Ultrabroadband two-beam CARS as a tool in diagnostics and therapy

Tissue-diagnostic techniques such as spontaneous Raman scattering suffer from low signal intensities and large fluorescent background. Nonlinear techniques such as Coherent Anti-Stokes Raman Scattering (CARS) may overcome these drawbacks, yet traditional CARS requires prior knowledge about the Raman transition to be probed. Ultrabroadband two-beam CARS combines the multiplex capability of spontaneous Raman scattering with laser-like signal detection. In our setup, compressed approximately 7 fs pulses act as pump and Stokes pulses which allow exciting both the fingerprint region (⪅ 1900 cm-1) and Raman transitions up to approximately 4000 cm-1. A probe pulse at approximately 515 nm is used to acquire broadband CARS spectra and to probe the temporal Raman decay. Apart from the diagnostic use, we demonstrate that such ultrashort pulses can be used for defined tissue ablation in human and animal tissue samples. Thus, a combined diagnostic with tissue removal is envisioned.