Ultrafast spectroscopic techniques are used to investigate the spectroscopy and dynamical processes that occur on subpicosecond and picosecond timescales in condensed phase materials. Our current themes involve the use of ultrashort terahertz pulses to measure the underlying low-frequency vibrational spectrum of crystalline solids, including threat materials. This project seeks to combine terahertz time domain spectroscopy (THz-TDS) and waveguide structures for the terahertz region in to develop methods to measure vibrational spectra with high sensitivity and much increased spectral resolution. Applications will include using THz technology for the detection of threat solids (e.g., explosives) and threat vapors.

The application of Fourier-transform methods to nonlinear-optical transients provides a powerful tool for investigating the Raman-active vibrational structure of materials in the spectral region between 1 and 800 cm^-1 through the Raman-induced Kerr effect. This method is particularly useful for probing the rapidly dephased intermolecular modes of disordered media, such as liquids and amorphous solids. Alternately, terahertz time-domain spectroscopy (THz-TDS) in the far-infrared (FIR) and vibrational pump-probe spectroscopy in the mid-IR are used to access unique information contained in dipole allowed spectra. Emphasis is placed on characterizing the energy relaxation and dephasing mechanisms for these intermolecular modes, and elucidating in detail the mechanical properties of the structural coordinates. These studies are being extended to interrogate the dynamics of super-cooled and glass phases of glass-forming liquids, polymer glasses, and liquid crystals in the femtosecond to microsecond temporal range. Other ongoing projects include investigation of the photophysical and carrier dynamics of thin-film materials fabricated at NRL (using optical and THz probes), and investigation into the effects of variations of growth and processing variables on the carrier dynamics of nonstoichiometric semiconductor materials including low-temperature grown GaAs.

Facilities include mode-locked femtosecond Ti:sapphire lasers, a Ti:sapphire regenerative amplifier and optical parametric amplifiers, a cavity-dumped femtosecond/picosecond dye laser pumped by a cw modelocked Nd:YLF laser, a Nd:YLF regenerative amplifier, and the electronic and optical equipment necessary for performing a range of spectroscopic and nonlinear-optical experiments.

 

key words

THz spectroscopy; Waveguides; Explosives; Condensed phase and condensation; Fourier-transformation techniques; GaAs; Intermolecular interactions; Nonlinear optics; Raman spectra; Thin films;

Citizenship:  Open to U.S. citizens and permanent residents

Level:  Open to Postdoctoral applicants