Figure 1
From: Dramatic enhancement of supercontinuum generation in elliptically-polarized laser filaments
Anomalous behavior in supercontinuum and polarization.
(a) Experimental setup to measure the supercontinuum spectrum and polarization ellipticity. The 50 fs, 2.8 mJ pulses at 800 nm are focused by a lens (f = 3 m) into a 4.5 m gas chamber. A quarter wave plate (QWP) is rotated to prepare the beam with different initial elliptical polarization. After attenuation by a neutral density filter (ND), the central part of the beam is selected by an aperture (A). A rotating polarizer cube and an energy detector (ED) are then used to record the polarization ellipse. A fiber-coupled spectrometer (S) records the scattering from a diffuser (D). (b) Spectral intensity of the supercontinuum spectrum as a function of wavelength and QWP angle measured in nitrogen (normalized to highest value in 2D map). White arrows indicate the angles for linear and near-circular polarization. The wavelength for which the power spectral density drops to 1% of its maximal value is found to be 725 nm for QWP angles of 0 and 90 degrees and 685 nm for 39 degrees. (c) Ellipticity measured after the filament (red) created in nitrogen and with the chamber evacuated (gray) as a function of the quarter wave plate angle. (d,e) Same measurements as in (b,c) for filaments in argon gas.
