Mode-switching in semiconductor lasers

In this paper, we experimentally analyze the modal dynamics of quantum-well semiconductor lasers. Modal switching is the dominant feature for semiconductor lasers that exhibit two or several active longitudinal modes in their time-averaged optical spectrum. In quantum-well lasers, these dynamics involve a periodic switching among several longitudinal modes, which follows a well-determined sequence from the bluest to the reddest mode in the optical spectrum. This feature is radically different from the well-known noise-driven mode-hopping occurring in bulk lasers which involves only two main modes. We analyze the differences in modal dynamics for these two kinds of laser by comparing the modal switching statistics and by studying the effects of noise and modulation in the pumping current.     

Dispersion compensation properties of grating-based temporal-correlation Optical Coherence Tomography systems

This article explores specific dispersion compensation properties of an OCT set-up based on temporal correlation performed by using a diffraction grating. The linear dispersion term introduced by a glass plate with a thickness of up to 9 mm has been experimentally compensated optically through the position adjustment of the output imaging lens and for a light bandwidth of 100 nm. The dispersion compensation principle is described theoretically and results obtained experimentally are compared successfully with simulated ones. System limitations are discussed, especially regarding compensation of second orders of dispersion. Perspectives are given to achieve such a dispersion compensation.     

Spatio-temporal dynamics of multicolor spatial Kerr solitons

We present numerical and experimental results showing the rich and complex spatio-temporal dynamics of multicolor spatial vector soliton generated by stimulated Raman scattering in a Kerr planar waveguide. By taking into account their temporal dimension, we found the precise domain of existence of multicolor soliton whose components are mutually guided and spatio-temporally superimposed. In addition, we observe the Raman Stokes component in the trailing edge of the pump pulse and show that it is associated with the slow-light process induced by the sharp resonance of the Raman gain medium.     

Sending femtosecond pulses in circles: highly nonparaxial accelerating beams

We use caustic beam shaping on 100 fs pulses to experimentally generate nonparaxial accelerating beams along a 60° circular arc, moving laterally by 14 μm over a 28 μm propagation length. This is the highest degree of transverse acceleration reported to our knowledge. Using diffraction integral theory and numerical beam propagation simulations, we show that circular acceleration trajectories represent a unique class of nonparaxial diffraction-free beam profile which also preserves the femtosecond temporal structure in the vicinity of the caustic.     

Multidimensional NMR cross-correlation relaxation study of carrot phloem and xylem. Part II: Thermal and high-pressure processing

The effects of thermal and high-pressure processing on the phloem and xylem tissue of carrots are investigated with a combination of optical fluorescence microscopy and two-dimensional nuclear magnetic resonance relaxometry. It is shown that precooking at 60 °C or rapid pressurization to 600 MPa prevents the cell-wall separation and that the combination of these two treatments may provide a commercially viable method for tissue texture preservation.     

Characterisation of Ripening and Pressure-Induced Changes in Tomato Pericarp Using NMR Relaxometry

A combination of two-dimensional nuclear magnetic resonance (NMR) relaxometry and optical microscopy is used to investigate the effects of ripening and high-pressure treatment on tomato pericarp tissue. It is shown that the relaxation times of the vacuolar water increase during the early stages of ripening even when there is no visible change and that this could be the basis of a useful on-line sensor for sorting tomatoes. The membrane rupturing and biopolymer denaturation associated with high-pressure treatments are also reflected in the NMR relaxation spectra.     

Multidimensional NMR cross-correlation relaxation study of carrot phloem and xylem. Part I: Peak assignment

We report, for the first time, a detailed analysis of the complicated two-dimensional (2-D) nuclear magnetic resonance relaxation spectra of the xylem and phloem of carrots. By combining chemical extraction with different 2-D pulse sequences attempts are made to assign relaxation peaks to cell components, including compartmentalized water, pectins, starch, proteins and hemicelluloses. In a separate report, we use these assignments to interpret the effects of thermal and high-pressure processing (M. E. Furfaro, N. Marigheto, G. K. Moates, K. Cross, M. L. Parker, K. W. Waldron, B. P. Hills: Appl. Magn. Reson. 35, 537–547, 2009).