Which of the following is NOT one of the three lasing mediums?

• A. Gases
• B. Crystals
• C. Frequencies
• D. Diodes

Answer: (C)

In the context of lasing mediums, the correct choice is frequencies because it is not a type of medium but rather refers to the specific oscillation rates of electromagnetic waves emitted by lasers. Lasing mediums are the substances in which the process of stimulated emission occurs, and they serve to amplify light. The three primary types of lasing mediums include gases, crystals, and diodes.

Gases, such as helium-neon or carbon dioxide, provide the necessary environment for stimulated emission by the interaction of atoms or molecules. Crystals are solid materials like ruby or Nd:YAG that can also function as lasing mediums by undergoing excited state transitions. Diodes, specifically semiconductor diodes, utilize a p-n junction to create a lasing effect when electrons recombine with holes, emitting light in the process.

These mediums all play a crucial role in laser technology, whereas frequencies pertain to the characteristics of the light produced rather than being a medium itself. Understanding the distinction between lasing mediums and other concepts like frequencies is key in mastering the principles of laser function and technology.