The present invention concerns a single crystalline diamond optical element production method. The method includes the steps of: ‐ providing a single crystalline diamond substrate or layer; ‐ applying a mask layer to the single crystalline diamond substrate or layer; ‐ forming at least one or a plurality of indentations or recesses through the mask layer to expose a portion or portions of the single crystalline diamond substrate or layer; and ‐ etching the exposed portion or portions of the single crystalline diamond substrate or layer.