Depth-Dependent Transient and Permanent Materials Modification Arising from Ultrafast Laser Induced Carrier and Phonon Excitations
Abstract
Ultrafast laser induced non-equilibrium transient states of matter can lead to non-thermal localized transient and permanent modifications of material. Exploring these phenomena at the quantum level is critical for further advances in modern nanoscience. Our approach to laser oriented materials science goes beyond traditional investigations of optical properties and provides the means to manipulate matter in a spatially and temporally localized non-thermal manner with nanometer scale accuracy. Simultaneously, this approach addresses fundamental unanswered questions concerning non-equilibrium many-body physics with regard to complex and highly correlated materials in the presence of defects, impurities and strain. We propose an experimental study of transient and permanent material modification at an arbitrary depth in semiconductors, for example, GaAs and Ge, created by localized high density excited electrons arising from a coupling between photons and coherent acoustic phonons (CAP). These studies recognize that the semiconductor band gap is transiently narrowed, and increased, by the CAP wave traveling through the material. This allows localized electronic excitation at a desired depth by properly timed laser pulses with photon energies just below the equilibrium band gap. The proposal is divided into four phases: (1) demonstration and characterization of localized electronic excitations at an arbitrary depth, utilizing CAP spectroscopy, (2) basic studies of energy flow and relaxation dynamics of transient, highly localized excited carriers at a given depth including the effect of defects, impurities and strain using ultrafast pump-probe techniques, (3) studies of dynamical processes leading to permanent modification, and in situ characterization of permanently modified regions by pump-probe techniques and CAP spectroscopy. In this proposal, we go beyond characterization and use the CAP wave to explore states of matter, both transient and permanent, unobtainable by conventional methods.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 16, 2018
- Source ID
- W911NF1710533
Entities
People
- Norman Tolk
Organizations
- Army Contracting Command
- United States Army
- Vanderbilt University