Image:BiodegradablePlasticUtensils2.jpg

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Description

Knives, forks, and spoons made from a biodegradable starch-polyester material. The photo has been realized using the photoelasticity method, an experimental method which gets a fairly accurate picture of stress distribution even around abrupt discontinuities in a material.

When a ray of plane polarised light is passed through a photoelastic material, it gets resolved along the two principal stress directions and each of these components experiences different refractive indices. The difference in the refractive indices leads to a relative phase retardation between the two component waves.

The setup used to photograph this photo was probably composed of:

A regular light source, with a quarter-wave plate installed to polarize the emerging light
A regular photo camera, with a quarter-wave plate installed in front of the lens

Light and camera being installed and oriented in the same direction, the two quarter-wave plates were turned with the polarizing axis in the same direction.

Source

United States Department of Agriculture (link)
cropped, noise removed with a Gaussian blur in The GIMP

Date

unknown

Author

Scott Bauer

Permission

This image is a work of a United States Department of Agriculture employee, taken or made during the course of the person's official duties. As a work of the U.S. federal government, the image is in the public domain.