Two- and three-beam photothermal vs. conventional stimulated Raman scattering

Photothermal stimulated Raman scattering (PT-SRS) was investigated without a probe beam in addition to the pump and Stokes beams, demonstrating that the thermal lens generated within stimulated Raman scattering (SRS) can be detected on one of the intrinsically involved beams as well. The additional signal contribution led to a twofold enhancement of the resonant SRS signal and allowed for a comparison between SRS and PT-SRS signal contributions when an iris aperture with appropriate size was implemented in front of the detector. Additionally, detailed investigations on the signal-to-noise ratio of both PT-SRS and SRS signals demonstrated that the experimental conditions and requirements predefine which technique is more sensitive and provide a decision-making aid based on available laser parameters and detection schemes.