Experimental application of orbital angular mometum (OAM) for enhanced laser absorption and neutron generation*

Laser driven neutron sources boast several desirable characteristics including synchronized ultrashort pulse duration (sub-ns), small source size (sub-mm), and intrinsic proliferation safety - but have struggled to provide widespread application for the likes of neutron imaging and prompt gamma ray activation given their low-average flux when compared to conventional devices. Here we take a significant step in bridging this gap and present the first demonstration of enhanced absorption by optical vortex beams in free-flowing D₂O streams to generate unprecedented neutron yields of 1.45 × 10⁶ n/s/sr on the high-repetition, λ³ Laser at the University of Michigan (16 mJ, 480 Hz, 67 fs). We show taking advantage of lasers carrying orbital angular momentum (OAM) with topological charge l = 1 & l = 5 impinging at grazing incidence on a free-flowing, ∼20 μm heavy-water jet provides marked enhancement in laser absorption and resulting fast neutron yields. The increased heating of the plasma by OAM beam is observed despite a decrease in intensity by two orders of magnitude relative to similar arrangements and relaxed target conditions. Tabletop neutron flux of this level is comparable to that characteristic of commercial generators and we anticipate repetition rate scaling (1-10 kHz) of this interaction could easily generate ∼10⁸ n/s and be well suited for a variety of commercial, industrial, scientific, and national security implications.