Transient Hole-burning Spectroscopy Research Articles

Protein-Matrix Solvation Dynamics in the α Subunit of C-Phycocyanin

We have used femtosecond transient hole-burning (THB) spectroscopy to study single-chromophore dynamics at room temperature in the α subunit of C-phycocyanin, a cyanobacterial light-harvesting protein. The α subunit contains a single phycocyanobilin (open-chain tetrapyrrole) chromophore. A reasonable description of the THB spectra requires the presence of a broad excited-state absorption (ESA) line shape underlying the entire photobleaching/stimulated emission (PB/SE) region. The time evolution of the THB spectrum involves line broadening on the 100−200-fs time scale and a <100-fs time scale dynamic Stokes shift of the SE component. We suggest that the dynamic Stokes shift can be attributed to transient solvation by the protein matrix. The solvent correlation function, C(t), exhibits a sub-100-fs component that describes 90% of the total C(t) response, with the remaining 10% of response occurring on a much longer time scale than the longest delay employed in these experiments (10 ps). We assign the ultraf...

Transient hole-burning and time-resolved fluorescence spectra of dye molecules in solution: Evidence for ground-state relaxation and hole-filling effect

A picosecond transient hole-burning (THB) spectroscopy has been performed for organic dyes in solution. The THB spectra of rhodamine 640 have been found to show a time-dependent spectral change. This phenomenon corresponds to the solvent relaxation effect observed in the time-resolved fluorescence (TRF) spectrum. Although TRF spectrum is related only to the excited-state relaxation, THB spectrum is affected by both ground- and excited-state relaxations. Comparing with the TRF spectrum measured under the same exciting energy, we have clarified the presence of the ground-state relaxation. Further, the THB spectrum of styryl-8 gives an antihole between well-separated two holes corresponding to ground- and excited-state contributions. This may originate from the hole-filling effect due to the nonadiabatic relaxation from the nonequilibrium excited state to the ground state. The analysis based on a configuration coordinate model gives an overall understanding for these phenomena.

Subwavelength optical magnetic-resonance imaging

We present a theoretical study of optical magnetic-resonance imaging (OMRI), an extension of magnetic-resonance imaging to the optical frequency domain. OMRI images the spatial distribution of centers with field-dependent optical transitions by projection reconstruction from multiple tomographic scans. Spatial resolution is limited by magnetic-field gradient strengths and transition linewidths. These restrict the choice of systems accessible to OMRI, and rare-earth ions are identified as possible candidates. High-resolution laser spectroscopic techniques that overcome the effect of inhomogeneous broadening of electronic transitions are discussed. OMRI by transient hole-burning spectroscopy is presented as one approach for subwavelength spatial imaging, and its sensitivity is calculated. Submicrometer spatial resolution is possible by employing very-high-field gradients (&gt;10 T/cm) and centers exhibiting megahertz linewidths.

Anharmonic vibrational relaxation dynamics for a molecular impurity mode in alkali halide crystals

High-resolution diode-laser spectroscopy and the nonequilibrium techniques of incoherent laser saturation and transient hole-burning spectroscopy have been used to measure the relaxation dynamics (specifically ${T}_{1}$ and ${T}_{2}$) of the ${\ensuremath{\nu}}_{3}$ internal vibrational mode of Re$\mathrm{O}_{4}^{}{}_{}{}^{\ensuremath{-}}$ molecules as functions of temperature and host alkali halide lattice. Inhomogeneously broadened linewidths less than 0.02 ${\mathrm{cm}}^{\ensuremath{-}1}$ were observed in annealed crystals at low temperatures. To retrieve the homogeneous linewidths from the inhomogeneously broadened lines, hole-burning measurements of ${T}_{2}$ were performed with the use of a C${\mathrm{O}}_{2}$ laser as a saturating pump and either a Pb-salt diode laser or another C${\mathrm{O}}_{2}$ laser as a tunable probe. Holes as narrow as 10 MHz (full width at half maximum) were observed in inhomogeneously broadened lines several ${\mathrm{cm}}^{\ensuremath{-}1}$ wide. Excited-state lifetimes ${T}_{1}$ were measured by C${\mathrm{O}}_{2}$-laser saturation measurements, which provide values for the saturation intensity ${I}_{s}$ and hence the product ${T}_{1}{T}_{2}$. Above 10 K the dominant dephasing (${T}_{2}$) mechanism is acousticphonon scattering, whereas below 10 K ${T}_{2}$ achieves the fundamental upper limit of ${2T}_{1}$, signifying that dephasing is lifetime limited. The results of a systematic study of the alkali halide host lattice dependence of the excited-state decay rate at low temperatures show that the decay channel consists of multistep emission of lower-energy internal modes, localized phonon modes, and band phonons.