(a) Transduction of first (f2) and second (f1+f2) order peaks (orange and light blue data points, respectively) while sweeping the piezo mirror position, with 10.5 nW optical power incident on the sample. The solid lines show sinusoidal fits to the data. The horizontal scale was derived from the fit to the band power of f2, and the data at f1+f2 was shifted horizontally by about 3% to compensate for measurement drift. (b) Spectra at f2 and 2f2 at optimal mirror positions for linear and quadratic transduction (red and light blue data points, respectively), taken with 12.8 nW of incident optical power. The black solid lines are Lorentzian fits, whose area was used to calibrate the vertical scale.