Non-intrusive measurement of magnetic field strengths in a low-pressure argon plasma using quantum beat spectroscopy

Abstract Accurate measurement of magnetic field strengths is critical in many plasma environments, ranging from astrophysical systems to fusion energy research. In this work, a non-perturbative laser-based optical diagnostic known as quantum beat spectroscopy is demonstrated to be good alternative for measuring the magnetic field strength in low-pressure laboratory plasmas. The technique is investigated using both ns and fs pulsed lasers in an argon plasma. Preliminary results for a helium plasma are also given. Zeeman-split J = 1 electron states with transitions from metastable states were identified and tested for neutral argon <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mo stretchy="false">(</mml:mo> <mml:mn>2</mml:mn> </mml:msup> <mml:msubsup> <mml:mtext mathvariant="italic">P</mml:mtext> <mml:mrow> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mtext>o</mml:mtext> </mml:mrow> </mml:msubsup> <mml:mo stretchy="false">)</mml:mo> <mml:mn>4</mml:mn> <mml:mi>p</mml:mi> </mml:mrow> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mi/> <mml:mn>2</mml:mn> </mml:msup> <mml:mo stretchy="false">[</mml:mo> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mn>2</mml:mn> <mml:mo stretchy="false">]</mml:mo> </mml:mrow> </mml:math> and neutral helium <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mi>s</mml:mi> <mml:mn>3</mml:mn> <mml:mi>p</mml:mi> </mml:mrow> </mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mi/> <mml:mn>1</mml:mn> </mml:msup> <mml:msubsup> <mml:mi>P</mml:mi> <mml:mn>1</mml:mn> <mml:mrow> <mml:mtext>o</mml:mtext> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> . Magnetic fields are measured with sub-Gauss precision at near single laser pulse acquisition rates.