Didymium Absorption Spectrum - Physics Demonstrations - Didymium Absorption Spectrum | Physics Undergraduate Labs

Sodium lamps produce intense light. Use appropriate shielding and instruct students not to stare directly at the lamp. The diffraction gratings safely reduce intensity while dispersing the spectrum.

Purpose

Didymium glass absorbs the yellow sodium D-lines, dramatically dimming a sodium lamp from bright yellow to a faint purple glow. With white light, the glass removes green and yellow bands from the continuous spectrum. Students see direct evidence that atoms absorb at the same wavelengths they emit.

$Composite image: top-left shows bright yellow sodium lamp, top-right shows yellow spectral line through diffraction grating, bottom-left shows faint purple glow of sodium lamp viewed through didymium glass, bottom-right shows the spectral line nearly eliminated$

Figure 1: Sodium lamp without (top) and with (bottom) didymium glass. The glass absorbs the dominant yellow D-lines, leaving a dim purple glow and nearly eliminating the spectral line.

Safety Warnings

Warning: Bright Light Source

Purpose