Note: Lossless laser beam combiner employing a high-speed rotating half-wave plate.

Area of Science:

• Optics and Photonics
• Plasma Physics
• Fusion Energy Engineering

Background:

• Thomson scattering is crucial for plasma diagnostics in fusion devices like ITER.
• Existing laser beam combining methods can introduce signal loss or instability.
• ITER requires robust and efficient diagnostic systems for real-time plasma analysis.

Purpose of the Study:

• To develop an advanced laser beam combiner for ITER's Thomson scattering diagnostics.
• To achieve high polarization extinction and stable beam pointing in the combined laser output.
• To ensure a lossless method for combining multiple laser beams.

Main Methods:

• Implementation of a high-speed rotating half-wave plate.
• Utilizing feedback control to maintain consistent rotation speed.
• Characterization of polarization extinction ratio and beam pointing stability.

Main Results:

• Achieved a polarization extinction ratio exceeding 1000.
• Maintained high polarization extinction for over 1 hour through feedback control.
• Observed pointing fluctuations on the order of microradians.

Conclusions:

• The high-speed rotating half-wave plate is an effective solution for laser beam combining in ITER.
• This technique offers lossless beam combination with excellent polarization control and pointing stability.
• The developed combiner meets the stringent requirements for Thomson scattering measurements in fusion research.