Achieving and maintaining narrow linewidth in lasers is a complex task, hindered by several factors:

Technical Challenges

Noise: Laser linewidth is broadened by various noise sources, including spontaneous emission, thermal fluctuations, and mechanical vibrations. Suppressing these noise sources requires sophisticated engineering and isolation techniques.  

Cavity Stability: The laser cavity's physical dimensions and alignment must be extremely stable to prevent frequency fluctuations. This necessitates precise manufacturing and environmental control.

Frequency Stabilization: Active feedback mechanisms are essential to counteract environmental disturbances and maintain a stable laser frequency. Developing robust and efficient feedback systems is challenging.

Material Limitations: The properties of laser gain media can limit the achievable linewidth. Finding suitable materials with low noise characteristics and wide gain bandwidth is ongoing research.

Cost and Complexity

High Manufacturing Costs: The precision engineering required for narrow linewidth lasers often results in high production costs, limiting their accessibility in some applications.

Complex Integration: Incorporating narrow linewidth lasers into systems can be challenging due to their sensitivity to environmental factors and the need for precise alignment and control.

Performance Limitations

Trade-offs: Improving linewidth often comes at the expense of other laser parameters, such as output power, efficiency, or tunability. Balancing these factors requires careful design and optimization.

Environmental Sensitivity: Narrow linewidth lasers are susceptible to temperature variations, vibrations, and electromagnetic interference, which can degrade performance.

Overcoming these challenges requires continuous advancements in laser technology, materials science, and control engineering. As research progresses, we can expect further improvements in narrow linewidth lasers and their integration into a wider range of applications.