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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
Laser resonator mirrors
How are mirrors we use in bathrooms, dressing
tables etc manufactured?
Ag is deposited on glass (soft glass) through achemical reaction and silver coating is protected
by a coat of paint
Back surface of the mirror is coated so both light
incident on the mirror and reflected one has to
pass through the glass substrate
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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
Mirrors for scientific equipment1. Substrate is carefully polished; accuracy depends
on application-mirrors used in lasers arepolished to l/20
2. Front coated mirrors; coating done in a vacuum
chamber evacuated to 10-6
to 10-10
torr (mm ofHg) pressure.
3. Coating materials are Al, Au and gold for visibleregion Gold, silver, Al etc R~90%
4. Thickness monitoring normally not needed asnatural adhesion determines the coatingthickness
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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
Reflectivity requirements of laser mirrors
1. One of the resonator mirror( back mirror)
should 100% reflecting-as close to it as possible.
2. Output coupler in some lasers should be with
reflectivity of the order of 99.5%
In single atom laser mirrors with R=99.9999 or
so are needed
Both these requirements cannot be achieved
through single element coatings.
multi-layer dielectric coatings-multi million
US$ industry world over.
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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
Thin films
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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
Reflection from soap bubble
Fresnel formula for
reflection at the interface
of n1 and n2R = (n1-n2)2/(n1+n2)
2
For glass n= 1.5, air
=1 R = 4%Phase change on reflection
If n1< n2 phase changes by 180o
n1>n2 no phase change
n1n2
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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
Conditions for reflection and transmission
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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
Effect of film thickness
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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
Multilayer coatings
Computer modeling and simulations
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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
Typical BB 3 layer coating
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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
l/4 stack of HL
refractive indexmaterials.Typically 20 ormore layers cangive ~100%R
/ / h l
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LPU/PHY 803/Laser Technology Autumn Term 2010-11
Lecture on laser mirrors for internal use in LPU only
Typical deposition chamber
