Fig. 4: Nonlinear interaction of BIC-based polaritons.
From: Nonlinear polaritons in a monolayer semiconductor coupled to optical bound states in the continuum
a Measured LPB reflectance spectra (solid black curves) under resonant illumination with laser pulses at \(k_x^{\left( 1 \right)}/k = 0.078\) for fluence increasing from bottom to top, together with the corresponding Fano fits (red dashed curves). The inset illustrates the measurement geometry; the arrow indicates the power-dependent LPB frequency; and the bottom panel shows the corresponding Lorentzian curves based on the extracted frequency and linewidth. b Reflectance spectra, fits, and corresponding Lorentzian curves for \(k_x^{\left( 2 \right)}/k = 0.024\). c Top panel: extracted LPB spectral blueshifts for laser excitation at \(k_x^{\left( 1 \right)}/k = 0.078\) (black squares) and \(k_x^{\left( 2 \right)}/k = 0.024\) (red circles) as functions of the incident fluence, together with the corresponding linear fits (black and red lines). Bottom panel: corresponding extracted linewidth (FWHM) as a function of the incident fluence
