Phase-sensitive narrowband heterodyne holography.

We report on amplitude and phase imaging of out-of-plane sinusoidal surface vibration at nanometer scales with a heterodyne holographic interferometer. The originality of the proposed method is to make use of a multiplexed local oscillator to address several optical sidebands into the temporal bandwidth of a sensor array. This process is called coherent frequency-division multiplexing. It enables simultaneous recording and pixel-to-pixel division of sideband holograms, which permits quantitative wide-field mapping of optical phase-modulation depths. Additionally, a linear frequency chirp ensures the retrieval of the local mechanical phase shift of the vibration with respect to the excitation signal. The proposed approach is validated by quantitative motion characterization of the lamellophone of a musical box, behaving as a group of harmonic oscillators, under weak sinusoidal excitation. Images of the vibration amplitude versus excitation frequency show the resonance of the nanometric flexural response of one individual cantilever, at which a phase hop is measured.

Experimental study of z resolution in acousto-optical coherence tomography using random phase jumps on ultrasound and light.

Acousto-optical coherence tomography (AOCT) is a variant of acousto-optic imaging (also called ultrasound modulated optical tomography) that makes possible to get resolution along the ultrasound propagation axis z. We present here AOCT experimental results, and we study how the z resolution depends on time step between phase jumps T(φ), or on the correlation length Δz. By working at low resolution, we perform a quantitative comparison of the z measurements with the theoretical point spread function. We also present images recorded with different z resolution, and we qualitatively show how the image quality varies with T(φ), or Δz.

Effect of the photon's Brownian Doppler shift on the weak-localization coherent-backscattering cone.

We report the first observation of the dependence of the coherent-backscattering (CBS) enhanced cone with the frequency of the backscattered photon. The experiment is performed on a diffusing liquid suspension and the Doppler broadening of light is induced by the Brownian motion of the scatterers. Heterodyne detection on a CCD camera is used to measure the complex field (i.e., the hologram) of the light that is backscattered at a given frequency. The analysis of the holograms yield the frequency and the propagation direction of the backscattered photons. We observe that the angular CBS cone becomes more narrow in the tail of the Brownian spectrum. The experimental results are in good agreement with a simple theoretical model.