Six-wave mixing coherent anti-Stokes Raman scattering microscopy

Agradecimentos: FAPESP (2013/16911-2); Instituto Nacional de Fotônica Aplicada à Biologia Celular-INFABIC (CNPq grant 465699/2014-6, FAPESP grant 2014/50938-8); Biologia das Doenças Neoplásicas da Medula Óssea (FAPESP grant 11/51959-0); CLC - CNPq produtividade grant (312049/2014-5); and Centro de Óptica e Fotônica - CEPOF (FAPESP grant 05/51689-2) Abstract: Acquiring images of biological tissues and cells without the assistance of exogenous labels with a fast repetition rate and chemical specificity is what coherent anti-Stokes Raman Scattering (CARS) imaging offers. Nonresonant background (NRB) is one of the main drawbacks of the CARS microscopy technique because it limits the detection of weak Raman lines and the detection of low-concentration molecules. We show that a six-wave mixing process with two beams, which is a cascade effect of CARS, show better signal/NRB ratio and can be utilized for biological tissues imaging. The cascade CARS (CCARS) depends on chi-3 to the fourth power, instead of chi-3 squared as in the usual CARS signal||therefore, the contrast ratio with NRB is higher for CCARS than for CARS. We present analytic calculations showing that CCARS have better contrast over CARS in any situation. Comparison of the signals of both techniques generated on water-ethanol solutions confirm these results. Finally, we acquired CCARS images of fresh biological tissues, attesting that it is a useful tool for biological studies FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Aberto