University of Connecticut (Strong Field Physics with Few-Cycle Pulses in the Long-Wavelength-Infrared)
Abstract
Lethality, defined as damage to a target due to light-matter interaction, can be achieved by two mechanisms; average power (heat) deposition or peak intensity. Either process can be described by the so called three-step-model of heating. First light gets absorbed by electrons over the first few attoseconds (10~18s) while the electric field is on. Second, the electrons deposit energy in the lattice through electron-phonon scattering over the next picoseconds (10~12s). Finally, heat propagates macroscopically through the medium and the surrounding environment. The outcome is the breaking of the molecular or atomic bond which is equivalent to locally reaching the melting temperature. In our opinion, of relevance to ONR is the fact that intense femtosecond pulses (10~15s, fs) with kHz rates can be a tool for delivering extremely localized damage to a target. Femtosecond pulses provide very high peak intensities, capable of generating damage in a single shot while kHz repetition rates (1 ms or less between shots) allows for quick adjustments from shot to shot. In addition, short laser pulses with kHz repetition rate have a very small duty cycle (30 fs pulses spaced over 1 ms) but extremely high peak intensities. For this reason, and in particular in the LWIR frequency range, this radiation is very inconspicuous but can generate vast damage. Furthermore, pulses in the long-wavelength infrared (LWIR) region will be able to reach the target without absorption, that is, without energy loss. That is possible because the LWIR region of the electromagnetic spectrum is located in the 8 to 14 ~m region where there are several atmospheric transparencies. These transparencies are collectively known as the IR window. We expect that LWIR intense pulses will generate vast damage inside a solid sample by accelerating electrons to very high kinetic energies. At 8~m, with the current laser intensities achievable in our lab, we can generate electrons with energies in excess of 250eV. These highly energetic electrons can generate secondary ionization as they propagate through a sample. This is fundamentally a different damage mechanism that allows, low-energy, inconspicuous laser beams to deliver very highly localized damage to a target. Because the peak power can be lower the average power and thus the repetition rate can be increased to several kHz. Under this proposal we will produce intense, tunable, short pulses in the long-wavelength IR region that are carrier-envelope-phase stable at kHz repetition rate. We will use such pulses to study strong field science inside materials as a means to target damage and strong field ionization and absorption of molecules as a path to molecular fingerprinting. We will study a broad range of materials spanning dielectrics, semiconductors, and metals. The study will be done for a range of wavelengths spanning a full decade (800 nm to 8000 nm) and for each wavelength as a function of the laser intensity. It is our opinion that this could be one of the broadest studies damage studies done with femtosecond pulses.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 15, 2019
- Source ID
- N000141912339
Entities
People
- Carlos Trallero
Organizations
- Office of Naval Research
- United States Navy
- University of Connecticut