George R. Harrison Spectroscopy Laboratory
The George Russell Harrison Spectroscopy Laboratory conducts research in modern optics and spectroscopy for the purpose of furthering fundamental knowledge of atoms and molecules and pursuing advanced engineering and biomedical applications. Professor Michael S. Feld is Director; Professor Jeffrey I. Steinfeld and Dr. Ramachandra R. Dasari are Associate Directors. As an Interdepartmental Laboratory, the Spectroscopy Laboratory encourages participation and collaboration among researchers in various disciplines of science and engineering. Professors Moungi G. Bawendi, Feld, Robert W. Field, Stephen J. Lippard, Keith A. Nelson, Steinfeld, Andrei Tokmakoff, all of the MIT Chemistry Department, and Dr. Dasari are core investigators.
The laboratory operates two laser resource facilities. The MIT Laser Biomedical Research Center (LBRC), a Biotechnology Resource Center of the National Institutes of Health, develops basic scientific understanding, new techniques and technology for advanced biomedical applications of lasers; core, collaborative and outside research are conducted. The National Science Foundation-supported MIT Laser Research Facility provides resources for core research programs in the physical sciences for 13 MIT Chemistry and Physics faculty. Information about the facilities of the LRF and the LBRC can be found in the Spectroscopy Laboratory Researcher's Guide.
Research Highlights
Professor Field and his associates discovered a route to "transition state spectroscopy" in the S0 state barrier region between acetylene and vinylidene. The cis-trans isomerization barrier on the S1 potential surface has been characterized. Field's group is collaborating with Professors Fleming Crim (U. Wisconsin), Soji Tsuchiya (Japan Women's University) and Anthony Merer (U. British Columbia) to analyze these interactions, and with Drs. J.K.G. Watson (Steacie Institute, Ottawa) and Matthew Jacobson (Columbia U.) to calculate the Franck-Condon factors needed to disentangle overlapping polyads illuminated via multiple "bright states". Professors Field, Frederic Merkt (ETH Zurich), Anthony Merer (UBC), and Christian Jungen (Aime Cotton, Orsay) studied electron-nuclear coupling dynamics in Rydberg states of the alkaline earth monohalides, and identified the optimal "launch state" from which to record millimeter-wave spectra of CaF.
Professors Field and William Green (Chemical Engineering, MIT) constructed a free-radical spectroscopy, dynamics, and kinetics facility. A variety of high sensitivity spectroscopic schemes, including a Herriott cell and an ultraviolet cavity ring-down (CRD) setup (collaboration with Professor Jeffery Steinfeld) yielded initial results. A systematic CRD study of the acetylene S1-S0 transition in the 210-240 nm spectral region has been completed.
Professors Field and Steinfeld, in collaboration with Drs. Manjula Canagaratna, Stephen Coy and Alexander Kachanov, used intracavity laser absorption spectroscopy to carry out a rotational analysis and make quantitative intensity measurements of the 3v1 band of HONO. This study provides refinements to the current model for solar generation of atmospheric OH radicals by near infrared absorption and dissociation of NOX species. The capabilities of this instrument are being extended to carry out kinetic intracavity absorption spectroscopy, which will enable time-resolved kinetic measurements to be carried out on weakly absorbing species.
Professor Bawendi and Dr. Hans-Jurgen Eisler, collaborating with a group at Los Alamos National Laboratory, showed that nanocrystal quantum dots undergo stimulated emission and, in collaboration with Professor Henry Smith (Electrical Engineering and Computer Science, MIT), they used microcavity resonators to obtain laser oscillations. Lasing in these systems had been discussed for the last decade, and this is the first demonstration.
MIT Professors Bawendi, Michael F. Rubner (Materials Science and Engineering), Klavs F. Jensen (Chemical Engineering), and Marc A. Kastner and Raymond Ashoori (Physics) investigated the physics of electron conductivity and the effect of charging on nanocrystal quantum dot solids. They discovered a Coulomb glass behavior, resulting in a power law decay of the conductivity of these thin films. They also discovered that charging the dots can control the intensity of the photoluminescence of a film of dots. This discovery is consistent with a previous speculation that dots that contain one electron or one hole are prevented from emitting a photon because of a fast competing Auger process.
Professors Mildred Dresselhaus and Katrin Kneipp, together with Drs. Gene Dresselhaus, Harald Kneipp and Ado Jorio, studied surface-enhanced Raman scattering of single wall carbon nanotubes on silver colloidal clusters at extremely high enhancement levels and discovered new effects, such as lowering the symmetry of the resonance Raman tensor and coupling and scattering power exchange between phonon modes, which can be explained in terms of the strong optical fields and very large field gradients in so-called "hot areas" on the metallic fractal cluster structures. Together with Dr. Sandra Brown, Dr. Paola Corio and Professor R. Saito, they also performed detailed analysis on the origin of the Breit-Wigner-Fano lineshape of the tangential G-band Raman feature of metallic carbon nanotubes.
Professor Michael Feld and Research Scientist Chung-Chieh Yu investigated photon statistics of the cavity QED microlaser. Measurements of microlaser output and second-order correlation were in good agreement with theory. The fluctuation time scale was found to exhibit a local maximum during the threshold. Numerical simulations for the many-atom microlaser showed that the system scales according to single-atom theory, with a small perturbation due to cavity decay during atom transit time.
Professor Lippard and Dr. Yuji Mikata continued to develop an efficient method for photocross-linking of cisplatin-modified DNA and damage-recognition proteins by laser irradiation. Only upon photocross-linking can the interaction of cisplatin-DNA 1,3-intrastrand d(GpTpG) or interstrand cross-links with HMG1 domainB protein be detected. Photocross-linking is thus an effective tool for investigating the interaction of cisplatin-modified DNA with damage-recognition proteins under heterogeneous conditions such those in cell extracts or living cells.
Professor Nelson and Dr. Christ Glorieux demonstrated a novel form of imaging interferometry through which real-space images of propagating acoustic and thermal responses can be recorded. The results have important fundamental and practical applications in characterizing complex media such as viscoelastic liquids. In separate work, they demonstrated optical excitation and time-resolved observation of interface acoustic waves whose properties reveal the viscoelastic properties of both interfacial constituents. The method was used to study the complex shear modulus of glycerol at MHz frequencies under conditions of both weak and very strong shear wave attenuation. It provides a new window into the onset of shear wave propagation, i.e. the onset of solid-like behavior, in viscoelastic media. Working in collaboration with Professor Michael Fayer and Dr. Gerald Hinze of Stanford University, they demonstrated observation of translation-rotation coupling in complex liquids through direct time-resolved measurement of flow-induced molecular orientational responses. The results illustrate polarization-based isolation of translational, orientational, and coupled contributions to time-resolved signals.
Professor Tokmakoff and his collaborators used polarization-selective femtosecond Raman spectroscopy to study collective motions of molecular liquids and solvated proteins. In liquids, such experiments reveal distinct collective molecular motions associated density fluctuations, and in proteins large-scale vibrational motion of secondary structures along hydrogen bond coordinates are revealed. An amplified system capable of producing pulses as short as 30 fs in the mid-IR is currently being constructed to investigate the hydrogen-bond dynamics of liquid water.
Professor Alexander Rich and Drs. Bernard Brown and Dr. Eugene Hanlon used solid-state Raman spectroscopy to confirm the left-handed Z conformation of RNA's complexed with the Z( domain of the human RNA editing enzyme ADAR1 in crystals of the protein-nucleic acid co-complex, and showed that the RNA in the crystals was indeed in the left-handed conformation prior to solving the crystal structure.
Professor Kneipp, together with Dr. Harald Kneipp and Drs. Dasari and Feld, continue single molecule Raman studies and applied non-linear Raman scattering. They showeed that surface-enhanced antiStokes Raman scattering provides a two-photon probe with an effective cross section at least seven orders of magnitude larger than typical two-photon fluorescence cross sections. Together with Professor Dresselhaus, they used surface-enhanced Raman scattering on aligned small carbon nanotube bundles to study the lateral confinement of hot areas in the local optical fields in the vicinity of silver nanostructures, as well as the polarization properties of the local fields.
Professor Feld and Drs. Charles W. Boone, Dasari, Annika Enejder, Joseph Gardecki, Irene Georgakoudi, Martin Hunter and Adam Wax pursued basic and applied applications of lasers and spectroscopy in biology and medicine at the LBRC. Fluorescence, reflectance, Raman, light scattering spectroscopy and low coherence interferometry are being used for histological and biochemical analysis of tissues, diagnosis and imaging of disease, and cell biology applications. Clinical studies are being conducted with researchers from the Cleveland Clinic Foundation, Medical University of South Carolina, Brigham and Women's Hospital, Metrowest Hospital, Beth Israel/Deaconness Medical Center, and New England Medical Center. Clinical studies using tri-modal spectroscopy, the combined application of intrinsic fluorescence, diffuse reflectance, and light scattering spectroscopies, demonstrated successful diagnosis of dysplasia in Barrett's esophagus, the urinary bladder, adenomatous polyps, the oral cavity and the uterine cervix. Light-scattering spectroscopy has been used to measure and image sub-cellular structures much smaller than an optical wavelength. Novel low coherence interferometry techniques use two harmonically-related wavelengths to measure optical phase. Exceedingly small refractive index and length changes, tomographically mapped, have been used to study structure and dynamics of cellular organelles. Raman spectroscopy has been used to measure blood analytes with clinical accuracy and identify morphology of breast lesions. This experimental and theoretical work is advancing new laser diagnostic technologies in the fields of medicine and cell biology.
More information about the Spectroscopy Laboratory can be found online at http://web.mit.edu/spectroscopy/.