RU2073950C1 - Waveguide co2 laser with lateral high-frequency pumping - Google Patents

Abstract

FIELD: laser physics, mechanical engineering, medical devices. SUBSTANCE: laser has sealed housing with high- frequency input and resonator mirrors. Resonator contains upper electrode plate which is connected to high-frequency input, lower electrode plate which has water cooling channel and to side plates which together with said electrode plates provide rectangular waveguide which has longitudinal gaps at its angles. Side plates are made from dielectric material and provide heat contact to electrode plates. In addition plates have lateral transversal convection channels to buffer space in sealed housing. Total area S_c of cross section of convection channels conforms to condition S_s≅S_c≪ S_h, where S_s is total area of longitudinal spaces in waveguide channel, S_h is total area of heat contact of side plates and electrode ones. EFFECT: increased functional capabilities. 1 dwg

Description

 The invention relates to the field of laser physics and can be used in engineering technology and medicine.

 A known laser with transverse RF excitation, containing two electrode plates and two side dielectric plates forming a waveguide channel with a rectangular cross section. A voltage in the range from 30 MHz to 3 GHz is applied to the electrode plates, which makes it possible to minimize the interaction of electrons in the discharge with the electrodes when the discharge is excited in the chamber. As a result, the working life of the laser increases, gas dissociation decreases, the stability and uniformity of the discharge increase, and the efficiency increases. the required excitation voltage is significantly reduced, the size of the laser is reduced, and its design is simplified (US Pat. No. 4,169,251, class H 01 S 3/097, September 25, 79).

A disadvantage of the known laser is due to the rate of gas renewal in the discharge zone, which in this case is realized only by convection of the gas through the ends of the waveguide channel. Gas renewal is necessary to remove from the discharge zone the products of dissociation of CO ₂ molecules and can significantly increase the laser power.

The closest in technical essence and the achieved effect of the present invention is a waveguide CO ₂ laser with transverse RF excitation (IG Xin, P. Van, GH Wei, RF-excited allmetall waveguide CO ₂ laser. "Appl. Plys. Zett. 59 / 26 /, 1991, p. 3363 3365.) The laser comprises a sealed housing with an RF input and resonator mirrors, inside of which there is an upper electrode plate connected to an RF input, a lower electrode plate equipped with a water cooling channel and two side metal plates placed with a gap with respect to said electrodes and a distance from each other. As a result of this arrangement is formed a waveguide channel of rectangular cross-section. The use of metal waveguide channel walls allows to organize efficient heat dissipation from the discharge zone and thereby increase the output power.

The main disadvantage of this laser is that the electrical insulation between the electrodes and the side metal plates, necessary for localizing the discharge in the area of the waveguide channel, is organized using gaps of the order of 0.1 mm and oxidation of the side walls of the waveguide channel. The electric strength of such gas gaps according to the Paschen law is determined by the product of the gas pressure P by the gap width d, which imposes a restriction on the ratio between the indicated values. Moreover, the products P • d that are optimal from the point of view of electric strength can be performed in the pressure range P which are not optimal for efficient excitation of the active medium of a CO ₂ laser. In addition, the upper and lower laser electrodes (also to localize the discharge in the area of the waveguide channel) do not have a dielectric oxide film, which increases the waveguide losses compared to a purely dielectric channel and reduces the laser life due to the inevitable oxidation of the electrodes when interacting with the discharge plasma.

 In addition, the lack of mechanical contact between the plates forming the waveguide reduces the cooling efficiency of the discharge zone due to heat removal to the lower electrode plate cooled by water. The use of independent water cooling of all elements of the waveguide channel significantly complicates the design of the laser.

 An object of the invention is to eliminate the above disadvantages to increase the power of the laser.

 The basis of the invention is the task of such a change in the design of the laser in order to exclude the possibility of igniting a discharge outside the zone of the waveguide channel with the simultaneous intensification of the processes of cooling and gas renewal in the waveguide channel by switching on the mechanism of diffusion heat removal to the cooled lower laser electrode and the mechanism of convective self-pumping through the gaps between the electrodes and the side walls of the laser.

The essence of the solution of the problem lies in the fact that in a CO ₂ laser with transverse RF excitation, containing a sealed housing with RF input and resonator mirrors, inside of which there is an upper electrode plate connected to an RF input, a lower electrode plate equipped with a channel for water cooling, and two side plates, forming together with the said electrode plates a waveguide channel of rectangular cross section with longitudinal gaps at the corners, the side plates are made of dielectric of the material and are in thermal contact with the electrode plates, and in the immediate vicinity of the contacting surfaces in the electrode plates there are transverse convection channels connecting the longitudinal gaps in the waveguide channel with the buffer volume of the sealed chamber, and the total area S of _the cross sections of the convection channels is selected from the ratio s _h ≅ s _{to the} << s _b where s the total area _of the longitudinal gaps in the waveguide channel, s _b the total surface area of thermal contact between the side electrode and s plates.

 Thanks to these innovations, the conditions for intensifying the process of updating the gas mixture in the waveguide channel are preserved, since convectional movement of the gas mixture in the waveguide channel through longitudinal gaps in the said channel and transverse convection channels made in the plates becomes possible. At the same time, the maximum heat removal efficiency is maintained and there are no restrictions associated with the localization of the discharge in the waveguide channel, that is, it is allowed to work at the ratios P • d that are optimal for pumping the laser, and the electrodes can have a dielectric coating, which reduces the waveguide channel loss and increases the laser life due to reducing the oxidation rate of metal surfaces in contact with the discharge.

The invention is illustrated in the drawing, which shows a cross section of a waveguide CO ₂ laser.

A transverse RF excitation waveguide CO ₂ laser comprises a housing 1 with an RF input 2. Inside the housing 1 is an upper electrode plate 3, with transverse convection channels 4, which is connected to an RF input 2. Dielectric plates 5 are installed between the upper electrode plate 3 and the lower electrode plate with convection channels 6. The lower electrode plate 7 is made wider than the electrode plate 3 and provided with channels for water cooling (not shown). The horizontal surfaces of the electrode plates 3, 7 facing each other, together with the vertical surfaces of the plates 5 facing each other, form a waveguide channel 8 in which the gas active medium is heated. Good thermal contact is ensured between the said electrode plates 3, 7 and the dielectric plates 5, for which purpose the contacting surfaces are either subjected to thorough machining or an intermediate layer of soft conductive material is introduced between them (indium, heat-conducting paste, etc.). The electrodes 3, 7 are made of aluminum or aluminum alloy, and their surfaces are coated with a special corundum film, which is polished to reduce waveguide losses, to prevent erosion (oxidation) under the action of a discharge. Between the walls of the waveguide channel 8, longitudinal gaps h are arranged, to which the upper 4 and lower 6 convection channels are suitable. The value of h is 0.05 0.1 of the width of the waveguide channel 8. An increase in h is advisable from the point of view of the conditions for convection renewal of the gas mixture in channel 8, however, an increase in waveguide optical losses is inevitable. The total area of convection channels is selected from the relation S _z ≅ S _to << S _b , where S _{z is the} total area of longitudinal gaps in the waveguide channel, S _{b is the} total thermal contact surface area of the side and electrode plates.

Before turning on the laser, the sealed housing 1 is filled with a CO ₂ He gas mixture at a pressure P in the range of 3 • 10 ³ 35 • 10 ³ Pa, water from the water cooling system is passed through the lower electrode plate 7.

The laser operates as follows. The RF input is supplied with voltage from the RF generator. Under the influence of the RF field in the waveguide channel 8 between the electrode plates 3, 7, a transverse gas discharge is ignited. Under the influence of an RF discharge due to collisions with electrons, the vibrational level (V 1) of nitrogen molecules is excited. In collisions with CO ₂ molecules, this excitation is most likely transmitted by the latter. This creates an inverse population between the levels 00 1 10 0 (02 0) of the CO ₂ molecule and such a medium is able to amplify radiation with a wavelength in the region of 9.4 10.7 μm. Due to the presence of a resonator formed by two flat mirrors M ₁ and M ₂ (not shown in the drawing) with a reflection coefficient (99% and 90 95%, respectively), light radiation arises and amplifies in the waveguide channel, part of which leaves the laser through a translucent mirror M ₂ , forming an output laser beam.

For effective laser operation, the gas temperature in the center of the waveguide channel 8 should not exceed 300 350 ^o C. Maintaining such a gas temperature requires effective cooling of the elements 3, 5, 7, forming the waveguide channel 8. In the laser under consideration, the gas is cooled by two processes. Firstly, due to the diffusion of “hot” gas molecules (mainly helium) onto the cooled elements of the waveguide channel 3, 5, 7. The time constant of this process is determined by the time the molecules diffuse to the channel walls and in practice is 1 m sec. The process is most effective when the “hot” molecules interact with the electrode plate 7 cooled by water. Elements of the waveguide channel 3, 5 also transfer heat to the electrode plate 7 due to thermal contact with the latter. However, at the same time, their cooling is less effective and, in general, they are at a higher temperature (actually several degrees C). However, such a process, when the above relations between the channel area and the area of thermal contacts (S _to << S _b ) are fulfilled, as well as subject to the quality requirements of the latter, is sufficient for cooling the waveguide channel 8, which is required for efficient laser operation. The second process that plays a role in gas cooling is the exit of “hot” molecules from the discharge zone due to transverse thermal convection in the gravitational field. The direction of convection gas flows is shown in dashed lines in the drawing. The heated gas from the waveguide channel 8 through the upper longitudinal gaps and convection channels 4 enters the buffer volume of the sealed enclosure 1. During convective movement of the heated gas, it gradually cools due to interaction with the walls of the convection channels and the inner surface of the sealed enclosure 1. Cooler gas from the buffer volume enters through the system of lower convection channels 6 and lower longitudinal gaps into the waveguide channel 8. This process is significantly slower (by one two oryadka) compared to the diffusion time and plays a role in the secondary cooling gas. However, such a process is extremely important from the point of view of gas renewal in the discharge zone. When burning an RF discharge in the waveguide channel 8, the dissociation of CO ₂ molecules into CO and O ₂ occurs. As a result of this reaction, the concentration of CO ₂ molecules in the gas mixture decreases, which leads to a significant (up to 30%) drop in the generation power. The time constant of this reaction is fractions of a second, that is, it turns out to be commensurate with the time of convective gas renewal in the waveguide channel. Thus, the process of transverse thermal convection allows you to effectively update the gas in the discharge zone and thereby prevents a drop in the generation power due to the dissociation of CO ₂ molecules. During the above convective motion of the gas, a partial recovery of the concentration of CO ₂ molecules occurs due to the reverse reaction. At the same time, additional elements can be located on the gas path, allowing to completely restore the gas mixture (catalysts, oxygen donors or CO ₂ , etc.).

According to the invention, a waveguide CO ₂ laser with RF excitation was created. The length of the laser electrodes was 350 mm. The side walls of the waveguide channel were made of leucosapphire and formed a waveguide channel with a cross section of 3.5 x 3.5 mm with electrodes. In this case S ² _of 70 mm, S _b 7000 mm ^2, S _to 750 mm ^2. The waveguide channel was mounted in a sealed cylindrical housing with an internal ⌀ 64 mm. The resonator was formed by two flat mirrors: a dense one with a reflection coefficient> 99% and a translucent one with a transmittance of 10%. The discharge was excited from an RF generator operating at a frequency of 108 MHz. The RF power was supplied to the sealed enclosure through a vacuum RF input. Studies have shown that the created laser allows to obtain a specific output power> 80 W / m, which significantly exceeds the result obtained in the prototype 40 W / m

Claims (1)

A transverse RF excitation waveguide CO ₂ laser comprising a sealed housing with RF input and resonator mirrors, inside of which there is an upper electrode plate connected to an RF input, a lower electrode plate equipped with a water cooling channel, and two side plates, together with the said electrode plates forming a waveguide channel of rectangular cross section with longitudinal gaps at the corners, characterized in that the side plates are made of dielectric material and are in thermal contact transverse convection channels connecting the longitudinal gaps in the waveguide channel with the buffer volume of the sealed enclosure, and the total area S _{to the} cross sections of the convection channels is selected from the relation
S _s ≅ S _to ≅ S _b ,
where S _{z the} total area of longitudinal gaps in the waveguide channel;
S _{b the} total surface area of the thermal contact of the side and electrode plates.