CO2 Lasers

DC-excited vs. RF-excited CO2 lases

laser tubes used in medical CO2 lasers use DC or RF excitation to energize the laser gas. The main difference in performance is related to the fact that systems with DC-excited tubes typically enable the user to adjust both power level and pulse width, whereas RF-excited tubes, such as that used in the Ultrapulse, only allow the user to vary pulse width. The power level for RF-excited tubes is usually set by adjusting the duty cycle at a fixed power level resulting in an adjustment to the average power during the pulse. Continue reading

Ultrapulse, Superpulse or chopped?

These are marketing terms. All modern medical CO2 lasers are pulsed by electronic gating, and all can run continuously (referred to as CW) for short time periods. Chopped is a historical term that refers to mechanically gating the laser beam with a mechanical shutter of that actually chopped the beam.

All modern lasers are electronically gated or chopped. In general RF-excited lasers are designed to operate at a CW fixed power level, (240w for the Ultrapulse), and are pulsed by gating their CW power level. DC-excited lasers are also pulsed by electronic gating, but have the ability for superpulse… Continue reading

What is the best spot size fractional treatment?

There are as many opinions as spot sizes. In general, with the correct parameters, slightly difference spot sizes will result in indistinguishable clinical results. It is more or less a utilitarian choice in that larger spot sizes are easier to use for full field resurfacing, and fractional spot sizes are less visible to the eye if they are smaller. Most modern CO2 lasers have diffraction limited beams, and can all provide about the same spot sizes with the proper selection of lenses, so it is usually a deign choice. My preference is to use the largest spot that is aesthetically pleasing. Aesthetic medicine is a subjective field after all. Anything less than 300 µm in diameter seems to blend very well without noticeable spots in a day or two. A side issue is that there is no standard definition used by manufacturers for the spot size specification so comparing lasers with different advertised spot sizes can be misleading. So when comparing spot sizes you need to know if they are defining it as the half power points, the area containing 90% of the energy, the pattern burned on laser paper, or the 1/e2 power points. Are they including the thermal coagulation zone or just the drilled channel, or are they measuring the laser beam itself? The lack of a precise and standard definition leaves a lto of room for marketing. Continue reading
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