LASER TUBE DIAGNOSTICS: BEAM MODE

The following information is provided for educational reference ONLY. All repairs should be undertaken by a qualified engineer. The use of the following information is done so entirely at your own risk!

There are many problems which can be present with cheaper CO2 laser systems, many issues can be avoided by choosing parts and components approved by your supplier.  

The main issues encountered with both Glass (DC, water cooled) and metal (RF Air cooled) laser sources is a loss in power output over time, this usually takes place over months or years, and is an unavoidable attribute of CO2 lasers. Tube longevity can be increased by running your system at the lowest possible power setting, however this does require a very finely tuned system, which is sometime not possible on generic or Chinese-made machinery.

In this tutorial, we will address, the other main, and often overlooked, symptoms of tube quality issues; beam mode, and modal "drift", which can have an equal effect on power output and quality of cut.

Symptom 1: Beam "Halo"

The "Halo" effect is often the first symptom that something is wrong with your laser tube. This can be caused by overheating, damage to the internal optics, or output window on your tube.

This issue will often first present with a loss in power, and strange cutting artefacts such as excessive burning around the cut, which damages the surface of cut items.

This effect usually represents the decline of older tubes, and can be present even when a power-test yields acceptable levels of optical output (power).

Unfortunately there is no work-around available for this fault, and the tube must be replaced, or serviced.

Symptom 2: "Sputtering"

Sputtering is a fairly terminal sign that your laser tube requires immediate replacement. This is often seen on low quality tubes, and is caused by the electrode material (The metallic tubes at each end of the laser) evaporating and plating itself on to the internal tube optics.

This causes a random/scattered radiation pattern as the light produced internally in the tube reflects of particles of contamination.

In the images opposite, you can clearly see the signs of heat build-up on the electrode. This looks like a purple "haze" or discolouration.

The resulting beam burn mark is scattered, with no distinct area of energy, producing lots off tiny dots of light output. The tube must therefore be replaced. 

Symptom 3: Elliptic Beam

Unfortunately any deviation from a perfectly round spot from your laser source will cause errors in cut. This is usually represented by a very thin line along one axis, and a thicker line along the opposing axis.

 

This is caused by the elliptic shape of the raw beam, as it cannot turn in sympathy with the motion system, leaving thicker cuts in one direction, and thinner cuts in the other.

The tube must unfortunately be replaced if any deviation from a circular dispersion pattern is observed. 

Perfect beam mode:

The only way to achieve consistent and accurate quality of cut is to ensure the laser tube is constructed in such a way as to avoid the quality issues described above.

 

This consists of using high-purity gasses, filled at a specific amount and pressure, as well as excellent bonding of the tube's parts and optical elements; this ensures no contamination can be present and gas pressure/fill does not change over time.

 

Furthermore, the electronic parts internal to the tube MUST be built utilising robust and non-reactive materials such as tungsten, or stainless steel. This ensures long lifespan and high-power density for efficient and clean cuts.

To discuss service of your equipment or any aspects detailed above please contact us.

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