URA Flexibility: PMT Window Coating

 

Just Another Big, Bulky Sample

Sample – The coated window material of an intact photo-multiplier tube, viewed end-on
There are many “real world” coatings that do not reside on nice flat one inch sized substrates. Many modern quality control specular reflectance samples are the finished manufactured part.
The picture at left shows such a sample.
The placement of this type of large sample on the Universal Reflectance Accessory is shown in the bottom left picture. Since the sampled area is flat and covers the entire beam entry aperture, there is no need for additional light cover. There spectra of the window coating are shown at bottom right. The PMT contents behind the window are far enough removed from the window (1 cm) so as not to interfere.

Sample Preparation
1) Sample is placed on the URA stage with the coated side contacting the opening in the sample stage.
2) The internal Common Beam Depolarizer was used to prevent polarization artifacts at incidence angles higher than 20 degrees.
Placement of the sample on the URA accessory is seen below.

Sample on URA

The spectral results of  an angular study of the reflectance of the PMT widow coating is seen below.

URA Specular Reflectance Results

Conclusion: The design of the URA , with it’s gravity held sample placement and lack of either width or height obstructions, makes it the reflectance accessory of choice for large, bulky, irregular shaped samples. For more info go to http://www.perkinelmer.com

Haze Measurements

In materials characterization, haze is often as important as color in the quality control of manufactured products. The term haze refers to the visual clarity of a material. The historical evaluation for haze was simply visual, where the operator would hold a piece of the material up to a bright light and check for cloudiness The presence of haze can either be wanted or unwanted. For example, the clear plastic panels which cover the LED’s of an instrument display are intentionally hazy. In other materials, however, the level of haze is tightly controlled, such as, for example, in the polymer sheets which are layered in between automotive glass.
A standard UV/Vis spectrophotometer fitted with an integrating sphere accessory can accurately measure haze. A % haze calculation is quite easy to perform on a Lambda UV/Vis spectrophotometer fitted with one of the Labsphere™ integrating sphere accessories
The procedure is described in the ASTM 1003-92 “Standard Method for Haze and Luminous Transmittance of Transparent Plastics” The procedure involves acquiring four transmission scans of the sample from 780 to 380 nm, each with a different configuration of the integrating sphere, integrating the area under each curve, and plugging the values into the following equation…
Haze = [(T4/T2) - (T3/T1)] x 100%
where T1 through T4 are changing configurations of the sample placement on the sphere.

First measurement: Background Correction T1

 

The Second Measurement T2

    

The Third Measurement T3

    

The Fourth Measurement T4

The figure below displays example spectra for these four haze component measurements made on a clear polymer sheet sample.

The areas for the entire spectral range is calculated and the data is processed in an Excel spreadsheet.

% Haze = [(T4/T2) - (T3/T1)] x 100%
      = [(1940/11781) – (0.194/40000)
      =[(0.1647 – 0.00000485)]
      = 16.47 %

Calculation of % haze is also part of the PerkinElmer Architectural Glass Software package.