Stimulated Raman scattering (SRS) offers high sensitivity to monitor low-concentration drugs in real time. However, the "needle" of a drug signal at millimolar concentrations is hidden in the "haystack" of tissue background Raman signals, which practically limits the specificity of the drug measurements. Here, we compare two promising solutions, namely frequency-modulated SRS (FM-SRS) and time-resolved phase-modulated SRS (PM-SRS). We show that the temporal response of FM-SRS is a simple sinusoidal function and its specificity must be compromised. However, the time-resolved PM-SRS with shaped probe pulses provides temporal high-pass filtering with steep cutoff characteristics, enabling higher specificity in the drug measurement.
|