Download Like a beam of high velocity electrons, a laser beam is also capable

Like a beam of high velocity electrons, a laser beam is also capable of producing very high power
density. Laser is a highly coherent (in space and time) beam of electromagnetic radiation with
wavelength varying operation from 0.1 – 0.7µm. However, the power requirement for machining
operation restricts the effectively usable wavelength range to 0.4 – 0.6µm. Because of the fact that
the rays of a laser beam area perfectly parallel and monochromatic, it can be focused to a very
small diameter and can produce a power density as high as 107w/mm2. For developing a high
power, normally a pulsed ruby laser is used. The continuous CO2-N2 laser has also been
successfully used in machining operations.
Fig. 15-6 shows a typical pulsed ruby laser. A coiled xenon flash tube is placed around the ruby
rod and the internal surface of the container walls is made highly reflecting so that maximum light
falls on the ruby rod for the pumping operation. The capacitor is charged and a very high voltage
is applied to the triggering electrode for initiation of the flash. The emitted laser beam is focused
by a lens system and the focused beam meets the work surface, removing a small portion of the
material by vaporization and high speed ablation. A very small fraction of the molten metal is
vaporized so quickly that a substantial mechanical impulse is generated, throwing out a large
portion of the liquid metal. Since the energy released by the flash tube is much more than the
energy emitted by the laser head in the form of a laser beam, the system must be properly cooled.