RU2229188C1 - Method for reducing pre-pulse concentration of electrons in active medium of metal halide vapor laser and active element of metal halide vapor laser - Google Patents

Abstract

FIELD: quantum electronics. SUBSTANCE: method includes selection of easy-to-ionize material whose atoms have ionization potential J_d lower than that of working metal atoms J_m as gaseous dope, concentration of the latter being 0.05 to 0.15% of that of working metal atoms. Laser active element has vacuum-tight enclosure provided with two electrodes at its ends and N containers disposed at regular intervals in its lower part. Vacuum-tight enclosure has cylindrical projections disposed either side of electrodes. Working metal hinges are arranged inside working channel at regular intervals through its length and heat insulation is provided on working channel exterior. EFFECT: enhanced frequency and power characteristics due to reduced pre-pulse concentration of electrons in active medium of laser. 3 cl, 4 dwg

Description

The invention relates to quantum electronics, metal vapor lasers, and can be used in the development of metal halide vapor lasers, such as copper bromide, for the purposes of medicine, microelectronic technology, navigation, scientific research, atmospheric sensing, etc.

There is a method of reducing prepulse electron concentration [P.A. Bokhan, V.I. Silantyev, V.I. Solomonov. On the mechanism for limiting the repetition rate of lasing pulses in a copper vapor laser. Quantum Electronics. 1980. T. 7. S.1264-1269; Withford MJ, Brown DJW, Piper JA Investigation of the effects of hydrogen and deuterium on copper vapor laser performance. Optics Communications. 1994. V. 110. P.699-707], which consists in introducing into the active medium of a metal vapor laser a molecular additive of hydrogen (H ₂ ) (in the range of several percent of the buffer gas concentration).

The disadvantages of the method: the elements of the active element contain hydrogen inside, which during operation is released into the active medium, which makes it difficult to control the level of hydrogen in the active element of the laser and the implementation of the method, in addition, the degree of decrease in prepulse electron concentration when introducing hydrogen additive at a low pulse repetition rate excitation is negligible.

The active element of a metal halide vapor laser is known [Batenin V.M., Buchanov V.V., Kazaryan M.A., Klimovsky II, Young E.I. Lasers based on self-limited transitions of metal atoms. M .: Scientific book. 1998, p. 69]. The active element of the laser is a vacuum-tight quartz shell, equipped with electrodes at its ends, covered with copper chips. The working channel of the active element of the laser is covered with a layer of heat insulator. The working metal is placed in the process, which is placed in a heating furnace. The end sections of the vacuum-tight shell have a diameter greater than the diameter of the working channel, and are equipped with reflectors and exit windows.

The disadvantages of the active element of the laser is that the introduction of a gaseous additive requires an additional power source, it is difficult to control the amount of introduced gaseous additives, it is impossible to achieve longitudinal uniformity of the introduction of a gaseous additive, and there is no possibility of independent adjustment of the amount of working metal and additive introduced into the working channel.

A known method of decreasing prepulse electron concentration [US, No. 6175583, publ. January 16, 2001], which consists in introducing into the active medium of a metal vapor laser a gaseous additive of hydrogen chloride (HCl) (in the range of several tenths of a percent of the buffer gas concentration).

The disadvantages of the method: for the implementation of the method it is necessary to create a complex bleeding system, which has a much lower reliability compared to sealed options. The implementation of the method is difficult due to the fact that the use of toxic HCl gas is associated with a risk to the life of the personnel serving this installation. Due to the small amount of the necessary HCl additive, which ensures a decrease in the prepulse electron concentration, the control over its level in the active medium is complicated. In addition, it is difficult due to the bulkiness of the product, the implementation of the method in an industrial environment.

Known active element of a copper vapor laser [US patent No. 3831107, published 20.08.1974]. The active element of the laser (figure 1) is a vacuum-tight shell 10, which inside contains electrodes 12 and 14, located opposite each other and connected through an insulating sleeve 27 by conductors 16 and 18 with a pulse generator 20, which, in turn, conductors 22 and 24 is connected to a power source 26. A working channel 48 is located between the electrodes 12 and 14. A reflector 28 is located directly on the edges of the working channel 48. Inside, in the upper part of the vacuum-tight shell 10, there is a metal condenser 30, which is cooled and leaking by the fluid pipe system 32 located inside it. The vacuum-tight shell 10 is equipped with evaporators of copper 34 and 36, which are hermetically isolated from the additive (cesium) evaporator 38. All evaporators 34, 36, 38 contain electrically heated containers that have a capillary or guide system 39 located along directions 46 located on top. Conductors 40, 42, 44 are connected respectively with evaporators 34, 36, 38 and with an additional power source. At the top, the vacuum-tight shell is connected to a vacuum pump 51.

The disadvantage of the active element of the laser is that the introduction of a gaseous additive requires the presence of an additional power source, it is also difficult to control the amount of introduced gaseous additives and it is impossible to achieve longitudinal uniformity of the introduction of a gaseous additive.

A known method of decreasing prepulse electron concentration [D.N. Astadjov, N.V. Sabolinov, N.K.Vuchkov. Effect of hydrogen on CuBr laser power and efficiency. Optics Coomunication. 1985. V. 56. P.279-282; C.E. Little, D.R. Jones, S.A. Fairlie, C.G. Whyte. Metal HyBrID lasers. Pulsed Metal Vapor Laser. The Netherlands: Kluwer. 1996. P.125-136], selected as a prototype, consisting in the introduction into the active medium of a laser on a metal vapor additive of hydrogen bromide (HBr) (in the range of several percent of the concentration of the buffer gas).

The disadvantages of the method: for the implementation of the method it is necessary to create a complex bleeding system, which has a much lower reliability compared to sealed options. The implementation of the method is difficult due to the fact that the use of toxic HBr gas is associated with a risk to the life of the personnel serving this installation. Due to the small amount of the necessary HBr additive, which ensures a decrease in the prepulse electron concentration, the control over its level in the active medium is complicated. In addition, it is difficult due to the bulkiness of the product, the implementation of the method in an industrial environment.

A known active element of a metal halide vapor laser [N.V. Sabotinov, I.K. Kostadinov, H.W. Bergmann, R. Salimbeni, J. Mizeraczyk. A 50-Watt copper bromide laser. SPIE. 2001. V. 4184. P.203-206], selected as a prototype. The active element of the laser (Fig. 2) consists of a vacuum-tight shell, which is equipped with electrodes at its ends. The electrodes are covered with copper chips. The working metal is placed in the processes located in the lower part of the vacuum-tight shell. The working channel of the active element of the laser, together with the containers, is surrounded by a metal casing in which the heaters are mounted, as well as means for controlling the temperature of containers with working metal, including a container temperature control unit and a thermocouple located directly on the wall of the container with working metal.

Disadvantages of the active laser element: when using the laser, two power sources are used - the power source of the active laser element and the power source of the container heaters, which require stabilization of its operation and their mutual stabilization for optimal operation.

The objective of the group of inventions is to increase the frequency, energy characteristics of metal halide vapor lasers by reducing the prepulse electron concentration in the active medium of the laser and creating for this a simple and reliable active element of the metal halide vapor laser for introducing an easily ionizable additive.

The problem is achieved in that in the method of reducing the prepulse concentration of electrons in the active medium of a metal halide vapor laser, including, as in the prototype, introducing a gaseous additive into the active medium, according to the invention, a readily ionizable substance whose atoms have the potential ionization J _d less than the ionization potential of the atoms of the working metal J _m , and its concentration is from 0.05 to 0.15% of the concentration of atoms of the working metal.

The problem is also solved due to the fact that in the active element of the metal halide vapor laser, containing, like the prototype, a vacuum-tight shell equipped with two electrodes at its ends and periodically located in the lower part of N containers, a heat chamber, a temperature sensor and the temperature control unit, according to the invention, the vacuum-tight shell is made with cylindrical protrusions on both sides of the electrodes, and working metal samples are periodically placed along its channel along its length, working metal is outside, The channel is provided with thermal insulation, and the heat chamber is located under a vacuum-tight shell, covering containers in which an easily ionized additive is placed, and the containers are attached to a vacuum-tight shell and their height is selected from 2.0 to 3.5 of the diameter of the working channel, and their length - not less than the diameter of the working channel, in addition, at least one temperature sensor and one fan are placed in the heat chamber, which are electrically connected to the temperature control unit.

When an easily ionizable additive, for example cesium, is introduced into the active medium of a metal halide vapor laser, for example copper bromide, the power introduced into the gas discharge tube decreases. This is due to the fact that to obtain the same number of electrons it is necessary to spend less energy, since the cesium ionization potential of 3.89 eV is much less than the copper ionization potential of 7.72 eV. This leads to increased laser efficiency. The experiments showed that the introduction of cesium additives leads to a decrease in the power spent on the ionization of the buffer gas atoms (Fig. 3, curves 2). This leads to a decrease in the degree of ionization of neon. The power densities that go to the ionization of copper atoms also decrease (Fig. 3, curves 4); as a result, the resulting ionization of copper decreases. This is due to the "interception" of a part of the energy deposited in the plasma (Fig. 3, curve 1) on the ionization of the easily ionized additive (Fig. 3, curve 5), and the density of the power flux spent on heating the gas in elastic collisions remains unchanged (Fig. 3, curve 3). With increasing concentration of additive atoms, this effect is most pronounced. It should be noted that in this case, the power fluxes spent on electron cooling due to elastic collisions with neon atoms and copper and cesium ions remain almost unchanged.

At the beginning of the excitation pulse, the main electron supplier is cesium atoms. They are quickly, almost completely, ionized, and with much lower energy costs than with the ionization of copper atoms. After this, the electrons are produced mainly as a result of the ionization of copper, but the final degree of ionization and electron concentration are less. After ionization of cesium atoms, the rate of increase in electron concentration decreases.

Let us now consider the processes occurring in the afterglow stage. It is known that the ionization of buffer gas atoms is negligible [Batenin V.M., Buchanov V.V., Kazaryan M.A., Klimovsky II, Young E.I. Lasers based on self-limited transitions of metal atoms. M .: Scientific book. 1998]. The total concentration of electrons at the relaxation stage is mainly determined by the contribution of electrons obtained as a result of ionization of copper atoms and electrons formed as a result of ionization of cesium atoms. The relaxation rate of electron concentration is determined by the following expression:

5.4 · 10 ^-27 · T $\genfrac{}{}{0ex}{}{\text{-45}}{\text{e}}$ ,

where Te is the electron temperature.

Thus, due to the lower ionization of copper atoms, the total electron concentration at the afterglow stage and, therefore, the prepulse electron concentration will decrease.

The value of the optimal concentration of a gaseous easily ionizable additive is determined by the following: at values less than 0.05% of the concentration of atoms of the working metal, the observed decrease in the value of the prepulse electron concentration does not provide a significant increase in the lasing characteristics of a metal halide vapor laser; exceeding the upper limit, i.e. 0.15% of the concentration of atoms of the working metal leads to an increase in the prepulse concentration of electrons, which affects the output characteristics of the laser.

Based on this, it can be concluded that the introduction of an easily ionized additive leads to an increase in the service life and an increase in the laser lasing characteristics by up to 50%.

The implementation of a vacuum-tight shell of the active element with the proposed design and the corresponding placement of easily ionizable additives relative to the working channel allows you to create conditions for self-heating laser operation in which the temperature of the working channel and the speed of rotation of the fans determine the temperature of the containers. As the active element of the laser is heated, conditions are created for melting the easily ionizable additive and supplying its vapor to the working channel through openings in a vacuum-tight shell.

The height of the container is selected based on the following: when the value is less than 2 diameters of the working channel, the container overheats, which leads to uncontrolled entry of vapors of easily ionized additives into the working channel. Exceeding the upper limit of 3.5 diameters of the working channel leads to underheating of the containers. The smallest container length is determined by the placement in it of an amount of easily ionizable additive sufficient for long-term operation and the heat removal necessary to create its vapor. The number of containers is determined by the uniform distribution of vapors of the easily ionized additive along the length of the working channel and is 1 container per 30-40 cm of the length of the working channel. The maximum length of the container can be increased up to their connection with each other, with the condition of maintaining a partition between them to prevent the penetration of a discharge into them.

Additional warming of the working channel with thermal insulation allows it to reach the working temperature.

Placing containers containing an easily ionizable additive in a heat chamber eliminates the need for thermal insulation to form vapor of the working metal and makes it possible to control their temperature. The heat chamber is air-cooled and can have either a rectangular or cylindrical shape. Its walls should be separated from the walls of the vacuum-tight shell at a distance that eliminates the occurrence of a discharge between them. The number of fans built into the outer wall of the heat chamber is determined by the length of the working channel of the active element.

The stationary mode of operation at the optimum vapor pressure of the easily ionized additive is maintained by cooling the containers inside the heat chamber. When the temperature in the chamber is exceeded, the fans automatically turn on and subsequently also automatically turn off when the optimum temperature is reached.

Additional advantages of the traps are to reduce the degree of contamination of the output windows and electrodes with working metal and an easily ionized additive, and thereby increase the laser life.

In this application, the requirement of unity of invention is met, since the device of the active laser element is intended to implement a method of reducing the prepulse electron concentration in the active medium of a metal halide vapor laser.

The claimed inventions solve the same problem - increasing the frequency and energy characteristics of metal halide vapor lasers by achieving the same technical result when implementing the inventions - reducing the prepulse electron concentration in the active medium of a metal halide vapor laser.

In FIG. 1 is a diagram of a copper vapor laser discharge tube. In FIG. Figure 2 shows the design of a discharge tube of a copper halide vapor laser. In FIG. Figure 3 shows the time dependences of the power Q introduced into the plasma of a gas-discharge tube (1), used for ionization of neon (2), spent on heating gas in elastic collisions (3), used for ionization of copper (4), used for ionization of an easily ionizable additive (cesium ) (5). The solid curves for N _Cs = 9 × 10 ¹² cm ^-3 , the dashed line for N _Cs = 0 cm ^-3 .

In FIG. 4 is a schematic representation of a metal halide vapor laser discharge tube.

The active element of the laser (Fig. 4) is a cylindrical vacuum-tight quartz shell 1 with electrodes 2 at its ends. Electrodes 2 are filled with copper shavings. The working channel 3 of the vacuum-tight shell 1 is provided with insulation 4 from the outside and has two openings 5 in its lower part. Inside, in the lower part of the working channel 3 there are four samples 6 of working metal, for example, copper bromide. In the lower part of the working channel 3 there are two containers 7 with an easily ionizable additive, for example cesium, in the solid state. At the ends of the vacuum-tight shell, exit windows are located 8. Traps 9 are installed on both sides of the electrodes 2, which are cylindrical protrusions in the vacuum-tight shell 1. From below, containers 7 with an easily ionizable additive are covered by a heat chamber 10. The longitudinal inner wall of the heat chamber 10 has holes 11 for heat dissipation. The outer wall of the heat chamber 10 is equipped with two fans 12, and a temperature sensor 13 is installed inside the heat chamber 10, for example, a thermocouple electrically connected to the temperature control unit 14 (BKT), which in turn is connected to the fans 12. The electrodes 2 are connected to a switching power supply 15 (IIP).

Thermal insulation 4 is, for example, kaolin wool.

Containers 7 with an easily ionized additive have a height of two diameters of the working channel 3 to 6 cm and a length of 3 to 3 cm in the diameter of the working channel.

This design of an active element of a metal halide vapor laser can, as a working metal, contain elements from the group CuF, CuCl, CuBr, CuI, PbBr, PbCl, SnBr, SnCl, SnF, AuCl, FeCl, HgBr, HgCl, HgF, ReCl, ReBr and others, and as easily ionizable additives - elements from the group K, Rb, Cs, Fr and others.

The temperature control unit 14 can be performed on the basis of the Intel 8051 microcontroller. The switching power supply 15 can be performed according to one of the standard schemes [Batenin V. M., Buchanov V. V., Kazaryan M. A., Klimovsky I. I., Young E.I. Lasers based on self-limited transitions of metal atoms. M .: Scientific book. 1998. P.86], for example, as follows: from an industrial three-phase network using a high-voltage three-phase transformer and a rectifier implemented according to the Larionov circuit, the storage capacitor of the discharge circuit, which contains the active laser element, is charged. With a given frequency, a switch, for example, a TGI-1000/25 thyratron, connects a storage capacitor to the electrodes of the active laser element.

The active element of a copper bromide vapor laser with cesium as an easily ionizable additive works as follows. When you turn on the switching power supply 15 to the electrodes 2 of the vacuum-tight shell 1 voltage is applied. In the working channel 3, a discharge is formed. Over time, conditions are created in the heat chamber 10 under which the samples 6 of copper bromide inside the working channel 3 reach the required temperature and begin to melt and enter the discharge in the form of vapors, where the pairs of copper bromide dissociate into bromine and copper atoms, followed by the excitation of copper atoms and the emergence of generation. In this case, the temperature of the containers 7 becomes sufficient to melt the easily ionized additive and cesium in the gaseous state enters the discharge. The cesium ionization potential J _d = 3.89 eV is much smaller in comparison with the copper ionization potential J _w = 7.72 eV. This by means of plasma-chemical reactions provides an increase in the lasing characteristics of a metal halide vapor laser. The concentration of the introduced cesium additive is 0.1% of the concentration of copper atoms. When the temperature inside the heat chamber 10 is higher than necessary to achieve a cesium atom concentration of 0.1% of the concentration of copper atoms, feedback is triggered through the temperature sensor 13 and the temperature control unit 14 turns on the fans 12 until the temperature reaches the previous level.

Thus, the proposed design of the active element of the laser on the vapor of a metal halide allows you to implement a method of reducing prepulse electron concentration. The presence of feedback allows us to maintain a constant temperature difference between the working channel of the vacuum-tight shell and containers, ensuring the optimal concentration of vapors of an easily ionized additive in an active medium, without the use of external heaters, unlike the known gas-discharge tubes on metal halide vapors. This leads to a significant increase in the service life of the active element and to increase the lasing characteristics of the laser.

Claims (3)

1. A method of reducing the prepulse concentration of electrons in the active medium of a metal halide vapor laser, comprising introducing a gaseous additive into the active medium, characterized in that a readily ionizable substance whose atoms have an ionization potential J _d lower than the ionization potential of the working metal atoms is selected as a gaseous additive J _m , and its concentration is from 0.05 to 0.15% of the concentration of atoms of the working metal. 2. An active element of a metal halide vapor laser containing a vacuum-tight shell equipped with two electrodes at its ends and periodically located N containers in its lower part, as well as a heat chamber, a temperature sensor and a temperature control unit, characterized in that it is vacuum-tight the shell is made with cylindrical protrusions on both sides of the electrodes, with inside of its working channel periodically along its length weighed portions of the working metal, the working channel is provided with heat insulation on the outside, and the heat chamber is located It is worn under a vacuum-tight shell, covering containers in which an easily ionizable additive is placed, the containers being connected to the volume of the vacuum-tight shell through the openings in it and the height of the containers is chosen from 2.0 to 3.5 times the diameter of the working channel, and their length is not less than the diameter of the working channel, in addition, at least one temperature sensor and one fan are placed in the heat chamber, which are electrically connected to the temperature control unit. 3. The active element of the metal halide vapor laser according to claim 2, characterized in that the thermal chamber is provided with a longitudinal partition with holes for removing heat.

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