Control of the Two-photon Visual Process in ex vivo Retinas and in Living Mice.

Palcewska et al. first demonstrated near infrared (NIR) visual response in human volunteers upon two-photon absorption (TPA), in a seminal work of 2014, and assessed the process in terms of wavelength- and power-dependence on murine ex-vivo retinas. In the present study, ex-vivo electroretinography (ERG) is further developed to perform a complete characterization of the effect of NIR pulse duration, energy, and focal spot size on the response. The same set of measurements is successively tested on living mice. We discuss how the nonlinear intensity dependence of the photon absorption process is transferred to the amplitude of the visual response acquired by ERG. Finally, we show that the manipulation of the spectral phase of NIR pulses can be translated to predictable change in the two-photon induced response under physiological excitation conditions.

Multiorder Nonlinear Mixing in Metal Oxide Nanoparticles.

Whereas most of the reports on the nonlinear properties of micro- and nanostructures address the generation of distinct signals, such as second or third harmonic, here we demonstrate that the novel generation of dual output lasers recently developed for microscopy can readily increase the accessible parameter space and enable the simultaneous excitation and detection of multiple emission orders such as several harmonics and signals stemming from various sum and difference frequency mixing processes. This rich response, which in our case features 10 distinct emissions and encompasses the whole spectral range from the deep ultraviolet to the short-wave infrared region, is demonstrated using various nonlinear oxide nanomaterials while being characterized and simulated temporally and spectrally. Notably, we show that the response is conserved when the particles are embedded in biological media opening the way to novel biolabeling and phototriggering strategies.

Multimode single-pass spatio-temporal squeezing.

We present a single-pass source of broadband multimode squeezed light with potential application in quantum information and quantum metrology. The source is based on a type I parametric down-conversion (PDC) process inside a bulk nonlinear crystal in a non-collinear configuration. The generated squeezed light exhibits a spatio-temporal multimode behavior that is probed using a homodyne measurement with a local oscillator shaped both spatially and temporally. Finally we follow a covariance matrix based approach to reveal the distribution of the squeezing among several independent temporal and spatial modes. This unambiguously validates the multimode feature of our source.