Giant nonlinear Raman responses from organic semiconductors

Organic semiconductors exhibit unique semiconducting behaviour due to π-electron delocalization along their molecular chains, making them attractive for various optoelectronic applications. However, their low optical damage thresholds have limited their use in nonlinear optics, particularly in stimulated Raman scattering. Here we demonstrate a general method to significantly amplify molecular vibrations in organic semiconductors by utilizing spectrally tailored gain from stimulated emission, bypassing the necessity for traditional optical cavities. This method achieves Raman thresholds as low as ~10-50 μJ cm^-2 or ~2-10 kW cm^-2, outperforming current Raman lasers by four orders of magnitude. The resulting nonlinear Raman response leads to cascaded Raman emission characterized by pump-dependent emission efficiency, a nonlinearity factor of 3.8, a signal-to-noise ratio of 30.9 dB and a bandwidth of 110 nm. Our study opens exciting prospects for the development of compact, efficient Raman amplifiers and lasers, leveraging the unique properties of organic semiconductors for advanced photonic applications, including high-sensitivity spectroscopy and versatile frequency conversion technologies.