Has anyone used Michelson's echelon (pictured below), a very famous type of diffraction grating in the 1920s? I am wondering how did the diffraction image look like from this type of transmission grating. Michelson's echelon was made from precisely cut glass/quartz slabs stacked like a staircase/ladder. Hence the term echelon for ladder rungs in French. However, these echelons are part of museums now. Unfortunately, I have never seen a real one. This grating was supposed to have extremely high resolving power because of a large number of diffraction orders. But, of course, no picture exists of the diffraction pattern from such an echelon. Has anyone ever used an echelon like this one or seen a published account of its "raw" diffraction pattern? Such gratings were used with a prism as an order sorter.

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In contrast, I took a picture of a diffraction pattern from a 5 cm long reflective echelle grating (~ 75 lines/mm) with a mercury street lamp. Such gratings are available from popular optics manufacturers, and they look like this (e.g., Thorlabs or Richardson gratings/Edmund, Image from Thorlabs)

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This is a mercury street lamp viewed at night with an echelle grating. Here one can see the beautiful overlap of several orders, and the green line of mercury gives some clue of the number of orders.

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    $\begingroup$ An article in Nature dated April 27, 1899 describes how the echelon was setup and used by a Mr Hilger. Included is a black and white photograph of the setup which features a telescope and a "collimater". Unfortunately, the photograph, being black and white, does not show the spectral output. $\endgroup$
    – nwr
    Commented Oct 19, 2021 at 19:03
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    $\begingroup$ That is a beautiful picture from 1899 and they talk about 8000th order! The echelle I have does not have more than 20-30 orders with ordinary light. It might have more...but still. Amazing. Why echelons vanished is a strange thing. $\endgroup$
    – ACR
    Commented Oct 19, 2021 at 19:48


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