We show that the axial spread of the focal volume of a tightly focused beam propagating through a glass-water interface is much reduced for Laguerre-Gaussian (LG) modes as compared to the TEM(00) mode. Therefore, use of the LG beam helps in achieving a significant improvement of the axial trapping range in optical tweezers. We demonstrate the use of LG modes to manipulate biological cells from the bottom layer of the medium to the top surface layer. Exposure of the cells to a higher oxygen concentration at the surface layer is used for estimation of the intramembrane oxygen diffusion rate.

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Abstract:We have numerically studied the effect of free-carrier-induced loss and dispersion on the modulational instability (MI) gain at low input powers in silicon-on-insulator (SOI) nanowaveguides with normal and anomalous second-order dispersion. We have shown that the free carriers affect the gain spectra even at low input powers. First time we have reported the gain in normal SOI nanowaveguides even in the absence of higher order dispersion parameters, which is due to the interaction of free-carrier-induced dispersion and nonlinearity. The MI gain in an anomalous SOI nanowaveguide vanishes even at a few milliwatt range of input power due to this interaction. We have shown that the gain could be achieved in an anomalous nanowaveguides by reducing the free carrier lifetime.

We have carried out an extensive theoretical study of cross-phase modulation induced modulation instability (MI) in a silicon-on-insulator nano-waveguide for two co-propagating waves. The analysis has been performed for two sets (with zero and varying non-zero walk-off parameter) of three different cases: when the two waves are in (i) normal dispersion regime, (ii) anomalous dispersion regime, and (iii) different dispersion regimes. In particularly, we have discussed the nonlinear losses due to two-photon absorption and free-carrier absorption. Further, we have investigated the impact of the walk-off parameter on the MI gain spectrum in the above three cases.

Absorption of intense ultra-short laser pulse 10 15 W/cm 2 <