Fabrication and application of plane and concave varied line-space gratings for the vacuum spectral domain by interference lithography

摘要

Subject of study. The feasibility of creating gratings with a spacing that varies on the grating surface according to a given law (that is, varied line-space gratings) with an average (approximately 600 mm-1) and high (up to 3000 mm-1) groove frequency by interference lithography at an argon laser wavelength of 488 nm is studied. Aim of study. The development of high-resolution flat-field varied line-space grating spectrographs for the vacuum ultraviolet and soft X-ray regions of the spectrum and their testing by recording line spectra of multiply charged ions in laser plasma is the goal of the study. Method. The developed method makes it possible to make diffraction varied line-space gratings for operation in spectrographs at the grazing incidence of radiation. In the first stage, the optical scheme with a spherical-mirror aberrator is designed, which provides the required frequency distribution of the interference fringes on the grating surface. After the "writing" of the grating on the photoresist and its development, the parameters of the resulting grating are measured by the diffraction of laser radiation (632.8 nm), the spectrograph is aligned, the line spectra are recorded in the soft X-ray region of the spectrum, and the characteristics of the instrument are evaluated. Main results. Varied line-space gratings with a gold reflective coating are fabricated: plane (with groove frequencies of 530 and 670 mm-1 at the edges of the grating) and spherical (curvature radius of 6 m and frequencies of 2100 and 2700 mm-1). The parameters of the varied line-space gratings are similar to the designed ones. The spectra of multiply charged ions were obtained in the range of 10-25 nm, and the spectral resolving power of 103, limited only by the pixel size (13 mu;m) of the CCD detector in use, was demonstrated. Practical significance. The capabilities of the domestic technology of interference lithography for the fabrication of varied line-space gratings and varied line-space grating spectrographs for the soft X-ray range of the spectrum are demonstrated. The spectrograph will be used to detect soft X-rays during the interaction of multiterawatt laser radiation with various targets. COPY; 2023 Optica Publishing Group