Optical Materials For Spectroscopy
|
Window
Material |
Useful Range
cm-1 |
Useful Range
microns |
Refractive
Index at 2000cm-1 |
General Properties
|
|
MgF2
|
91,000-1,100
|
0.11-9.09
|
1.37
|
Almost insoluble in water. Hard material suited to relatively high pressure applications. Bi-refringent and subject to thermal shock. Should not be used above 500°C.
|
|
LiF
|
83,000-1,200
|
0.12-7.14
|
1.33
|
Slightly water soluble. Hard, brittle material. Subject to thermal shock. Should not be used above 400°C.
|
|
CaF2
|
77,000-900
|
0.13-11.11
|
1.40
|
Insoluble in water, resists most acids and alkalis. Soluble in ammonium salts. Its high mechanical strength makes it particularly useful for high pressure work. Sensitive to mechanical and thermal shock. Does not fog.
|
|
BaF2
|
66,666-800
|
0.15-12.5
|
1.45
|
Insoluble in water, soluble in acids and NH4Cl. Very sensitive to mechanical and thermal shock. Good resistance to fluorine and fluorides. Does not fog.
|
|
NaCl
|
40,000-600
|
0.25-16.67
|
1.52
|
Soluble in water and glycerine. Slightly soluble in alcohols. Fair resistance to mechanical and thermal shock and can be easily polished.
|
|
AMTIR
|
11,000-725
|
0.91-13.79
|
2.50
|
Amorphous Material which Transmits Infrared Radiation. A chalcogenide glass which although relatively hard is brittle. Insoluble in water, resistant to acid but attacked by alkalis.
|
|
AgBr
|
22,000-300
|
0.45-33.33
|
2.30
|
Insoluble in water, soluble in acids and NH4CL. Very sensitive to mechanical shock and is malleable. Will cold form. Good resistance to thermal shock. Corrosive to metals and alloys. Sensitive to strong UV radiation and will darken with long exposure.
|
|
KCl
|
33,000-400
|
0.30-25.00
|
1.47
|
Hygroscopic material similar to NaCl but with extended transmission range. Less soluble an lower reflection losses.
|
|
KBr
|
43,500-400
|
0.23-25.00
|
1.54
|
Hygroscopic material similar to NaCl. Soluble in water, glycerine and alcohols. Slightly soluble in ether. Fairly good resistance to mechanical and thermal shock.
|
|
KRS-5
|
17,000-250
|
0.59-40.00
|
2.38
|
This material is a mixture of Thallium Bromide and Thallium Iodide salts and is extremely toxic. Orange/red in colour. Slightly soluble in water, soluble in bases, but not soluble in acids. Not hygroscopic. Good transmission range and is ideal for ATR work. Soft, hence easily deformed.
|
|
CsBr
|
42,000-250
|
0.24-40.00
|
1.66
|
Hygroscopic material. Soluble in water and acids. Soft, hence easily deformed.
|
|
CsI
|
42,000-200
|
0.24-50.00
|
1.74
|
Extremely hygroscopic material. Soluble in water and alcohols. Useful because of wide transmission range. Mildly toxic.
|
|
Silica SiO2
UV Grade IR Grade |
59,000-3,700
40,000-3,000 |
0.17-2.70
0.25 - 3.33 |
Both
1.46 at 20,000cm-1 |
Resistant to acids and alkalis and unaffected by most solvents. Transmission at 50,000cm-1 is 98% for UV grade and 40% for IR grade
|
|
ZnS
(CLeartran) |
50,000-770
|
0.20-12.99
|
2.25
|
Insoluble in water, normal acids and bases and virtually all organic solvents. Reacts to strong oxidising agents. Good resistance to thermal and mechanical shock. Suitable for work in temperature range -200°C to 800°C.
|
|
ZnSe
|
20,000-500
|
0.50-20.00
|
2.43
|
Toxic, hard and brittle material. Amber/yellow in colour. Insoluble in water, but attacked by strong acids and bases (pH range 4 to 11 tolerant). Organic solvents have no effect. Ideal for ATR work. Low absorption at 10.6microns hence popular window material for CO2 lasers.
|
|
Ge
|
5,000-550
|
2.00-18.18
|
4.01
|
Hard and very brittle material. Is temperature sensitive and loses transmission when heated. Optically opaque at 190°C. Insoluble in water. Soluble in hot sulfuric acid and aqua regia. Suitable for ATR work where high pressure contact is not required.
|
|
Diamond
|
40,000-10
|
0.25-1,000
|
2.40
|
Very hard and extremely chemically resistant. The type IIA diamond is often chosen for high pressure applications. Excellent for ATR work.
|
|
Si
|
8,333-33
(not continuous) |
1.20-303.00
|
3.42
|
Very hard, but brittle and relatively inert material. Is attacked by a combination of HF and HNO3. Withstands thermal shock. Useful for Far IR in the region 400-30cm-1.
|
|
Polyethylene
|
625-4
|
16.00-2,500
|
1.52
|
Inexpensive Far IR window material. Insoluble in water but tends to swell and be contaminated with some organic solvents. Melting point 110°C.
|
|
TPX
|
50-4
|
200-2,500
|
1.43
|
Similar material to polyethylene for Far IR work, but has advantage of being transparent in the visible region.
|
|
Sapphire (Al2O3)
|
40,000-1,667
|
0.25-6.00
|
1.76
|
Material is generally recognised to be safe. Resistant to strong acids and bases. Very durable and withstands high temperatures and pressures.
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