A laser resonator, also known as an optical resonator, is an essential component of a laser system. It is designed to provide the necessary feedback and amplification of light to generate a coherent and powerful laser beam.

The laser resonator consists of two mirrors placed at either end of the laser’s active medium, which could be a solid, liquid, or gas. One mirror is fully reflective (high reflector or HR mirror), while the other mirror is partially reflective (output coupler mirror). The mirrors are carefully aligned to form an optical cavity or resonant cavity.

When energy is supplied to the laser medium, it stimulates the emission of photons. These photons bounce back and forth between the mirrors, repeatedly passing through the laser medium. As they interact with the medium, more photons are generated through stimulated emission, resulting in the amplification of the light.

The resonator’s function is twofold:

1. Feedback: The fully reflective mirror reflects most of the light back into the laser medium, ensuring that the photons keep circulating within the resonator. This feedback allows for the amplification of the light and the build-up of coherent waves.
2. Output Coupling: The partially reflective mirror allows a small portion of the laser light to escape from the resonator. This escaping light forms the laser beam that is utilized for various applications.

The combination of amplification and feedback within the resonator enables the laser to produce a high-intensity, monochromatic, and coherent beam of light. The properties of the laser beam, such as its wavelength, intensity, and spatial characteristics, are determined by the design and characteristics of the laser resonator.

It’s worth noting that laser resonators can have different configurations, such as plane-parallel, hemispherical, or ring-shaped, depending on the specific laser system and its intended application.