New Mexico Geochronology Research Laboratory
Hardware — CO2 Laser

CO2 Laser
CO2 laser chamber in use by the NMGRL. Copper sample disks in background.

The CO2 laser system used by the NMGRL consists of...

  • Advantages of a CO2 laser system
    • Inexpensive to purchase, operate and maintain
    • excellent beam coupling to silicate minerals
    • rapid sample heating relative to the resistance furnace
    • very low argon background or blank levels relative to resistance furnace
    • ideal for identifying sample heterogenities (e.g. non-desirable mineral phases, xenocrysts)
    • capable of step-heating with special lenses
  • Disadvantages of a CO2 laser system
    • incapable of very small (<1 mm beam spot sizes, as is necessary for in-situ argon extraction (see UV laser)
    • even with special lenses for step-heating, homogeneous heating difficult

 

 

 

 

Schematic of NGMRL CO2 laser system

 

CO2 laser schematic

 

Components of the NMGRL CO2 laser system.

  1. Color CCTV camera (Polnux TMC-574)
  2. Optical lens
  3. IR transparent optical mirror
  4. Vibration isolated workstation/table (Newport Corporation)
  5. Automated stage:
  6. Sample chamber: base = 3.375" flange; window = ISI ZnSe 1.5 window mounted in 3.375" flange
  7. Copper sample holder; 6 to 221 sample pits
  8. Potassium bromide cover slip: 2mm thick x 38.1 mm diameter
  9. first surface silicon mirror
  10. 1" diameter by 5" focal length ZnSe meniscus lens, II-VI #376587
  11. Beam integrator lens
  12. Laser power meter head; Molectron PM150-19-C, swings in or out of beam path to measure beam intensity
  13. Laser feedback diode, Synrad CA-48-CL
  14. 50-watt CO2 laser, Synrad 48-1-28W
  15. He-Ne pointer laser, Synrad He-Ne
  16. Two-axis motion controller with IEEE.488 communications, Newport PMC200-P
  17. Laser power meter, Powermax 5100
  18. CO2 laser controller with 0-10 volt DC input, Synrad UC-1000
  19. 0-40 volt, 10 amp power supply with 0-10 volt input, Lambda LLS8040

 

 

Video Clip of CO2 laser fusion

 

Explanation

The field of view in the video is approximately 5 mm across. Each hole (~1.7 mm in diameter) contains an individual sanidine feldspar crystal. The computer moves the sample chamber/tray (x-y position) to the next hole to be analyzed and activates the CO2 laser (power = ~2 watts). The laser begins to fuse the silicate mineral. To ensure complete argon extraction, the tray is then jogged through all four quadrants of the hole (only the beginning of the job cycle is shown). After approximately 15 seconds, the laser is deactivated and the argon gas is cleaned and moved to the mass spectrometer to be analyzed.