Recent advances in nonlinear microscopy show great potential to study organization and morphology of biological structures [1]. This is especially important for biomedical applications where structural changes can lead to, or be utilized as diagnostic tools of severe diseases [1]. Nonlinear microscopies are in general minimally invasive facilitating in vivo imaging, and can provide deeper penetration than traditional linear microscopy techniques. In addition, coherent nonlinear modalities, such as second-harmonic generation (SHG) microscopy, can provide more quantitative morphological information of the protein conformational order than traditional linear techniques [2,3]. This is due to the intrinsic sensitivity of SHG to symmetry properties of the excited matter, which in conjunction with polarization measurements can be utilized to extract microscopic morphological information [3]. But all the developed quantitative approaches require a varying degree of a priori information, such as knowledge of the overall symmetry or orientation of the material. Neither are they applicable for extracting the complex susceptibility tensor limiting the potential applicability of the techniques [4].
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