Which of the following describes the frequency of a LASER?

The frequency of a LASER (Light Amplification by Stimulated Emission of Radiation) is fundamentally determined by the energy difference between the excited and ground states of the electrons in the material being used. This is based on the principle that when electrons transition between energy levels, they emit or absorb photons at specific frequencies that correspond to those energy differences.

Thus, the frequency of a LASER is closely tied to the properties of the gain medium—such as whether it is a gas, liquid, or solid—and the specific atomic or molecular transitions that are possible within that material. This characteristic makes the frequency essentially fixed based on the material employed in the LASER system.

Other options suggest variability or adjustability that does not accurately reflect how laser frequency is inherently defined by its physical properties. In practical terms, while you can select different gain materials to achieve lasers of various frequencies, within a specific LASER device, the frequency remains constant for that particular configuration.