Abstract:
A laser apparatus comprises a hollow waveguide containing a lasing gas composition; structure for directing radiation into the waveguide and for directing radiation out of the waveguide; and electrical exciting structure operatively associated with at least part of the waveguide. The waveguide defines a convoluted, continuously curved path having a helicoidal shape. The waveguide has a concave, non-closed transverse section with an open inner portion and is disposed within a gas-tight container containing the lasing gas composition. The waveguide is a laterally open groove formed internally in a cylindrical block disposed within the container.

Description:
DESCRIPTION 
     The present invention concerns an apparatus for emitting a laser, beam, of the type comprising an amplifying gaseous medium and means for exciting this medium. The invention may be used for producing lasers as well as amplifiers of laser beam. 
     The current technology of these apparatuses consists in placing in a cavity under vacuum where a laser producing rarefied gas circulates, a certain number of mirrors of which one is partially reflecting, which define a trajectory for the luminous beam consisting of rectilinear segments whose length is much greater than that of the apparatus. 
     This technology presents the disadvantage of being complicated and of rapidly becoming out of order as a result of transportation, shocks and/or overheating. Moreover, the size of the apparatuses is important as soon as some outlet power is required. 
     The aim of the invention is to provide an apparatus which is reliable and of reduced dimensions. 
     For this purpose, it is an object of the invention to provide an apparatus of the above-mentioned type, characterized in that the amplification medium is bounded by a reflecting guide which defines a continuously curved guiding trajectory of the laser beam along a plurality of turns. 
     The guide may for example consist of a groove hollowed out in a rigid support block and having a concave cross-section. 
     The trajectory guide may particularly be helicoidal. 
    
    
     Certain embodiments of the invention will now be described with, reference to the annexed drawings in which: 
     FIG. 1 is a side view, partially in cross-section, of an apparatus for amplifying a laser beam according to the invention; 
     FIG. 2 is a side view showing the side opposite that of FIG. 1, of the same apparatus; 
     FIG. 3 is a partial end view, partially cut away, taken along arrow III of FIG. 2; and 
     FIGS. 4 to 7 schematic illustrations of a plurality of embodiments of the means of excitation associated with the guide. 
    
    
     The apparatus illustrated in FIGS. 1 to 3 is intended to serve as an amplifier for a low power laser 1 (for example a few tens of watts). It comprises a generally cylindrical amplifying enclosure 2, having a horizontal axis X--X, which is connected on the one hand to a vacuum pump 3 by means of a duct 4 from an end wall 5, and on the other hand to a source of laser forming gas 6 by means of a duct 7 which originates from the other end wall 8 of the enclosure. The laser forming gas is for example a mixture of helium, nitrogen and CO 2  and may also contain hydrogen, carbon monoxide, oxygen and/or xenon. The enclosure 2 is mounted on a stand 9 which also carries the laser 1 (FIG. 2). 
     An annular block 10 is mounted in the space 11 provided in the enclosure 2, against the internal cylindrical wall of the latter. In the radially internal face of this block a helicoidal groove 12 has been hollowed out, whose extremity (on the left of FIG. 1, on the right of FIG. 2) is opposite an inlet port 13 (FIG. 2) and whose other extremity is opposite an outlet port 14 (FIG. 1) of the enclosure 2. The port 13 is in the diametrically horizontal plan of the enclosure 2, at the bottom of a channel 13A provided in the enclosure 2 (FIG. 2), also, the port 14 is in the vertical diametrical plane of the enclosure 2, at the bottom of a channel 14A of the enclosure 2 (FIG. 1). The cross-section of the groove 12 is an arc of a circle. Its surface carries a protective and reflecting coating 15 which is analogous to those, used in known manner for the total laser reflection mirrors. 
     The central space defined by the block 10 is partially occupied by a combination comprising a heat exchanger 16, for example made of a metallic trellis provided with cooling fluid inlet, circulation and outlet ducts 17, this exchanger being surrounded by a cylindrical electrode 18 having an axis X--X. The combination is overhangingly supported by means of a portion 5A of wall 5, connected to the latter by means of radial ribs 5B. The other electrode 19 of the apparatus is also cylindrical and has the same axis X--X, and is mounted in a cavity 20 provided in the cylindrical wall of the enclosure 2 around the block 10. This cylindrical wall is also provided with a cooling fluid inlet and with circulation and outlet ducts 21. The electrodes 18 and 19 are connected to an appropriate source of energy (not represented) which can for example be a radio-frequency or microwave source. 
     The shaft of a centrifugal ventilator 22 sealingly extends through the front wall 8, the shaft being inside space 11 and being rotated by a motor 23 provided outside the enclosure 2. 
     In operation, the vacuum pump 3 and the source 6 maintain in the enclosure 11 a laser producing gaseous atmosphere under low pressure which is circulated by ventilator 22 along the arrows indicated in FIG. 1, i.e. radially towards the outside of this ventilator, along wall 8, then longitudinally along block 10, then radially towards the inside along wall 5, then axially towards the ventilator through the heat exchanger 16, which, enables cooling down the pump as well as the electrode 18. The ducts 21 cool the electrode 19 and block 10, the latter constituting an important heat exchange surface. 
     The laser 1 produces a low power laser beam 24 parallel to the axis X--X. The latter is vertically reflected 90° by means of a 45° mirror 25 which is mounted on the base 9 and is also directed towards the inlet port 13. In the enclosure 11, this beam hits the adjacent extremity of the groove 12 along a tangential direction, and this groove guides the latter by reflection up to the outlet port 14 along a multiple turn helicoidal trajectory. During this trajectory, the power of the beam is progressively amplified by the excitation produced by the two coaxial electrodes 18 and 19. 
     The apparatus described above provides a compact amplification trajectory of great length and makes possible a laser beam of considerably increased power with respect to the initial beam 25, for example of the order of a kilowatt, to exit through the port 14. 
     According to a variant which has not been represented and constitutes a limit case, the depth and the curvature of the groove 12 can be zero, and the laser beam is then guided by a smooth cylindrical surface. 
     The same apparatus can itself constitute a laser. In this case, the laser 1 is omitted and the inlet port is replaced by a totally reflecting mirror while the outlet port is constituted of a partially reflecting mirror, so as to constitute a resonating cavity as it is known in the laser technique. 
     FIGS. 4 to 7 show other ways of exciting the beam which is carried by the guide 12. 
     In FIG. 4, a helicoidal conductor 18A, replacing the interior electrode 18, follows the guide 12, substantially on the axis of the cross-section of the latter. The other electrode follows a parallel trajectory outside the guide and may be constituted by the guide itself, as shown. 
     In FIG. 5, the two electrodes 18B and 19B follow the edges of the guide 12. In FIG. 6, a supplementary deflection electrode 26, also helicoidal, is provided between the electrodes 18B and 19B and serves to confine the excitation discharge in the groove defined by this guide. 
     In the embodiment shown in FIG. 7, there is seen the exterior annular electrode 19 of FIG. 1, however the interior electrode consists of an axial conductor 18C.