title: Nonlinear dark-field microscopy.
abstract: Dark-field microscopy is a background-free imaging method that provides high sensitivity and a large signal-to-noise ratio. It finds application in nanoscale detection, biophysics and biosensing, particle tracking, single molecule spectroscopy, X-ray imaging, and failure analysis of materials. In dark-field microscopy, the unscattered light path is typically excluded from the angular range of signal detection. This restriction reduces the numerical aperture and affects the resolution. Here we introduce a nonlinear dark-field scheme that overcomes this restriction. Two laser beams of frequencies ω1 and ω2 are used to illuminate a sample surface and to generate a purely evanescent field at the four-wave mixing (4WM) frequency ω4wm = 2ω1 - ω2. The evanescent 4WM field scatters at sample features and generates radiation that is detected by standard far-field optics. This nonlinear dark-field scheme works with samples of any material and is compatible with applications ranging from biological imaging to failure analysis.
authors.affiliation: Institute of Optics, University of Rochester, Rochester, New York 14627, United States.
authors.forename: Hayk
authors.initials: H
authors.lastname: Harutyunyan
authors.forename: Stefano
authors.initials: S
authors.lastname: Palomba
authors.forename: Jan
authors.initials: J
authors.lastname: Renger
authors.forename: Romain
authors.initials: R
authors.lastname: Quidant
authors.forename: Lukas
authors.initials: L
authors.lastname: Novotny