Optical parametric oscillator system for CARS microscopy

Coherent anti-Stokes Raman scattering (CARS) microscopy as a labelling free nonlinear imaging technique has been extensively researched and been employed for many applications, e.g. live cell imaging, cell membrane studies, tissue imaging as well as brain tumour imaging. The most common optical system for CARS microscopy employs two tightly synchronised ultra-short pulsed lasers overlapped temporally and spatially. Not only is this expensive, however, but this approach is also complex and the stability of the system is almost entirely dependent upon the electronic locking mechanism. For CARS microscopy to become routinely applied in a research or a clinical environment, improved photonics technology is clearly required. As a consequence of this need, the authors demonstrate a flexible CARS imaging system based on a synchronously pumped optical parametric oscillator (OPO) based upon a periodically poled lithium niobate (PPLN) crystal. This approach circumvents the need for two costly platform laser sources yet provides a wide wavelength tuning range to facilitate a wide range of CARS imaging experiments.