18.2 nm Schwarzschild microscope for plasma diagnosis

A Schwarzschild microscope at 18.2 nm for ultra-fast laser produced plasma diagnosis is developed. According to the requirements of plasma diagnosis, the microscope is designed for numerical aperture of 0.1 and magnification of 10. It is found that spatial resolution of the designed objective achieves 1 250 lp/mm within the field of ±1 mm with respect to the calculation of modular transfer function. Based on the working wavelength and incidence angle of light, the Mo/Si multilayer film with period of 9.509 nm and layer number of 30 is designed and the coatings are deposited with magnetron sputtering. The reflectivity of the developed optical elements at 18.2 nm is about 30%. In order to demonstrate the resolution of microscope, a 24 lp/mm copper grid backlit by laser produced plasma is imaged via the Schwarzschild microscope on CCD. The result shows a resolution of 3 μm at the center field and 5 μm in 600 μm field, which can meet the requirement of laser produced plasma diagnosis. (authors)