Frequency doubling of images through a self-imaging cavity

Frequency doubling of a laser beam in a non-linear crystal has proven to be a very efficient way of accessing new wavelengths. Since it is a nonlinear effect, its efficiency can be improved by inserting the nonlinear medium in a resonant cavity. In this situation the ratio between the output frequency-doubled beam power and the pump power has been measured at values exceeding 80%. However, a single-mode optical cavity acts as a spatial filter, and can double efficiently TEM
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beams but not complex spatial patterns such as images. We present here an experiment where we have been able to frequency double low power cw images using a self-imaging cavity.