We introduce and demonstrate a dual-channel radially-polarized surface plasmon microscopy (SPM) system with
capability down to single nanoparticle detection. For nanospheres stained with fluorescent molecules, we are able to
simultaneously collect both fluorescence and elastic scattering images. By using a radial polarizer, the entire incident
beam is TM-polarized, which enables formation of a dark circular ring in the reflected image, thus providing higher
sensitivity to refractive index changes. The fluorescence intensity is clearly enhanced by more than 50% under radial
polarization as compared to a linear one. The complementary signals acquired from the two separated channels jointly
lead to well-co-localized images in scanning mode. This technique is currently extended to study two photon
fluorescence (TPF) signals from nanospheres, as well as second harmonic generation (SHG) signals from noncentrosymmetric
nanocrystals. It also provides a way to compensate for the eventual blinking of the fluorescence, which
does not affect the elastic scattering channel.
We demonstrate the association of two-photon nonlinear microscopy with balanced homodyne detection for investigating second harmonic radiation properties at nanoscale dimensions. Variation of the relative phase between second-harmonic and fundamental beam is retrieved, as a function of the absolute orientation of the nonlinear emitters. Sensitivity of ≈ 1.6 photon per second, in the spatio-temporal mode of the local oscillator, is obtained. This value is high enough to efficiently detect the second-harmonic emission from a single KTiOPO4 crystal of sub-wavelength size, embedded in a thin polymer film.
Two-frequency solid-state lasers are shown to provide beat notes at frequencies from dc to the THz range with continuous tunability, high spectral purity and 100% modulation depth. Depending on the desired range, one- and two-axis cavities are built. Applications of such lasers as a local oscillator in radio-over-fiber communication systems or as a quasi-absolute tunable frequency source for highly-dense wavelength division multiplexed networks are emphasized.
We describe an ongoing experiment to measure parity violation in atomic caesium, based on detection by stimulated emission. Our goal is to measure to 1 percent a left-right asymmetry of 10-6 to test electroweak theory and look for new physics beyond the standard model. The Cs highly forbidden transition, 6S.5 - 7S.5, is excited by a pump laser pulse in a longitudinal electric field E. the PV asymmetry resulting from the weak interaction during optical excitation is converted into an anisotropy in the gain of a probe laser pulse, which stimulates the allowed transition 7S.5 - 6P3/2, and manifests itself as a tiny E-odd rotation of the probe linear polarization. Differential polarimetry allows dark- field detection of the rotation angle and discrimination of the PV effect is based on several concepts of symmetry. Original amplification of polarization asymmetry by stimulated emission is presented with perspectives for signal-to-noise improvements.