Terahertz (THz) radiation interrogates the lowest frequency collective motions of biomolecular systems. These collective modes characterize the incipient motions for the large-scale conformational changes along the torsional coordinates responsible for the flexibility of protein, polynucleotide, and polysaccharide backbones during folding and activation. THz studies are a sensitive probe of crystalline order, conformational form, peptide sequence, solvent interactions, H-bonding force constants, and anharmonic character of the force fields.  Continuous-wave and phase-coherent chirped-pulse methods are used to measure the spectra of bulk (pellet) samples, thin-film samples on waveguide interfaces and gas phase samples over temperature ranges from 1.7 K to 350 K. The experimental results are modeled using high-level quantum mechanical methods (DFT/MP2/MRCI) to characterize the nuclear motions associated with the observed THz features. 

New methods based on electro-optical dual-optical-frequency combs and room-temperature multi-heterodyne detection are under development to enhance sensitivity across the region from 0.05 to 2 THz. 

In other research areas, chirped pulse THz measurements are performed using amplifier/multiplier chains in a long pass (White) cell on samples prepared in a slit jet nozzle and from an effusive beam source. Fragmentation products are detected after passing the seeded gas through a heated quartz pyrolysis source or following electric discharge in a pulse nozzle source. Other THz applications are to studies of the magnetic spin flip transitions (magnons) in anti-ferromagnetic materials and to voltage standards using superconducting Josephson junctions.  In the UV, the doubled output from continuous-wave ring-dye and ring-Ti:Sapphire lasers are used to perform UV studies of biomolecules at a sub-Doppler resolution of 3 MHz to 20 MHz.

key words

Biophotonics; Biomolecules; THz spectroscopy; Electro-optic Dual-optical-frequency THz Combs; Chirped Pulse THz; Polypeptides; Quantum Chemical Theory; Vibrational anharmonicity

Citizenship:  Open to U.S. citizens

Level:  Open to Postdoctoral applicants