A versatile, low cost light source module for multiphoton imaging

Multiphoton imaging methods such as Coherent Raman Scattering (CRS) microscopy which also comprises Second Harmonic Generation (SHG) and Two Photon Excited Auto-Fluorescence (TPEAF) imaging (termed as multimodal Coherent Raman microscopy), have greatly facilitated the advancement of biomedical research due to their unique features. Multimodal CRS microscopy, is label free, chemically specific, inherently ‘confocal’ offering three independent contrast mechanisms which can be associated in a composite image comprising a wide range of chemical and structural information about the interrogated sample. The standard light source for multimodal CRS microscopy is a picosecond pumped Optical Parametric Oscillator (OPO) which has exhibited excellent performance but due to its associated high cost, maintenance, complexity and requirement of a dedicated optics laboratory, has hindered the wider adoption of multimodal CRS microscopy and especially its deployment in clinical applications. Here we present a novel, low cost Optical Parametric Amplifier (OPA) based on a MgO doped Periodically Poled Lithium Niobate (PPLN) crystal seeded by a continuous wave (CW) laser source and pumped by a picosecond laser at 1031nm, which removes any synchronisation requirements. We show that this OPA is a versatile light source module that can be tailored to the tunability and affordability requirements of the specific application. We demonstrate that it can be used either in association with an OPO or on its own as a light source for multimodal CRS microscopy and we show its performance by imaging a variety of standards and biological samples.