초록
Varied-line spacing concave grating을 이용하여 결상면에서 거의 균일한 분해능을 갖는 평면결상 극자외선 분광기를 설계하엿다. 레이저-프라즈마에서 복사되는 발산광의 집속과 분광기의 수차보정을 위해 toroidal mirror를 사용하였고, 비축광선에 의한 수차를 줄이기 위해 toroidal mirror와 회절격자 사이에 10$\mu \textrm m \times2$mm크기의 입사슬릿을 두었다. 평면결상이 가능한 파장영역은 50~300$\AA$이고, 계산된 분해능은 4000이상이다. 회절격자의 효율과 toroidal mirror에서의 반사율을 고려하면 복사 에너지의 집속도는 toroidal mirror를 사용하지 않았을 때보다 3.5배 증가하고, fluorescence는 파장 100.angs.에서 1000배 이상 증가했다.
The design of a flat-field XUV spectrograph is optimized for a high throughput, aberration-corrected spectral image in the wavelength region of 50-300 $\AA$ The varied-line spacing (VLS) concave grating theory for an XUV spectrograph with a toroidal mirror in front of an entrance slit is derived. Since the derived theory includes the arbitrary shaped source, it is able to correct the limit of the simple optimization theory which considers only a point source at the center of the entrance slit. The reflection matrix at the toroidal mirror and the diffraction matrix at VLS grating are derived and compared with those of a holographic grating. The absolute energy efficiency of a flat-field spectrograph is calculated by considering the reflectivities of the toroidal mirror and the Au coated concave grating and the grating efficiency. The alignment sensitivity of the toroidal mirror and the concave grating is investigated, and the method to achieve the best imaging of XUV spectrum is discussed. The calculated resolving power of the flat-field XUV spectrograph is more than 4000 in the aberration-corrected wavelength range. The focused spot size at the dispersion plane is less than $20\mu \textrm m\times \mu \textrm m$at the wavelength 100$\AA$ It is shown that a high throughput characteristic can also be achieved through a careful adjustment of alignment parameters.
