This spatial filter is an elegantly simple device featuring an accessible design with precision micrometer control over pinhole placement and objective lens focus. The pinhole mount is magnetically registered against the machined faces of the non-rotating X-Y adjustment spindles. A precision-machined slot in the pinhole mount mates repeatably to the spindle face, resisting accidental motion of the mount while permitting fine adjustment. The objective lens Z-axis motion is provided by a precision linear bearing, so that focus is found and maintained without jitter or side-play. The long-travel focus adjustment accommodates virtually any objective lens. The open architecture of this spatial filter makes it especially easy to change pinholes and objectives.
The 900 (M-900) comes standard with a 900PH-25 pinhole and M-10X microscope objective. This pinhole and objective combination may not be correct for your particular application. Different objective lenses and mounted pinholes can be ordered separately (see Objective Lenses and High-Energy Pinhole Apertures). These spatial filters are designed to accommodate all M- and MV-Series Objective Lenses, the L-4X and L-50X Infinity-Corrected Objective Lenses, and 900PH-Series Mounted Pinholes. For information on how to pick the correct objective and pinhole see Spatial Filters.
Alignment
Aligning our Model 900 Spatial Filter is straightforward. Start by positioning the spatial filter assembly in the laser beam while observing the back reflections from the objective lens to bring both into alignment. To align the pinhole, first defocus the lens, then while observing the pinhole substrate, adjust the pinhole position until a faint light appears at the output. Alternate the lens Z-axis adjustment with X-Y pinhole position corrections until the best throughput and focus are achieved. This is indicated when a deliberate pinhole movement causes the symmetric output pattern to quickly disappear. A slow smear means a poor focus.
Objective lenses and mounted pinholes install easily into the positioning stage body.
Lens/Pinhole Selection Guide
|
Objective Lens |
Recommended Max.
Input Beam Diameter
( mm) |
Calculated Pinhole Diameter*
( µm) |
Recommended Pinhole Diameter
( µm) |
Recommended Pinhole |
| M-5X
or MV-5X
|
5.0 |
32.2 |
50 |
900PH-50
|
| M-10X
or MV-10X
|
5.5 |
20.9 |
25 |
900PH-25
|
| M-20X
or MV-20X
|
5.0 |
11.4 |
15 |
900PH-15
|
| M-40X
or MV-40X
|
4.0 |
5.7 |
10 |
900PH-10
|
| M-60X
or MV-60X
|
3.5 |
3.7 |
5 |
900PH-5
|
* For 1 mm diameter beam at 632.8 nm
For a tutorial on Spatial Filters see Spatial Filters.
