Carbon Dioxide Gas Lasers Fredrick Brown

Carbon Dioxide Gas LasersCarbon Dioxide Gas Lasers

Fredrick BrownFredrick Brown

Spring 2004Spring 2004

OverviewOverview

QuestionsQuestionsIntroduction of CO2 Gas lasersIntroduction of CO2 Gas lasersGas Flow CO2 LaserGas Flow CO2 LaserSealed Tube CO2 LaserSealed Tube CO2 Laser(T.E.A.) CO2 Laser(T.E.A.) CO2 LaserPower Supplies for CO2 Gas LaserPower Supplies for CO2 Gas LaserApplicationsApplicationsAnswers to questionsAnswers to questions

QuestionsQuestions

How do you control the voltage and gas How do you control the voltage and gas flow rate in a Flowing Gas CO2 Laser?flow rate in a Flowing Gas CO2 Laser?

What is the operating voltage and current What is the operating voltage and current for a typical Sealed CO2 Gas Laser?for a typical Sealed CO2 Gas Laser?

IntroductionIntroduction

CO2 laser emits an invisible CO2 laser emits an invisible infrared beam of a single infrared beam of a single wavelength in the form of a wavelength in the form of a small, intense beam. small, intense beam. Specifically, CO2 emits Specifically, CO2 emits photons at 10.6 and 9.6um. photons at 10.6 and 9.6um.

The laser gases for CO2 The laser gases for CO2 lasers normally contain a lasers normally contain a mixture of helium, nitrogen, mixture of helium, nitrogen, and carbon dioxide. Some and carbon dioxide. Some laser types also require small laser types also require small amounts of CO, H2 or Xe in amounts of CO, H2 or Xe in the laser gas mixture because the laser gas mixture because of dissociation of gas of dissociation of gas molecules.molecules.

http://www.repairfaq.org/sam/laserpic/laserpic.htmhttp://www.repairfaq.org/sam/laserpic/laserpic.htm

Fig. 1 Laser warning tag 60 W max for the CO2 beam.

Types of CO2 Gas LaserTypes of CO2 Gas Laser

Flowing Gas LaserFlowing Gas Laser

Sealed Tube Gas LaserSealed Tube Gas Laser

T.E.A. Gas LaserT.E.A. Gas Laser

Flowing Gas LaserFlowing Gas Laser

Gas Mixtures are pumped from Gas Mixtures are pumped from one end of the tube and out one end of the tube and out other to provide fresh gas to other to provide fresh gas to replace the CO2 depleted mix replace the CO2 depleted mix due to the seperation of gas due to the seperation of gas molecules.molecules.

He and N2 are added to the He and N2 are added to the mixtures to boost efficiency mixtures to boost efficiency the laser.the laser.

plovdiv.techno-link.com/ClientsSites/ladec/default.htm

Fig. 2 Flowing Gas Laser.

Fig. 3 CO2 mix bottle and primary regulator

Flowing Gas Cont.Flowing Gas Cont.

Power output is typically 40 to Power output is typically 40 to 80 watts/meter of the tube 80 watts/meter of the tube length.length.

A device called the Variac A device called the Variac (Variable Transformer)(Variable Transformer) can be can be used for voltage control. A used for voltage control. A control valve is used to adjust control valve is used to adjust the rate of gas flow. the rate of gas flow.

In commercial lasers, the In commercial lasers, the Variac and the control valve is Variac and the control valve is coupled together so that when coupled together so that when the voltage is increased the the voltage is increased the flow valve is opened in flow valve is opened in proportion to the power setting. proportion to the power setting.

http://www.elect-spec.com/variacy.htmhttp://www.elect-spec.com/variacy.htm

Fig.4 Output voltage Variac.

Sealed Gas LaserSealed Gas Laser

The typical Sealed CO2 The typical Sealed CO2 Laser tube has an Laser tube has an operating voltage operating voltage between 3 to 12KV and a between 3 to 12KV and a operating current of 2 to operating current of 2 to 15mA DC.15mA DC.

A high starting voltage A high starting voltage usually 2-5 times the usually 2-5 times the operating voltage is operating voltage is needed to initiate the needed to initiate the discharge.discharge.


Fig.5 Low voltage sealed CO2 laser

Fig.6 Gas discharge tube for Sealed CO2 Laser

Sealed Tube Cont.Sealed Tube Cont.

There are separate control There are separate control loops for the voltage and loops for the voltage and currents.currents.

- Voltage:- Voltage: An auxiliary winding on An auxiliary winding on the transformer feeds a bridge the transformer feeds a bridge rectifier and filter capacitor rectifier and filter capacitor which provides a feedback which provides a feedback voltage proportional to the voltage proportional to the output of the power supply.output of the power supply.

- Current: - Current: The current control The current control returns the current through a returns the current through a sensing resistor (with a filter sensing resistor (with a filter capacitor) providing a voltage capacitor) providing a voltage proportional to the tube proportional to the tube current.current.


Fig.7 Sealed CO2 Laser connected to power supply.

T.E.A. Gas LaserT.E.A. Gas Laser

Most high power CO2 lasers are Most high power CO2 lasers are constructed using TEA (Transverse constructed using TEA (Transverse Excited Atmospheric) designs. Rather Excited Atmospheric) designs. Rather than having a long tube with a than having a long tube with a electrical discharge along its length electrical discharge along its length and the CO2 gas mixture flowing from and the CO2 gas mixture flowing from one end to the other, a series of one end to the other, a series of electrodes and gas inlets are spaced electrodes and gas inlets are spaced along the tube. along the tube.

- Chamber with CO2 laser gas in it. Chamber with CO2 laser gas in it. - Two electrodes run down the length of the Two electrodes run down the length of the

chamber. chamber. - The pulse excites the CO2 laser gas, which The pulse excites the CO2 laser gas, which

then begins spontaneous emission. then begins spontaneous emission. - A reflector and an output coupler outside A reflector and an output coupler outside

the chamber form the resonating cavity. the chamber form the resonating cavity. - The "TE" in "TEA" comes from the fact that The "TE" in "TEA" comes from the fact that

the excitation is performed transverse to the the excitation is performed transverse to the direction of the laser output, as opposed to direction of the laser output, as opposed to down the length of the tube like in the down the length of the tube like in the Flowing CO2 laserFlowing CO2 laser. .

Fig. 8 TEA Diagram

Fig. 13 View of a TEA CO2 Laser in operation

T.E.A. ContinuedT.E.A. Continued

SpecificationsSpecifications

- pulse duration: 15 ns - 20 µs - pulse duration: 15 ns - 20 µs - peak power: 100 kW - 500 MW - peak power: 100 kW - 500 MW - wave length: 9.12 µm - 11.22 - wave length: 9.12 µm - 11.22

µm µm - average power: 5 mW - 150 W - average power: 5 mW - 150 W

Fig. 11 Using TEA laser on a uncooperative computer monitor


Fig. 10 TEA CO2 Laser cutting metal sheet

Power Supplies For CO2 Gas Power Supplies For CO2 Gas LaserLaser

Fig. 12 View of the power supply and a Variac (autotransformer) for the primary voltage adjustment.

Fig. 13 View of the power supply powering up a CO2 laser


ApplicationsApplications

The beam for a CO2 Gas The beam for a CO2 Gas Laser produces a very Laser produces a very high temperature that high temperature that may be used for may be used for engraving, cutting, engraving, cutting, drilling, marking, welding drilling, marking, welding and in various medical and in various medical applications such as applications such as dermatology and as a dermatology and as a medical tool for producing medical tool for producing clean cuts with little clean cuts with little bleeding.bleeding.


Fig. 14 Laser cuts/breaks and or

inscribes based upon power settings

Fig. 15 Laser cutting thin piece of wood

Answers to QuestionsAnswers to Questions

1.) How do you control the voltage and gas flow rate in 1.) How do you control the voltage and gas flow rate in a Flowing Gas CO2 Laser?a Flowing Gas CO2 Laser?

- A device called the Variac can be used for voltage A device called the Variac can be used for voltage control. A control valve is used to adjust the rate of gas control. A control valve is used to adjust the rate of gas flow.flow.

2.) 2.) What is the operating voltage and current for a What is the operating voltage and current for a typical Sealed CO2 Gas Laser?typical Sealed CO2 Gas Laser?

- - The typical Sealed CO2 Laser tube has an operating The typical Sealed CO2 Laser tube has an operating voltage between 3 to 12KV and a operating current of 2 voltage between 3 to 12KV and a operating current of 2 to 15mA DC.to 15mA DC.

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Carbon Dioxide Gas Lasers Fredrick Brown