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9 November 2001 Production of high-order micromachined silicon echelles on optically flat substrates
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Infrared spectrometers using silicon immersion gratings and prisms can have substantial performance advantages over conventional instruments. The immersion gratings and grisms share a common geometry: prism-shaped pieces of silicon with blazed grooves along one side. The grooves can either be machined directly into substrates or the grooves can be machined into thin wafers which are then bonded to flat-surfaced prisms. Chemical micromachining currently is the best method of ruling grooves directly into silicon surfaces. The tolerances for near-IR diffraction gratings make direct machining of the grooves onto one surface of a bulky, prism-shaped substrate very difficult. We encountered a number of issues that we had to resolve when we tried to etch precisely positioned grooves into massive pieces of silicon: silicon substrate purity, lithography mask alignment, photoresist thickness uniformity, temperature control, wet etching vs. reactive-ion etching. We have successfully manufactured 7 line / mm gratings on 15 mm thick substrates. We performed optical tests with these gratings used as front-surface devices to determine efficiency and diffraction limited performance. Our echelle gratings have 70\% efficiency in 365th-368th order at 632.8 nm. Testing shows that the grating preserves a diffraction-limited point-spread function making them good dispersing elements for applications requiring high spectral resolving power.
© (2001) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Oleg A. Ershov, Daniel T. Jaffe, Jasmina P. Marsh, and Luke D. Keller "Production of high-order micromachined silicon echelles on optically flat substrates", Proc. SPIE 4440, Lithographic and Micromachining Techniques for Optical Component Fabrication, (9 November 2001);

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