The line shapes and intensities in coherent multidimensional vibrational spectra are determined by amplitude level interference between different nonlinear processes. The relative amplitude and phase of each process is controlled by the transition moments and dephasing rates associated with each coherence in a nonlinear pathway. The important nonlinear pathways involve processes that are doubly vibrationally enhanced (DOVE) and nonresonant. The DOVE processes are sensitive to dephasing-induced resonances that change the appearance of two-dimensional spectral features. To understand how these contributions interfere to create a twodimensional vibrational spectrum, line shapes were measured in the frequency domain for a set of model compounds over a range of vibrational frequencies. The amplitudes and dephasing rates for each pathway were determined by modeling spectra. By comparing the amplitudes with a deuteriobenzene internal standard, quantitative values were obtained for the DOVE processes. The results agree with recent ab initio calculations of the third-order DOVE susceptibilities, previous measurements of the concentration dependence, and estimates based on the absorption and Raman cross-sections of each resonance. The interference effects make the DOVE measurements sensitive to the sign of the transition moments.

No abstract

First operation of the 4F₉/₂ → 6H₁₃/₂ laser transition in dysprosium doped yttrium aluminum garnet is reported. Efficient room temperature operation at 583 nm was obtained using 447 nm GaN diode lasers pumps. Gaussian single-mode operation was demonstrated with a non-optimized slope efficiency of 12%. Millisecond pulsed operation generated 150 mW with power limited by the pump diodes' brightness.

Doubly vibrationally enhanced (DOVE) resonances have been observed in the infrared four-wave mixing (IRFWM) spectra of crotononitrile. The 2D DOVE-FWM spectra of the cis and trans isomers of crotononitrile showed cross peaks between the CN stretching fundamental and the CN + C=C stretch and the CN + C-C stretch combination bands for each of the two isomers that were observed, demonstrating the isomer selectivity of DOVE-IRFWM. Frequency-domain simulations were able to reproduce the features of the observed spectra, so the values for the nonlinearity and dephasing rates of all of the nonlinear processes could be measured. The results are compared to the calculations of the third-order susceptibility based on the transition moments, line positions, and line widths observed in the infrared absorption and the Raman spectra of crotononitrile.

No abstract

There is currently great interest in developing the vibrational analog to two-dimensional NMR spectroscopy. One approach to implementing two-dimensional vibrational spectroscopy is to use doubly vibrationally enhanced (DOVE) four-wave mixing (FWM). Nonlinear signals occur because of correlations and mode coupling that are induced by interactions involving the driven modes. Since cross peaks do not occur between modes if interactions are absent, spectral congestion is removed and only the coupled modes remain. We describe the development of a two-dimensional doubly vibrationally enhanced four wave mixing method that extends the doubly resonant nonlinear spectroscopies to vibrational nonlinearities. We demonstrate the selective enhancements of coupled modes that are possible with the double resonances where the intensity of the enhancements reflects the strength of the interactions that are responsible for the vibrational mode coupling. We also demonstrate the capabilities for selectively enhancing specific sample components in an isotopic mixture. Since biological applications of DOVE require aqueous environments, we have examined the ability of DOVE methods to discriminate against the strong water absorption and have found that water has a small vibrational nonlinearity that allows DOVE of the solutes. Our results demonstrate the feasibility and features required to make DOVE methods practical for a wide range of scientific applications where identification of intra- and intermolecular interactions is important.

Apert's syndrome is a congenital disorder characterized by the premature fusion of the cranial sutures and early epiphyseal closure. Severe pustular acne is a common feature. We report a case that failed to respond to conventional antibiotic treatment but resolved following isotretinoin therapy. The patient's permanent tracheostomy proved a management challenge during isotretinoin treatment. The role of androgen-sensitivity is discussed in relation to the skin and bones.

No abstract