Talk:Nicol prism

Complexity

Is there any reason why the Nicol prism is so much more complicated than the Glan-Air or Glan-Thompson prism? It is easier to manufacture? Does it have wider viewing angle? 10:08, 28 December 2005 Arnero

• I once read a book about making crystals as a hobby, that told its readers how to make a sodium nitrate crystal and how to make that into a Nicol prism! It works; but they are fragile and soluble. Anthony Appleyard 12:03, 18 February 2006 (UTC)

Sodium nitrate is, IIRC, isomorphous with calcite as used in the Nicol's original prisms. So one would expect comparable optical properties. However, for the reasons of solubility, I'd be surprised to hear of sodium nitrate being used for this (unless you were building an instrument for quite obscure conditions, or wavelengths where calcite is opaque).

As I remember the description (from an early edition of Rutley's "Elements of Mineralogy", I think ; not a book I have access to now. Hmm, I wonder if I can find it online?), Nicol had worked out the geometry necessary with the most strongly-birefringent mineral that he could readily acquire in large, transparent blocks, and found that he could conveniently make a Nicol-esque prism from cleavage fragments of calcite. (In it's natural variety of [Iceland Spar], large perfect cleavage rhombs of calcite have been well known for centuries. This made it a very convenient starting material.) The most difficult part of the manufacture was the accurate cutting of the crystals obliquely to their natural cleavage, then polishing the cut surfaces optically flat. Being able to cleave the other optical surfaces after doing this most-difficult step would have considerably simplified the overall manufacturing process, and improved yields.

I don't know the comparative difficulty of making Glan-X polarisers. For petrological use, the appearance of polarising films in the early 20th century spelled the death of Nicols in normal manufacture. That doesn't make them unused - but I only used one once in 4 years as a geology student. By comparison with a film polariser, a Nicol doesn't change the colour as much. However, the field of view is dimmer, due to the small aperture of the Nicols.

I came onto this page following a crossword clue ; I've updated the Petrology article to point to here.

A Karley (talk) 12:38, 8 December 2007 (UTC)

Nicol Prism

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