Two-color trapped-particle optical microscopy

We demonstrate a method for nonintrusive scanned near-field optical microscopy. The microscope utilizes an optical trap to position accurately a 50-100-nm-diameter lithium niobate particle. The infrared trapping beam is frequency doubled in the particle, resulting in a visible microscopic optical probe. By separation of the trapping and detection wavelengths, objects that are transparent in the infrared (e.g., biological) may be positioned close to the particle, resulting in high resolution. The current experimental resolution is limited to approximately 500 nm by the properties of the test objects. The theoretical resolution is less than 100 nm.