@@ The low frequency mode lower than 50 cm-1 is much lOwer than a traditional notch or an edge filtercut of most Raman spectrometers. Measurement of Raman bands with frequencies very close to theexcitation line has traditionally been possible with the use of a triple monochromator system and its low inthroughput is a bottleneck for many materials, for example, graphite and few layer graphenes.