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Phase modulation failsafe system for multi-kJ lasers based on optical heterodyne detection
D J Armstrong1, Q M Looker1, J W Stahoviak1
1Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185, USA.
The Review of Scientific Instruments
|November 8, 2018
Summary
A new high-speed phase modulation failsafe system (PMFS) prevents optical damage in high-energy lasers by detecting failures and blocking single-frequency light. This engineered safety system protects large aperture optics from stimulated Brillouin scattering (SBS).
Area of Science:
- Laser Physics and Engineering
- Optical Damage Mechanisms
- High-Energy Laser Systems
Background:
- Stimulated Brillouin scattering (SBS) amplification can cause optical damage in large aperture optics of high-energy lasers.
- Optical phase modulation (PM) broadens laser bandwidth, suppressing SBS by distributing energy across spectral sidebands.
- Failure of PM systems can lead to the injection of damaging single-frequency light into laser amplifiers.
Purpose of the Study:
- To develop and implement a high-speed phase modulation failsafe system (PMFS) to prevent optical damage in high-energy lasers.
- To ensure the reliable suppression of SBS by detecting and mitigating PM failures.
- To enhance the safety and operational integrity of large aperture laser systems like the Z-Beamlet Laser (ZBL).
Main Methods:
- Development of a novel PMFS utilizing optical heterodyne detection to convert phase modulation (PM) to amplitude modulation (AM).
- Passive AM power detection to identify PM failures.
- Deployment and testing of the PMFS on the Z-Beamlet Laser (ZBL) at Sandia National Laboratories.
Main Results:
- The PMFS demonstrated a rapid response time of as little as 7 ns to PM failures.
- The system effectively blocks single-frequency light, providing a 30-50 ns safety margin during laser shot initiation.
- The PMFS can detect PM for pulse durations of ≥2 ns and is adaptable for shorter pulses.
Conclusions:
- The implemented PMFS provides a critical safety function, preventing optical damage by mitigating the risks associated with PM failures.
- The system's rapid response and autonomous operation align with engineered safety principles for high-energy laser facilities.
- This failsafe technology is essential for supporting advanced research programs, such as magnetized liner inertial fusion, at facilities like Sandia's Z Facility.
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