Configuration of the apparatus for (a) polarization or (b) high resolution spectral measurements. Optical fiber and electronic connections are shown by dashed and solid lines, respectively. The laser beam (LB, dot-dash line) is prepared using the half wave plate (HWP), prism polarizer (POL), liquid crystal variable wave plate (LCVWP), and long wave pass filter (RG780) before being focused into the sample in the scattering cell assembly (CELL). In (a) the output light (HRS) from the sample cell assembly is sent through the selected filters (DE, F) to the detector (PMT), and the polarization controller synchronizes the switching of the LCVWP, analyzing polarizer (in CELL), and the photon counting electronics (CNT). In (b) the fiber switch (FS) transmits either HRS or REF light to the scanning confocal Fabry-Pérot (FP) interferometer and the spectral data is accumulated in the multichannel scaler (MCS). The scan controller synchronizes the operation of the reference shutter (SH), FS, FP, and MCS, and also generates a feedback signal during the REF spectral scan that is used to stabilize the FP scan with respect to the frequency of the second harmonic light (SHG) from the laser.
(a) Top view of the optical components in the scattering cell assembly. The laser beam (LB) is focused by a lens (L1) into the sample cuvette (CUV), and the scattered light is collected and collimated by an aspheric lens (L2), with NA set by the aperture stop (AS). The collimated beam transmitted through the dichroic polarizer (DP) is focused by another aspheric lens (L3) into the optical fiber at the output port (HRS). (b) Cross section showing mechanical details of the scattering cell assembly. The main components are the laser focus lens mount (1), cuvette holder (2), collection lens and iris plug (3), collection lens mounting collar (4), rotatable support disk with angle scale on rim (5), ring with tilt adjusters and magnetic coupling to the support disk (6), motor body (7), motor mounting plate (8), motor rotor and fiducial ring (9), fiber lens mounting plate (10), threaded barrel (11), SMA fiber socket with focus adjust thread (12), and focus lock ring (13). (c) Cross section showing the taper socket (14) in the collection lens mount, and the matching taper nose (15), iris disk (16), and extraction thread (17) in the iris plug.
Extrapolation to NA = 0 for measurements of the HRS polarization ratios (a) I VV/HV , (b) I HV/VH , and (c) I HH/VH for C6D5NO2. The solid lines are empirical fits to the first four of the data points (open circles), while the dashed curves are based on a theoretical model. Alternative NA estimates for the largest aperture give the data points plotted as open triangles and diamonds.
Fabry-Pérot scan data are shown for the VH (filled circles) and HV (open circles) HRS spectra for C6D5NO2. The solid curves show the instrumentally broadened SHG reference spectrum and the fits to the VH and HV HRS spectral data. The longitudinal polar mode induced by dissolved ions in the sample produces the characteristic instrumentally broadened spike seen in the high resolution VH HRS spectrum but absent from the HV HRS spectrum. The spike/background integrated intensity ratio S/B determined from the high resolution VH HRS spectrum is used to assess and correct for the ion contribution to the HRS signal.
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