Definition:
An attenuator is a filter coating designed to reduce the intensity of light passing through an optical system, across a specified range, whilst maintaining the integrity of the lights wavelength and polarisation.
Design and Manufacture:
At Vortex we manufacture custom attenuators between 300nm and 6000 nm to any specified transmission or reflection level.
All of our Attenuator coatings are deposited using sputter deposition technology which typically has a process energy 1000 times that of thermal evaporation. This means that the coatings are highly durable in challenging environments and very stable with temperature change. More information about this can be found below.
Applications:
Attenuators are used for the following,
- Protecting sensitive equipment such as detectors from overload and being burned out, thus prolonging the lifetime and reliability of the instrument.
- In laser systems an attenuator is a useful device for measuring the power of a laser, it can be used to send a fixed ration of the laser power onto a detector and knowing the rating of the attenuator, the power of the full beam can be determined.
- In filter wheel systems the system will normally have one detector, an attenuator can be used to moderate particularly strong signals in certain wheel positions to balance the system and give protection to the sensitive detector.


Case Studies

Spectral Balance Filters

Laser Attenuator Filters

MID IR Broadband Attenuator
Spluttering Vs Evaporation
Traditional Thermal Evaporation
- Voids in coating.
- Poor environmental performance.
- High shift with temperature change.

Open structure of traditionally evaporated coatings with gaps and voids.

Sputter Deposition
- Voids eliminated.
- Excellent environmental performance.
- Extremely low temperature shift.

Densely packed sputtered coating with no gaps
or voids.

Coating Durability:
We carry out the following MIL-C-48497A tests on samples from every coating run to ensure all coatings are durable and will stand the test of time.
Adhesion Test:
The adhesion test is an indicator of how well adhered the coating is to the substrate. The test involves pressing 3M scotch tape against the coating and then pulling it off, there should be no coating removal.
Humidity Resistance Test:
The humidity test assesses the durability of the coating when subjected to 24 hours humidity. The filter is exposed to 95% relative humidity, there should be no delamination or damage to the coating or change in optical performance. Sputtering deposition is key to ensuring high levels of durability and physical integrity in humid environments.
Mild Abrasion Test:
The mild abrasion test evaluates the resistance of the coating to surface wear. The filter is subjected to the 50 cycles of dry rubbing with a loaded cheesecloth abrader tool. After cleaning there should be no change in appearance or coating performance. This test helps determine the filter’s ability to withstand everyday handling.
Severe Abrasion Test:
The severe abrasion test is similar to the mild abrasion test but involves 10 cycles of rubbing with a more aggressive abrader, again after cleaning the coating should show no damage or change in performance. This test is particularly important for filters used in tough environments or applications with high mechanical stress.
Cleanability Test:
The cleanability test assesses the ease of cleaning the filter surface with a range of lab standard cleaning agents such as acetone and isopropanol. In assembly filters and coatings will require cleaning, the test helps ensure the filter is comfortable with this type of handling.
Water Solubility Test:
Surviving 24 hours in water without deterioration ensures the coating is also suitable for cleaning with water-based cleaning agents without compromising performance.