Near 2π solid angle fluorescence collection for laser-induced breakdown spectroscopy.

Detecting heavy metal and radioactive elements distributed in the environment and human body is crucial for life and environmental safety. A lens with a high numerical aperture (NA) is used in laser-induced breakdown spectroscopy to collect the plasma fluorescence as much as possible and improve the limit of detection. However, even a lens with NA up to 0.6, only the fluorescence in a solid angle of 0.4π can be collected. In this work, a novel, to our knowledge, fluorescence collecting scheme composed of a parabolic mirror and a lens is proposed which can collect the plasma fluorescence in a solid angle of ∼1.4π for an opaque material and ∼1.9π for a transparent material. Simulation results show that for opaque samples, this method can improve the fluorescence collection ability by 3.8 times compared to a single lens (NA = 0.5) collection scheme, and for transparent samples 4.5 times may be achieved. In experiments, a 2.8-fold enhancement in the fluorescence collection ability is demonstrated, and the signal-to-noise ratio is increased by 2.5 times for opaque samples.