title: Hyper-numerical aperture (NA = 2.8) microscope using λ = 1.56 µm femtosecond source for multi-photon imaging.
abstract: A new microscope is discussed, where the scanning illumination has a numerical aperture of 2.8 with λ = 1.56 µm femtosecond fiber laser. Samples are placed or grown on a silicon substrate. Multi-photon emission is imaged in transmission on a cooled CCD. Two-photon and three-photon effects are observed from the silicon/water interface and gold nanoparticles. Images of cells, reference spheres and gold nanoparticles illustrate imaging properties of the microscope. Spectral characteristics of individual particles are achieved with a blazed transmission grating. Emission properties of differently sized gold nanoparticles are studied in detail, which indicate that their emission is a two-photon effect due continuum generation. Interestingly, spectral shape and emission power are similar for 20nm, 40nm and 60nm diameter gold nanoparticles for the cases studied.
authors.affiliation: College of Optical Sciences, The University of Arizona, 1630 E. University Blvd. Tucson, AZ 85721, USA.
authors.forename: Youngsik
authors.initials: Y
authors.lastname: Kim
authors.forename: Phat
authors.initials: P
authors.lastname: Lu
authors.forename: Tom D
authors.initials: TD
authors.lastname: Milster
authors.forename: Khanh
authors.initials: K
authors.lastname: Kieu
keywords: (180.4243) Near-field microscopy; (180.4315) Nonlinear microscopy