An educational report on different types of laser used in LBM

1. April 28, 2016
Types of Laser used in Machining
Name: Marwan Shehata Mohamed Zeitoun
No: 159

2. PAGE 1
Laser Beam Machining
Modern machining methods are established to
fabricate difficult-to-machine materials such as
high-strength thermal-resistant alloys; various
kinds of carbides, fiber-reinforced composite
materials, Satellites, and ceramics.
Conventional machining of such materials
produces high cutting forces that, in some
particular cases, may not be sustained by the
workpiece. Laser beam machining (LBM) offers
a good solution that is indeed more associated
with material properties such as thermal
conductivity and specific heat as well as melting
and boiling temperatures. Laser is the
abbreviation of light amplification by
stimulated emission of radiation. A highly
collimated, monochromatic, and coherent light beam is generated and focused to a small spot. High
power densities (106 W/mm2) are then obtained. A large variety of lasers are available in the market
including solid-state, ion, and molecular types in either continuous wave (CW) or pulsed mode (PM) of
operation

3. PAGE 2
Types of laser
i- Solid state laser
Ruby is a very important solid state laser. Ruby consists of aluminum oxide in which a small percentage
(0.01 ~ 0.05) of Al+3 have been replaced by Cr-3 ions. The aluminum and oxygen ions are inert, only the
chrome ions participate in the laser action. Ruby lasers have a relatively short wavelength ~0.69
microns, so they are restricted in applications. Other solid state lasers are YAG (yttrium-aluminum-
garnet) laser and neodymium-glass lasers
ii- Gas Lasers: The most popular gas used for laser is carbon dioxide CO2. It has a waverlength
of 10.6 microns. The CO2 laser is specially used for machining nonmetals as nonmetals have
high energy absorption at the wavelength CO2. Other gasses like argon, helium-neon are also
used as gas lasers.
iii- Liquid Lasers: They are used in research and in medical applications.
iv- Semiconductor Laser: These lasers find use in communication systems
Reference: Manufacturing Technology by M Adithan
Laser
Gaseous
CO2
Argon
Helium-neon
Solid-state
Ruby
YAG
Neodymium-
glass
Liquid
Medical
Applications
Semiconductor
Communication
Systems

4. PAGE 3
NEODYMIUM-YAG LASER
An example of a solid-state laser, the
neodymium-YAG uses the Nd3+ ion to dope
the yttrium-aluminum-garnet (YAG) host
crystal to produce the triplet geometry
which makes population inversion
possible. Neodymium-YAG lasers have
become very important because they can
be used to produce high powers. Such
lasers have been constructed to produce over a kilowatt of continuous laser power at 1065 nm and can
achieve extremely high powers in a pulsed mode.
Neodymium-YAG lasers are used in pulsed mode in laser oscillators for the production of a series of
very short pulses for research with femtosecond time resolution.
NEODYMIUM-GLASS LASERS
Neodymium glass lasers have emerged as the design choice for research in laser-initiated
thermonuclear fusion. These pulsed lasers generate pulses as short as 10-12 seconds with peak powers of
109 kilowatts.
RUBY LASER
The ruby mineral (corundum) is aluminum oxide with a small amount (about 0.05%) of chromium
which gives it its characteristic pink or
red color by absorbing green and blue
light.
The ruby laser is used as a pulsed laser,
producing red light at 694.3 nm. After
receiving a pumping flash from the
flash tube, the laser light emerges for as
long as the excited atoms persist in the
ruby rod, which is typically about a
millisecond.
A pulsed ruby laser was used for the
famous laser ranging experiment which
was conducted with a corner reflector
placed on the Moon by the Apollo astronauts. This determined the distance to the Moon with an
accuracy of about 15 cm.

5. PAGE 4
ND:YAG LASERS
YAG crystal has a higher thermal conductivity than glass, so the thermal dissipation in Nd:YAG laser
cavity can be improved, operation power can be up to several hundred watts in continuous mode, and
high pulse rates (50kHz) can be reached. YAG is a complex crystal of Yttrium-Aluminium-Garnet with
chemical composition of Y3Al5O12, it is transparent and colorless. About 1% Nd3+ ions are doped into
the YAG crystal, the crystal color then changed to a light blue color. The wavelength of Nd:YAG laser is
1.06m m.
EXCIMER LASERS
generate laser light in ultraviolet to near-ultraviolet spectra, from 0.193 to 0.351 microns. Since excimer
lasers have very short wavelengths, the photons have high energy. This results in reduced interaction
time between laser radiation and the material being processed, therefore the heat affected zone is
minimized. The above feature makes it ideal for material removal applications. They are used to
machine solid polymer workpieces, remove polymer films from metal substrates, micromachine
ceramics and semiconductors, mark thermally sensitive materials. They are also used in surgical
operations. Processing using excimer lasers is proved to have higher precision and reduced heat
damage zones compared with CO2 and Nd:YAG lasers. So the applications of excimer lasers in industry
have increased.
Excimer lasers are said to be able of "laser cold cutting", what does this mean? Normally when we use
CO2 and Nd:YAG lasers for material removing, the energy is transformed from optical energy to
thermal energy, the material is heated to melt or vaporize, then material changes from solid state to
liquid or gaseous state. But excimer lasers can remove material through direct solid-vapor Ablation!
The incident photon energy is high enough to break the chemical bonds of the target material directly,
the material is dissociated into its chemical components, no liquid phase transition occurs in this
process. This chemical dissociation process has much minimized heat effects compared with the
physical phase change process. UV laser is capable of ablating organic compounds. Though laser beam
has high energy, the energy is used to break chemical bonds, heat generation can be neglected, it is
truly Cold Cutting.