Optomechanical effects in polar solids result from the combination of two main processes, electric field-induced strain and photon-induced voltages. Whereas the former depends on the electrostrictive ability of the sample to convert electric energy into mechanical energy, the latter is caused by the capacity of photons with appropriate energy to generate charges and, therefore, can depend on wavelength. We report here on mechanical deformation of BiFeO 3 and its response time to discrete wavelengths of incident light ranging from 365 to 940 nm. The mechanical response of BiFeO 3 is found to have two maxima in near-UV and green spectral wavelength regions. DOI: 10.1103/PhysRevB.85.092301 PACS number(s): 78.20.hb, 75.85.+t, 78.20.nc Cross-functional materials, where structure, charge, and magnetism are strongly interrelated, present high interest opportunities to realize new functionalities. In particular, photoelasticity in electrically polar materials is an extraordinary property with valuable remote light-controlled applications. [1][2][3] Due to the spontaneous polarization in polar dielectrics, light-generated charges distribute along the internal electricfield direction, thus changing the total electric field, and can cause sample deformation via the electrostrictive effect. Although some practical devices have been developed, the best response time with typical values of tens of seconds 4 must be improved. In that respect, our recent report on photoelastic effect in BiFeO 3 (BFO) with a fast response time may boost this research direction.5 Moreover, the observed magnetic field dependence can offer additional functionality in future photoelastic-multiferroic devices where strain, magnetization, and polarization can potentially be changed simultaneously by light as well as applied magnetic and electric fields. The BFO is a well-documented magnetic and ferroelectric compound in which both properties have been investigated rather extensively.6 Very interesting recent reports on optical properties in BFO include magnetochromism 7 and photovoltaic effects. 8,9 In this Brief Report, we investigate the wavelength dependence of the photoinduced strain in BFO single crystal for the purpose of finding an optimal cross-operational energy window of this intriguing property. Such measurements can also provide an independent indirect insight into the optical sensitivity of this extraordinary room temperature multiferroic compound.A BFO single crystal with thickness of 90 μm and lateral dimensions in the mm scale, shown on Fig. 1, was used for this study. The sample was selected using polarized light with an optical microscope revealing its single ferroelectric domain state with its spontaneous ferroelectric polarization along the [111] direction in the pseudocubic lattice description.Side 1 of the crystal is flat and reflective, allowing an easy verification of the sample ferroelectric state by polarized light in reflection mode, while side 2 exhibits a significant light absorption and indicates directions of crystal...