Question

Explain why the fluorescence emission is detected perpendicular to the excitation beam in a fluorimeter.

Answer 1

Generally in spectroscopy, the detector is placed parallel to the sample but in the case of fluoroscence spectroscopy it is different. Fluorescence is measured at a 90° angle relative to the excitation light. This is to minimize the risk of transmitted or reflected incident light reaching the detector.

If the detector placed parellel that is 180 ⁰ to the exitation source, then it will interfere with the flouroscent light which has to be analsed alone. The monochromatic light is always not gives the single wavelength beam so when we use detector at 180° geometry, it will cause the unwanted fluorosence enhancement. but if we choose the detector at 90° angle, only the light scattered by the sample only focus on the detector. So this results in a better signal-to-noise ratio, and lowers the detection limit of the sample.