Second Harmonic Generation

A newer optical technique called Second Harmonic Generation (SHG) has become prevalent as it offers specific advantages over conventional microscopy. The main problem with conventional microscopy is signal from out-of-focus structures, creating low signal-to-noise ratios. Another means of depth resolved imaging is multi-photon microscopy which utilizes non-linear optical processes to excite only the target region of the sample, thereby eliminating out-of-focus light altogether and giving it the ability to resolve 3-dimensional structures. One particular two-photon process called Second Harmonic Generation (SHG) requires two photons to interacting with a non-centrosymmetric molecule and converting it to a single photon at half the wavelength. Fortunately, the unique non-symmetric structure of collagen makes it one of the few biomolecules that can be probed via SHG.