GB2035674A

GB2035674A - TEA laser apparatus

Info

Publication number: GB2035674A
Application number: GB7939382A
Authority: GB
Original assignee: Eltro GmbH and Co
Current assignee: Eltro GmbH and Co
Priority date: 1978-11-22
Filing date: 1979-11-14
Publication date: 1980-06-18
Also published as: DE2850521A1; GB2035674B; FR2442523A1; DE2850521C2; FR2442523B1

Abstract

A gas laser has an elongate cylindrical housing (2) containing an inner electrode (11) and two outer electrodes (10, 14) which are connected in a Blumlein discharge circuit. The opposing faces of the electrodes define two parallel channels, and optical means (not shown) situated in the region of one end (5) of the housing reflect light between the channels. For compactness, the capacitive elements of the Blumlein circuit are an integral part of the housing, in that the housing wall comprises two coaxial cylindrical plates (2<II>, 2<III>) separated by a dielectric layer (2IV). Connection of the outer electrodes (10, 14) to the capacitor is achieved by direct mounting of the electrodes on the internal surface of the inner plate (2<III>), and a switch (3) connected between the inner electrode and the outer plate (2<II>) is provided to discharge the capacitor when closed. In an alternative embodiment the housing includes three coaxial capacitor plates. <IMAGE>

Description

SPECIFICATION TEA laser apparatus This invention relates to a TEA laser or laser amplifier having an electrode system arranged in a resonator or discharge chamber of a housing with a high voltage lead extending to the outside, which housing has optical means at one end face thereof reflecting the laser beam in the direction of the other end face during laser operation. In particular, the invention relates to a laser in which the electrode system is symmetrical in structure and, together with the surrounding optical and mechanical components, is arranged substantially symmetrically inside the housing so as to produce a correspondingly symmetrical distribution of discharge current when discharge takes place.

A laser as described above, in which a high voltage switch and an energy storage capacitor are arranged coaxially, provides a structure of low inductance and hence enables rapid high voltage switching.

Various lasers with a Blumlein circuit are known from the technical articles "TRAVELLING WAVE EXCITATION OF HIGH POWER GAS LASER" by John D. Shipman, APPLIED PHYSICS LETTERS, 1.1.1967, pages 3 and 4, and "A Continuously Pulsed Copper Halide Laser with a Cable-Capacitor Blumlein Discharge Circuit" by Noble M. Nerheim, Alaudin M.

Bhanji and Gary R. Russell, IEEE JOURNAL OF QUANTUM ELECTRONICS, Vol. OE-14, No.9, September 1978, pages 686 to 693 (in particular page 692, Figure 11). A laser in which a so-called stripline capacitor composed of two spirally wound cylinders is used has been disclosed in "Compact High-Power N2 Laser: Circuit Theory and Design" by Adolf J.

Schwab and Fritz W. Hollinger, IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL QE-12, No.3, March 1976, pages 183-188 (in particular page 183, Figure 1 and page 188, Figure 14 and corresponding text). A CO2 laser having its discharge circuit in the form of a Blumlein circuit is disclosed for the first time in "A Simple Self-Mode-Locked Atmospheric Pressure CO2 Laser" by T. Y. Chang and 0. R. Wood, IEEE JOURNAL OF QUANTUM ELECTRONICS, August 1972, pages 721 to 723 (in particular page 722, lefthand column, last paragraph and Figures 1 and 3).

It is an object of the present invention to provide an improvement to the known type of TEA laser amplifier so that its capacitive elements assist the aim of obtaining a small and compact structure and are optimally adapted to it.

According to one aspect of this invention, a TEA laser amplifier comprises a housing enclosing a resonator or discharge chamber which contains at least two outer electrodes and a middle electrode, the housing having optical means in the region of one end of the chamber to reflect a laser beam between the electrodes in the direction of the other end, wherein that part of the housing which constitutes the outer boundary of the amplifier is in the form of a coaxial capacitor.According to another aspect of this invention a TEA laser amplifier comprises an electrode system arranged in the resonator or discharge chamber of a housing with a high voltage lead extending to the outside, which housing has optical means at one end face reflecting the laser beam in the direction of the other end face during laser operation, which optical means cooperate with a totally reflecting mirror and a partially transmittent mirror fixed in the region of this second end face, whilst during amplifier operation the mirrors are replaced by closing windows which transmit the amplified laser beam, the mirrors, windows and operative surfaces of the optical means being arranged in the spaces between the electrodes, the electrode system, which is substantially unchanged in its mass, being sub-divided into a middle electrode, which is discharged through a switch and has at least two surfaces for electric discharge, and at least two outer electrodes situated opposite the said surfaces, the electrode system being symmetrical in construction and the electrode system together with the surrounding optical and mechanical components being arranged substantially symmetrically inside the housing, the system producing a correspondingly symmetrical distribution of discharge current when discharge takes place, wherein the housing part which constitutes the outer boundary to the laser is in the form of a coaxial capacitor. Afurther saving in space is obtained if the energy storing capacitor is not a discrete structure but forms part of the housing which must in any case be provided. In this respect, the capacitor is comparable to a rolled stripline capacitor.

The coaxial capacitor may comprise two hollow concentric cylinders with a dielectric between them, the inner cylinder being electrically connected to the outer electrodes which are situated opposite each other. In a capacitor constructed in this manner, the inductance can be adapted in various respects to the gas discharge; firstly, through the ratio of its length to its diameter, and secondly by varying the distance between the outer electrodes and the inner hollow cylinder which also serves as supportforthese electrodes.

With regard to what has been said above, it may be advantageous if each hollow cylinder on its own constitutes a capacitor, and the two capacitors so formed are placed directly adjacent to each other without any gap between them. In this case, the outer capacitor is the first to be discharged and is discharged suddenly, limited only by intrinsic and circuit inductances. One variation of this arrangement, which may be particularly compact, lies in the possibility of adapting the inner cylinder to a form of the middle electrode (e.g. in the form of a pot capacitor) and integrating it with the middle electrode.

In accordance with the invention the two hollow cylinders may be angular in cross-section with rounded edges and may be made of metal in the region of the electrodes. The latter feature is necessary for the sake of electrical breakdown resistance.

The switch which discharges the middle electrode is generally arranged coaxially but it may be placed in a separate gas chamber extending parallel to the resonator or discharge chamber. This special device enables the electric leads to the individual electrodes to be made of different lengths if necessary or to be placed obliquely to make use of the transit time effect. This enables the point on the electrode at which the discharge is introduced to be selected.

A construction of resonator which is exceptionally stable and substantially protected against the effects of twisting of the cavity uses a triple mirror as the optical means for deflecting the beam. Such a mirror may comprise a circular or angular glass or metal body having its optically operative surfaces coated with a layer of gold or copper or of a light pervious optical material treated for the laser wavelength.

This treatment is carried out by vapour deposition and ensures good reflection properties.

Such a Blumlein circuit type of construction has the advantage of enabling high voltages to be stored which, in a suitable design, provides the possibility of extremely rapid discharge.

The invention will now be described by way of example with reference to the drawings in which similar parts shown in the individual figures carry the same reference numerals. In the drawings: Figure 1 is a longitudinal section through a laser having a housing designed as a coaxial energy storage capacitor; Figure 2 is a cross-section through the laser of Figure 1 taken on the line AB; Figure 3 is the equivalent circuit diagram of the laser of Figures 1 and 2; Figure 4 is a longitudinal section through a laser having a housing in the form of two concentric coaxial capacitors; Figure 5is a cross-section through the laser of Figure 4taken on the line CD; Figure 6 is the equivalent circuit diagram of the laser of Figures 4 and 5 arranged as a Blumlein circuit;; Figure 7 is a longitudinal section through a laser in which the second, internal capacitor (pot capacitor) is integral with the middle electrode; Figure 8 is a cross-section through the laser of Figure 7 taken on the line EF; Figure 9 is the equivalent circuit diagram of the laser of Figures 7 and 8 in the form of a Blumlein circuit; Figure 10 is a simplified cross-section of a laser having a triple mirror for beam deflection; Figure 11 is a view of the triple mirror of Figure 10 in a rectangular form; Figure 12 is a view of the triple mirror of Figure 10 in circular form; and Figure 13 is a simplified transverse cross-section of a laser having a high voltage switch arranged in a cavity alongside the main cavity.

Referring to Figures 1 to 3, a symmetrically constructed TEA laser 1 with its electrode system 10 to 14 has a housing 2 comprising two cylindrical non-magnetic metal plates 21 and 2, made for example of aluminium, enclosing a dielectric layer 2lv and thus constituting an energy storage capacitor C. Whereas the dielectric and the outer plate 2" extend as far as the lateral boundary walls 8, the inner capacitor plate 2lv extends only over the region of the length of the outer electrodes 10 and 14 for reasons of resistance to electrical breakdown. The inner plate 21V can be longer, provided the plate is kept at a minimum distance from the other metal parts to prevent accidentei discharges.The electrodes 10 and 14 are directly aPPached to the inner capacitor plate. However, in another embodiment, not shown in the drawings, the electrodes may be spaced from the housing gJall by a substantial distance, and the connection may extend through an electrode support. The dielectric 21V has a high sand high electrical breakdown resistance. A high voltage switch 3 is operable to discharge the middle electrode 11 which has Rogowski profiles. One of the end walls 8 contains a totally reflecting mirror 18 and a partially transmittent mirror 21. The equivalent circuit diagram (Figure 3), illustrating Blumlein circuit configuration of the amplifier, has the characteristic feature that the two capacitors are substantially equal in magnitude.The capacitor values are determined by the dielectric, the required storage voltage, and the geometrical dimensions so as to be suitable for the performance specifications of the laser.

A second preferred embodiment, illustrated in Figures 4 to 6, differs from that of Figures 1 to 3 only in the number of capacitors. Only one capacitor was used in Figures 1 to 3 whereas in this case there are two capacitors comprising hollow cylinders placed coaxially one inside the other. The two capacitors or hollow cylinders are placed adjacent to each other without any gap between them. The high voltage supply is provided via the lead 22 and a charging resistance RL. Coupling resistances 23 are connected between the middle electrode 11 and the capacitors 9 and 92 and have their other ends earthed at 34.

In another embodiment, illustrated in Figures 7 to 9, the second or inner capacitor C2 is integrated with the middle electrode 11 as a pot capacitor. The open end of this pot projects from one end of the electrode and is conductively connected to the wall 8. The construction of the capacitor C1 is similar to that of Figure 1 and again, the inner metal plate is only as long as the outer electrodes 10 and 14 attached to it.

45" prisms 19' and 22' situated opposite the mirrors 18 and 21, each serving to deflect the laser beam, are attached to an intermediate wall 9, fabricated from an insulating material.

As regards the function of the capacitors, the capacitor C1 is the first to be discharged, the discharge being limited only by the intrinsic inductance and the inductance of the closed switch 3. An oscillation is produced in this primary discharge circuit and a potential difference is established between the middle electrode 11 and the outer electrodes 10 and 14. This potential difference ionises the gas between the electrodes Fn ' a gas discharge sets in thereby also discharging the condenser C2.

Afurther preferred embodiment, shown in Figure 10, allows for distortion of the wall 2'1 by twisting. A triple mirror 19", 20" has optically active surfaces which have been treated with, for example, a layer of gold or copper, or the surfaces may be made of a light pervious optical material treated for the laser wavelength. The direction of the beam depends only on the two mirrors 18 and 21.Twisting about the longitudinal axis has no influence on the adjustment of the resonator. The three reflecting surfaces of the triple mirror are shown in Figures 11 and 12, which show mirrors having rectangular and circular outlines respectively.

Figure 13 shows how, in contrast to the preceding embodiments in which the switch 3 is arranged on the longitudinal axis of the middle electrode, the switch may also be placed laterally to the electrode system 10 to 14 in a gas chamber separated from the electrode system 10 to 14 by a wall 37 of insulating material.

Claims

1. TEA laser apparatus comprising a housing enclosing a resonator or discharge chamber which contains at least two outer electrodes and a middle electrode, the housing having optical means in the region of one end of the chamber to reflect a laser beam between the electrodes in the direction of the other end, wherein that part of the housing which constitutes the outer boundary of the amplifier is in the form of a coaxial capacitor.

2. A TEA laser amplifier comprising an electrode system arranged in the resonator or discharge chamber of a housing with a high voltage lead extending to the outside, which housing has optical means at one end face reflecting the laser beam in the direction of the other end face during laser operation, which optical means cooperate with a totally reflecting mirror and a partiallytransmittent mirror fixed in the region of this second end face, whilst during amplifier operation the mirrors are replaced by closing windows which transmit the amplified laser beam, the mirrors, windows and operative surfaces of the optical means being arranged in the spaces between the electrodes, the electrode system, which is substantially unchanged in its mass, being subdivided into a middle electrode, which is discharged through a switch and has at least two surfaces for electric discharge, and at least two outer electrodes situated opposite the said surfaces, the electrode system being symmetrical in construction and the electrode system together with the surrounding optical and mechanical components being arranged substantially symmetrically inside the housing, the system producing a correspondingly symmetrical distribution of discharge current when discharge takes place, wherein the housing part which constitutes the outer boundary to the laser is in the form of a coaxial capacitor.

3. A laser amplifier according to claim 2, wherein the coaxial capacitor comprises two hollow cylinders arranged concentrically one inside the other with a dielectric between them, the inner of the two cylinders being electrically connected to the outer electrodes which are situated opposite each other.

4. A laser amplifier according to claim 2 or claim 3 wherein each hollow cylinder taken on its own constitutes a capacitor and the two capacitors are adjacent to each other without any space between them.

5. A laser amplifier according to claim 2 or claim 3 wherein the inner hollow cylinder is adapted to the form of the middle electrode and integrated with it.

6. A laser amplifier according to any of claims 2 to 5, wherein the two hollow cylinders have an angular cross-section with rounded off edges and are made of metal in the region of the electrodes.

7. A laser amplifier according to any of claims 2 to 6, wherein the switch, which is discharged through the middle electrode, is arranged in a separate gas chamber extending parallel to the resonator or discharge chamber.

8. A laser amplifier according to any preceding claim, wherein the optical means used for deflecting the beam comprises a triple mirror.

9. A laser amplifier according to claim 8, wherein the triple mirror comprises a round or angular glass or metal body whose optically active surfaces are coated with a layer of gold or copper or of a transmittent optical material treated for the laser wavelength.

10. A laser amplifier according to any preceding claim in the form of a Blumlein circuit.

11. A laser or laser amplifier constructed and arranged substantially as herein described and shown in the accompanying drawings.