Noise auto-correlation spectroscopy with coherent Raman scattering

Ultrafast lasers have become one of the most powerful tools in coherent nonlinear optical spectroscopy. Short pulses enable direct observation of fast molecular dynamics, whereas broad spectral bandwidth offers ways of controlling nonlinear optical processes by means of quantum interferences. Special care is usually taken to preserve the coherence of laser pulses as it determines the accuracy of a spectroscopic measurement. Here we present a new approach to coherent Raman spectroscopy based on deliberately introduced noise, which increases the spectral resolution, robustness and efficiency. We probe laser induced molecular vibrations using a broadband laser pulse with intentionally randomized amplitude and phase. The vibrational resonances result in and are identified through the appearance of intensity correlations in the noisy spectrum of coherently scattered photons. Spectral resolution is neither limited by the pulse bandwidth, nor sensitive to the quality of the temporal and spectral profile of the pulses. This is particularly attractive for the applications in microscopy, biological imaging and remote sensing, where dispersion and scattering properties of the medium often undermine the applicability of ultrafast lasers. The proposed method combines the efficiency and resolution of a coherent process with the robustness of incoherent light. As we demonstrate here, it can be implemented by simply destroying the coherence of a laser pulse, and without any elaborate temporal scanning or spectral shaping commonly required by the frequency-resolved spectroscopic methods with ultrashort pulses.Comment: To appear in Nature Physic

Kurzzeitspektroskopie zum Energietransport im ungeordneten Molekuelkristall 2,3-Dimethylnaphthalin

SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Homogeneity, transport, and signal properties of single Ag particles studied by single-molecule surface-enhanced resonance Raman scattering

We extended the sensitivity of Raman correlation spectroscopy in solution to the single-molecule level by applying surface- and resonance-enhanced Raman scattering (SERRS) combined with time-gated, confocal signal detection. The brightness of the SERRS signal of single Rhodamine 6G molecules adsorbed on a single silver nanoparticle is comparable to fluorescence. Rare event analysis reveals the existence of few particles with simultaneous SERRS and fluorescence signal. The observation of a dynamic exchange between heterogeneous binding sites is supported by the existence of multiple SERRS brightnesses in the signal intensity distribution and by signal fluctuations in the 60 μs time range detected by autocorrelation analysis. Finally, polarization-dependent SERRS autocorrelation curves and single-particle analysis allowed us to measure individual rotational diffusion times and to directly analyze the heterogeneity of the ensemble in solution. © 2001 American Chemical Society

Inkjet printing of polyurethane colloidal suspensions

An aqueous 40 wt% dispersion of polyurethane has been successfully printed at room temperature using a piezoelectric inkjet printer. Simple layered structures, as well as dots, were made and subsequently analyzed using white-light interferometry. A single layer was found to have a structure height of 10 µm; a value that suggests that this polyurethane dispersion may be suitable for use in rapid prototyping, since tall structures can be rapidly produced using only a few printing passes. Finally, by the simple addition of a water-soluble dye, colour gradients were produced using this printing techniqu

Polymeric foam properties derived from 3D images

We demonstrate the ability to calculate thermal conductance and elastic properties on three-dimensional images of industrial polymer foamed materials. Results for thermal conductivity and elasticity show little scatter and provide the basis for accurate empirical correlations between phase fraction and material properties. The correlations differ markedly from common theoretical and empirically derived estimates