. Fusion, v. 44, pp. 247-S253 (2004).

Claims (2)

1. A device for the directional transportation of microwave electromagnetic radiation, including an ultrashort laser pulse generator, a tube laser beam forming system, an adaptive mirror with a control unit and a transmitter of transmitted microwave electromagnetic radiation, said laser pulse generator further comprises a frequency multiplication system for the generated laser radiation, a pulse train generation system the specified laser radiation of the multiplied frequency excimer laser amplifiers and system in water of the transmitted microwave radiation into the space bounded by the wall of the tubular laser beam created during the operation of the device, and the indicated system for forming the tubular laser beam is telescopes consisting of spherical or parabolic and conical optical elements, and an adaptive mirror is installed after the excimer laser amplifiers in front of the system for the formation of a tubular laser beam, and immediately after this formation system, a beam splitter with a wavefront sensor connected to a control unit of said adaptive mirror. 2. The device according to claim 1, characterized in that said generator is a titanium-sapphire generator of ultrashort laser pulses, said frequency multiplication system is a frequency tripler, said train formation system is a system of two parallel parallel translucent mirrors, excimer amplifiers represent are krypton-fluorine laser amplifiers pumped by an electron beam, the system for forming a tubular laser beam is telescopes from at least two spherical and at least two conical lenses, and the input system is a microwave mode transformer, a horn microwave antenna emitter located outside the internal space of a tubular laser beam generated during operation of the device, and a metal rotary microwave mirror placed inside specified interior space.

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