Gradient Filters

Circular & Linear Variable Neutral Density Filters

Variable ND Filters:

• Attenuates light by rotation or translation
• Attenuate large apertures by counter rotating two wheels
• Filters are neutral
  • Work over wide wavelength range
• 10% to 35% absorption from metal materials
• Good for low power applications
  • limited by metal coating materials
• Limited distributions at about 4 orders of magnitude

Circular Variable Neutral Density Filters

The circular variable neutral density filter (ND Filter) wheel is a device to linearly attenuate light as the filter is rotated. The filter can be used for white light as well as for lasers. A large finite aperture can be attenuated by counter rotating two filters in series. Sizes are available from 25 mm to over 200 mm in diameter. The usable wavelength range is from 200nm to 15.0 microns.

Linear Variable Neutral Density Filters

The linear variable neutral density filter (ND Filter) is used to attenuate light as the filter is translated. The filters can be used with white light as well as with low power lasers. A large finite aperture can be attenuated by translating two filters in opposite directions. The usable wavelength range is from 200nm to 15.0 microns. The filters are available in lengths from 5mm to over 200mm. These filters are more sensitive to position at lower density values than are linear transmission filters.

Circular & Linear Apodizing Filters

Apodizing Filters: Applications and general characteristics:

• Eliminates diffraction patterns
  • Reduced transmission at the center will favor performance at high frequencies
  • Reducing transmission at the edge will favor low frequency performance
• Corrects for non-uniformity in illuminations systems
• Changes a Gaussian Distribution to a Top Hat Distribution
• Eliminates detector saturation when using an iris aperture
• 10% to 35% absorption, depending on coating materials
• Good for low power applications
  • Limited by metal coating materials
• Produce almost any distribution
  • There is a limit below 1mm in size

Bullseye^® Apodizing Filters

Bullseye^® Apodizing Filters are a part of the Bullseye^® apodizer line of customizable gradient filters. The Bullseye^® Apodizing Filters are used to eliminate undesirable intensity variations in optical systems. The density of the filter can either decrease or increase radially from dark to light or from light to dark.

The density of the Bullseye^® Apodizing Filter decreases radially from a dark center, where light is usually at its peak intensity, to the outside edge, where it can become completely transparent.

The density of the Bullseye^® Apodizing Filter can also increase in the radial direction from a light center to the outside edge towards the center.

Linear Apodizing Filters

Linear Apodizing Filters are one type of Reynard Corporation’s full line of Apodizing filters. These filters have a static coating in one direction and a variable coating in the other direction that changes on either side of a central line. The filters can be specified for changes in terms of either density or transmission.

There are two basic types: Clear in the center to dark on the edge, and dark in the center to clear on the edge. The variable function of these filters is customer defined to meet specific requirements.

The function can be defined in most any manner, from a set of data points to full algebraic functions that represent Gaussian, exponential, polynomial, or linear changes.

Apodizing filters can be designed to work in the UV, visible, and out to the Far IR for either narrow band or wide band applications.

Depending on the application requirements, apodizing filters can be made with metal coating materials for multi-wavelength variable transmission needs, or with all-dielectric coating materials for narrow, single-wavelength requirements.

The filters can be supplied with Anti-reflection coatings on one or both sides to maximize transmission.

Variable Circular & Linear Phase Plates

Variable Phase Plates: 

• Generally used for narrow band or laser applications
• Little or no absorption from dielectrics materials
• Good for high power applications
  • Dielectric materials
• Can produce almost any distribution
  • Similar to Apodizing Filters
• Current size limitation
  • Up to 8" diameter for circular plates
  • Up to 6" long for linear plates
• Working wavelengths range is 200nm to Far IR

Others:

• Arch Segments
• Comb Gradient Filters
• Fine Comb Gradient Filters
• Photolithography Step Filters
• Gradient Step Filters

*All filters can be supplied to work from the UV to the Far IR

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Reynard Corporation operates per Military Specification MIL-PRF-13830B and MIL-I-45208A.