| Transmission VPHG (volume phase holographic grating) has the characteristics of high diffraction efficiency, low noise and high resolution and is widely used for astronomical spectroscopy, ultrafast lasers, and wavelength division multiplexing. The prism - grating– prism (PGP) imaging spectrograph, in which a transmission VPHG sandwiched by two prisms is used as a dispersive element, acts an important role in high resolution aerial and remote sensing applications.In this paper, the high diffraction efficiency transmission VPHGs have been studied theoretically and experimentally.The research background and progresses of the VPHGs are introduced firstly. For theories calculation, RCWA (rigorous coupled wave analysis) and Kogelnik's coupled wave theory are introduced briefly. The two theories have been compared and described by correlation and the approximate condition of Kogelnik's coupled wave theory has been studied. The results show that the consistency of the two theories is related to the grating fringe density, the medium thickness and refractive index modulation. RCWA and Kogelnik's coupled wave theory are used to design the high diffraction efficiency transmission VPHG with 462 lp/mm and 1000lp/mm, respectively.For fabrication technique, by adjusting and controlling the preparation conditions of dichromate gelatin (DCG) plates, the exposure time and the post-processing technique of the grating, the transmission VPHGs with high diffraction efficiency approximately accord with the design requirements have been obtained.Finally, the 1st order diffraction efficiency and angle selectivity of the transmission VPHGs were measured and analyzed. In visible spectral region, the maximum 1st order diffraction efficiency of the transmission VPHG with 462lp/mm and 1000lp/mm is nearly up to 92% and 98%, respectively. The above results provide a technical support for further research on the application of transmission VPHGs in PGP imaging spectrograph. |
PDF Full Text Request