Glossary
- Absorption of radiation
- Receiving electromagnetic radiation by interaction with the material, and
transforming it to different form, which is usually heat. The absorption process
is dependent on the wavelength of the electromagnetic radiation and on the
absorbing material.
- Active Medium
- Collection of atoms or molecules which can be stimulated to a population
inversion, and emit electromagnetic radiation in a stimulated emission. Amplification
The process in which the electromagnetic radiation inside the active medium
within the laser optical cavity increase by the process of stimulated emission.
- Amplitude
- The maximum value of a wave, measured from its equilibrium.
- Aperture
- A small opening through which the electromagnetic radiation pass.
- Attenuation
- The decrease in radiation energy (power) as a beam passes through an absorbing
or scattering medium.
- Beam Diameter
- Defined as the diameter of a circular beam at a certain point where the
intensity drop to a fraction of its maximum value. The common definitions
are 1/e (0.368) and 1/e2 (0.135) of the maximum value.
- Beam Divergence
- Angle of beam spread, measured in (milli)radians. Can be approximated for
small angle by the ratio of the beam diameter to the distance from the laser
aperture.
- Black Body Radiation
- Any object surface can radiate heat to and receive heat from outside, if
an object can absorb all the incident radiation, regardless of the frequencies
and directions, this object is called Black Body. A ball cavity with a small
hole can be regarded as a black body, since any radiation entering the ball
cavity can only reflect inside it, thus totally absorbed.
- Brightness
- The brightness of a light source is defined as the power emitted per unit
surface area per unit solid angle.
- Coherence
- Coherence can be devided into spatial and temporal coherence. For any em
wave, if at time t=0 and t0 the phase diference between two points in space
remains the same, we say the em wave has spatial coherence; If at a point
P, the em wave at t and t+dt has same phase difference if dt is the same,
temporal coherence exists.
- Composite
- A "matrix" and an additional phase or additional phases consisting
of particles, whiskers, fibres or any combination thereof, present for a specific
purpose or purposes.
- DOF
- The depth of focus is the distance over which the focussed beam has about
the same intensity, it is defined as the distance over which the focal spot
size changes -5%~5%.
- Electronic assembly
- A number of electronic components (i.e., "circuit elements", "discrete
components", integrated circuits, etc.) connected together to perform
(a) specific function(s), replaceable as an entity and normally capable of
being disassembled.
- Evaporative Laser Cutting
- Evaporative laser cutting is the laser cutting process that target material
is ablated through direct vaporization, typical applications are laser cutting
of low vaporization temperature and low thermal conduction materials.
- Excimer Lasers
- Lasers which use the noble gas compounds for lasing. Excimer lasers generate
laser light in ultraviolet to near-ultraviolet spectra, from 0.193 to 0.351
microns. Gas Laser A laser in which the active medium is gas. The gas can
be composed of molecules (like CO2), Atoms (like He-Ne), or ions (like Ar+).
- Laser Fusion cutting
- Laser fusion cutting is laser cutting through melting and gas jet blowing.
- Ground State
- Lowest energy level of an atom or molecule.
- Heat Affected Zone
- Heat affected zone is the region close to the laser irradiated area that
obvious temperature change from original area happens, or obvious strain state
change happens.
- Hologram
- An interference phenomena captured on a plate (or film). It can contain
enormous amount of information and a 3 dimensional image can be constructed
from it.
- Knudesen layer
- In laser processeing, strong evaporation occurs. The gas near the phase
interface is not in translational equilibrium and the translational equilibrium
is achieved within a few mean free paths by collisions between particles in
a thin region. This region is called Knudsen layer
- Laser
- Laser is the acronym of Light Amplification by Stimulated Emission of Radiation.
Laser is light of special properties, light is electromagnetic (EM) wave in
visible range. Lasers, broadly speaking, are devices that generate or amplify
light, just as transistors generate and amplify electronic signals at audio,
radio or microwave frequencies. Here light must be understand broadly, since
lasers have covered radiation at wavelengths ranging from infrared range to
ultraviolet and even soft x-ray range.
- Laser machining
- Laser machining is material removal accomplished by laser material interaction,
generally speaking, these processes include laser drilling, laser cutting
and laser grooving, marking or scribing.
- Laser Mode
- Laser mode is the possible standing em waves in laser cavity.
- Longitudinal (Axial) Modes
- Axial standing em waves within the laser cavity.
- Laser Resonator or Laser Cavity
- The optical mirrors, active medium and pumping system form the laser
resonator, which is also called Laser Cavity. Laser cavities can be divided
into Stable Cavities and Unstable Cavities according to whether they make
the oscillating beam converge into the cavity or spread out from the cavity.
- Linewidth
- The linewidth of laser is the width of laser beam frequency. Laser linewidth
is much narrower than normal light.
- Liquid Laser
- Lasers which use large organic dye molecules as the active lasing medium.
- M2 of the beam
- M2 is a beam quality index that measures the difference between
an actual beam and the Gaussian beam.
- Matrix
- A substantially continuous phase that fills the space between particles,
whiskers or fibres.
- Marangoni Mechanism
- Liquid surface force due to temperature gradient (thermal) or composition
gradient (chemical)
- Microcircuit
- A "monolithic integrated circuit" or "multichip integrated
circuit" containing an arithmetic logic unit (ALU) capable of executing
a series of general purpose instructions from an external storage. N.B.1:
The "microprocessor microcircuit" normally does not contain integral
user-accessible storage, although storage present on-the-chip may be used
in performing its logic function. N.B.2: This definition includes chip sets
which are designed to operate together to provide the function of a "microprocessor
microcircuit".
- Multichip
- A "integrated circuit" where two or more "monolithic integrated
circuits" bonded to a common "substrate".
- Mode Locking
- A method to create very short laser pulses. It makes the phase difference
of many modes (frequencies) in the laser cavity fixed, or locked, thus very
narrow pulses (in time) are created.
- Mushy region
- Phase changes happen over a temperature region in general, thus solid and
liquid state coexist during phase changes. The region of this mixture of solid
and liquid is called Mushy region.
- Photon
- The minimum quantity of light energy that can be exchanged is called a light
quantum or photon.
- Polarized Light
- If the light has a dominant direction of the E vector, we say the light
is polarized. Natural light is not polarized, while laser beam is polarized.
Polarization can be created and adjusted by polarizer.
- Population Inversion
- Normally the number of atoms at high energy level(E1) is less than those
in low energy level(E1), N2(E2) < N1(E1). If N2>N1, we say population
inversion exists, which is a necessary condition for lasing.
- Pumping
- The process to raise atoms from lower level to upper level is called pumping.
- Q-Switching
- A method to create laser pulses. It modualates the Q (Quality) of laser
cavity to build population inversion first, then release the accumulated energy
suddenly, in this way high energy pulses can be created.
- Recombination Radiation
- In semiconductors, when the electrons combine with the holes, photons are
emitted, this is called Recombination Radiation.Semiconductor Lasers
are based on this mechanism.
- Resolution
- The least increment of a measuring device; on digital instruments, the least
significant bit. (Reference: ANSI B-89.1.12)
- Solid State Laser
- A laser in which the active medium is in solid state (usually not including
semiconductor lasers).
- Semiconductor Lasers
- Lasers which use semiconductor as active medium. The majority of semiconductor
materials are based on a combination of elements in the third group of the
Periodic Table (such as Al, Ga, In) and the fifth group (such as N, P, As,
Sb) hence referred to as the III-V compounds.
- Spontaneous Radiation
- According to quantum mechanics, the electrons of atoms can take different
energy states, say E1, E2, E3, etc., E1<E2<E3<…. Lower energy
level is more stable than higher energy levels, so electrons at high energy
levels tend to decay to low energy levels, the energy difference between the
two levels can be given out as electromagnetic radiation. This process is
called Spontaneous Radiation.
- Stable Cavity and Unstable Cavity
- Cavities can be identified as stable or unstable according to whether they
make the oscillating beam converge into the cavity or spread out of the cavity,
if converge it is stable, if spread out, it is unstable.
- Stimulated Absorption
- When the atoms at lower energy levels absorb the incident energy with corresponding
frequency, they jump to upper level states, this is called Stimulated Absorption.
- Stimulated Emission
- Under the action of the incident electromagnetic field with the corresponding
frequency, the atoms at upper level have a certain possibility to jump to
the corresponding lower levels, emitting electromagnetic waves or photons
with the same frequency, direction and phase with the incident waves. This
process is called Stimulated Emission.
- Substrate
- A sheet of base material with or without an interconnection pattern and
on which or within which "discrete components" or integrated circuits
or both can be located.
- Superalloy
- Nickel-, cobalt- or iron-base alloys having strengths superior to any alloys
in the AISI 300 series at temperatures over 922 K (649º C) under severe
environmental and operating conditions.
- TEM Mode
- Transverse Electromagnetic Mode (TEM) of laser beam is called TEM mode.
Three index are used to indicate the TEM modes. TEMplq, p is the number of
radial zero fields, l is the number of angular zero fields, q is the number
of longitudinal fields.
- YAG
- yttrium/aluminum garnet
- Ultrashort Pulsed Laser
- Laser whose pulse duration time is very short, below 1 ns, usually in the
fs scale.