Kumar Mukund, Modi Mohd Hussain, Singhal Himanshu, Sendhil Raja S, Chakera Juzer Ali, Gupta Raj Kumar, Naik Prasad Anant, Lodha Gyanendra Singh, Gupta Parshotam Dass
Raja Ramanna Centre for Advanced Technology, Indore, India.
Appl Opt. 2013 Mar 10;52(8):1725-30. doi: 10.1364/AO.52.001725.
An UV cleaning technique has been used for the removal of carbon contamination from grating surface, using oxygen free-radicals generated by the absorption of UV radiation (172 nm) in atmospheric oxygen. The extent of restoration of absolute diffraction efficiency (ADE) and grating blaze angle of a carbon-contaminated variable line-spaced concave grating (average line spacing of 1200 lines/mm, blaze angle 3.2 deg, and blaze wavelength 10 nm) has been studied over a 5-70 nm wavelength range. The contamination (due to prolonged use in extreme-ultraviolet spectrograph) resulted in a drastic reduction in the diffraction efficiency of grating, along with a change in the blaze angle. The UV cleaning led to the restoration of blaze angle as well as to an increase in the ADE by more than an order of magnitude for the first two diffraction orders (i.e., from ~0.2 to ~7.2%) for the first diffraction order and 0.1 to ~5% for the second diffraction order at the blaze wavelength. The study is useful for the restoration of carbon-contaminated costly optics.
