DE3035142A1 - WAVE GUIDE GAS LASER - Google Patents

Description

103162

Waveguide gas laser

The invention relates to lasers, and more particularly to a waveguide gas laser with RF excitation.

Attention is drawn to US Pat. No. 4,169,251, where one of the applicants has described a waveguide laser, which by means of a transverse discharge with high frequency in the range of approximately 30 MHz to about 3 GHz is excited and a laser gas is placed in an elongated chamber, and the discharge in the gas is built up by means of an alternating electric field, which is applied to the chamber along one direction applied transversely to its length wii-d. The superior one Performance of such an RF transversely excited waveguide laser, as well as its reduced size and complexity, compared with known lasers according to US Pat. No. 3,772,611 and 3,815,047 are disclosed in US Pat explained.

The invention also relates to a waveguide laser with RF excitation, taking many of the advantages of the waveguide laser according to the US-PS mentioned at the beginning,

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however, there are also difficulties and unity be overcome, which can occur in the laser according to the US-PS mentioned above. One such improvement consists in the use of longitudinal excitation which depends on selection of waveguide bore size and electrode separation results in independent parameters and in this way the optimization of the RF frequency selection independent of the bore size enables.

Cinema further improvement of the present invention compared to the aforementioned RF-excited gas waveguide laser consists in new means for eliminating a first and limiting disadvantage of the device mentioned above, namely the formation of non-uniformities or "hot spots", evidently due to the bistable discharge impedance characteristics result. Such hot spots tend to increase the gain, the efficiency and to decrease the output power of the laser. To overcome this disadvantage in the known device, sees the present invention introduces improvements in structure and circuitry, including use a serial capacitive ballast formation, which results in new improvements in terms of the waveguide structure. A further improvement is achieved by means of a unique driver circuit which is used to to determine the appearance of the low impedance hot spots and the input power adjusted accordingly so as to minimize the otherwise non-uniform negative impedance characteristics. Another improvement is the use of a totally homogeneous structure which eliminates the hot spot problem further improved and results in a more compact waveguide laser which is more stable in terms of gas composition and is more reliable than this for the transverse, RF-excited waveguide laser according to the US-

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PS applies.

Accordingly, the present invention has all the advantages of the waveguide laser according to the US Pat. namely, a high frequency transverse excitation waveguide laser is provided, but the present one is additionally provided The invention still overcomes the difficulties and limitations of the high frequency transverse excitation method. Of the The main advantage of longitudinal RF excitation over transverse RF excitation is the resulting impedance in the selection of the active bore size of the laser chamber and the electrode separation abotand for the excitation means. Alternatively, the advantage is the RF drive frequency to optimize regardless of the bore size.

In the US-PS mentioned at the outset it is taught that efficient lasers with RF excitation require an RF drive frequency which is sufficiently high so that the electrons only over a negligible distance with respect to the electrode gap separation drift during a half cycle of the alternating electric field. Otherwise, space charge zones will form in close to the electrodes, resulting in a higher electric field at the electrode gap and thus higher electron temperatures has the consequence. It is also known that in the field of molecular gas laser physics, the optimum electron temperature for maximizing the laser head efficiency tends to be considerably lower than the electron temperature in self-sustaining discharges. Furthermore, higher electron temperatures lead to higher COp dissociation rates, which leads to a shorter tube life leads. In the case of self-sustaining discharges, it is therefore advisable to minimize the electron temperature and therefore also to minimize the electron field intensity required to maintain the discharge. Accordingly there is a minimum HF drive frequency for HF discharges

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for maximizing laser head efficiency for a given Electrode gap separation.

In a "transversal RF excited waveguide laser according to of the US-PS mentioned at the beginning, the laser bore size and electrode gap separation are inherently the same. Accordingly the bore size dictates the minimum RF drive frequency, and as the RF drive frequency is increased so will the coupling efficiency between the RF energy source and the discharge diminishes, and it becomes increasingly difficult to be efficient RF driver sources. Thus, the overall laser efficiency suffers for the transverse HF discharge of the US-PS mentioned above due to the low laser head efficiency, '3, if the RF drive frequency is below the desired one Minimum. On the other hand, if the RF drive frequency is too high, the efficiency suffers because of the lowering the coupling efficiency between the HF source and the discharge.

The above-mentioned upper and lower RF frequency limits are particularly problematic when the bore size is small and therefore a relatively high RF drive frequency is required in view of laser head efficiency. Unfortunately such a high RF drive frequency has less coupling and lower power supply efficiency resulting in a paradoxical situation. Due to the longitudinal RF excitation of the present It is the invention and the resulting independence between electrode split separation and bore size but now possible, for the first time, the HF driver frequency for high coupling and power supply efficiency and then separately the electrode gap separation for optimal laser head efficiency.

Summary of the invention. The present invention

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sees a waveguide laser device through the longitudinal RF excitation which gives a higher overall efficiency than the above-mentioned transverse RF excitation. Further is determined by the degree of efficiency improvement obtained by using the longitudinal instead of the transverse RF excitation, the additional benefit in terms of higher RF driver frequencies achieved that would otherwise be for a smaller one Boring devices using the transverse excitation configuration would be required.

By using the longitudinal excitation, the present invention creates an additional overall efficiency improvement compared to the transverse excitation, either because the electrode separation is greater or because the electrode area is smaller than is the case for corresponding electrodes in the transverse excitation device. As a result, the capacitance of the resulting waveguide structure is lowered and this gives a lower loaded ¹¹ Q "for the waveguide structure. The term loaded" Q "is referred to as the" Q "during discharge ignition. A lower loaded" Q "gives greater coupling efficiency Because of the reduced circulating power and the reduced power dissipation in other circuit elements. Allowing a lower RF drive frequency for a given bore size further reduces the circulating power while maintaining the same laser head efficiency, resulting in an even higher overall efficiency.

The typical structure of the above-mentioned transverse discharge waveguide laser has a transverse discharge section, coupled to a 50 ohm transmission line circuit and matched by a resonant pi circuit. It will a transformer with a shunt inductance at the discharge section used to tune the reactance. The unloading section is used in a floating weight mode.

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The transformer / shunt inductor structure allows for that close coupling of the HF driver to the discharge and also the independent adjustment of the impedance matching with regard to the reactance tuning. The one mentioned, which is in equilibrium Structure of the invention minimizes the stored charge, with the voltage versus ground at each electrode is equal to half of the total gap voltage.

In various embodiments of the invention, a Number of new improvements planned to eliminate or reduce the problems caused by hot spots, which would otherwise seriously degrade the performance of the waveguide laser. According to one embodiment a new and inventive modification in the basic structure of the laser is provided. Transversely excited HF load ;; they are typically made in the usual sandwich construction, which consists of two metal strips that are sandwiched are provided between two blocks of alumina. The one between the metal strips and the aluminum oxide blocks

The waveguide bore formed is typically 1 to 3 mm. This construction delivers on the order of half a watt per inch of laser length for a COp waveguide laser.

As the laser length is increased, at approximately 8 "in length and approximately 5 to 10 watts / inch of power, the Reached point where the laser discharge becomes bistable and the the aforementioned hot spots of discharge will develop. It was found experimentally that raw aluminum electrodes are a preferred material because this material is more resistant to spraying than most common materials. However, a problem that arises when using raw aluminum electrodes is that electrode oxidation occurs, which is quite serious in nature and affects the long-term stability of the gas composition. The oxidation problem was in the present invention by means of a hard

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th anodizing coating on the aluminum electrodes. This aluminum oxide coating forms an insulating layer on the metal. U - A also addresses the problem of hot spots mentioned above to solve? especially with higher power loads, according to the invention means are provided to provide a structural provide dielectric ballast for the longitudinally excited RF waveguide laser. This structure consists of two Aluminum oxide strips 1 to 3 mm thick, sandwiched arranged between two aluminum oxide panel elements.

ρ The resulting waveguide bore is 1 to 3 mm, and the aluminum oxide surface elements are between 1/2 to 2 mm thick. The electrodes are outside the discharge waveguide structure. The resulting structure is a completely homogeneous aluminum oxide and can therefore be solder sealed, and the gas can then be confined to the borehole alone. This is in contrast to the one mentioned, transversely excited laser, which is completely arranged in a gas-filled cavity. Another advantage of the invention is in that the electrodes are completely isolated from the discharge and therefore do not degrade as quickly over time, as is the case with known devices.

In a further embodiment of the invention, there has been a tendency in known devices to generate localized heat Spots are further reduced through the use of a new driver circuit design. When an excited waveguide discharge laser section is properly excited, the impedance curve is positive and the discharge takes place uniformly along the length of the device. In this operating mode or mode, if the reactance is tuned out, the Discharge impedance appear ohmic and is tuned to 50 ohms through a tightly coupled ferrite transformer. If the discharge develops hot spots, measurements have shown that the total voltage and the discharge impedance decrease approximately 20 to 40%. In one embodiment of the

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invention, the applicants have provided a driver circuit, to instantly reduce the input power when a lowering of the impedance is bottled. As a result, can the discharge section is not in an unstable or "hot spot" mode work and continuous proper excitation of the discharge is obtained.

In one embodiment, such a driver circuit consists of a quarter wavelength transmission line having a higher impedance than the 50 ohm laser head matched impedance. For example, a quarter wavelength section of a 75 ohm cable can be selected as a proper driver circuit because a quarter wavelength section has the ability to convert impedance changes around its characteristic value. If a 75 ohm load is applied to the section, the result at the cable input is a real impedance of 75 ohms. If a 50 ohm load is applied to one end, there is a real impedance of 112 1/2 ohms at the other end. Alternatively, if the load drops to 25 ohms, which is typical of the hot spot mode, the input impedance increases to 225 ohms. If such a quarter wavelength section is used between a 50 ohm laser head and a source matched to 50 ohms for maximum power, the power delivered would drop almost instantaneously, resulting in a cancellation of the hot spot mode.

In a further embodiment of the invention, an improved laser head structure is used in which the laser bore is formed by opposing aluminum electrodes, sandwiched between two aluminum oxide blocks. This assembly is held in alignment and compressed by a resilient tube, the tube as a spring-like, evacuable housing and serves as a heat sink that holds the waveguide and optical components in the correct orientation.

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Objectives of the invention. A main object of the invention is to provide an improved RF-excited waveguide laser device that reduces certain disadvantages IIF-excited waveguide lasers or completely overcomes, wherein, however, still the numerous advantages of this other waveguide laser devices, these have the advantage over conventional excited waveguide lasers. Another object of the invention is to provide a waveguide laser with RF longitudinal excitation to allow the selection of the waveguide bore size independently of the selection of the RF frequency of the excitation signal, thus permitting the selection of parameters for a more efficient laser device. Another object of the invention is to provide a waveguide laser which uses the high-frequency excitation, and wherein providing the ballast formation means for hot spot problems to reduce or substantially eliminate, the latter result from an unstable discharge ■, namely caused by operation in bistable impedance zones. Another object of the invention is to provide a novel structure for a RF angeiugte waveguide laser device _9, wherein said structure has an extended life span, has a reduced size and a more reliable and efficient operation permits, as compared with known RF excited waveguide lasers. Another object of the invention is to provide a driver circuit for matching an RF source with a laser head so as to automatically reduce the input RF power when a low impedance is detected due to hot spot operation that is otherwise constant higher performance levels would occur "

Another object of the invention is to provide a new housing for a waveguide assembly which enables the low cost, low cost mass production of waveguide lasers structures enabled, and furthermore, the training

1 ,'

direction and the compression of the waveguide arrangement is achieved by an elastic tube, which serves as a spring-like evacuable housing to serve, and also as a heat sink, in which way the waveguide and the optical elements wi rden arranged in the correct orientation.

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3035U2

Further objects and advantages of the invention are particularly evident from the claims and from the description of exemplary embodiments based on the drawing; shows in the drawing;

1 shows a partially schematic cross section

a prior art transverse discharge waveguide gas laser;

Fig. 2 is an isometric view of an out

management example of the longitudinal discharge excitation arrangement for waveguide gas lasers;

Fig. 3 is a cross-sectional plan view of the

Electrode configuration of the waveguide gas laser along line 3-3 in Fig. 2;

Fig. 4 is a front view of a homogeneous embodiment

Approximate example of the longitudinal discharge configuration according to the invention;

Figure 5 is a graph of the bistable

Impedance characteristic that has certain problems with both transversal and Caused longitudinal excitation waveguide gas lasers, but by the present Invention to be overcome or substantially reduced;

Fig. 6 is a cross-sectional end view of a trans-

versal discharge waveguide gas laser, in which the capacitive ballast formation of the Invention is used to overcome the mentioned bistable impedance problem;

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7 shows a schematic representation of the equiva

lenten circuit (equivalent circuit) of FIG. 6;

Figure 8 is a cross-sectional end view of the also

longitudinal discharge excitation waveguide gas laser using capacitive ballast;

9 shows an additional representation of the longitudinal

nalen waveguide gas laser with capacitive bailasting, but the side of the Waveguide is shown to better illustrate its structure;

Fig. 10 is a schematic representation of the replacement

Circuit of the longitudinal excitation gas waveguide laser working with capacitive ballast Figures 8 and 9;

11 is a schematic circuit drawing for

Explanation of a new driver circuit according to an embodiment of the invention;

Fig. 12 is a graphical representation of a performance

excitation / time characteristic curve, used in one embodiment of the invention for further reducing the likelihood of deleterious effects of those shown in FIG bistable impedance characteristic;

13 is a three-dimensional view of a before

additional embodiment of the longitudinal excitation waveguide according to the invention

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tergaslasers;

14 and 15 examples of two alternative exemplary embodiments of laser head configurations embodying the waveguide of FIG. 13;

Fig. 16 shows an electrical circuit showing the type

and illustrates manner in which the waveguide of FIG. 13 is used with a suitable driver circuit and connected to an RF voltage source for laser excitation;

17, 18 and 19 show a further exemplary embodiment of the laser head configuration, which uses a resilient metal tube designed to accommodate the waveguide laser holds in compressed aligned relation to its container =

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The invention will now be described in detail.

From the following detailed disclosure of the invention inclusive various embodiments thereof result in improvements in waveguide gas lasers, including an HF energy excitation referred to below as longitudinal excitation. A number of additional improvements those in both transverse and longitudinal excitation waveguide gas lasers are also described. These additional enhancements are intended to support the Increase performance even further and a bistable impedance characteristic overcome the two forms of excitation waveguide gas lasers is peculiar, which will be described in detail below.

To fully understand the improvements in waveguide gas laser technology the aforementioned US Pat. No. 4,169,251 is briefly discussed. Fig..1 represents the basic configuration of a transverse discharge waveguide gas laser according to this cited U.S. patent, wherein the waveguide laser 10 a pair of opposing elongated, having electrically conductive electrode members 12 "and 14, the disposed between a pair of opposing elongated dielectric members 16 and 18 in the manner are that an elongated chamber 20 is defined in which a laser excitation discharge must be created. Chamber 20 can have a length of approximately 20 cm for reasons of illustration and also have a square cross-section, the sides are 2 mm long. The electrode members 12 and 14 are made of metal such as aluminum while the dielectric members 16 and 18 are made of a material such as beryllium oxide, aluminum oxide or glass can. The waveguide structure can be made of a material with high thermal conductivity, such as Copper, manufactured in block 22, rest so as to

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drive to dissipate heat from the waveguide assembly. The discharge chamber 20 is filled with a desired laser gas, such as a standard COp laser gas mixture.

An RF power source V_ is connected between the electrode members 12 and 14 to generate the appropriate discharge excitation which builds up an electrical discharge in the laser gas} sufficient to population inversion of the energy levels of the desired laser transition. A pi-coupling circuit with adjustable capacitors C and inductance "L" operates as an impedance matching network _s to cancel the reactive impedance of the structure defining the discharge chamber and to match the real part of the input impedance, which is typically about 50 µm.

An important difference between an embodiment of the invention and the device according to FIG. 1 is that that the electric field generated for discharge purposes at the Chamber 20, extends in the vertical direction between the electrodes 12 and 14 and thus transversely to the longitudinal axis of the Chamber 20. It is clear that the electrode separation distance is inherent Way is the same as the chamber vertical gap separation. Thus, the waveguide bore size dictates the minimum RF drive frequency, and the above-mentioned result Limitations on the overall laser efficiency.

According to the invention, the applicants have discovered means by which the electric field excitation is parallel to the longitudinal axis the waveguide bore is created. A special embodiment, which provides the longitudinal excitation, is shown in Figures 2 and 3, and is a preferred embodiment the longitudinal structure of the invention is shown in FIG.

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As shown in FIG. 2, the laser configuration according to the invention a pair of ceramic blocks 30 and 32 substantially parallel to one another and separated from one another through a pair of dielectric blocks 34 and 36 ', which in turn are spaced apart, around a waveguide bore 38 to form the discharge zone of the waveguide laser forms.

The electrodes for the waveguide laser in the exemplary embodiment according to FIG. 2 are on the corresponding inner sides of the ceramic blocks 30 and 32, i.e. on the surfaces adjacent to the dielectric blocks 34 and 36, and which define the waveguide bore or chamber 38. the Electrode configuration is best illustrated in Figure 3, which shows the interior surface of ceramic block 32. As As shown in Figure 3, there is a first polarity electrode 40 and a second polarity electrode 42. The electrodes 40 and 42 are arranged along the edge of the ceramic block 32 and run essentially parallel to the waveguide bore 38. Each electrode has a series of generally perpendicular portions 41 and 43, respectively, which extend transversely across the Waveguide chamber 38 extend overlapping.

It's another pair of electrodes with an identical configuration provided on the corresponding inner surface of the upper ceramic block 30. Electrodes 40 and 42 are respectively equipped with a solder ball 39 to allow the electrical connection to be described below. Is special the electrode 40 electrically connected to the corresponding electrode, which is directly above and parallel to it along the Top of the upper ceramic block 30 is. Likewise, electrode 42 is electrical with the corresponding electrode connected, which is immediately above and parallel to it also on the upper ceramic block 30. The electrodes 40 and 42 and the corresponding electrodes on the upper ceramic

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block 30 to which they are connected are each electrically connected to the opposite phase connections an HF voltage source, such as that shown schematically at V in FIG. 1, the connection is made via a suitable driver circuit to be described below. As a result of the electrical connection mentioned and geometry of the electrodes according to the invention becomes an electric rf field in a direction parallel to the longitudinal axis of the chamber 38, the inner walls of which are positioned with respect to the electrodes such as this is shown by the dashed lines in FIG.

The distance ^11A "between the center lines of the perpendicular overlapping portions 41 and 43 of electrodes 40 and 42 can be varied as a function of the high frequency of the applied source, and as previously mentioned, the change is independent of the dimensions of the waveguide bore or chamber 38 , in contrast to the configuration according to FIG. 1. Typically, operation according to the invention takes place with a dimension "A" in the range of approximately 0.2 "to 0.5" - with a corresponding voltage differential between approximately 500 V and 1000 V occurring. It is contemplated that the electrodes could be attached to the surface of the ceramic blocks by a plating process, such as a sputtering process, however, any of the methods which are capable of depositing a thin film of high conductivity metal are suitable for practicing the invention a ceramic substrate, the dimension "B", corresponding to the typical width of the Te ile 41 and 43 is approximately 0.02 ".

Fig. 4 shows a preferred embodiment of the longitudinally exciting waveguide gas laser the invention. The preferred configuration of the invention of FIG. 4 has one Number of additional advantages over the waveguide gas laser of FIG. 1. It has been experimentally demonstrated that one

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high or pure aluminum electrode is a preferred choice for the electrode material, since aluminum over Effects of laser discharge seems to be more persistent. However, if the laser length is increased, it becomes approximately 8 "reaches a point where the power load is in the vicinity of 5 to 10 watts / inch, and the laser discharge is a shows bistable impedance characteristic which leads to the above-mentioned hot spot problem. In addition, aluminum electrodes oxidize fast, and one that occurs after just a few hours of operation severe oxidation becomes strong enough to decrease the conductivity of the wall and deteriorate the wall conductivity To produce laser power. Strong oxidation is likely due to that formed in the discharge Acid vapor caused. The novel configuration according to the invention as shown in FIG. 4 solves the electrode oxidation problem the tendency to reduce the hot spot problem and, moreover, sees extremely beneficial structural improvements which result in a more compact and reliable laser device.

Specifically, the longitudinal waveguide gas laser according to FIG. 4 has a pair of aluminum oxide surface elements 50 and 52, between which two aluminum oxide strips 54 and 56 for defining the waveguide chamber 55 are arranged. In addition, a thin-film metallization is applied to the aluminum oxide substrates in order to form the excitation electrodes on the outer surfaces 58 and 60 of the surface elements 50 and 50, respectively. It can be clearly seen that the surfaces 58 and 60 are isolated from the discharge chamber 55 of the waveguide. The electrodes on opposite sides of the waveguide structure are interconnected by electrical conductors 62 and 64 which also provide electrical access to a driver circuit. Typically, the aluminum oxide strips 50 and 52 are between 0.5 and 2 mm thick, measured along dimension ^11C ", and the aluminum oxide

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strips 54 and 56 are typically 1 to 3 now thick, measured along dimension "D". The bore or chamber 55 is typically square in cross section 1 to 3 mm long sides.

The structure of the embodiment of FIG. 4 is completely homogeneous in that all interface surfaces, and also all surfaces of the walls of the chamber 55, are made of aluminum oxide, i.e. AlpO- ,, which is due to the hard anodization of aluminum results. This structure can be solder sealed so that only the chamber 55 is filled with gas for laser operation must be filled. This is in contrast to the laser configuration according to FIG. 1; there is the difficulty of sealing dissimilar materials covering the respective sides of the chamber 20 of the transversely excited waveguide gas laser 1, so that it is necessary that the entire structure is arranged in a gas-filled cavity or housing becomes, which increases the size of the forest. Accordingly In the invention, the structure is more compact, and because the electrodes are isolated from the gas discharge, it is in accordance with the invention Lasers are more reliable and durable than known devices.

The bistable impedance problem mentioned above occurs with gas waveguide lasers regardless of whether they have a longitudinal or transverse electrode configuration, where In any case, the performance of this laser is reduced. Accordingly, the additional ones are described below Improvements that focus on means of eliminating or significantly reducing the difficulty in terms of workability and efficiency due to the mentioned bistable impedance problem, both applicable to waveguide gas lasers with both transverse and longitudinal electrode configurations. Specially have the inventors recognized that by providing capacitive

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Ballasts, a new driver circuit and a new type of controlled Switching on the bistable impedance problems avoided with either individual or combined use of the measures mentioned.

The reason for the noted hot spot problem is represented by the graph of FIG. 5, where the limited Input power range is shown, over which the RF-excited discharge is stable and spatially uniform is. If the input power is sufficiently low, the discharge breaks open. In the case of the known transverse discharge waveguide gas laser the discharge is ignited during unstable operation, and only along limited parts of the Waveguide length, and the discharge length and also the discharge site appear randomly. A similar effect occurs longitudinal waveguide gas lasers according to the invention, where not all discharge segments to form a continuous unite stable laser discharge and ignite the various discharge segments apparently randomly and Clear. At higher input power, the same kind of non-uniformity becomes both transverse and longitudinal Devices observed.

It is believed to be at both ends of the power range occurring instabilities result from the bistable discharge impedance characteristic result. The effects of such a bistable impedance characteristic can thereby be mitigated be that one uses a higher HF driver frequency or a larger bore size or an impedance ballast arrangement. The stabilization of the discharge by means of ballast formation is considered to be the most expedient, because this does not impair the usability of the waveguide in terms of high frequency or the size of the bore. The preferred solution is hence the formation of ballast, i.e. the addition of a series impedance, the effect of the impedance change in the wave

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Minimized conductor discharge as a function of input power. It is best to use a series ballast capacitor, compared to, for example, a series ballast resistor, because no power is used in the ballast element. In addition, a series capacitor is in waveguide structures easy to implement, which is explained in connection with FIGS. 6 to 10 in the following.

In the case of the known type of transverse discharge configuration, capacitive ballasting is achieved, as shown in FIG. 6, where the waveguide bore or chamber 70 is offset from the center of the ceramic block 72 which separates the two electrodes 74 and 76. In the example according to FIG. 6, a waveguide bore with a height "a" is offset by a distance "d" from both electrodes by ceramic blocks with a dielectric constant t. The equivalent circuit is shown in Fig. 7, it being seen that the equivalent impedance of the discharge or replacement represented by the parallel relationship of the discharge capacity C2 and the Entladungsleiti'ähigkeit G2 in series with the ballast capacitor C1 lie _ö t. As shown by the partial differential equations of Figure 7, the change in waveguide length "X" of the corresponding capacitance can be defined as the width of the cross-section of waveguide structure ¹¹ W "multiplied by the dielectric constant ε and divided by the distance" d " Change in discharge capacitance C2 with respect to waveguide length can similarly be defined as the width "W" multiplied by a or dielectric constant <£ and divided by the height of the waveguide bore "a". It is thus clear that by changing the dimension "d "With respect to dimension" a ", it is possible to insert a stable large capacitance in series with the discharge capacitor, giving a more stabilized impedance characteristic, which increases the likelihood of hot spots appearing in the discharge for a waveguide laser with transverse excitation

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of any length avoided or substantially reduced.

8 and 9 show an analogous form of the capacitive Ballasting for the longitudinal excitation waveguide gas laser in one embodiment in which at least one set of the electrodes opposite the waveguide chamber by a thickness "t" of dielectric material, such as a ceramic material or aluminum oxide. The overlapping electrode parts, corresponding to parts 41 and 43 in FIG of Fig. 3, as shown in Fig. 9, are offset from one another by a distance "ds" and are in turn vertically opposed the chamber 82 offset by a thickness of the dielectric 80.

Fig. 10 is an equivalent circuit showing the various 8 and 9, assuming the lower dielectric Block 84 is connected to electrical ground, for example, by sitting on a ground plane. The transfer of the Electrodes across from the chamber wall through the dielectric 80 for a thickness "t" increases the ballast capacitance C-. between the discharge capacity C i and each electrode. There is also a capacity between each side of the discharge and of the earth via the lower dielectric block 84. As shown in Fig. 10, the value of ballast capacitance, C, is between each Electrode and the discharge conductivity G ^ approximately the same the distance between the electrodes "ds", multiplied by the dielectric constant £ - of the dielectric Blocks 80 and divided by four times the thickness "t" of the dielectric block 80. It can now be seen that the unique Position of the electrodes, namely on the top of the waveguide structure spaced apart by a dielectric Medium from the waveguide chamber is doubly advantageous in that it is in addition to the insulation of the electrodes to otherwise worsening effects caused by direct contact with the discharge within the wave

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conductor chamber, also a ballast capacity is provided, which the effects of the bistable impedance characteristic of the discharge minimized.

Reference is now made to FIGS. 11 and 12 to illustrate further means which can be used to overcome or to achieve considerable Reduction of harmful effects of the bistable impedance characteristic are used.

In Fig. 11, the discharge capacity is C-, with a voltage generator V_ over a coaxial line 90 with a predetermined length "1" expressed in wavelengths with a characteristic impedance Z, as well as connected via a transformer "T" with a turns ratio "N". In addition, it is a tunable Coil L connected in parallel to the discharge capacitance and adjusted in such a way that the capacitance for the excitation frequency is highlighted in terms of resonance.

If the coaxial line 90 is a quarter wave line the following applies:

Input voltage and current are given by:

^V in

where I ₀ = I _d N and V _Q = V _d / N and I _d and V _d are the discharge current and the discharge voltage (assuming resonance).

V. and I. are related as follows: < ² ' ^v in = ^V 3 - Vin

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Substituting V, and I, gives: (3) -jV r ZNI + ^Rs ν

This equation is the equation of a load line. The only significance of "j" is that the discharge current and voltage are 90 degrees out of phase with the source. the effective source impedance is therefore given as follows:

Z ² N ²
(R ₃ ) eff = g

Stability is obtained by ensuring that:

(b) 3Vj _{+ (R} j _{eff > Q} ( _{because the} net impedance is positive ' ^6l d. )

Thus, by using a characteristic impedance, which is significantly greater than the source impedance, the effective source impedance can be increased dramatically. This allows the Condition of equation (5) must be observed.

An alternative way of looking at this condition is to consider quarter wavelength conduction as one Impedance inverter to look at. When the discharge begins to ignite, the discharge impedance drops. At the entrance of the fourth When the length of the line is reached, the impedance begins to rise. in the in general, this results in less power being delivered to the load, which in turn breaks the ignition (arc).

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If the coaxial line 90 is a half-wave line, so The following applies:

The load line equation in this case is the following;

¹ C ^{N +} V ^H

The effective source impedance is therefore: (7) (KJ _<irf = I <“N ²

The discharge stability is guaranteed by:

^ d ₊ R ₃ N ² > 0.

³¹ Cf

Unlike the quarter wavelength case, the one is effective Source impedance just that of the source and tends to be much smaller. For a 25 ohm source impedance and a 25 ohm cable is the effective source impedance

(divided by N) 225 ohms for a quarter-wave section " and only 25 ohms for a half-wave section.

As shown in Fig. 11, the configuration according to the invention, uses an HF generator to excite HF lasers

V on, connected to a coaxial cable of length s

and the characteristic impedance Zq, where the latter in turn is connected to the primary side of the transformer T. The secondary side of the transformer is at the discharge section, in which the capacitance C-, by a Parallel coil L is influenced by resonance.

As is also shown in Fig. 11, the impedance results looking into the line as follows:

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ζ -ζ

² I + JZ ₀ tan kl

can «f +

where Z is the impedance when looking into the transformer and kl is 2 / T //? m, (where / im. is the wavelength).

The voltage V. is given by:

Ιΐΰ \ ν. _s v_ ^z in = V ⁺ c ^Jltl ₊ ν "

• ^{in s} K + Z.

where V ⁺ and V ~ denote the forward and backward running wave, where the solution for V ^{+ is} as follows:

^Z »n

-Jkl

The voltage at the input of the transformer is given by:

(12) V _n = V ⁺ + V "= V ^v (1 ♦ ^x -—2)

To evaluate Z _{1 it} can easily be shown that this is given as follows:

where Q is the unloaded Q and N is the turns ratio. In a typical example with C = AO pf,

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f = 40 MHz land N = 4 and Q _u = 100 the following results:

_ 100

"16 x 2 χ π χ AO χ i0- ^li? X 40 χ ΙΟ ^{6 6} °° ^Ω

Assume that Z ^ ? / * "Zq, we get (15) V ₀ = 2 V ⁺

Looking at the two special cases of Viertelv / Ellen- and half-lines is obtained for the quarter-wave long transmission line (ie 1 = Jl / 4) comprising;

116) Z _n = 2

2j Z ₀ ZZ ₁ 2 R ₃

or

^V in "

The voltage at the discharge section is therefore given as follows:

U9) V. , VN ² ^ O

^{d s R} ₃

For the half-wave length line (i.e. 1 = - ^ / 2) results the following:

(20) Z. = ζ

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(21) V ⁺ = ^V 3 ² In ~ V "/ 2

s * in

The voltage at the discharge section is therefore

122) V _d = 2V ⁺ H ² = ITV ₈

Assuming a source impedance of 50 ohms and a characteristic impedance (wave resistance) of 50 ohms, the two cases ( A / k or Jt / Z for the line length) are equivalent. In the half-wave case, however, the voltage is independent (up to the first order) of both the source impedance and the cable impedance, whereas in the quarter-wave case a voltage drop can be caused by using a cable with an impedance greater than the source impedance. For example, a 75 ohm line and a 50 ohm source impedance result in a 50% voltage rise.

It can thus be seen that by using the new driver circuit, consisting of a coaxial line or another suitable transmission path, depending on the operating frequency, where the line length is equal to a quarter wavelength and the characteristic impedance is equal to or greater than 1.5 R ,,, the , Discharge stability is ensured and become a considerable Increase in discharge voltage compared to source voltage, results.

Fig. 12 shows further means by which the problem of

1300U / 1300

hot spots, caused by the bistable impedance characteristic of the laser discharge, can be considerably reduced or eliminated in both the transverse and the longitudinal excitation configuration. These additional means consist in the controlled application of power to the excitation electrodes, as graphically shown in Pig. 12 is shown, namely the almost instantaneous application of sufficient power to cause a breakdown, and then a gradual increase in power over a period of time equal to or exceeding a minimum of 1 msec, until the maximum excitation or excitation power is reached is. For example, _{P.20 ¥ and P mQV is} 80 ¥ for the parameters mentioned with reference to FIG. It is believed that the improved stability results from the gradual application of the excitation power, which, as shown in Fig. 12, is due to the tendency of the discharge to operate along its more stable impedance curve of the two positive sloped portions of the impedance curve , these parts of the curve forming the aforementioned bistable characteristic. The provision of automatic means for the gradual application of the excitation power can easily be implemented by means of a suitable capacitive circuit on the HF voltage generator, this circuit being known and need not be described in detail here.

Figure 13 is a three-dimensional view of a preferred embodiment of a longitudinal excitation waveguide 100 of the invention, wherein the waveguide bore 102 is formed by a pair of alumina side blocks 104 and 106, which in turn are sandwiched between two ceramic plates 108 and 110. Each such ceramic plate is longitudinal its outer surface, as in FIG. 13 for the top plate 108 shown covered by elongated electrodes like this previously discussed, these being shaped such that

1300 U / 130Q

a longitudinally directed electric field within the Waveguide bore 102 is provided. In particular, electrode 112 and its perpendicular parts, such as part 114, at any point in time of opposite polarity with respect to the corresponding electrode 116, including its vertical parts, such as part 118.

In the preferred embodiment of FIG. 13, the size "F" is typically 0.02 ", size ¹¹ G" is typically 0.04 "and the variable" H "is typically 0.25". In addition, the waveguide bore 102 is square in cross-section with walls 0.08 "long defining the chamber.

Figures 14 and 15 illustrate two alternative laser head configurations using the waveguide 100 of Fig. 13. As shown in Fig. 14, there is such a configuration from the arrangement of the laser waveguide 100 from a metal RF shielding cup 120 with a rectangular cross-section. The waveguide is centered therein by means of a stand 122. The stand 122 has a chamber 124 with a rectangular Cross-section and serves as a gas reservoir for the waveguide structure. Chambers 102 of waveguide 100 and 124 of the Stand 122 are both at a suitable sub-atmospheric pressure for laser operation. The remaining interior volume of the HF shielding can 120 is at ambient pressure and provides an enclosed channel for forced air cooling of waveguide 100.

In the alternative laser head configuration according to FIG. 15, a waveguide structure 100 is arranged within a metal pot, which is suitable for creating an RF shield and for maintaining a substantial vacuum. The waveguide structure is arranged between ceramic blocks 132 and 134, which discharge the discharge outside of the waveguide bore 102 prevent.

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The remaining volume between the walls of the RF pot 130 and the waveguide structure is also with a Laser gas is filled to serve as a reservoir, the gas being at the same sub-atmospheric pressure as that Laser gas is located within the waveguide bore 102.

Fig. 16 schematically illustrates the electrical system interface of a preferred embodiment of the invention, wherein the various means used to reduce or eliminate the hot spot problems are used. For example the waveguide 100 employs electrodes as shown in Fig. 13, i.e. in the form of thin film metallization, applied to the upper and lower surfaces of the Ceramic plates 108 or 110. The distance between the electrodes

108 and above the chamber through the plates / 110 provides the aforementioned Ballast capacity. A resonance inductance (inductor) L is applied to the electrodes, and the upper and lower electrode pairs of the same polarity are connected to one another by conductors 140 and 142, respectively, and these also see the electrical connection to the transformer 144. The transformer is connected to a suitable voltage source V via the new driver circuit, consisting from a quarter wavelength line 146 having a characteristic impedance equal to or greater than 1.5 times the source impedance. In Fig. 16 it is assumed that the source impedance is 50 ohms and that the characteristic impedance (wave resistance) of line 146 is equal to or greater than 75 ohms, in accordance with the improvement described above. In addition, the delayed excitation intensity characteristic curve illustrated in connection with FIG. 12 is represented in FIG. 16 by the presence of a suitable generator control device 148, the details of which are known to those skilled in the art are.

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3Q35H2

Figures 17, 18 and 19 show another embodiment of a laser head assembly employing an improved method of construction which makes the invention more suitable for low cost mass production. As In the configurations described above, the laser bore or chamber is through opposing, spaced apart arranged aluminum electrodes are formed, which are sandwiched are arranged between two aluminum oxide blocks. The arrangement is illustrated by a cross-section shown in FIG elastic tube 150 held in alignment and under pressure. The elastic tube serves as a spring-like, evacuable one Housing and a heat sink, which keeps waveguides and optical elements in proper alignment.

In the illustrated embodiment, the resilient tube or cylinder 150 consists of a circular cylindrical tube with an outer shell 152 and a pair of spaced parallel flanges 158 which extend longitudinally and parallel to the axis of the cylinder 150 _% . The flanges 158 extend along the length of the tube 150 from opposing locations along the inner periphery of the shell 152 by respective collars 154. Each such flange 158 has a pair of parallel, generally perpendicular walls 156 to the Formation of rectangular grooves suitable for receiving and aligning the aluminum oxide blocks 132 and 134 of the waveguide structure. Typical dimensions of an embodiment of the invention using the resilient metal tube 150, which can now be readily made by extrusion materials such as 6063-T5 aluminum and the like, can be defined by FIGS. 17 and 18, specifically in FIG Connection with the following table:

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Reference numerals in FIGS. 17 and 13

Typical
Dimensions (inch)

K 0.475 +.01 L. 0.390 +.01 M. 0.125 +.01 N 0.375 +.01 S. £ 0.025 .005 P. 1.25 +.01 Q 0.035 + .. 005 R. 0.125 +.01

Typically, the distance between opposing outer surfaces of the alumina blocks is 132 and 134 somewhat larger than the pre-installation distance L. Therefore, in order to insert the waveguide structure into the elastic tube 150, xvird exerted a compressive force on planes 151 and 153, as shown in Fig. 18, causing the distance L increases between the flanges 158 to a distance suitable for receiving the waveguide structure. Then she has Removal of the force applied in planes 151 and 153 results in a compressive force between the flanges, which over the Waveguide structure is applied, namely iiu area of 200 to 1000 psi (pounds / square inches). As a result, realizes that the flanges 158 pressure alignment of the alumina blocks 132 and 134 and the entire waveguide structure cause by the spring action of the new tube 150. In addition to creating structural rigidity for the Overall laser configuration, the tube 150 also provides a considerable amount improved thermal contact with more efficient heat dissipation.

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3035U2

As shown in FIG. 19, the ends of the tube 150 are tapered at an angle θ of preferably approximately 45 °. This has the significant advantage of producing an automatic alignment for mirror mounts 160 becomes, which proves to be a clear advantage for the person skilled in the art, whereby for the configuration according to the invention such Mirror end surfaces are occasionally useful. When the mirror bracket 160, also shown in FIG. 19, tapers is, the bracket 160 can easily with the end of the tube 150 are vacuum sealed, for example by means of a continuous soldering tape 162 which is around the entire circumference of the interface between mirror holder 160 and tube 150 is arranged around.

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A waveguide gas laser has been disclosed above which is superior Has properties in terms of performance, efficiency, reliability and durability. One improvement according to the invention is that the longitudinal The laser discharge is excited within a waveguide chamber containing a suitable laser gas. The longitudinal The spacing geometry of the electrodes makes the excitation variable, independent of the waveguide chamber geometry, which results in an increased efficiency. Man recognizes that the invention provides a number of significant improvements which substantially address hot spot problems reduce or eliminate these hot spots commonly in waveguide gas lasers both in the Transverse as well as longitudinal excitation configurations occur. Failure to remove these hot spots would degrade the performance of the laser. To the invention Improvements include, for example, the following: The capacitive loading (ballasting), achieved through new structural configurations, including the isolation of the electrodes from the waveguide chamber by a suitable one dielectric spacer medium such as ceramic or alumina; a new driver circuit with preselected Length and with selected 'wave impedance; the controlled application of the excitation power over a minimal period of time away.

Modifications are possible within the scope of the invention, both with regard to special dimensions, materials and geometric configurations.

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- JO -

Another improvement according to the invention consists in an elastic metal tube for housing the waveguide structures and to use spaced parallel flanges (support members) formed within an extruded Metal tube for pressure engagement with and alignment of the waveguide structure. Such a tubular Housing serves as a spring-like vacuum container and as a heat sink, the waveguide and the optical Items are positioned in proper alignment.

1300U / 1300

Claims (1)

PATENT CLAIMS Waveguide laser structure with means for defining an elongated chamber with cross-sectional dimensions suitable for guiding laser light, a laser gas arranged in the chamber and means for building up an alternating electric field in the chamber for building up the laser excitation discharge in the laser gas,
characterized by an elongated resilient metal tube containing the means defining the elongated chamber in pressure engagement along the entire length thereof. 2. Waveguide laser structure according to claim 1, characterized in that that the means defining the elongate chamber is a pair of spaced apart electrically conductive ones Having blocks sandwiched between a pair of electrically non-conductive blocks, and wherein the metal tube further comprises: a pair of elongated, spaced-apart parallels Splashes (158) extending from opposite points along the inner circumference of the tube; along at least a portion of the length of the tube and adapted to receive those defining the elongate chamber Means by pressure engagement of the electrically non-conductive blocks. 3. Waveguide laser structure according to claim 2, characterized in that 1300U / 1300 that each of the parallel flanges has substantially perpendicular walls around a rectangular groove having a width substantially equal to the width of the electrically non-conductive blocks to to effect their automatic alignment. 4. waveguide laser structure according to claim 3> characterized in that the elastic metal tube for receiving a compressive force serves along a plane essentially parallel to the flanges to temporarily reduce the distance between the parallel flanges without destroying their parallelism and without deforming the rectangular grooves. 130.0 U / 130 0