WO2001035055A1

WO2001035055A1 - Sacrificial cathode on a ring laser gyro block

Info

Publication number: WO2001035055A1
Application number: PCT/US2000/030600
Authority: WO
Inventors: Carol M. Ford; David J. Zook
Original assignee: Honeywell Inc.
Priority date: 1999-11-08
Filing date: 2000-11-07
Publication date: 2001-05-17
Also published as: AU1587001A

Abstract

A ring laser gyro having a sacrificial cathode positioned on a surface of the laser block of the ring laser gyro. The sacrificial cathode is connected to a source of electrical potential that maintains the polarity of the sacrificial cathode more negative than the excitation electrodes that are attached to the laser block. In this manner, a significant portion of the migratable components in the laser block, such as alkalai metal ions, are attracted to the sacrificial cathode as compared to the excitation electrodes on the laser block, thus increasing the useful life of the excitation electrode seals.

Description

SACRIICIAL CATHODE ON A

RING LASER GYRO BLOCK

Technical Field

The present invention is related to a ring laser gyro. More specifically, the invention is a ring laser gyro having a sacrificial cathode in contact with the outer surface of the laser block to attract migratable components in the laser block to the sacrificial cathode.

Background of the Invention

Ring laser angular rate sensors, commonly referred to as ring laser gyros, are well known and in widespread use today. For example, ring laser gyros are frequently used in guidance and navigation modules on a variety of vehicles, including airplanes, unmanned rockets, and military tanks. In addition, ring laser gyros are used in down-hole drilling operations, such as for oil, for providing precise locations of a drilling bit. A typical ring laser gyro includes a laser block having a plurality of interconnected passages formed within the block. The passages are arranged in a closed loop polygon shape, such as a triangle or a rectangle, and reflective surfaces are positioned at the intersection of each passage with another passage. In this manner, an optical closed loop path is created within the laser block. A lasing gas, such as helium-neon for example, is contained within the closed loop path.

A pair of electrodes are mounted to the laser block in fluid communication with the lasing gas in the closed loop path. One electrode serves as a cathode, and the other electrode serves as an anode. An electrical potential is created across the cathode and anode through the lasing gas. This electrical potential creates a population inversion in the lasing gas, which in turn generates a laser that traverses the optical closed loop path of the laser block. The ring laser gyro can include a third electrode that serves as a second anode. An electrical potential created across the cathode and the second anode creates a counter-rotating laser traversing the optical closed loop path. Conventionally, the laser block of the ring laser gyro is formed from a material having a low coefficient of thermal expansion such as glass or glass- ceramic. A lithium-aluminum-silicate glass ceramic material, for example, has been found to be well suited for ring laser gyro blocks. As is well known, glass or glass ceramic materials are subject to ionic conductivity. Due to the ionic conductivity of the laser block material, an ionic current can be created through the laser block whenever an electrical potential is applied across the block, such as exists between the cathode and the anodes of the ring laser gyro, due to the flow of the cations created by the electrical potential. That is, positively charged migratable components of the block material, (i.e. alkali ions such as lithium ions), are transported as ionic current toward the negatively charged cathode of the ring laser gyro.

The accumulation of these positively charged ions at the cathode can have an adverse impact on the performance of the ring laser gyro, however. For example, lithium is a highly reactive metal that can interact with the seal of the electrode, and the excess lithium that accumulates about the cathode may thus weaken the electrode seal over time and lead to failure of the ring laser gyro. In addition, the ionic current may cause the positively charged ions to migrate toward and be deposited on the inside walls of the optical pathway and/or on the reflective surfaces positioned at the intersection of the laser block passages. This buildup of lithium or other alkalai ions at the optical closed loop path may also negatively impact the performance of the ring laser gyro over time.

There is thus a continuing need for an improved ring laser gyro that overcomes the shortcomings created by the accumulation of migratable components at various locations of the laser block.

Summary of the Invention The present invention is a ring laser angular rate sensor that overcomes the shortcomings of current ring laser angular rate sensors. The present invention comprises a laser block formed from a material having a relatively low coefficient of thermal expansion, a first electrode, and a second electrode. The laser block includes an optical closed loop path formed within the block, and the optical closed loop path contains a fluid that is adapted to conduct an electrical current potential for creating a laser within the optical closed loop path. The first electrode is connected to a positive terminal of a first source of electrical potential, and thus serves as an anode on the ring laser angular rate sensor. The second electrode is connected to a negative terminal of the first source of electrical potential, and thus serves as a cathode on the ring laser gyro. The anode and cathode are mounted on the laser block in fluid communication with the fluid contained within the optical closed loop path within the laser block, and an electrical current is thus created through the fluid. This electrical current causes laser beams that traverse the closed loop path of the laser block.

The ring laser angular rate sensor further includes a third electrode positioned on the laser block and connected to a negative terminal of a source of electrical potential. The third electrode functions as a sacrificial cathode, and is maintained at an electrical potential that is at least as negative as the cathode of the ring laser angular rate sensor. In this manner, the sacrificial cathode will attract positively charged migratable components within the laser block. In a first embodiment, the sacrificial cathode is positioned on a surface of the laser block at a region that is adjacent yet spaced apart from the cathode to optimize the attraction of migratable components to the sacrificial cathode. The sacrificial cathode can also be accurately shaped to partially surround the cathode to further increase the attraction of migratable components to the sacrificial cathode. The present invention also contemplates a method for reducing the migratable components within a laser block that are attracted to a cathode used to form a laser in a ring laser angular rate sensor. The method includes the steps of positioning a sacrificial cathode on a laser block, and maintaining the sacrificial cathode at an electrical potential that is at least as negative as that of the cathode of the ring laser angular rate sensor. The sacrificial cathode can be positioned on the laser block through the use of an indium seal, it can be vapor deposited on the laser block, or it can be painted on the laser block.

It is contemplated that the present invention can be used in conjunction with an aggressive cleaning technique to further reduce the negative effects of migratable components within a laser block. An aggressive clean technique that removes migratable components from regions adjacent the surfaces of the laser block, including removing migratable components at or adjacent to the position of the sacrificial cathode, by leaching out alkali ions in the laser block is desirable.

Brief Description of the Drawings

Figure 1 is a perspective view of a ring laser gyro in accordance with the present invention having a sacrificial cathode mounted to a surface of the laser block.

Figure 2 is a top view of the ring laser gyro of Figure 1 shown partially in section to illustrate the optical closed loop pathway formed within the laser block. Figure 3 is a schematic view of a ring laser gyro in accordance with the present invention having a sacrificial cathode interconnected to a second source of electrical potential to maintain the sacrificial cathode more negative than a cathode of the ring laser gyro.

Figure 4 is a top view of a portion of a ring laser gyro in accordance with the present invention showing an alternative embodiment for a sacrificial cathode.

Detailed Description of the Preferred Embodiments

With reference to Figures 1-3, a ring laser angular rate sensor 10, more commonly referred to as a ring laser gyro, in accordance with the present invention is shown. Ring laser gyro 10 includes a laser block 14 having an optical closed loop pathway filled with a lasing gas that is adapted to be electrically charged to conduct an electrical current. The ring laser gyro 10 further includes structure for creating an electrical potential through the lasing gas, which creates a population inversion in the lasing gas and generates a laser within the optical closed loop pathway of the laser block 14. A sensor array 12 attached to the ring laser gyro 10 measures the angular rate experienced by the ring laser gyro 10 as a function of the deflection of the laser. In a conventional sensor array, the array measures the angular rate as a function of the interference of two counter-rotating laser beams (described in more detail below) formed within the closed loop pathway. More particularly, the laser block 14 includes a closed loop path 16 comprising a plurality of interconnected passages 16a, 16b, and 16c (shown partially in phantom). In the embodiment of Figure 1, laser block 14 is substantially triangularly shaped, with passages 16a, 16b, and 16c formed within block 14 parallel to a side of the triangular block 14. The three individual passages 16a, 16b, and 16c are connected at their ends with the neighboring passages to create a closed loop path 16 in a triangular shape. Reflective surfaces, such as mirrors 20, are positioned and appropriately angled at the intersection of the individual passages 16a, 16b, and

16c to reflect light from one passage into another passage. In this manner, an optical closed loop path is defined within the closed loop passage 16 of the laser block 14.

While the overall shape of the laser block 14 and the closed loop path 16 are shown in Figures 1-3 and described as being triangular, the closed loop path 16 of ring laser gyro 10 can be in the shape of any polygon. The laser block 14 itself can be any shape desired.

Laser block 14 is formed from a dielectric material, such as glass or glass-ceramic, having a relatively low coefficient of thermal expansion. One particularly well-suited material is a lithium-aluminum-silicate glass ceramic material marketed under the tradename Zerodur®, available from Schott Glass Technologies, Inc. of Duryea, Pennsylvania. Zerodur® brand glass ceramic material has a coefficient of thermal expansion that is substantially 0.

The structure for generating the laser that traverses the optical closed loop path includes a gas discharge fluid, commonly referred to as a "lasing gas," contained within the closed loop path 16 that is capable of being electrically charged to conduct an electrical current, and at least two excitation electrodes 30 and 32 that are mounted to the laser block 14 in communication with the lasing gas. A mixture of helium and neon can be used as the lasing gas within the block 14. To facilitate the insertion of the lasing gas into the laser block 14, one of the electrodes mounted to the laser block, such as excitation electrode 32, can be fitted with a fluid port, as is known. Excitation electrodes 30 and 32 are in communication with the lasing gas contained within the closed loop path 16 through apertures 22a and 22b, respectively, formed in block 14 between the region where excitation electrodes 30 and 32 are mounted on block 14 and the passages 16a and 16b. The excitation electrodes 30 and 32 of the ring laser gyro 20 are each adapted to be connected to a source of electrical potential 60. Excitation electrodes

30 and 32 can be formed from known materials, such as beryllium or aluminum.

One material well suited for excitation electrodes 30 and 32 is invar or super invar, a nickel - iron alloy commercially available from a number of sources, such as

Atlantic Equipment Engineers of Bergenfield, New Jersey, and having a coefficient of thermal expansion that is also substantially 0. Excitation electrode 30 is connected to the negative terminal 62 of the source of electrical potential 60, and thus functions as a cathode. Excitation electrode 32 is connected to the positive terminal 64 of the source of electrical potential 60, and thus acts as an anode. In this manner, an electrical potential can be placed across the cathode and the anode through the lasing gas. The lasing gas in the laser block 14 thus becomes electrically ionized to conduct an electrical current (i.e. typically known as a "gas discharge"), and, when the electrical current is sufficiently large to create a population inversion within the lasing gas, a laser is generated. The closed loop path 16 and the mirrors 20 of the ring laser gyro 10 will cause the beams to traverse the optical closed loop pathway of the laser block 14.

As shown in Figure 1 , a third excitation electrode 34 can be included in the ring laser gyro 10. Third excitation electrode 34 is positioned on the third side 16c of the laser block 14, and is in communication with the lasing gas in the closed loop passage 16 through transverse aperture 22c (shown in phantom) formed between passage 16c and excitation electrode 34. Similar to second excitation electrode 32, the third excitation electrode 34 is attached to a positive terminal 64 of the source of electrical potential 60, and thus functions as a second anode. To ensure the proper operation of ring laser gyro 10, the cathode excitation electrode 30 and the anode excitation electrodes 32 and 34 must be effectively sealed to the laser block 14. An electrode seal 50 is created between the excitation electrodes 30, 32, and 34 and the laser block 14 to bond the excitation electrodes 30, 32, and 34 to the laser block 14 in a gas-tight manner. Seal 50 prevents leakage of ambient atmosphere of the lasing gas from outside block 14, prevents the intrusion of ambient gases into optical pathway 16, and provides mechanical support for each of the electrodes 30, 32, and 34. Electrode seal 50 can be formed from a thin ring of ductile metallic sealing material that is compressed between the individual electrodes

30, 32, and 34 and the laser block 14. Indium is one material that is useful in this regard due to its ductile nature and bonding characteristics, although other suitable sealing materials can of course be used. Unoxidized material from the interior of the sealing material is exposed to oxide-containing laser block surfaces during this compression operation, which allows chemical and physical bonds to be formed between the sealing material and block 14, and between the sealing material and the excitation electrodes 30, 32, and 34. A compression force of approximately 4500 pounds per square inch has been found to be sufficient to create the seal 50 between the excitation electrodes 30, 32, and 34 and the laser block 14. The seal can also be formed by a glass frit process.

As described above in the Background section, materials typically used to form laser block 14 are susceptible to ionic transport through the laser block. Preferred laser block materials, such as Zerodur®, commonly contain alkali species such as sodium, potassium, and lithium, which possess desirable glass forming properties. These species can also act as ionic conductors within the laser block 14, however, thus, alkalai metal ions, such as positively charged lithium ions, can be attracted to and migrate toward the negative electrode (i.e. cathode) 30 of the ring laser gyro 10 when the electrical potential is applied across the electrodes 30, 32, and 34. These lithium ions are higly reactive, and can interact with the sealing material that is used to form seal 50 between electrode 30 and block 14. The accumulation of lithium about electrode 30 may degrade seal 50, and over time, cause seal 50 to delaminate and ultimately fail.

It is advantageous to subject the laser block material to an aggressive cleaning process to reduce the amount of migratable components within the laser block 14 prior to attaching the electrodes to the laser block 14. One purpose of aggressive cleaning is to remove substantial portion of the migratable ion species, including lithium ions, from a portion of the exposed outer surfaces of the laser block, typically within the first one to six micrometers of the block 14. One preferred aggressive cleaning process includes placing the laser block 14 in a high purity water bath having an elevated temperature for a sufficient period of time. As is known, water is an effective solvent for the ionic species within the block 14, and leaches them from the exposed surfaces of the block 14. Other known aggressive cleaning techniques to reduce the amount of migratable components within block 14 can also be used, such as partial etching the top portion of block 14 with an appropriate etchant. Suitable etchants for such a process include Mirco Detergent brand etchant, commercially available from International Products Corporation of Trenton, New Jersey, and Oakite brand etchant, commercially available from Oakite Products, Inc., of Berkeley Heights, New Jersey. While it is advantageous to utilize an aggressive cleaning technique to control the presence of migratable components within a laser block 14, it is contemplated that the sacrificial cathode described below used to control migratable components can be used in place of or in combination with such an aggressive cleaning technique.

Additionally to overcome the undesirable effects of ionic transport, in the present invention ring laser gryo 10 includes a sacrificial cathode 40 positioned upon the surface of laser block 14 of ring laser gyro 10. In the embodiment of

Figure 2, voltage is applied to cathode 40 from source of potential 60 in such a manner that, as compared to electrodes 30, 32, and 34, cathode 40 is at least as negative as cathode 30. Preferably, however, and as described in more detail below, cathode 40 is maintained at a voltage that is more negative than cathode 30. Toward this end, as shown in Figure 3, a second source of electrical potential 80 can be used to maintain cathode 40 at a voltage more negative than cathode 30. The sacrificial cathode preferably does not affect the gas discharge within the optical closed loop path of laser block 14, and is thus not in communication with the lasing gas contained within the optical closed loop path. By maintaining sacrificial cathode 40 at as least a negative electrical potential as that of cathode 30, the positively charged migratable components within laser block 14 will be attracted to a region 42 surrounding sacrificial cathode 40. Since sacrificial cathode 40 is preferably not used to effect the gas discharge (i.e. to create a laser beam within the optical closed loop path of laser block 14 or to seal the lasing gas within the block 14, the negative effects of the accumulation of the migratable components around sacrificial cathode, such as the possible delamination of the sacrificial cathode 40 from laser block 14 will not adversely affect the performance of the ring laser gyro 10. That is, as migratable components, such as lithium and other alkali ions, collect in region 42 around sacrificial cathode 40, any adverse effects caused by the migratable components such as delamination of the sacrificial cathode 40 from the laser block 14 will not impact the performance of the ring laser gyro 10 because the sacrificial cathode 40 is not integral to the primary desired function of the ring laser gyro 10. It is desirable that the area of sacrificial cathode 42 be sufficiently large and mechanically secured to the laser block 14 so that the unavoidable build-up of alkali ions m region 42 and at the interface between the sacrificial cathode 40 and laser block 14 will not produce delamination of the sacrificial cathode 40, however. Even though weakness in the interface between block 14 and sacrificial cathode 40 will not degrade the vacuum and gas discharge withm the closed loop pathway of the laser block 14, it is desirable to maximize the useful life of the sacrificial cathode 40. As mentioned above, the sacrificial cathode 40 is preferably maintained at an electrical potential that is at least as negative as the potential of the cathode 30. This can be accomplished by connecting cathode 40 to the same source of electrical potential 60 as cathode 30 is connected to. The migratable components in laser block 14 will thus be attracted to sacrificial cathode 40 by an amount substantially equal to the attraction to cathode 30. As such, a significant portion of the migratable components will be attracted to sacrificial cathode 40 rather than cathode 30, which will reduce the interaction between the seal 50 between cathode 30 and laser block 14. In this manner, the useful life of cathode 30, and thus πng laser gyro 10, can be extended. Moreover, sacrificial cathode 40 positioned on the surface of laser block 14 will draw migratable components away from the passages 16a, 16b, and 16c, and away from mirrors 20 of ring laser gyro 10. This will prevent the accumulation of migratable components on the optical closed loop passage of the laser block 14, which may also extend the useful life of ring laser gyro 10. As mentioned above, sacrificial cathode 40 is preferably held at an electrical potential that is more negative than cathode 30. As shown in Figure 3, this can be accomplished with the use of a second source of electrical potential 80, the negative terminal of which is connected to cathode 40. A more negative sacrificial cathode 40 will provide a greater attractive force for migratable components within laser block 14 as compared to the attraction provided by cathode 30. An even greater portion of the migratable components will thus be attracted to sacrificial cathode 40 as opposed to cathode 30, which may enhance the useful life of cathode 30, and thus ring laser gyro 10, even further.

The seal 50 between cathode 30 and laser block 14 can also be made less susceptible to delamination by the migratable components, such as lithium or other alkali ions, in laser block 14 through the appropriate positioning of sacrificial cathode 40 on laser block 14 and through the appropriate shaping of sacrificial cathode 40. That is, sacrificial cathode 40 can be preferably shaped and positioned around cathode 30 to act as a "shield" to cathode 30. As shown in Figure 2, sacrificial cathode 40 can be arcuately shaped, and is preferably positioned at a region that is in proximity to cathode 30 (i.e. adjacent yet spaced apart from cathode

30) so that the migratable components in the laser block 14 will encounter the sacrificial cathode 40 before they encounter the cathode 30. An appropriately shaped and positioned sacrificial cathode 40 thus can be used to optimize the attraction of migratable components in laser block 14 in such a manner that cathode 30 is effectively shielded from migratable components as they are transported through block 14. The amount of migratable components attracted to cathode 30 will be accordingly reduced. Other shapes, positions, and configurations for sacrificial cathode 40 can also be used as desired.

For example, in one embodiment shown in Figure 4, a sacrificial cathode 140 is provided having a pattern of holes 150 formed in the conductive material of the cathode 140 and mounted on laser block 114. In an embodiment where sacrificial cathode 140 is vapor deposited on the surface of the laser block 114, the holes can be formed by controlling the vapor deposition process, as is known. After cathode 140 is positioned on block 14, the cathode 140 and region 142 surrounding the cathode 140 can be coated with a non-conducting adhesive, such as epoxy, to provide mechanical strength to the sacrificial cathode 140. The epoxy surrounding the cathode 140 and in the holes 150 can provide the primary mechanical mount of cathode 140 to block 114, or it can provide additional strength to a previously mounted cathode 140, thus better avoiding delamination of the sacrificial cathode 140 due to the build-up of migratable components at the interface between cathode 140 and block 114.

Sacrificial cathode 40 can be formed from any conductive material, such as beryllium, aluminum, or invar. Sacrificial cathode 40 is affixed to a surface of laser block 14 using known techniques, such as the with an indium seal as described above. Alternatively, sacrificial cathode 40 can be deposited on to laser block 14 using known vapor deposition techniques, or it can be painted on to a surface of laser block 14. In a preferred embodiment described above, a coating of non-conducting adhesive can be used to bond the sacrificial cathode to block 14, or to provide mechanical strength to the sacrificial cathode after it is mounted to block 14. Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows: 1. A ring laser angular rate sensor, comprising: a laser block formed from a material susceptible to the formation of migratable components, the laser block having an optical closed loop path formed within the block, the optical closed loop path containing a fluid adapted to conduct an electrical current for creating a laser within the optical closed loop path; a first excitation electrode adapted to be connected to a positive terminal of a source of electrical potential and function as an anode, the anode in communication with the fluid contained within the optical closed loop path within the laser block; a second excitation electrode adapted to be connected to a negative terminal of a source of electrical potential and function as a cathode, the cathode in communication with the fluid contained within the optical closed loop path within the laser block, a potential across the cathode and the anode creating an elecfrical current potential through the fluid contained within the laser block to create a laser within the optical closed loop path; and a third electrode positioned on the laser block and adapted to be connected to a negative terminal of a source of electrical potential to function as a sacrificial cathode, the sacrificial cathode being maintained at a negative electrical potential to attract positively charged migratable components within the laser block to the sacrificial cathode.

2. The ring laser angular rate sensor of claim 1 , and further in combination with a source of electrical potential, the first electrode connected to a positive terminal of the source of electrical potential, the second electrode connected (Claim 2 continued) to a negative terminal of the source of electrical potential, and the third electrode connected to the negative terminal of the source of electrical potential to maintain the sacrificial cathode at an electrical potential that is at least as negative as the cathode of the ring laser angular rate sensor.

3. The ring laser angular rate sensor of claim 1 , and further in combination with a first source of electrical potential and a second source of electrical potential, the first electrode connected to a positive terminal of the first source of electrical potential, the second electrode connected to a negative terminal of the first source of electrical potential, and the third electrode connected to a negative terminal of the second source of electrical potential, wherein the sacrificial cathode is maintained at an electrical potential that is more negative than the cathode of the ring laser angular rate sensor to attract a greater portion of the positively charged migratable components within the laser block than are attracted to the cathode.

4. The ring laser angular rate sensor of claim 1 , wherein the sacrificial cathode is positioned at a region that is adjacent yet spaced apart from the cathode.

5. The ring laser angular rate sensor of claim 4, wherein the sacrificial cathode is shaped to optimize the amount of migratable components within the laser block that are attracted to the sacrificial cathode.

6. The ring laser angular rate sensor of claim 5, wherein the sacrificial cathode is accurately shaped to partially surround the cathode.

7. The ring laser angular rate sensor of claim 5, further including an indium seal between the sacrificial cathode and the laser block.

8. The ring laser angular rate sensor of claim 5, wherein the sacrificial cathode is vapor deposited on the surface of the laser block.

9. The ring laser angular rate sensor of claim 5, wherein the sacrificial cathode is painted on the surface of the laser block.

10. The ring laser angular rate sensor of claim 5, wherein the sacrificial cathode includes a plurality of holes formed in the sacrificial cathode, the angular rate sensor further including a layer of non-conducting adhesive positioned over the sacrificial cathode.

11. A method for reducing the migratable components that are attracted to a cathode in a ring laser angular rate sensor having a laser block that includes an optical closed loop path containing a fluid adapted for creating a laser within the optical closed loop path, an anode mounted to the laser block in fluid communication with the fluid, and a cathode mounted to the laser block in fluid communication with the fluid, the method comprising the steps of mounting a sacrificial cathode on the laser block and causing the sacrificial cathode to be maintained at an electrical potential that is at least as negative as the potential of the cathode of the ring laser angular rate sensor to attract positively charged migratable components in the laser block.

12. The method of claim 11 , wherein the step of mounting a sacrificial cathode on the laser block includes securing the sacrificial cathode to the laser block surface with an indium seal.

13. The method of claim 11, wherein the step of mounting a sacrificial cathode on the laser block includes vapor depositing the sacrificial cathode on the laser block.

14. The method of claim 13, further including the step of providing a layer of non-conducting adhesive over the sacrificial cathode after the cathode has been mounted to the laser block.

15. The method of claim 1 1 , wherein the step of mounting a sacrificial cathode on the laser block includes painting the sacrificial cathode on the surface of the laser block.

16. The method of claim 1 1, wherein the step of mounting a sacrificial cathode on the laser block includes positioning the sacrificial cathode on the laser block and providing a layer of non-conducting adhesive over the sacrificial cathode.

17. The method of claim 11, wherein the sacrificial cathode is mounted to the laser block at a region that is adjacent yet spaced apart from the cathode of the ring laser angular rate sensor.

18. The method of claim 17, wherein the sacrificial cathode is arcuately shaped to optimize the amount of migratable components that are attracted to the sacrificial cathode.

19. The method of claim 1 1, further in combination with the step of aggressively cleaning the laser block prior mounting the cathode, the anode, and the sacrificial cathode to the laser block by immersing the laser block in a bath of high purity water to leach migratable components from a top portion of the exposed surfaces of the laser block.