THG analysis for an efficient selection of objectives in non linear microscopy design

Abstract: A theoretical and experimental study of the THG signal from a reference interface in non linear microscope allows precise analysis of beam propagation and optimisation of the focusing optics. Multiphoton laser scanning microscopy has become an important tool for the investigation of biological phenomena where high resolution, three-dimensional imaging is essential for understanding the underlying biological function [1-3]. Two-photon laser scanning microscopy produces high-resolution images of thin optical sections that can provide complete three-dimensional information. The success of the two-photon absorption fluorescence has generated substantial interest in the scientific imaging community in further developing and exploiting optical nonlinearities for generating image contrast. Some of these techniques such as second harmonic generation (SHG) [4,5] and coherent anti-Stokes Raman scattering microscopy (CARS) [6,7] have been around for a number of years, but have recently benefited from the development of compact, reliable ultrashort laser sources and thus are being looked at with renewed interest. Other techniques such as third-harmonic generation imaging are the result of work in only the past few years [8,9] but once again benefited from the fact is easier than ever before to generate ultrashort pulses at virtually any desired wavelength [10]. Unfortunately the pulse characteristics in such extreme conditions (ultrashort and strongly focused) are deeply affected by all the optical components between the laser source and the sampl