Fig. 3: Theoretical polarization-intensity spectrum (PIS) curves under different strain states.
From: Quantifying the in-plane strain influence on second harmonic generation of molybdenum disulfide
a A PIS curve under the state free from strain. Based on the crystal coordinate system, the six petals of the PIS are named as P1, P2, P3 and P1′, P2′, P3′, respectively, starting from the positive [010] axis counterclockwise. The blue solid line with arrows indicates the height of a petal (petal amplitude ξ). Each PIS curve has 3 independent petal amplitudes denoted as ξ1, ξ2 and ξ3. Examples of PIS curves under different strain states are shown, including (b) uniaxial strain state according to Eq. (14), (c) equal-biaxial strain state according to Eq. (16), (d) non-equal biaxial strain state according to Eq. (17) and (d) non-equal biaxial strain state with shear strain according to Eq. (11). For each strain state, four PIS curve lines from the outside to the inside are depicted in the color order of black, red, blue and green, corresponding to the strain εxx value of 0%, 0.1%, 0.3% and 0.5% for (b); the strain ε value of 0%, 0.1%, 0.2% and 0.3% for (c); the strain ε value of 0.1%, 0.2%, 0.3% and 0.4% for (d); the strain (ε, γ) values of (0.1%, –0.2), (0.2%, –0.3), (0.3%, 0.2) and (0.4%, 0.1) for (e). The ratio α between the two normal strain components are both set as 0.5 for (d) and (e).
