Discharge instabilities prevent operation of CW CO2 lasers at pressures above about 100mbar. Pulses in the nanosecond to microsecond duration range can be produced by passing a pulsed current transversely through the lasing gas. Such TEA (transversely excited atmospheric) lasers operate at gas pressures of one atmosphere and above in order to obtain high energy output per unit volume of gas. A transverse discharge from two long electrodes is employed (see Fig.3). Prior to application of the pulsed discharge, a form of pre-ionisation is used to ionise the space between the electrodes uniformly, thus allowing the discharge to proceed in a uniform fashion over the entire electrode assembly. The prime attractions of TEA lasers are their ability to generate short intense pulses and the extraction of high power per unit volume of laser gas. Pulse duration as low as a few tens of nanoseconds up to a few microseconds are possible. Pulse energies range from the millijoule region to 500Joules at pulse repetition rates from about 300Hz down to single shot.
Reflective mirrors - silicon with high reflectivity coatings, gold coated copper. Lenses and windows - gallium arsenide and germanium (not transparent in visible region) and coated zinc selenide (orange in the visible region). Wallplug Efficiency between 5% and 16% The shape and length of the laser cavity and nature of the resonator optics determine the beam diameter and divergence of the CO2 laser. Typical ranges are:
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Optics for CO2 Lasers: