GB2052141A - Improvements in or relating to gas lasers - Google Patents

Abstract

A gas laser in which the lasing medium is preionized by means of a radio-frequency electromagnetic field. Forms of laser are described in which the energy is supplied via waveguides 4 which are incorporated in the structure of the electrodes 2, 3 which are used to excite the main discharge in the lasing medium. <IMAGE>

Description

SPECIFICATION Improvements in or relating to gas layers Pulsed gas lasers frequently require that the lasing medium should either be pre-ionized before being energised to create the conditions necessary for the appropriate lasing transition to occur, or that it should be subjected to ionization throughout the lasing process. A continuously acting source of auxilliary ionization has also been used in some types of continuously operating gas lasers. Methods of providing this ionization which commonly are used include: (i) Electron beams (ii) Sources of ultra violet light (iii) Small auxiliiary electric discharges to one of the electrodes of the laser.

All of these methods have disadvantages. For example, (i) requires relatively complex and expensive ancilliary equipment; (ii) often requires the addition of special additives to the lasing medium which may interFere with the desired lasing transition, and may not even work at all under certain operating conditions; and (iii) is not particularly effective.

According to the present invention in one aspect there is provided a gas discharge laser including an envelope for containing a gaseous lasing medium end a cathode and an anode electrode whereby the gaseous lasing medium can be excited to lasing action, wherein there is included means for applying to the gaseous iasing medium an electromagnetic field having a frequency in the radio region of the spectrum and energy sufficient to ionize the gaseous lasing medium.

Preferably the laser is one which includes carbon dioxide in the iasing medium, and the electro-magnetic field has a wavelength in that region of the electro-magnetic spectrum known as X-band.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 is a cross-sectional view of a laser embodying the invention.

Figure 2 is a cross-section of a second form of laser embodying the invention, and Figure 3 is a cross-section of a third form of laser embodying the invention.

Referring to Figure 1, a transversely excited gas laser includes a cylindrical chamber 1 which forms part of an optical cavity in which lasing action takes place in a lasing medium consisting of a mixture of the gases helium, carbon dioxide, nitrogen and hydrogen at a pressure of sone 0.1 - 500 torr. Extending parallel to the longitudinal axis of the optical cavity are an anode electrode 2 and a cathode electrode 3 to which a potential is applied to cause a discharge to take place in the lasing medium to cause lasing action to take place.

One of the electrodes, preferably the cathode 3 has incorporated into it a waveguide 4 of internal dimensions 0.9 x 0.4" so that it will transmit electro-magnetic energy in the X-band region of the radio frequency part of the electro-magnetic spectrum. The surface 5 of the cathode 3 facing the anode 2 has formed in it a system of holes, or slots 6 which enable energy to be coupled from the guide 4 into the space 7 between the anode 2 and the cathode 3. The holes or slots 6 are sealed with a dielectric material 8. The radio frequency energy is supplied from a magnetron, which is not illustrated, which operates at a frequency of 9.4 GHz with a pulse length in the range 0.5 to 2tis.

The pulse power varies according to the dimensions of the cylindrical chamber 1 and the pressure of the lasing medium, but typically lies in the range 20-250 kW. The resulting radio frequency field in the space 7 causes electrical breakdown to occur in the lasing medium. To prevent electrical breakdown within the waveguide 4, it is pressurised with a gaseous medium of high dielectric strength such as air, sulphur hexafluoride or a freon-type gas.

Alternatively, the waveguide 4 is filled with a suitable low-loss solid dielectric material and coupling holes are made in the inward facing wall of the waveguide 4. These hcles can be continued into the dielectric medium if desired.

If the laser cavity has a transverse size such that an X-band waveguide Is too small to create sufficient electrical breakdown over a large enough region of the lesing medium, either more than one X-band waveguide can be used, or a lower frequency electro-magnetic field, and hence larger waveguide can be used.

An alternative construction is shown in Figure 2, in which the waveguide 21 is not within the cathode 22 as before, but is mounted alongside it.

A sheet 23 of dielectric material is interposed between the waveguide 21 and the electrodes 22 and 24 of the laser. The dimensions and construction of the waveguide 21 are as before.

A third position for the waveguide 21 , which is not illustrated, is beneath the cathode 22 instead of alongside the electrodes 22 and 24. Again, it is desirable to include a sheet of dielectric material between the waveguide and the adjacent electrode to prevent electrical breakdown from the electrode to the waveguide.

A further arrangement which can be employed is to use a metallic vacuum vessel for the laser cavity of dimensions such that the vacuum vessel itself can be used as a waveguide, albeit for a lower frequency electro-magnetic field. The transmission mode is chosen to maximise the field between the electrodes within the vacuum vessel.

If the vacuum vessel is cylindrical, a suitable mode is the TM, mode. Mode conversion and launching structures of suitable types are well known in the radio communication art, and it is not thought necessary to detail them here.

Also, if a non-conducting vacuum vessel is used, the waveguide can be placed outside the vacuum vessel. Yet another technique is to use the electrodes within the vacuum vessel as an opensided parallel plate transmission line.

For the additional methods of pre-ionization described, the electro-magentic field typically will be at a frequency within the L, S or C bands, of the radio frequency region of the spectrum.

Gas lasers according to the present invention are suitable for use either as later oscillators or laser amplifiers.

Claims (14)

1. A gas discharge laser including an envelope for containing a gaseous lasing medium and a cathode and an anode electrode whereby the gaseous lasing medium can be excited to lasing action, wherein there is included means for applying to the gaseous lasing medium an electromagnetic field having a frequency in the radio region of the spectrum and energy sufficient to ionize the gaseous lasing medium.

2. A gas discharge laser according to claim 1 wherein the energy to generate the electromagnetic field is applied via a waveguide device positioned within the said envelope.

3. A gas discharge laser according to claim 2 wherein the waveguide device is pressurized with a gaseous medium of high dielectric strength.

4. A gas discharge laser according to claim 3 wherein the gaseous medium is air, sulphur hexafluoride or a freon gas.

5. A gas discharge laser according to claim 2 wherein the waveguide device is filled with a lowloss dielectric medium.

6. A gas discharge laser according to any of claims 2 to 5 wherein at least one of the electrodes is adapted to act as the waveguide device.

7. A gas discharge laser according to claim 6 wherein the electrode which is adapted to act as the waveguide device is the cathode electrode.

8. A gas discharge laser according to any of claims 2 to 5 wherein the waveguide device is situated to one side of the electrodes, parallel thereto and so as to inject the ionized electromagnetic field into the region between the electrode.

9. A gas discharge laser according to any of claims 2 to 5 wherein the waveguide device is positioned adjacent the cathode electrode, parallel thereto and on the side remote from the anode electrode.

10. A gas discharge laser according to claim 8 or claim 9 wherein a sheet of dielectric material is interposed between the waveguide device and the electrode or electrodes.

11. A gas discharge device according to any preceding claim wherein the electro-magnetic field has a frequency in the range of 5 to 11 GHz.

12. A gas discharge laser according to claim 1 wherein the vessel containing the gaseous lasing medium is metallic and is utilised as a waveguide for the electro-magnetic energy to generate the electro-magnetic field.

13. A gas discharge lase according to claim 1 wherein the electrodes are planar and are utilised as a transmission line for the electro-magnetic energy to generate the electro-magnetic field.

14. A gas discharge laser according to any proceeding claim wherein the gaseous lasing medium includes carbon dioxide.

1 5. A gas laser according to claim 14 wherein the gaseous lasing medium is at a pressure in the range of 1 to 500 torr and the electro-magnetic field is pulsed with a pulse length in the range of 0.5 to 20 sss and a power in the range of 20-250 kW per pulse.

1 6. A gas laser substantially as hereinbefore described with reference to the accompanying drawings.