Breaking the diffraction limit in nonlinear materials

Optical writing of small structures is usually governed by the diffraction limit. However, if the substrate exhibits nonlinear properties, it is possible to break this limit with conventional optical focusing systems. We estimate here theoretically the fundamental limits of resolution achievable in two different classes of nonlinear materials using a scalar approximation. Within this approximation our calculations suggest that the best possible resolution is given by 0.45λ0/(NASNR), where λ0 is the wavelength in vacuum, NA is the numerical aperture of the focusing system, and SNR is the signal to noise ratio of the system. Thus, we find that nanometer resolution is only feasible if the SNR is sufficiently large.