How do you image at the molecular level without disturbing the natural state of a system? Try stimulated Raman spectroscopy (SRS)—a label-free imaging method for a real-time, non-perturbing way of looking at cells and other organisms based on molecular vibrational spectroscopy. The authors of this JOSA B paper, have developed a new single-beam coherent Raman microscopic technique with improved spectral sensitivity and vibrational imaging capability. They split a single femtosecond pulse beam into three specrtral bands in which the pump beam is made to excite multiple Raman modes. A specific Raman mode is then selected by the other two probe beams—a local oscillator and a phase-modulated one, which are temporally coupled by the Raman-induced refractive index modulation. All this is achieved by incorporating spectrally focussed detection and specific shaping of the femtosecond probe pulses. The potential of this technique lies in detecting the Raman signals from small-sized molecules in emerging applications, such as imaging metabolites and drugs.

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