Which configuration uses one photodetector and a chopper/rotating sector mirror to alternate beams in time?

Which configuration uses one photodetector and a chopper/rotating sector mirror to alternate beams in time?

• A. Double-beam in space
• B. Double-beam in time
• C. Single-beam
• D. Triple-beam

Answer: (B)

This setup is a double-beam in time arrangement. The key idea is to use one photodetector and a chopper or rotating sector mirror to switch between two optical beams in time rather than keeping them on separate paths simultaneously. The rotating mirror alternates directing the beam from the reference path and the beam from the sample path onto the same detector in quick succession. Because the detector sees each beam in alternating time slots, you can compare the two signals while the instrument conditions stay nearly the same, which helps cancel out drift and fluctuations from the light source or detector. If the beams were split and observed at the same time along different paths (space division), you’d typically need two detectors or a more complex arrangement to capture both signals simultaneously. A single-beam setup wouldn’t provide a second path to compare. A triple-beam setup would involve an additional beam path not described here. So the described configuration, using one detector and time-division switching between two beams, is the double-beam in time approach.

This setup is a double-beam in time arrangement. The key idea is to use one photodetector and a chopper or rotating sector mirror to switch between two optical beams in time rather than keeping them on separate paths simultaneously. The rotating mirror alternates directing the beam from the reference path and the beam from the sample path onto the same detector in quick succession. Because the detector sees each beam in alternating time slots, you can compare the two signals while the instrument conditions stay nearly the same, which helps cancel out drift and fluctuations from the light source or detector.

If the beams were split and observed at the same time along different paths (space division), you’d typically need two detectors or a more complex arrangement to capture both signals simultaneously. A single-beam setup wouldn’t provide a second path to compare. A triple-beam setup would involve an additional beam path not described here. So the described configuration, using one detector and time-division switching between two beams, is the double-beam in time approach.