Application of Ultrafast IR Lasers to Remote Detection, Beam Steering and Terahertz Generation

Abstract

Mid-infrared (mid-IR or MIR) and long-wave-infrared (LWIR) laser pulses constitute an interesting area of study for high intensity laser physics, as for many applications longer wavelengths provide advantages over shorter wavelengths for laser-plasma interaction. In this dissertation, we present and discuss results for three primary experiments using MIR and LWIR laser systems. We start by presenting experiments conducted at the University of Maryland (UMd) and Brookhaven National Laboratory (BNL) on the remote detection of radioactive sources with MIR (3.9 µm) and long-wave IR (LWIR, 9.2 µm) laser systems. In these experiments we drive and monitor avalanche breakdowns seeded by the weak air ionization generated by the radioactive source, at standoff distances exceeding the attenuation range of the radiation source by orders of magnitude. We also explore the possibility of scaling the avalanche method to greater range, and discuss the possible use of more compact laser systems. The second topic explores the use of avalanche ionization to form efficient plasma-based diffraction gratings for MIR light. The gratings are generated using long-pulse near-infrared 1 µm laser to drive avalanche plasma grating structures for diffraction of 3.9 µm light. We discuss the advantages and drawbacks of this method as well as scalability to standard laser wavelengths such as 800 nm. Finally, we discuss the generation of THz radiation by two-color MIR laser pulses, enabling the generation of high efficiency coherent radiation in this band.