Fig. 6b shows experimentally determined relative frequency shifts of silicon-rich silicon nitride (SRN) strings as a function of string length. Again, each measurement was repeated three times, and based on these measurements the average relative frequency shift and standard deviation were calculated. In this case, the linear dependence of the relative frequency shift on string length, which is expected from Eq. (4), is not obvious, but the tendency of the relative frequency shift increasing with string length is clear. If the absorbed power is calculated from the slope of the linear fit, it becomes 2.3 μW, approximately 1% of the readout laser power.