A laser cavity, also known as an optical cavity or resonator, is a fundamental component of a laser system. It is a confined region or space where light undergoes multiple reflections, leading to the amplification of coherent light. The laser cavity consists of mirrors that form the boundaries of the cavity, and it plays a crucial role in sustaining the laser action.
Key components and characteristics of a laser cavity include:
Mirrors: A laser cavity typically includes two mirrors, one highly reflective (called the rear or output mirror) and the other partially transparent (called the output coupler). The mirrors are positioned facing each other, forming the optical cavity.
Gain medium: The gain medium is a material placed between the mirrors that amplifies light through stimulated emission. Common gain media include gases (in gas lasers), liquids (in dye lasers), or solid-state materials (in solid-state lasers).
Amplification: When light passes through the gain medium, it undergoes stimulated emission, producing more photons of the same wavelength and direction. The photons bounce back and forth between the mirrors, undergoing further amplification with each pass.
Feedback: The mirrors provide optical feedback, allowing only specific wavelengths to be amplified and constructively interfere. This feedback is essential for the generation of a coherent and collimated laser beam.
Mode structure: The laser cavity supports specific modes or resonant frequencies of the laser light. The modes depend on the cavity's dimensions and the distance between the mirrors.
Q-factor: The quality factor (Q-factor) of the cavity is a measure of how well the cavity can store energy. A higher Q-factor results in a more stable and narrow linewidth laser.
The laser cavity is responsible for confining and amplifying light, creating a population inversion within the gain medium, and producing the coherent and monochromatic output characteristic of laser light. The choice of cavity design, mirror coatings, and gain medium depends on the specific requirements of the laser system and its intended applications.