Crystals and Crystal Growth

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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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