Impact of the Kerr effect on FM-to-AM conversion in high-power lasers

Area of Science:

• High-power laser physics
• Nonlinear optics
• Optical engineering

Background:

• Phase modulation is used to smooth the focal spot of high-power energetic lasers.
• Propagation impairments can convert phase modulation into power modulation, known as frequency modulation to amplitude modulation (FM-to-AM) conversion.
• FM-to-AM conversion can lead to increased laser damage and operating costs.

Purpose of the Study:

• To investigate the impact of the Kerr effect on FM-to-AM conversion for the first time.
• To identify conditions that lead to a significant increase in FM-to-AM conversion.
• To develop strategies to mitigate or avoid detrimental FM-to-AM conversion.

Main Methods:

• Theoretical analysis of the interplay between phase modulation, Kerr effect, and dispersive transfer functions.
• Identification and characterization of a specific type of FM-to-AM conversion termed 'anomalous'.
• Assessment of various methods to remove or compensate for contributing factors to anomalous FM-to-AM conversion.

Main Results:

• The Kerr effect, when followed by a dispersive transfer function, can dramatically increase anomalous FM-to-AM conversion.
• Anomalous FM-to-AM conversion is particularly sensitive to the sequence of Kerr effect and dispersive elements.
• An efficient inspection method was developed to detect and avoid anomalous FM-to-AM conversion.

Conclusions:

• The Kerr effect plays a critical role in exacerbating FM-to-AM conversion under specific conditions.
• Mitigation strategies involve addressing phase modulation, anomalous FM-to-AM conversion, the Kerr effect, or the dispersive function.
• The developed inspection method provides a practical solution for preventing laser damage caused by anomalous FM-to-AM conversion.