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Raw Calcite |
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The selection of calcite to be used on
optical components is no simple process. When mining it is necessary
to recognize the portion of the material which has optical quality,
usually just a small part of the vein. The internal part of the
calcite is then searched for defects and to define how the crystal
will be cut. The size of the usable crystals varies widely, reflecting
on the yield for prism manufacture.
Our crystals are extracted from the deposits
of our own, assuring the best quality through a careful selection
of calcite pieces. Thanks to the quality of the deposits we may
supply raw calcite on a variety of sizes going from very small
rhombs to crystals with more than 10cm size.
The following table gives an idea of the typical dimensions of
raw calcite pieces that can be mined, helping with the selection
of type and quality.
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Raw
Calcite Selection Guide
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Grade
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Typical
Size(cm3) |
Max.Size
(cm3) |
Longest
dimension (cm) |
| IA |
400 |
560 |
10 |
| IB |
1200 |
1900 |
15 |
| IC |
1500 |
1900 |
15 |
| IIA |
1200 |
1500 |
20 |
| IIB |
1200 |
1500 |
20 |
| IIC |
1500 |
2000 |
20 |
| IIIA |
2000 |
2500 |
25 |
| IIIB |
2000 |
3900 |
25 |
| IIIC |
2500 |
4100 |
25 |
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| Polarizing
Prisms |
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| Typical
Specifications for Finished Polarizing Prisms*
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| Product |
Calcite
Grade |
1/2
(T1 + T2)>
|
Field
Angle |
Clear
Aperture
mm |
Spectral
Range (nm) |
Damage
Threshold |
Characteristics |
| Glan-Thompson
Polarizing Prisms** |
IA or IIA |
35% |
26°
or 15°
| 10x10
15x15
20x20 |
350-2500 |
1W/cm2(CW) |
Cemented,
mounted or unmounted. L/A=3:1 or 2.5:1 |
| Glan-Taylor
Polarizing Prisms** |
IA or IIA |
37% |
6°
| 10x10
20x20 |
230-2500 |
10W/cm2(CW)
20MW/cm2(1ns) |
Air-spaced,
mounted |
| Glan-Laser
Polarizing Prisms** |
IA, IIA or IIIA |
40% |
6°
| 10x10
or
20x20 |
230-2500 |
100W/cm2(CW)
300MW/cm2(1ns) |
Air-spaced
and mounted, with two escape windows
20/10 scratch&dig |
| Rochon
Polarizing Beam-Splitter Prisms |
IA or IB |
80% |
10°
| 10x10
or
20x20 |
350-2500 |
1W/cm2(CW) |
10°
nearly symmetrical beam deviation, mounted or unmounted
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| Wollaston
Polarizing Beam-Splitter Prisms |
IA or IB |
80% |
20°
| 10x10
or
20x20 |
350-2500 |
1W/cm2(CW) |
18°
extraordinary
ray deviation, mounted or unmounted
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- T1
: > 90%
- T1
T2 : <1x10-5
- 1/2
(T12+ T22)
: > 25%
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*
Some of the specs above can be changed on customer request. Unless
otherwise noted surface quality for all calcite prism polarizers
is 60/40 scratch & dig, with better than
l/8 flatness
over the useful aperture. Tolerances are ±0.2mm
on linear dimensions.
**
Maximum beam deviation is 3 arc-minutes.
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