Types of Industrial Lasers

The advantages and disadvantages of typical sources for ablation energy are discussed below in the order of decreasing pulse width.
Arc Lamp, also called Flash Lamp produces a relatively long pulse (milliseconds). This can cause significant substrate heating. Furthermore, the broad distribution of the light makes it unsuitable to use with an optical fiber for delivery to a lightweight, portable tool. The laser source itself must be physically close to the coating being removed.
CO2 Laser Two types of CO2 lasers are in use: Continuous Wave (CW) lasers, which generate continuous light, and Transversely-Excited Atmospheric pressure lasers (TEA), which are pulsed. The CW are not suitable for laser ablation, because light intensity is typically below threshold levels for surface ablation until subsurface temperatures decompose the substrate material. The TEA lasers have pulse widths in the 100 nsec range and would be appropriate for coating removal, but their far-infrared wavelength (10.6 um) precludes their use with optical fiber delivery systems. This limitation means that the laser itself must be physically proximate to the stripping, or a series of movable mirrors must be used. TEA lasers also require gas delivery systems and high-voltage power supplies that can complicate system maintenance.
Diode Laser These lasers are semiconductor diodes that create laser light directly from electricity. They are the most efficient in converting electrical input power to laser output power, but they are either CW or long pulse so they have coating removal characteristics similar to flash lamps.
Neodymium-doped: Yttrium Aluminum Garnet (Nd:YAG) Laser An Nd: YAG is a solid state laser and is the most frequently used for laser ablation. They are available commercially in several configurations with varying characteristics. All share the same near-infrared wavelength (1.064 um) that works well for optical fiber delivery. The differences are in the pumping mechanism and pulse width.
The flash lamp pumped, Q-switched Nd: YAG laser provides the shortest pulses (10 nsec range). These short pulses make for efficient stripping, but they are difficult to deliver through optical fibers at high average power, because peak power levels often exceed fiber capacity. Furthermore, these lasers use pulsed high-voltage supplies and flash lamps with relatively short operating lives (hundreds of hours), imposing maintenance and reliability constraints. In addition, the electrical efficiency is low, requiring larger chillers.
The arc-lamp pumped, Q-switched Nd: YAG laser provides a somewhat longer (100ns) pulse that is effective for stripping. These lasers suffer the efficiency and reliability problems associated with the flashlamp-pumped lasers, but to a somewhat lesser extent.
The diode-pumped Q-switched Nd: YAG laser recently attained the high average power needed for laser coating removal. These lasers use a diode laser to pump the Nd: YAG material. They have the pulse characteristics of the arc-lamp pumped laser, but with vastly increased electrical efficiency and reliability. Because of their high efficiency, cooling requirements are greatly reduced. Reliability is also significantly improved with diode lifetimes specified at 10,000 hours. This is the laser of choice for coating removal applications.
Femto-second lasers provide extremely short pulses with correspondingly high peak power. They are used in micro-ablation applications and produce virtually no substrate heating. But their cost, reliability, and beam delivery issues make them impractical for coating removal applications.

Fiber Lasers There are two varieties of fiber lasers: CW (continuous wave) and Q-switched.
CW fiber lasers are presently leaders in high average power, with levels up to 50K watts available. Despite their high average power, the difficulty of delivering high peak power density to the work surface makes it difficult to remove coatings without heating the substrate. This challenge is similar to that posed by CW CO2 lasers.
Q-switched fiber lasers are very similar in performance to diode-pumped Q-switched Nd:YAG lasers.