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Keywords:

  • CuCl;
  • excitons;
  • room temperature;
  • nonlinear optical response;
  • superradiance

Abstract

We report observation of anomalous temperature dependences of degenerate four-wave mixing (DFWM) spectra in CuCl thin films with high crystalline quality and thicknesses in the order of 10–100 nm. The behavior of temperature dependence can be explained by the change in the relative intensities among component spectra. The excitonic state with large radiative width can be observed at high temperatures due to the superradiance faster than the nonradiative decay process. We succeeded in observing the DFWM signal up to room temperature based on the extremely large radiative width peculiar to the size region beyond the long-wavelength approximation regime.