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We enhance an optical flow cytometer with a photon-number statistics measurement. Our technique allows for an absolute measurement of biomarker concentration and proves sensitivity to a single biomarker (a colloidal quantum dot).

Using single-shot pump-probe spectroscopy, the carrier relaxation and phonon oscillation in highly photo-excited bismuth are coherently controlled with double-pulse excitation. Beside phonon amplitude and phase, the magnitudes of monotonic decays also oscillate with interpump delay.

Absolute, ultrafast measurements of the optical nonlinearity in gases are performed using spectral interferometry in thin targets. Notably, we are able to isolate the rovibrational component of the nonlinearity using resonant two-beam coupling.

We demonstrate a background-free (to within experimental uncertainty) frequency up-converter. In addition, high fringe contrast at a single-photon-level in an up-converting interferometer is demonstrated, an enabling step towards faithful up-conversion of entangled photon pairs.

We demonstrate single-photon-level phase preservation in an up-converting interferometer. The up-conversion process is background-free to within experimental uncertainty, allowing high fringe contrast even at low photon levels. This enables faithful up-conversion of entangled photon pairs.

The nonlinear refractive index in air components and noble gases is measured absolutely using spectral interferometry in a thin gas target. Contributions from bound electronic states, molecular alignment, and free electrons from ionization are observed.

We show that femtosecond filaments produce mass density holes that decay over milliseconds in gases. Propagation of high repetition rate lasers is strongly affected, influencing the filament collapse point, supercontinuum generation, and pointing dynamics.

We measure the polarization dependence of the Kerr effect in air using single-shot supercontinuum spectral interferometry, enabling separation of the instantaneous and rotational components of the nonlinearity.