Reflectance Standards Kits & Accessories

Technical questions about these products?
Contact Art Springsteen: Email or (603)526-2420


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Contact Kathy Springsteen: Email or (603)526-2420

Reflectance Standards Kits

The CIE and ASTM both specify either packed barium sulfate or packed polytetrafluoroethylene (PTFE) powder as standards for the measurement of diffuse reflectance. Both powders are very close in reflectance and scattering to the 'perfect reflecting diffuser' that is the idealized model for diffuse reflectance. Avian Technologies offers kits for the accurate and reproducible fabrication of such standards. Kits are available to produce both 25 mm and 52 mm diameter standards. Barium sulfate kit is available in 25 mm size only.

The kits consist of a three part press, two calibrated cups for the production of the standards, and 500 g of either highly purified barium sulfate or PTFE powders which have been finely ground to remove lumps which may cause a reduction in reflectance from the literature reflectance values. Additional refills of the standard powders are also available. Instructions for use of the presses are included.

Part #

Description

AT-PTP-01 PTFE Standard Press Kit. Press, powder cups, and 500 g high purity optical grade PTFE powder. Produces 1" standards.
AT-PTP-02 PTFE Standard Press Kit. Press, powder cups, and 500 g high purity optical grade PTFE powder. Produces 2" standards.
AT-PTFR-500 Replacement PTFE (500 g).
AT-BRS-500 Replacement Barium Sulfate for barium sulfate presses (500 g).

Powder Cell Kits

Powder cells are useful for reflectance measurements on loose powders, crystalline materials, fiber, or other materials that are not easily compressed to pellet form. By controlling the amount of material used, a consistent packing density can be achieved, giving very reproducible results.

The powder cell set consists of a sintered or packed powder PTFE standard with a UV-grade silica window and two cells, one 3 mm deep and one 7 mm deep along with two removable silica windows. Typical reflectance data for the standard cell is provided in 5 nm intervals from 250-2500 nm Both 1" and 2" powder cell kits are available.

To use the powder cell set, the reflectance instrument is baseline corrected using the standard cell. The sample cell then replaces the standard and the spectrum run. The reflectance of the powdered sample is thus:

(reflectance of standard) x (measured reflectance of sample).

Powder cells are useful for both hemispherical and directional/directional (ie. 0/45) geometries.

Avian Technologies cells are fabricated from Delrin and are quite chemically inert. The cell bodies may be cleaned by washing with dishwashing detergent. The windows should be handled carefully but may be cleaned as would any silica or glass surface, taking care not to scratch them.

Part #

Description

AT-PC-02 2" Powder Cell Kit. 2" diameter (50.8 mm) Standard cell, 3 mm deep cell, 7 mm deep cell, Suprasil windows. Instruction sheet.

Light Traps

Light traps are an essential part of any reflectance spectrometry system. They can be used to establish the sphere zero. In reflectance, all Incident light should all hit the sample. In most sphere systems, however, due to scatter from optical components, there is a small component that hits sphere wall instead of the sample. This must be quantified. To do this, a light trap is used. Any residual light shows up as a positive reflectance value, which should be subtracted from both the sample and reference scans. Light traps are also useful in removing the transmitted component in translucent samples so that radiation cannot reflect inside the sample compartment and return to the sphere, giving erroneously high reflectance readings.

Avian Technologies offers two types of light traps. The black glass trap, modeled after the Clarke-Compton light trap designed by the National Physical Laboratory, uses a cavity with two pieces of black glass to form a semi-cone. The light enters the cavity and by multiple reflections off the black glass is absorbed. Typically, such light traps give a reflectance in the order of <0.1%. The Avian Technologies design is compact (25 mm high, 44 mm square) and can be designed to fit any sample holder configuration.

The second type of light trap offered is a simple box that has been coated with a very low reflectance diffuse coating or material. While not as efficient as the black glass trap, Avian Technologies "diffuse trap" is still highly efficient due to the use of a proprietary material that is <1.3% reflective (typical black paint is about 5%R) and highly diffuse. The overall efficiency of this trap is >99.5% (ie. <0.5%R).

Part #

Description

AT-LTRP-BG Black Glass Light Trap, Aperture 20 mm. Overall size is 35 mm x 44 mm. Efficiency >99.8% .
AT-LTRP-DC Black Light Trap, Diffuse Coating Aperture 20 mm. Overall size is 35 mm x 44 mm. Eff.>99.5% .