FR2652956A1 - GAS LASER. - Google Patents

Abstract

Gas laser (1) comprising at least one laser tube (2, 3) on which there is, for the capacitive HF excitation, at least one pair of electrodes (10, 11, 12, 13) with opposite electrodes, characterized in that at least one of the electrodes consists, in the peripheral direction of the laser tube (2) of at least two segments, the spacing of which is such that a discharge takes place, approximately homogeneous, at inside the laser tube (2).

Description

The present invention relates to a gas laser comprising at least one tube

  laser on which is located, for the capacitive HF excitation, at least one pair of electrodes with opposite electrodes. High frequency, fast axial flow gas lasers need gas discharge

  homogeneous for the excitation of the corresponding laser level.

  In the case of capacitive HF excitation, we place

  curved electrodes on the cylindrical discharge vessel.

  The cooling capacity of the device depends, among other things, on the length of the electrodes, the wall thickness and the dielectric characteristic of the tube.

  discharge as well as gas parameters.

  A gas laser of this type is known with electrodes for capacitive HF excitation, for example by European patent applications EP 0183023 and 0215458. To prevent non-uniform distribution of energy and to obtain distribution of energy which increases uniformly, from the center of the laser tube, it is proposed, in these documents, to offset the pairs of electrodes or their sections, in the peripheral direction of the tube. In this case, at least one pair of electrodes is placed so that it can rotate by

  relation to gas flow or laser beam.

  Known devices have in particular this drawback that they are relatively complex due to the need for electrodes of particular shape and also

rotation devices.

  The present invention proposes to improve a gas laser of the aforementioned type so as to obtain a homogeneous and efficient discharge in the tube.

  laser, by simple and inexpensive means.

  This object is achieved by means of the gas laser according to the invention, in that at least one of the electrodes consists, in the peripheral direction of the laser tube, of at least two segments whose spacing is such that '' there is an almost homogeneous discharge inside the

laser tube.

  The basic idea of the invention is therefore to segment the electrodes peripherally, to produce a homogeneous HF field and therefore also a homogeneous gas discharge. It is particularly advantageous for the electrodes to consist of at least three segments, the border segments being arranged symmetrically around a central segment and a dielectric layer being provided between the laser tube and the border segments. The embodiments of the invention are described below in more detail, with reference to the accompanying drawings in which: FIG. 1 schematically represents the construction of a gas transport laser with HF electrodes; FIG. 2 shows the arrangement of the electrodes of known type on the laser tube; Figures 3 to 9 show different embodiments of the arrangement of electrodes according to the invention and Figure 10 shows the arrangement of the central segments in the longitudinal direction of the laser tube. In FIG. 1, the reference I designates a laser device which is known, for example, from document EP 0111045. It essentially consists of two longitudinal tubes 2 and 3 which form the laser tube or the laser resonator . The longitudinal tubes are fixed in optical supports 4 and 5 as well as in a conical collector 6. At the outlet of the conical collector 6 is placed a radial compressor 7 which, for its part, is connected to the optical supports 4 and 5, by conduits 8 and 9 in which the gas is cooled. The heated gas therefore leaves the longitudinal tubes 2 and 3 to reach the conical manifold 6, then into the radial compressor 7; after which it is cooled in the conduits 8 and 9 and returns to the longitudinal tubes 2 and 3 by the optical supports. The laser gas is excited in the longitudinal tubes using HF energy. To this end, pairs of electrodes 10, 11 or 12, 13 are located on the longitudinal tubes 2 and 3. An HF generator 18 is connected to the pairs of electrodes, by the electrical lines.

14, 15 or 16, 17.

  FIG. 2 shows, by way of example, the longitudinal tube 2 with the electrodes 10 and 11 and the

power lines 14 and 15.

  As already mentioned above, this known arrangement of electrodes, as shown in FIG. 2, has this drawback of not, as a rule, giving a homogeneous radial discharge profile, so that the laser power is less than theoretical power. FIG. 3 represents a simple embodiment of the invention. The electrodes are designated by the references 30 and 31. While the electrode 30 is not segmented, the electrode 31 has two segments 31 ′ and 31 ". The two electrode segments 31 ′ and 32" are held at the same electrical potential and are connected by the electrical line 14 (see Figure 1). The size of the electrodes which, in the present example, is defined by the angles ai, a2, a3, as well as the spacings between the electrodes which are characterized by the angles I1 and B2, must be determined in each case, for a type of concrete laser. Since the gas flow inside the laser tubes is frequently non-homogeneous, the values of a and B can

  be different for different types of laser.

  FIG. 4 represents an exemplary embodiment in which two electrodes 40 and 41 are

  segmented and have the segments 40 ', 40 "or 41', 41".

  Figures 5, 6 and 7 show electrode arrangements in which the electrodes 50, 51; 60, 61; 70, 71 of a pair of electrodes each consist of three segments. The border segments 50 "1 51 '' '; 61" - 61' ''; 70 "- 71 '' 'are each arranged symmetrically around a central segment 50', 51 '; 60', 61 '; 70', 71 '. To standardize the HF field or for gas discharge, the segments of border do not rest directly on the laser tube 2, but a dielectric layer 54, 55, 56, 57 or 64, 65, 66, 67 is found, in the embodiments of Figures 5 and

  6, between the laser tube 2 and the 50 "border segments -

  51 '' '; 60 "- 61". The thickness of this layer must be determined experimentally. In a practical example, it was 0.6 mm for a specific power coupling (ratio between the power introduced into the discharge volume and the length of

the electrode) of approximately 15 kW / m.

  In the case of the exemplary embodiment of FIG. 7, a layer of air is located between the electrodes

  border 70 ", 70 '' ', 71", 71' '' and the laser tube 2.

  FIG. 8 represents an exemplary embodiment in which the pairs of electrodes are each made up of five segments. On the other hand, FIG. 9 shows another example of embodiment in which

  the electrodes consist of seven segments.

  To standardize the axial discharge profile, it has been found to be advantageous for the electrodes to have, at their ends in the direction of gas flow, a conical space filled with a dielectric. We thus obtain that the value E / n (E: electric field intensity, n: particle density) critical for a homogeneous discharge, is not exceeded. In fact, the discharge gives rise, in the discharge enclosure, to a temperature gradient, that is to say that the temperature of the gas increases with the length of the electrode. However, an increase in temperature causes a decrease in the density of the particles, so that at constant electric field intensity, there is an increase in the quotient E / n. This increase must remain below a given critical value. According to the invention, this is achieved by reducing the intensity of the electric field at the end of the electrodes, through the slot and the dielectric which is introduced therein. Figure 10 shows, by way of example, a means of this type for the central segments 50 'and 51' of the electrodes 50 and 51 shown in Figure 5 (the figure is a cross-sectional view along line V - V). As shown in FIG. 10, the central segments 50 ′ and 51 ′ have, at their ends in the direction of gas flow 53, a conical space in which a dielectric 52 is placed. The same also applies to the segments border 50 "to 51 '' '(not shown). In other words, the segments (51' to 51 '' ') have, in addition to the dielectric layers 54 to 57 described above, a dielectric placed in a split space at their

  ends in direction of gas flow 53.

Claims (6)

  1. Gas laser (1) comprising at least one laser tube (2, 3) on which is located, for capacitive HF excitation, at least one pair of electrodes (10, il; 12, 13) with opposite electrodes , characterized in that at least one of the electrodes (30, 31, 40, 41; 50, 51; 60, 61;, 71; 80, 81) is formed, in the peripheral direction of the laser tube (2) , of at least two segments (31 ', 31 "; 40', 40", 41 ', 41 "; up to 80' - 81V) whose spacing is such that a discharge occurs, at little   almost homogeneous, inside the laser tube (2).   2. Gas laser according to claim 1, characterized in that the two electrodes (40, 41) of a pair of electrodes each consist of two segments (40 ', 40 "; 41', 41").   3. Gas laser according to claim 1, characterized in that the two electrodes (50, 51; 60, 61; 70, 71) of a pair of electrodes each consist of   at least three segments (50 '- 50 "', 51 '- 51"'; 60'-   60 "', 61' - 61" '; 70 '- 70 "', 71 '- 71"'), each of the border segments (50 ", 50" ', to 71 ", 71"') being arranged symmetrically with respect to a central segment (50 ', 51 '; ', 61'; 70, 71 ').   4. Gas laser according to claim 3, characterized in that between the laser tube (2) and the edge segments (50 ", 50" '; 51 ", 51"'; 60 ",   "'; 61", 61 "') a dielectric layer (54 - 57; 64-   67). 5. Gas laser according to claim 4, characterized in that an air layer is located between the laser tube (2) and the edge segments (70 ", 70" ', 71 ", 71 "').   6. Gas laser according to one of claims 1   to 5, characterized in that the electrodes 30 to 81 have, at their ends in the direction of flow of the   gas 53, a conical slot which is filled with a dielectric (52).