A chopper system for shortening the duration of pulsed supersonic beams seeded with NO or Br2 down to 13 microseconds

TL;DR

This paper presents a chopper wheel system that significantly shortens the duration of pulsed supersonic molecular beams seeded with NO or Br2 to as low as 13 microseconds, improving temporal resolution without additional pumping stages.

Contribution

The study introduces a high-speed spinning chopper wheel setup capable of reducing molecular beam pulse durations to 13 microseconds, demonstrating effective beam control and background suppression.

Findings

Pulse duration reduced to 13 microseconds

Effective background gas elimination without differential pumping

Consistent results for NO and Br2 beams

Abstract

A chopper wheel construct is used to shorten the duration of a molecular beam to 13 microseconds. Molecular beams seeded with NO or with Br2 and an initial pulse width of greater or equal to 200 microseconds were passed through a spinning chopper wheel, which was driven by a brushless DC in vacuo motor at a range of speeds, from 3,000 rpm to 80,000 rpm. The resulting duration of the molecular-beam pulses measured at the laser detection volume ranged from 80 microseconds to 13 microseconds, and was the same for both NO and Br2. The duration is consistent with a simple analytical model, and the minimum pulse width measured is limited by the spreading of the beam between the chopper and the detection point as a consequence of the longitudinal velocity distribution of the beam. The setup adopted here effectively eliminates buildup of background gas without the use of a differential pumping stage, and a clean narrow pulse is obtained with low rotational temperature.