Chapter 18 - Control of nonlinear optical excitation with multiphoton intrapulse interference

Abstract

This chapter presents the latest results focused on the design of tailored femtosecond pulses to achieve control of nonlinear optical excitation in large molecules based on the concept of multiphoton intrapulse interference (MII). This chapter aims to elucidate well-defined and reproducible pulse shapes that can be used to enhance or suppress particular nonlinear optical transitions in large molecules such as laser dyes and proteins in solution. Further, this chapter demonstrates the use of MII to probe the local and microscopic environment of molecules by selective two-photon laser induced fluorescence (LIF).This chapter discusses the MII method, which couples the sensitivity of multiphoton excitation on the spectral phase of the laser pulses to probe microscopic chemical environment induced changes in the multiphoton excitation spectrum of sensitive reporter molecules. The optimization of the required phase functions in solution is carried out and theoretical simulations are provided. The chapter also presents experimental images, whereby the pH-selective two-photon microscopy is achieved. The chapter demonstrates how selective excitation can be used to enhance contrast and, consequently, to achieve functional imaging, using fluorescent probes sensitive to changes in their local environment.