Physics Chat
Employing quasi-degenerate resonant states in chirality sensing
Speaker: Shaikhah Almousa (Dr Sang Soon Oh's group)
Date: Thursday 27 April 2023
Time: 15:00
Venue: Translational Research Hub Seminar Room 0.01
The significant role of chirality in life science applications and drug development generates a wide interest in improving chirality sensing. Designing chirality sensors essentially requires enhancing the optical response of chiral molecules and weakly chiral natural materials, leading to implications in understanding the underlying physics and fabrication of optical systems. Utilizing quasi-degenerate pairs of resonant states (also known as quasi-normal modes) is very promising for chirality sensing, due to a linear dependence of energy splitting on the chirality perturbation. The unperturbed resonant states of a homogeneous dielectric sphere exhibit a considerable energy splitting between the transverse electric (TE) and transverse magnetic (TM) polarizations of light, even for very large values of the angular momentum and high quality factor (Q-factor) of modes. Introducing a layer of different refractive index on the sphere surface can compensate on the asymmetry between the TE and TM polarizations, for some modes making their energies arbitrarily close to each other. In our work, we find the analytical solution of a spherically symmetric core-shell dielectric system and study the degeneracy pattern of the resonant states. The latter are properly normalized for their use in the resonant-state expansion (RSE) which is a very suited tool for treating chiral perturbations. Using the RSE, we demonstrate a linear energy shift of the perturbed modes in the presence of a chiral medium or a chiral molecule, which implies a chiral sensitivity of the optical system enhanced by orders of magnitude.