Abstract
In optical microscopies which implement a forward detection scheme such as Coherent Anti-stokes Raman Scattering (CARS), Stimulated Raman Scattering (SRS) or Second - and Third-Harmonic Generation, efficient detection is usually achieved by collecting the signal with high Numerical Aperture (NA) objectives. While the use of high-end well-corrected high-NA microscope objectives for excitation is necessary to achieve high resolution, to efficiently induce non-linear effects and to have excellent imaging capabilities, the detection optics only requires the collimation of the highly divergent beam coming from the excitation path. Moreover, high NA objectives feature short working distances which render them incompatible with top stage incubators, which are the solution of choice for controlled long term experiments on live cells. Among the mentioned techniques, SRS strictly requires the collection of the full excitation beam NA to avoid spurious background signal caused by cross phase modulation (XPM) which can spoil the sensitivity of the system [1].