PRAXIS：用于光纤光栅OH抑制的低本底NIR光谱仪
PRAXIS: a low background NIR spectrograph for fibre Bragg grating OH suppression
摘要：
光纤布拉格光栅（FBG）OH抑制能够大大减少近红外光谱仪看到的明亮天空背景。通过在光进入摄谱仪之前以高分辨率滤除气辉发射线，该技术防止从发射线散射到线间区域，从而减少所有波长的背景。为了充分利用这种天空背景的减少，摄谱仪必须有非常低的仪器背景，使它保持天空噪声限制。原型GNOSIS系统的模拟和实际经验都表明，为更高的天空背景水平设计的现有光谱仪将无法充分利用天空背景减少。因此，我们提出了PRAXIS，一种专门为此目的而优化的光谱仪。PRAXIS概念是用于J和H波段的光纤馈入、完全低温、固定格式光谱仪。暗电流将通过使用最新一代的近红外探测器最小化，而热背景将通过使用低温光纤狭缝减少。优化的光谱格式和高通量体相位全息光栅的使用将进一步提高灵敏度。我们的建议是一个模块化的系统，包括可更换的前光学单元，积分场单元和OH抑制单元，使PRAXIS作为一个访问者的仪器上的任何大型望远镜，并使新的发展FBG OH抑制被纳入，因为他们变得可用。作为一个高性能的光纤光谱仪，PRAXIS也可以作为其他天文光子技术的测试平台。
英文摘要：
Fibre Bragg grating (FBG) OH suppression is capable of greatly reducing the bright sky background seen by near infrared spectrographs. By filtering out the airglow emission lines at high resolution before the light enters the spectrograph this technique prevents scattering from the emission lines into interline regions, thereby reducing the background at all wavelengths. In order to take full advantage of this sky background reduction the spectrograph must have very low instrumental backgrounds so that it remains sky noise limited. Both simulations and real world experience with the prototype GNOSIS system show that existing spectrographs, designed for higher sky background levels, will be unable to fully exploit the sky background reduction. We therefore propose PRAXIS, a spectrograph optimised specifically for this purpose. The PRAXIS concept is a fibre fed, fully cryogenic, fixed format spectrograph for the J and H-bands. Dark current will be minimised by using the best of the latest generation of NIR detectors while thermal backgrounds will be reduced by the use of a cryogenic fibre slit. Optimised spectral formats and the use of high throughput volume phase holographic gratings will further enhance sensitivity. Our proposal is for a modular system, incorporating exchangeable fore-optics units, integral field units and OH suppression units, to allow PRAXIS to operate as a visitor instrument on any large telescope and enable new developments in FBG OH suppression to be incorporated as they become available. As a high performance fibre fed spectrograph PRAXIS could also serve as a testbed for other astrophotonic technologies.
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