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             - Lasers 85/95 Specifications Charts

Features of LEXEL™ Lasers

          Laser head
          Plasma tube
          Optical resonator
          Power supply
              - Power supply interior
          Single-frequency operation
              - Model 503 Etalon
              - Typical frequency stability

Lexel plasma tube - click to enlarged viewThe LEXEL™ plasma tube design is the result of a major to eliminate each of the failure mechanisms that existed in other tube designs. The tube design uniquely combines high vacuum technology and ceramic power tube construction methods for the ultimate in rugged, reliable high performance. Consequently, the LEXEL™ tube has a proven record of reliable, long-life operation that is unmatched in the industry.

To view a close-up picture of a LEXEL™ plasma tube, click the photo at right.

Conduction cooled Be0 bore

    > Low temperature operation with unprecedented thermal stability
    > Eliminates water boiling, frequency jitter and thermal drift

The choice of bore material is the most important aspect of any ion laser plasma tube design. Beryllium Oxide (Be0) ceramic has proven to be the best material. Its exceptionally good thermal conductivity allows a tube design that transfers all of the thermal energy to the cooling water by direct conduction at very low temperatures.

All other bore materials must operate at extremely high temperatures and dissipate their heat by radiation which may result in local water boiling and thermal instabilities.

Conduction cooled Be0 plasma tubes store little or no residual heat. Thus LEXEL™'s plasma tubes reach thermal equilibrium almost instantaneously after start-up or changes in operating level. It is not necessary to wait for bore material to heat up and realign to the new operating temperature, as with radiation-cooled designs. Since there is virtually no heat stored in the Be0 plasma tube, the laser and cooling water can be shut off simultaneously without any damage to the tube. With a radiation-cooled plasma tube, a water shutdown can cause violent water boiling, and could even cause explosive failure.

The LEXEL™ Be0 plasma tube is efficiently cooled by low velocity water flow. There is no local water boiling or turbulent flow vibration such as is common to other designs. The LEXEL™ plasma tube cooling was designed to yield the best frequency stability and lowest frequency jitter of all existing ion lasers.

Rugged ceramic and metal construction

    > Strongest, most compact and stream­lined structure
    > Eliminates glass tube and pin seal breakage

The rugged and compact LEXEL™ plasma tube structure is built using ceramic and metal construction exclusively. Electrodes and feed-thru leads are rugged brazed-and-welded assemblies.

Other manufacturers' plasma tube designs, even those using Be0 bore material, use a glass envelope construction with fragile electrode pin seals. The major cause of failure of glass envelope tubes is glass and pin seal breakage.

The LEXEL™ ceramic and metal design has completely eliminated this failure mechanism and has proven to be the strongest and most reliable plasma tube in the industry.

High-conductance internal gas return system

    > Provides optimum pressure equalization and dependable starting
    > Eliminates fragile external glass tubing

LEXEL™ plasma tubes use an innovative high conductivity gas pressure equalization system that is completely isolated from the discharge bore yet entirely contained within the ceramic tube structure (patent pending). This exclusive LEXEL™ design feature assures optimum pressure equalization through the plasma tube and easy, reliable starting every time.

Other laser designs require the use of external glass tubing for the gas return path -- a another source of breakage.

Contoured bore profile

    > Matches discharge with magnetic field for long bore life
    > Minimizes bore enlargement and particle drop-out noise

The discharge bore profile in LEXEL™ plasma tubes is contoured to match the discharge current density with the axial magnetic field from the surrounding electromagnet. This important design step, coupled with the high erosion resistance of Be0 ceramic, eliminates the problems of particle deposits and dusting on Brewster windows and particle "drop-out noise" often reported in other designs.

Ceramic-insulated electrodes

    > Allows complete cooling with ordinary tap water
    > Eliminates electrolysis tube failures

Ceramic insulated electrodes of a Lexel laser tubeIn the LEXEL™ plasma tube, the heat from both electrodes (anode and cathode) is transferred through high thermal conductivity ceramic into the surrounding cooling water. Virtually all of the heat is removed from the electrodes to the water by conduction without being allowed to transfer into the surrounding laser head. Since the cooling water does not contact any metal parts of the plasma tube, there is no possibility of electrolysis. The LEXEL™ laser can be cooled with ordinary city tap water. It is never necessary to use special deionized water.

Other conductive cooled plasma tube designs have the high voltage anode in direct contact with the cooling water, a situation which requires special high resistivity water and inevitably leads to electrolysis tube failure.

Radiation-cooled designs do not fully contain the electrode and discharge heat, thus allowing substantial thermal losses to be radiated to the surrounding optical structure.

Only the LEXEL™ plasma tube eliminates both the electrolysis failures and thermal radiation problems of other designs.

Large capacity free flow gas supply

    > Provides optimum gas supply through­out tube life
    > Eliminates gas fill valves and fill system failures

Gas pressure is maintained at the optimum range, for Lexel laser tubesA large capacity stainless steel gas supply tank is an integral part of the LEXEL™ plasma tube. The gas supply tank holds up to 1,600 milliliters of argon or krypton, enough for 8,000 to 10,000 hours of full-power operation. This large amount of reserve gas, combined with LEXEL™'s Be0 bore design, maintains the gas pressure in the optimum range throughout the tube life.

LEXEL™'s Free Flow design eliminates the need for gas valves, refill buttons, and pressure monitoring required in other plasma tube designs. A LEXEL™ laser will never fail because of a sticking or leaking fill valve, nor will it ever run out of gas because gas pressure monitoring was neglected.




High-temperature Brewster window seals

    > Strain free non-organic quartz to quartz window seal  
        > Strain free single crystal quartz metal window seal

LEXEL™ Brewster's Angle windows are sealed using a fused quartz-to-quartz glass seal which is bakeable to over 1,000°C. This proprietary LEXEL™ seal completely eliminates window leaks, water vapor diffusion, birefringent strain, and window contamination commonly observed on epoxy-bonded tubes.

The combination of the LEXEL™ quartz window seal, 1,000°C window bake, and proprietary window material selection yields the best low-loss, distortion-free and color-center-controlled Brewster windows available for long lifetime operation.

Ultra-high vacuum processing

    > Uses only high vacuum materials and techniques
    > Eliminates window, cathode and gas contamination

The materials used in LEXEL™ plasma tubes are completely compatible with high temperature ultra-high vacuum processing. There is absolutely no epoxy, rubber O-rings or any other organic material used in LEXEL™ plasma tubes. Other ion laser manufacturers appear to compromise their plasma tube vacuum integrity by using either epoxy seals, rubber O-rings or organic fill valve seals. The use of any organic material in a plasma tube means that the tube cannot be completely out-gassed by a high temperature bake-out, and there will be some residual contamination gases to slowly evolve and contaminate the windows, cathode or discharge plasma.

One of LEXEL™'s major contributions to ion laser reliability is the completely vacuum compatible plasma tube. The entire tube is processed at high temperatures and at an ultra-high vacuum of better than 10-9 torr. The result is the ultimate in long lifetime, contamination-free laser operation.

Contamination-free copper pinch-off

    > The ultimate seal-off method
    > Eliminates O-ring leaks and glass stress cracks

After a plasma tube is completely processed it must be sealed off and separated from the vacuum processing station without affecting the vacuum integrity of the tube or the gas purity. We use a copper pinch-off, the most advanced, most reliable and truly contamination free method.

Other designs use either an O-ring seal or a glass "tip-off," neither of which is completely satisfactory. The O-ring seal method has tended to introduce air into the tube at the time of seal­off and can slowly leak or outgas contaminants into the tube during life. The glass tip-off requires melting of a glass exhaust tubing which sometimes results in leaks or glass stresses which can crack at a later time.

The LEXEL™ copper pinch-off is the method used on virtually all high power vacuum tubes for over 25 years. It has proven to be 100% reliable and absolutely contamination-free.

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