Parallax Technology, Inc

Hard Seal Glass-to-Metal Technology

There are currently two types of dc-excited, sealed co2 laser tubes available in the market (photos shown below).

Type 1- Laser tubes which have Hard-Seal, Glass-to-Metal connections at both ends

and

Type 2- Laser tubes which have the ends Glued to the tube.

Type 1- "... glass-to-metal seal is defined as one in which glass is heated to the point where intimate 'wetting' is attained on a hot metal surface and is retained when the glass and metal are cooled to room temperature. This requires, among other factors, that the glass and metal components have somewhat similar expansion coefficients and rate of expansion" ( 'Rosebury').

Glass-to-metal hard-seal technology has been around for over 60 years. It was developed during World War II for long life, temperature stable vacuum tubes needed in radar applications.
Metal and glass have different coefficient of expansions and when heated, the metal will expand faster than glass and the joint will crack. Therefore, not all metals can be hard-sealed (melted) onto all glass.

For this purpose a special alloy, Kovar, was developed at Stupakoff (a Carborandum Co.) to have a coefficient of thermal expansion very close to a type of glass from Corning Glass.

Today, only expert glass blowers, such as our own, can do the Kovar-to-Glass graded seal on the 16 cm circumference of a 1 inch diameter Kovar tubing used in our 100 Watt laser tubes. The 'glass-to -metal' seal is stable at elevated temperatures up to 300 degrees C and is leak tight beyond any measurable amount.

Type 2- Metal and glass are joined with Glue. No explanation is necessary! Examples follow.

What is wrong with using Glue ?

Here is the very short answer:   in order to achieve long-life for the operation of the laser, all air inside the tube is pumped out and high purity gases, Helium, Nitrogen and co2, are admitted inside the tube. Nothing else should get in or get out. But, all epoxy and Glue emit gases and that is why most Glues 'smell'. The emission of these gases increases as the temperature goes up. The more glue that is used on a laser tube, the more noxious gases get inside the tube and the shorter the life of the tube.

The following photographs demonstrate the issue.

1. Example of a Parallax PLX model laser tube with Glass-to-Metal Hard Seal.

2. Example of a co2 laser tube with Glued ends.

 

3. Examples of Chinese made co2 laser tubes with Glued ends.

4. Another third party co2 laser tube with Glued ends.

5. And again, a Parallax laser tube with glass-to-metal hard seal.

In Conclusion:

of the many factors that determine "the life" of a sealed co2 laser tube, its construction is of paramont importance. CO2 laser tubes with glued ends are much cheaper than Hard Sealed tubes.

If you are a hobbyist that occasionally uses a co2 laser, then by all means, buy the cheapest laser tube you can afford BUT, profesionals and equipment manufacturers must consider the following:

a Medical laser that fails after 20 hours of operation will:
anger the doctor
upset the patient
and Most Importantly, destroys your reputation.

Worst yet,
an Industrial tube that fails due to its short life-time will shut down the factory line and may cause thousands of dollors in loss AND you will lose that client for ever.

Famous Chinese proverb says "you always get what you pay for".