Diffraction from a Machinist's Scale - Physics Demonstrations - Diffraction from a Machinist's Scale | Physics Undergraduate Labs

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Diffraction from a Machinist's Scale

He-Ne lasers are Class 2 or 3A devices. Never look directly into the beam or view specular reflections. The grazing angle geometry creates a bright specular reflection—ensure it does not shine toward audience seating. Use appropriate laser safety signage and inform students before activating the laser.

Purpose

A laser beam grazes a machinist's scale at a shallow angle, and the regularly spaced rulings act as a reflection diffraction grating. Students see multiple diffraction orders and can connect the grating equation to an everyday object.

$Green laser on a lab jack with beam grazing a machinist's scale, producing a vertical column of bright diffraction spots on the wall above; a ring stand rod is visible behind the setup$

Figure 1: The laser beam grazes the machinist's scale at a shallow angle, producing a vertical column of diffraction order spots on the wall. The lab jack allows height adjustment for optimal grazing angle.

Machinist's Scale

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Safety Warnings

Warning: Laser Eye Safety

Purpose