Balanced homodyne detection in second-harmonic generation microscopy
  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 beams is retrieved, as a function of the absolute orientation of the nonlinear emitters. Sensitivity down to approximately 3.2 photon/s in the spatio-temporal mode of the local oscillator is obtained. This value is high enough to efficiently detect the coherent second-harmonic emission from a single KTiOPO4 crystal of sub-wavelength size. 
Loc Le Xuan (LPQM), Fran\c{c}ois Marquier (EM2C), Dominique Chauvat   (LPQM, PALMS), Sophie Brasselet (LPQM), Fran\c{c}ois T...