T.E.A. Co2 Lasers - Their Development and Application

Transversely Excited Atmospheric (T.E.A.) lasers have been in general industrial use for laser marking operations starting approximately in the early 1970s and late 1960's. The T.E.A. Co2 laser has been used extensively for laser marking and laser etching in many industries and on many different types of products. The T.E.A. Co2 laser has been used extensively in the dry food and pharmaceutical industries for laser marking and laser etching of buy dates, product expiration dates, lot numbers and serial numbers.

T.E.A. Co2 laser marking is achieved via the use of a mask or stencil. As the laser beam passes through the stencil, the outline of the mask or stencil is laser marked or laser etched onto the product. Changing the laser mark requires changing of the mask or stencil. In the past this was accomplished by an operator who manually changed the mask or stencil. This process continued until the introduction of automatic mask changers or time clocks several years after the introduction of the T.E.A. Co2 laser. Generally speaking, the use of T.E.A. Co2 mask lasers is limited to applications where the laser mark does not require frequent changes and the laser mark can be altered infrequently. Examples include, once at the end each shift, once a day, or after a long batch processing run of products. Automatic time clock modules are available but generally increment the time only every 15 or 30 minutes.

The T.E.A. Co2 laser requires the use of an external laser gas bottle generally consisting of the following components and approximate % combinations:

- Carbon dioxide (CO2) (around 10-20 %)
- Nitrogen (N2) (around 10-20%)
- Hydrogen (H2)
- Helium (He) (The remainder of the gas mixture)

The gas mixture flows though the laser by use of an internal fan assembly inside the laser head. The medium is combined with an electrical discharge that excites the atmosphere and generates the laser beam. This gas mixture is a consumable of the T.E.A Co2 laser marking or laser etching process. For spark gap driven T.E.A. Co2 lasers a dry air or nitrogen supply to the spark gap is also required.

T.E.A. Co2 lasers employed for laser marking and laser etching are generally air cooled except for the highest speed operations where water cooling may be required. T.E.A. Co2 lasers generally used in industrial laser marking and laser etching applications are capable of laser marking or laser etching up to 90,000 parts per hour. Generally T.E.A. Co2 lasers used in industrial laser marking or laser etching applications produce power levels from 2.0 joules to 5.5 joules depending on the internal configuration of the main capacitor size and rating coupled with the reflectivity of the laser font optic.

T.E.A. Co2 laser produce a very high peak power, up to 10x the peak power of continuous wave Co2 lasers and therefore are extremely useful for Co2 laser marking and laser etching of products that can be difficult for Co2 lasers such as some plastics and resins. With some materials, laser marking and laser etching with T.E.A. Co2 lasers will produce a visible color change to the product. Laser marking and laser etching sealed beam RF excited Co2 lasers will only produce an etch with no color change. The T.E.A. Co2 lasers can produce the change in color for some products along with a laser etch due to the high peak power produced by the T.E.A. Co2 laser pulse.

T.E.A. Co2 lasers have been used extensively up till now for laser marking and laser etching of discrete electronic components such as T0220's and SOT23's. The T.E.A. lasers produce a white or blue appearing laser mark on the component when the laser beam interacts with a 'laser friendly' ink on the surface of the component. In many of these applications the T.E.A. Co2 laser is coupled with a component tester. If the component passes the test a laser mark is applied. If the component fails the test the part is rejected from the line.

The newest generation of T.E.A. Co2 lasers has very high repetition rates and are used extensive in the Kapton industry for laser drilling purposes.

T.E.A. Co2 lasers generally operate in the infrared light spectrum at 10.6 and 9.4 micrometers. Generally rear optics in the laser cavity are 100% reflective to an extent causing self generated laser beams inside the electrode gap and laser head. The front optics in industrial applications vary between 40% to 70% reflective based on the material being Co2 laser marked, laser etched or laser drilled.

An important advantage of the T.E.A. Co2 laser is that laser light wavelength can be changed from 10.6 micrometers to 9.4 micrometers. This is achieved with the change of the font optic coating. The use of laser light at 9.4 micrometers is very important for Co2 laser marking of certain plastics such as PET or PETE and producing readable color changed Co2 laser marks on bottles. Generally speaking T.E.A. Co2 laser front optics in industrial applications are geranium coated though sometimes zinc selenide is used. Mirrors for turning the laser beam are gold coated and the laser beam profile can approach sizes of approximately 1" x 1" depending on the gap of the electrode set.