TEA CO₂ laser parameters and marking application

Introduction

Transversely electrically excited laser operated on atmospheric pressure (TEA) filled by carbon dioxide (CO₂) is used as a source of light with sufficient energy density for laser marking. The projection of a mask motif through calcium fluoride (CaF) positive lens is summarized on fig. 6.1. The magnification (in fact the reduction) m is defined as a ratio a/a'.

Consider lens equation one can derive position of mask for selected magnification as a = f (1+m)

Goal

Measure TEA CO₂ laser pulse temporal profile and energy stability. Mark color paper using different mask and different reductions.

Instructions

1. Prepare aparatus, i.e.
   • switch on power source 24 V / 7 A
   • switch on the oscilloscope
   • switch on control laptop and run installed control application
   • remove the cap from laser output aperture
2. Test laser action and verify experiment optical axis.
3. Setup beam direction to temporal profile detector input. (approximate distance 1 m)
4. Setup the scope to store and memory mode 50 – 100 ns/div.
5. Setup the scope triger level to record real optical laser signal (not electrical noise signal)
6. Record required temporal profiles and its parameters.
7. Insert energy detector into laser beam.
8. Setup scope to slow record mode 10 – 20 ms/div.
9. Record detector signal on scope and measure its amplitude.
10. Setup laser repetition rate to ½ Hz, it is one shot per 2 seconds.
11. Record separate peaks amplitude for approx. 100 pulses and evaluate energy stability.
12. Calculate distance for proper mask projection, place mask, lens, and object (color paper or paper covered by graphite) and mark it by selected number sequence for three different reductions (m > 2).

Requested results

1. The value of FWHM of the first maximum of TEA CO₂ laser pulse temporal profile.
2. The value of entire width of TEA CO₂ laser optical pulse.
3. The graph of energy in time and its standard deviation for n measurements, where n is about 100. Optionally add the energy histogram.
4. Several successfully marked samples attached to the protocol.

References

Melles Griot - Transforming a Gaussian Beam with Simple Lenses

Melles Griot: Transformation and Magnification by Simple Lenses

Yariv - chapter 7.6 - 7.7

gas laser theory