The Q value for a laser cavity is a measure of the quality of the cavity's resonator, which determines the efficiency and stability of the laser. It is defined as the ratio of the energy stored in the cavity to the energy lost per round trip.
The Q value is calculated by dividing the total energy stored in the cavity by the energy lost in one round trip. This can be determined by measuring the output power of the laser and the round-trip time of the light in the cavity.
A high Q value indicates a high quality resonator, meaning that the energy loss in the cavity is low compared to the energy stored. This results in a more efficient and stable laser with a narrow linewidth.
The Q value can be affected by various factors such as the reflectivity of the mirrors, the size and shape of the cavity, and the materials used in the cavity. Temperature changes and mechanical vibrations can also impact the Q value.
The Q value is an important parameter for lasers as it affects the output power, stability, and spectral purity of the laser. A higher Q value allows for more energy to be stored in the cavity, resulting in a more powerful and stable laser beam.