False spectra from a plane grating produced by laser illumination.

Area of Science:

• Optics and Spectroscopy
• Diffraction Gratings

Background:

• Intense coherent illumination can generate spurious spectral lines, termed false spectra or Rowland ghosts.
• Understanding the formation and characteristics of these ghosts is crucial for accurate spectral analysis.

Purpose of the Study:

• To explain the formation and location of Rowland ghosts using a geometrical scheme.
• To determine the limitations on the number of ghosts produced by a spectral line.
• To experimentally validate Rowland's formula for calculating ghost wavelengths.

Main Methods:

• Utilized a well-established geometrical scheme to model ghost formation.
• Applied Rowland's formula for calculating ghost wavelengths.
• Conducted experiments using a pulsed ruby laser as the coherent light source.

Main Results:

• The geometrical scheme demonstrates a finite number of ghosts per spectral line.
• The number of ghosts is consistent for both blazed and unblazed grating regions.
• Extreme Rowland ghosts were experimentally recorded at 1336.9 Å and 10761.5 Å.

Conclusions:

• The number of Rowland ghosts is limited and predictable based on grating geometry.
• Rowland's formula accurately predicts ghost wavelengths, especially for those distant from the parent line.
• Experimental verification confirms the theoretical predictions for false spectra generation.