Source: ResearchGate

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Understanding Single-mode Operation in Lasers

Single-mode Operation Explained

Single-mode operation in lasers can refer to two main concepts:

Single-Transverse-Mode Operation

When a laser operates in a single transverse resonator mode, typically a Gaussian mode, it is said to be in single-transverse-mode operation. This results in diffraction-limited beam quality. However, the laser may still oscillate on multiple axial (longitudinal) modes with similar transverse shapes but different optical frequencies.

Single-Longitudinal-Mode Operation

In some cases, single-mode operation refers to operating on a single resonator mode, often a Gaussian axial mode. This is known as single-longitudinal-mode or single-frequency operation, where the laser emits a single frequency with a small linewidth.

Factors Affecting Operation Modes

The number and type of resonator modes in a laser depend on various factors:

• Excitation of higher-order transverse modes can be avoided by pumping only the volume covered by the axial modes.
• Multiple axial modes may still be excited if the gain bandwidth exceeds the axial mode spacing.
• Single-frequency operation is more challenging due to factors like mode competition and inhomogeneous saturation.

Challenges and Solutions

Achieving single-frequency operation is more complex than single-transverse-mode operation. Spatially varying loss or gain alone is not sufficient; challenges include reducing mode competition and addressing issues like spatial hole burning.

Conclusion

Understanding single-mode operation in lasers involves grasping the distinctions between single-transverse-mode and single-longitudinal-mode operation. Overcoming challenges in achieving single-frequency operation requires addressing factors that impact mode competition and laser performance.

Source: Ansys Customer Center
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