NIRSpec optics development: the final report

Geyl, Roland; Ruch, Eric; Vayssade, H.; Leplan, H.; Rodolfo, Jacques

doi:10.1117/12.894430

Cited by 4 publications

(2 citation statements)

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“…Its optical train is reflective throughout, save for the order-separation filters and the low resolution dispersive prism. The three primary optical modules of NIRSpec are each implemented in the form of three-mirror anastigmats employing high-order aspherical surfaces [2]. Counting the five plane fold mirrors and the disperser, the light entering NIRSpec undergoes a total of 15 reflections (in the FS/MOS mode) before reaching the detector array.…”

Section: Photon-conversion Efficiencymentioning

confidence: 99%

Optical throughput and sensitivity of JWST NIRSpec

Giardino

Bhatawdekar²,

Birkmann³

et al. 2022

Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave

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To achieve its ambitious scientific goals, the Near-Infrared Spectrograph, NIRSpec, on board the Webb Space Telescope, needs to meet very demanding throughput requirements, here quantified in terms of photon-conversion efficiency (PCE). During the calibration activities performed for the instrument commissioning, we have obtained the first in-flight measurements of its PCE and also updated the modeling of the light losses occurring in the NIRSpec slit devices.The measured PCE of NIRSpec fixed-slit and multi-object spectroscopy modes overall meets or exceeds the pre-launch model predictions. The results are more contrasted for the integral-field spectroscopy mode, where the differences with the model can reach −20%, above 4 µm, and exceed +30%, below 2 µm. Additionally, thanks to the high quality of the JWST point-spread function, our slit-losses, at the shorter wavelength, are significantly decreased with respect to the pre-flight modeling.These results, combined with the confirmed low noise performance of the detectors, make of NIRSpec an exceptionally sensitive spectrograph.

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Section: Photon-conversion Efficiencymentioning

confidence: 99%

Optical throughput and sensitivity of JWST NIRSpec

Giardino

Bhatawdekar²,

Birkmann³

et al. 2022

Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave

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“…A notable example is the primary mirror segment for the Herschel telescope [9]. Techniques used for fabricating SiC mirror surfaces may include 1) use of Si cladding on top of the SiC mirror substrate [10], 2) computer-controlled polishing (CCP) together with ion beam figuring (IBF) utilizing a polishing database [11], 3) advanced flow polishing [12,13], and 4) diamond turning followed by traditional polishing performed by an optician [14]. With such techniques used today, small and medium size SiC mirrors are readily available in the market, although meter class SiC mirrors have not reached the mass production stage.…”

Section: Introductionmentioning

confidence: 99%

Novel orthogonal velocity polishing tool and its material removal characteristics from CVD SiC mirror surfaces

et al. 2016

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A new and patented polishing tool called Orthogonal Velocity field Tool (OVT) was built and its material removal characteristics from Chemical Vapor Deposition Silicon Carbide (CVD SiC) mirror surfaces were investigated in this study. The velocity field of OVT is produced by rotating the bicycle type tool in the two orthogonal axes, and this concept is capable of producing a material removal foot print of pseudo Gaussian shapes. First for the OVT characterization, we derived a theoretical material removal model using distributions of pressure exerted onto the workpiece surface, relative speed between the tool and workpiece surface, and dwell time inside the tool- workpiece contact area. Second, using two flat CVD SiC mirrors that are 150 mm in diameter, we ran material removal experiments over machine run parameter ranging from 12.901 to 25.867 psi in pressure, from 0.086 m/sec to 0.147 m/sec tool in the relative speed, and 5 to 15 sec in dwell time. Material removal coefficients are obtained by using the in-house developed data analysis program. The resulting material removal coefficient varies from 3.35 to 9.46 um/psi hour m/sec with a mean value of 5.90 ± 1.26(standard deviation). We describe the technical details of the new OVT machine, the data analysis program, the experiments, and the results together with the implications to the future development of the machine.

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