Focusing transmission gratings for high-energy lasers

To focus the third harmonic of high energy neodymium glass laser, the usage of focusing transmissions diffractive gratings ion etched directly into fused silica blank brings major benefits in comparison with classical optical solutions using aspheric lenses. The damage threshold of such a diffractive component is the same as the damage threshold of a high grade, thin, fused silica plane window. The transmission efficiency reaches 94 percent for polarization s or p. The image quality is nearly perfect: this diffractive component acts as a stigmatic lens. It separates the remaining first and second harmonic from the third one and in addition it creates a focused reflective order with 0.5 percent efficiency which offers the possibility to get a well focused sampling beam.