Time-resolved nonlinear microscopy

One of the most promising methods of chemical imaging below the diffraction limit of visible light is to scan a tip that is much smaller than the wavelength across the sample. When this tip is irradiated with a laser, the light field is significantly concentrated under the tip, leading to an enhancement of light-matter interaction. Consequently, the spatial resolution of imaging modalities that derive the signal from the enhanced light-matter interaction is mainly determined by the size of the tip. Such methods can also be combined with femtosecond time resolution by a pump-probe scheme using time-delayed pulses. We propose to develop a multi-channel nonlinear nanoscope with femtosecond time resolution that uses nonlinear optical processes to probe the sample. We envision a proto-type instrument that can produce images with sub-wavelength resolution by detecting (i) third-harmonic generation (THG), (ii) stimulated parametric four-wave mixing (SPFWM), (iii) second-harmonic generation (SHG) or (iv) multi-photon fluorescence (MPF). The key milestone of Phase I will be the successful completion of a proof-of- principle experiment using one nonlinear process (THG) and demonstrating combined temporal and spatial resolution. If awarded, we will construct a proto- type nanoscope in Phase II. Besides the obvious multiple applications in biology in medicine, this device can be used to scrutinize the physical processes when optical surfaces are damaged by high-intensity laser radiation. Potentially, this could lead to enormous improvement of the optics in high-power laser systems, e.g. in the National Ignition facility.