Thin film detection of High Energy Materials: Optical Pumping Approach

We present our work on High Energy Material detection based on thin film of Lithium using the phenomenon of Optical Pumping. The Li atoms present in the thin film are optically pumped to one of the ground hyperfine energy levels so that they can no more absorb light from the resonant light source. Now in presence of a RF signal, which quantifies the ambient magnetic field, this polarized atomic system is again randomized thus making it reabsorb the resonant light. This gives a quantified measurement of the magnetic field surrounding the thin film detector. This is then mapped to the presence of magnetic HEM and hence the HEM are detected. Our approach in this regard starts with verifying the stability of Lithium atoms in various solvents so as to get a suitable liquid medium to form a thin film. In this regard, various UV-visible characterization spectra are presented to finally approach a stable system for the detection. We have worked on around 10 polar and non- polar solvents to see the stability criteria. UV-Vis probe has been found to be quite effective in addressing issue of hosting Lithium atoms by various solvents. Further results on the atomic system size as dispersed in the various solvents are presented. Atomic system size gives us a good quantitative estimate of the density of Lithium dispersed system in the thin film. Finally a separate atomic system under Ultrahigh vacuum is presented to achieve optical pumping wherein the polarization and depolarization of atomic system is seen using a 670 nm diode laser system which is electronically locked using a double window Hollow cathode lamp. These both systems will finally be combined together to give the final form to the detection system. As this whole system measures relative change in magnetic field due to the presence of HEM,it gives a more reliable and accurate detection method compared to the absolute measurement detectors.