Addressing the Experimental Challenges in the Four-Wave Coherent Raman Scattering

Four-wave mixing scattering is the basis of a variety of coherent Raman spectroscopies. The former micro-spectroscopy has developed into powerful nonlinear microscopy over the last decade. It is due to advances in laser and detection systems that utilize ultrafast solid-state technology. The myriad scientific publications demonstrate a deeper theoretical understanding of signal generation and data processing, which has also contributed to the trend toward novel applications. We present our recent progress on a special 3-color broadband method for low-frequency phonon measurements on crystal samples. Applying specific polarization conditions and a novel three-dimensional focusing geometry, we measured vibrational bands that obey polarization selection rules consistent with the crystal's factor-group characterization. Stimulated spontaneous Raman spectra were also measured to facilitate comparison.  The research is a continuation of our former results published, e.g., in L. Ujj, T. Olsson, B. Schundelmier, T. Bestor, “Effective Polarization Suppression in Two-Beam 3-color Broadband Coherent Raman Micro-Spectroscopy (3CBCRS)”, Vibrational Spectroscopy, 108, 103056 (2020).