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Top: Schematic top-view of a portion of the 3-mm long mask used for the fabrication of the microfluidic channel with 10 μm-thick PDMS walls positioned periodically along its length with a 40 μm period. Bottom: A 3D image of the fabricated microfluidic channel showing the fluctuations of the volume of each PDMS pegs at different depths, recorded using a profilometer. The green stripe represents the pumping scheme used for performing random laser emission studies.
(a) The emission intensity of the optofluidic random laser is plotted against the input fluence, and the threshold of lasing is determined to be about 80 μJ/mm2. Inset to the left is a photograph of the emission of the dye filled optofluidic channel when pumped by a green laser. (b) Emission spectrum of the random laser with its modes appearing at random spectral positions, recorded at a pump fluence above the lasing threshold at 233 μJ/mm2. The pulse to pulse variations in the spectrum and the averaged spectrum are plotted.
(a) A 300 μm long pump stripe is translated along the length of the channel, varying d, to study the spectral sensitivity of the random lasing modes to the pumped region. The spectra recorded for three different values of d are plotted in (b).
(a) An optical microscope image of the dye filled and perturbing channel is shown. (b) The plot shows the effect of a local refractive index perturbation on the random laser modes when the ethanol in the perturbing channel approaches the 800 μm long partially pumped zone marked by the green rectangle in the plot. The spectra for the case of fully air-filled and fully ethanol-filled perturbing channel are shown in (c).
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