While generally advantageous, a very narrow linewidth can have drawbacks in specific situations:

l Increased Sensitivity to Reflections: Due to their extreme coherence, even weak reflections within the laser cavity can cause interference effects. This can distort the laser beam and affect its performance.

l Speckle Pattern Formation: The highly coherent nature of narrow linewidth lasers can lead to the formation of speckle patterns when the light interacts with a rough surface. This can be undesirable in applications like laser holography or laser displays.

l Limited Applications in High-Power Scenarios: Achieving very narrow linewidths often comes at the expense of output power. This can be a limitation for applications requiring high-power lasers.

In conclusion, narrow linewidth lasers offer exceptional control over the wavelength and coherence of light, making them invaluable tools for various scientific and technological advancements. However, it's important to consider the potential downsides depending on the specific application.