- Dual surface reflector for equalizing S & P polarization
- The two planes of reflection are orthogonal
|
 |
| Single Surface Poloration Problems |
| A single surface reflection at 45° is often used to sample a
laser beam for profile measurements or for monitoring power or energy. However,
as shown, at 45° a single surface reflects the S polarization component
at more than 10 times the reflection of the P component. Depending on the
laser polarization content, or stability, this sampling can provide very
misleading and unreliable measurements. (The BT-I-YAG has both surfaces
A/R coated for 1064nm so the reflection for both polarizations is equal
at 0.5%. At other wavelengths far from 1064nm the above discussion applies.) |
| Equalizing S & P reflected polarization |
 |
| Any arbitrary polarization component can be broken into equivalent
S & P components. With complimentary sampling surfaces any given component
gets reflected once as the S polarization, and the second time as the P
polarization. Thus using 2 surfaces, the total reflected energy for all
polarization components is the sum of the S reflectance and the P reflectance.
This causes the sampled beam to have S & P components that are identical
to the original beam. |
| Beam path through beam tap |
| The Beam Tap II uses two reflecting surfaces such that the two planes
of reflection are orthogonal. The standard Beam Tap I rear surface is AR
coated form 250-700nm. |
| |
 |
This diagram shows the 6mm offset of the through
beam that is created by the reflecting optic. The deflection angle
of the output beam is less than 0.007 degrees. The rear surface of
the flat is AR coated to maximize the throughput of the main beam.
The standard Beam Tap II rear surface is AR coated for 400nm-700nm.
The YAG version is AR coated for 1064nm on both surfaces. |
|
| Beam tap relection vs wavelength |
| Shown is the Beam Tap II final sampled reflection vs. wavelength.
As shown both the S & P reflection are nearly constant at 0.05%
from the UV to the infrared. |
| |
| Ordering Information |
| Model |
Surface |
Wavelength range |
Optical Material |
Reflection |
P/N |
| BT-I |
Single surface, 1 cube |
250-700nm |
UVFS |
4% Ravg |
SP90135 |
| BT-II |
Dual surface, 2 cubes |
400-700nm |
UVFS |
0.16% Ravg |
SP90133 |
| BT-I-YAG |
Single surface, 1 cube |
1064nm |
BK7 |
0.5% Ravg |
SP90173 |
| BT-II-YAG |
Dual surface, 2 cubes |
1064nm |
BK7 |
0.0025% Ravg |
SP90172 |
|
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Beam Tap I & II
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