Nonlinear absorbance in dielectric multilayers

Within the last two decades dispersive dielectric multilayer mirrors (DMs), also known as chirped mirrors (CMs), have played a significant role in the progress of ultrafast science. Their ability to manipulate the phase of a light pulse has advanced the synthesis of intense femtosecond optical pulses followed by remarkable progress in the disciplines of nonlinear optics. Meanwhile, the performance of the mirrors themselves has been strictly limited to the linear regime, as essential mirror characteristics such as reflectance, transmittance, and dispersion are evaluated with only intensity-independent values of refractive indices and extinction coefficients taken into the design formalism. Here, we report, to the best of our knowledge, the first observation of a strong nonlinear response of the DMs. We have found that the DM's multilayer stack causes very significant enhancement of the internal electric field that becomes sufficient to enable third-order nonlinearity. Remarkably, in our particular case, the response is solely emerging in the form of nonlinear absorbance. By modifying the multilayer structure of the mirror, we gained control over observed nonlinearity and were able to predict and to some extent to tune the magnitude of the response, without perturbing the dispersive properties of the DMs. This demonstration not only expands the functionality of DMs into the nonlinear domain, but also marks a new approach to the development of multilayer coatings for applications in ultrafast science. (C) 2015 Optical Society of America