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Zero field level crossing in the helium atom Bardsley, Robert Eckardt

Abstract

Zero-field level crossing techniques have been used to measure some upper state lifetimes of the helium atom. The upper states of the atom were excited in a discharge between two capacitor plates. A radio frequency voltage was applied to these plates by a 450 MHz source. The emitted light was modulated by rotating a quarter-wave plate in front of a polaroid in the beam of emitted light. The polarization, which is directly related to this modulation, was measured by a phase sensitive lock-in amplifier. The halfwidths of curves obtained by plotting the polarization against the magnetic field strength for the n¹D - 2¹P transitions yielded lifetimes of; 2.71 x 10(-8) sec. for the 3¹D state, 3.97 x 10(-8) sec. for the 4¹D state and 4.48 x 10(-8) sec. for the 5¹D state.

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