Hyper-numerical aperture (NA = 2.8) microscope using λ = 1.56 µm femtosecond source for multi-photon imaging

• Published in: Biomedical optics express Vol. 4; no. 10; pp. 1786 - 1794
• Main Authors: Kim, Youngsik, Lu, Phat, Milster, Tom D, Kieu, Khanh
• Format: Journal Article
• Language: English
• Published: United States Optical Society of America 2013
• Subjects: Microscopy; (180.4243) Near-field microscopy; (180.4315) Nonlinear microscopy
• ISSN: 2156-7085; 2156-7085
• DOI: 10.1364/BOE.4.001786

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.