研究目的
To constrain the models of dark energy with a five-year galaxy and quasar redshift survey by measuring the baryon acoustic oscillations and the growth of structure through redshift-space distortions.
研究成果
The VPH gratings meet DESI performance requirements with high consistency in area-weighted efficiency and wavefront errors, and have been approved for integration. The measurements showed that the gratings are suitable for the DESI spectrograph, despite some performance losses in the red gratings at wavelengths above 700 nm.
研究不足
The test configuration measured the wavefront errors at different incidence angles than designed for, and the Zygo wavelength is out-of-band for the blue and NIR gratings. The incidence angles were arbitrarily chosen to prevent beam clipping, complicating the measurement of the full clear aperture.
1：Experimental Design and Method Selection:
The methodology involves measuring the incidence angle, area-weighted efficiency, and wavefront errors of VPH gratings. A custom measurement rig was built to measure the +1 order diffraction efficiency of the gratings, allowing for comprehensive performance characterization across the entire clear aperture.
2：Sample Selection and Data Sources:
Thirty-six VPH gratings were produced and their performances were evaluated at the Lawrence Berkeley National Laboratory.
3：List of Experimental Equipment and Materials:
The measurement rig includes Mightex LEDs, a Newport 1/8 m monochromator, a Newport 1936-R power meter, and a Zygo interferometer for wavefront error measurements.
4：Experimental Procedures and Operational Workflow:
Each grating was inspected for visible defects, then placed in the measurement rig for performance tests including optimal incidence angle determination, full-grating area-weighted efficiency measurement, and wavefront error assessment.
5：Data Analysis Methods:
Data were analyzed to determine the optimal incidence angles, calculate the area-weighted efficiency, and assess wavefront errors. The analysis included spline interpolation of efficiency data and Zernike fringe polynomial fitting for wavefront error analysis.
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