Source: De Gruyter

The Concept of Multipass Amplifiers in Optics

Introduction

In the field of optics, the gain medium of an optical amplifier can only achieve a limited amount of gain. To overcome this limitation, the concept of multipass amplifiers has been developed. A multipass amplifier involves multiple passes of light through an amplifier, enabling a much higher gain to be obtained compared to single-pass amplifiers.

Working Principle of Multipass Amplifiers

Multipass amplifiers are typically based on a laser crystal that can be end pumped or side pumped. These amplifiers contain multiple laser mirrors that fold the signal beam path, allowing it to undergo several passes through the crystal. The beams corresponding to different passes are usually slightly angled to ensure they remain well separated within the crystal.

Benefits of Multipass Amplifiers

By utilizing multiple passes through the crystal, a multipass amplifier can significantly increase the overall gain of the system. The gain in decibels can be estimated by multiplying the number of passes with the single-pass gain. Additionally, multipass amplifiers help in reducing the effective saturation energy, especially in cases of small overall gain.

Challenges and Considerations

Designing and aligning a multipass amplifier system can be a complex task, especially when arranging a large number of passes with beam directions that do not lie in a single plane. Factors such as thermal lensing, nonlinear effects, and beam divergence need to be carefully considered and mitigated using focusing optical elements in the setup.

Regenerative Amplifiers

A regenerative amplifier is a special type of multipass amplifier where multiple passes are achieved using an optical switch instead of a geometric beam path. This method is particularly useful for generating very high overall gain in ultrashort pulse applications.

Conclusion

Multipass amplifiers play a crucial role in optical amplification systems by enabling higher gains and improved performance compared to single-pass amplifiers. Understanding the principles and considerations of multipass amplifiers is essential for designing efficient and effective optical amplifier systems in various applications.

Source: De Gruyter
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