FIG. 5.
Demonstration of reversible resonance tuning for split-disks on elastomer substrates: The spectral positions of lasing modes separated by the free spectral range are plotted in dependence of the derived coupling gap size d in differently colored symbols. A second x-axis on the top shows the dependence on the substrate elongation Δx. The left part (shaded in grey) corresponds to a gap reduction (substrate stretching) inducing a blue-shift of all resonances. Subsequent relaxation of the substrate strain results in a gap increase and complete reversal of the spectral shifts (right part, shaded in red). A total gap change of Δd = 920 nm corresponding to wavelength tuning of Δλtot = 4.4 nm =̂ 3.3 × FSR is identified. As expected, the modal shift is linearly dependent on the gap size and the substrate elongation. Straight lines have been fitted to the data. The lasing modes corresponding to the spectra shown in Fig. 4(a) are shaded in corresponding colors.