Optical Vortices through Laser Beam Engineering for Remote Sensing Applications

Because it can be used in situ without the need for any sample preparation, optical emission spectroscopy (OES) techniques, such as laser-induced breakdown spectroscopy (LIBS) are favored as a spectroscopic tool to remotely detect and interrogate nuclear materials. Although they have been successfully demonstrated in the lab, results taken at test fields are lacking because high laser intensity is needed at standoff distances. Furthermore, the return signal from optical interrogation drops drastically as 1/r2with r being the distance from the detector to the sample. We propose using optical vortices to confine the optical LIBS emission within a small conic angle to increase its signal strength, particularly in the direction of the user for remote sensing applications. This is different when using Gaussian beams for LIBS where the emission of laser plasma is isotropic. We have successfully demonstrated in Phase I that the detected signal strength can be doubled when using vortices compared to conventional Gaussian beams without additional improvement or modification to the laser system. Vortices are also known to be particularly robust against atmospheric turbulences. This will enable a stronger and precise intense laser beam delivery at range for interrogation of nuclear materials. Furthermore, our technology can be applied to various nanosecond, picosecond and femtosecond laser pulses, and can be used not only in LIBS, but also for absorption, fluorescence and Raman spectroscopy. In addition to using optical vortices for LIBS, we will combine Gaussian and vortex beam collinearly to further increase the LIBS signal at the detector. These Gaussian and vortex beams may be femtosecond, nanosecond or both, and be of different wavelengths. Outdoor LIBS experiments are also planned to demonstrate the viability of this technology for field applications. Because of the versatility of optical vortices for ablation, we will also develop an optical spectrometer based on dual frequency comb for multi-element and multi-isotope detection of nuclear materials. Commercial Applications and Other Benefits: The proposed technology using high energy nanosecond optical vortices will be able to detect a wide range of materials, such as explosives, organic, radiological and special nuclear materials at standoff distances. Due to its long-range capability, this sensor can also be used for weather monitoring LIDAR, remote sensing, optical communication and material processing. Our dual frequency comb will be an alternative to mass spectrometer for on-site field tests of nuclear materials.