mode hopping

Mode hopping in the context of lasers refers to a phenomenon where a laser system abruptly switches from one longitudinal mode to another. In a laser, different longitudinal modes represent distinct allowed frequencies or wavelengths of the laser cavity. These modes are the specific solutions to the laser cavity's resonant conditions.

Several factors can contribute to mode hopping in a laser system:

Temperature changes: Variations in temperature can affect the refractive index of the laser gain medium, altering the resonance conditions and causing the laser to switch between modes.

Mechanical vibrations: External mechanical vibrations or acoustic noise can disturb the stability of the laser cavity, leading to mode hopping.

Changes in pumping conditions: Variations in the pumping conditions, such as changes in the pump power or pump beam profile, can influence the gain distribution within the laser cavity and trigger mode hopping.

Optical feedback: Optical feedback, especially from external surfaces or reflections within the laser system, can affect the laser cavity's resonance conditions and contribute to mode hopping.

Nonlinear effects: Nonlinear optical effects within the laser cavity, such as four-wave mixing, can sometimes lead to mode hopping.

Mode hopping can be undesirable in certain applications, especially when a stable and single-frequency laser output is crucial. It can lead to fluctuations in the laser output power, frequency, or both, impacting the laser's performance and stability. Techniques such as active stabilization methods or external cavity designs may be employed to minimize mode hopping and maintain a more stable laser output.