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Crystals and crystal growth-an introductory survey-
The regular surface geometry and the shiny and often colorful appearance have made
crystals from the mineral kingdom fascinating objects for everybody. Natural crystals
have often been formed at relatively low temperatures by crystallization from solutions,
sometimes in the course of hundreds and thousands of years. Some natural crystals:
Crystals Polished Fluorite Angels ChrysanthemumStone
Crystal Singing Bowls Celestite Clusters Polished flat stones Jewellery
Black
Tourmaline
Green
Tourmaline
Golden
Topaz
Pink
Tourmaline
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Clear Quartz Crystal Points Top Grade Uruguayan Amethyst Clusters
Snowflake photography
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Nowadays, crystals are produced artificially to satisfy the needs of science, technology
and jewelry. The ability to grow high quality crystals has become an essential criteria for
the competitiveness of nations.
Crystals are solids in which the elementary building blocks, the atoms, are arranged
regularly in a space lattice with specific geometrical symmetry elements. There is no
ideal atomic lattice in nature, and it would be not very useful either. Certain
imperfections of the chemical and structural atomic arrangement are essential for theusefulness and value of crystals.
The artificial crystal kingdom can be divided into three sectors:
-Technical crystals belong to one of the two big sectors of the single crystal market. They
are widely present, often in hidden form. We eat crystals (salt, sugar), we use crystals as
clocks in watches and computers (quartz), for information processing and storage
(silicon), for switching TV-sets (gallium arsenide), for telecommunication (gallium
arsenide) and for transport (turbine blades from nickel-aluminum compounds). Huge salt
crystals (CaF2) are used as UV-light lenses in the submicron structuring during electronic
device fabrication.
- Jewellery forms the second big sector of the single crystal market.
- The market of research crystals is relatively small but extremely diversified. Artificial
research crystals of high quality are the basis of solid state research activities. Natural
crystals are normally not sufficiently qualified for research purposes. Crystals are also
required for modern light and particle scattering and diffraction instruments as
monochromators and detectors. A broad range of geometrically well prepared crystals is
required for thin film, catalysis and electrochemical studies.
Some artificial crystals:
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Laser Crystals
Nd:YAG
Nd:YAG for use in industrial, medical, military andscientific applications. YAG is grown utilizing theCzochralski technique. The as-grown crystals are then
processed into laser rods or slabs, coated in house and
inspected per customer specifications.
Er:YAG
Er:YAG is a crystal with a wide pump band of 600 -800 nm. It has numerous applications in a wide range
of medical and dental applications.
Cr, Tm, Ho:YAG
Cr, Tm, Ho:YAG is a crystal material which lasers at
210nmm. This highly efficient crystal can be either flash-lamp or diode pumped and has applications in
medical, military, and meteorological fields.
Nd:YLF
Nd:YLF as a standard product and produces YLF
doped with other rare earths as required. YLF offers
an alternative to the more common YAG host for near IR operation.
Nd:YV04
Yttrium Vanadate (or orthovanadate) doped with Neodymium, Nd:YVO 4 , is a promising material for
diode pumped lasers. Several advantages over
Nd:YAG include a higher gain cross-section, lower threshold, a wider Nd absorption peak and polarized
output.
Alexandrite - ALLEXITETM
Alexandrite is the leader of a class of tunable solid-
state laser materials. Enhanced by several years of research and development, it features a broad
wavelength tuning range of 710 - 800 nm with the
capability to store and efficiently extract multijoule pulses of energy.
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Er, Cr:YSGG
YSGG (Yittrium Scandium Gallium Garnet) doped
with Chromium and Erbium provides an efficientlaser crystal for generating 2.8 micron light in an
important water absorption band.
Nd:GGG
Nd:GGG (1061nm) (Gadolinium Gallium Garnet
doped with Neodymium) for Military Laser Systems
Specialty Crystals
KTP (KTiOPO4 - Potassium Titanyl Phosphate)
KTP can be used in applications such as Harmonic
Generation for Frequency Doubling,Optical
Parametric Oscillator, Electro-optic Pockels Cells andQuasi Phase Matching.
Cr 4+:YAG (Yttrium Aluminum Garnet doped with Chromium)
Passive Q-switches or saturable absorbers providehigh power laser pulses without electro-optic Q-
switches, thereby reducing the package size and
eliminating a high voltage power supply. Cr4+:YAGis more robust than dyes or color centers and is the
material of choice for 1 micron Nd lasers.
TGG (Terbium Gallium Garnet)
Terbium Gallium Garnet (TGG) is a crystal material
for optical isolator devices. Optical isolator devices
make use of the non-reciprocal Faraday effect inTGG. The Faraday effect is the rotation of the plane
of polarization of a light beam as it is transmittedthrough a TGG crystal in the presence of an externalmagnetic field coaxial with the light.
Undoped YAG (Yttrium Aluminum Garnet)
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Undoped YAG is a substrate material that can be used
for both UV and IR optics. It is particularly useful for
applications in the 2 - 3 µm region where glasses tendto be highly absorbent due to the strong H2O band.
Co:Spinel - Cobalt Spinel - Passive Q Switch
Passive Q-switches or saturable absorbers generatehigh power laser pulses without the use of electro-
optic Q-switches, thereby reducing the package size
and eliminating a high voltage power supply.Co2+:Spinel (MgAI2O4) is the material of choice for
the important eye-safe wavelengths near 1.5 microns.
It has useful absorption that covers 1.2 to 1.6 micron
laser transitions. Spinel is a hard, stable crystal that polishes well.
Neodymium: Gadolinium Vanadate (Nd:GdVO4) Gadolinium vanadate doped with neodymium,
Nd:GdVO4, is a promising material for diode pumped lasers. Like neodymium doped yttrium
vanadate, the gadolinium vanadate exhibits a larger
absorption and emission cross section compared to
Nd:YAG
Optical Assemblies
The quality and performance of our optical components are unparalleled in the
industry.
Faraday Rotators & Optical Isolators
Laser users and designers are becoming increasingly
aware of the detrimental effects of back reflections in
their complex optical systems. Stray beams,instability and even component damage can result
from these undesirable reflections. To combat
unwanted back reflections, an optical isolator can beused.
Air-Spaced Polarizers
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Originally designed to conform to stringent military
specifications, SYNOPTICS’ Air Spaced Polarizer is
now being offered for commercial applications. TheAir Spaced Polarizer is an alternative to calcite and
Brewster-type polarizers.
Crystal growth techniques
Classifications of growth techniques based on formal expressions of the driving force for crystallization and on methods used to attain meta-stability of the mother phase.
− Growth of crystals from the melt: Czochralski (CZ), Kyropolous, Bridgman,Verneuil, Edge-defined film-fed growth (EFG), Stepanov (ST), Floating zone
(FZ) methods.
− Growth of crystal from solution: hydrothermal method, crystal growth in gels,
electro-crystallization.
− Growth in vapor phase: chemical vapor deposition (CVD), metallo-organic vapor
phase epitaxy (MOVPE), etc.
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