Talk:Waveplate

Half-wave plate error?

Currently the article states:

"The other common type of wave plate is a half-wave plate, which retards one polarization by half a wavelength, or 180 degrees. This type of wave plate rotates the polarization direction of linear polarized light. Wave plates in general as well as polarizers can be described using the Jones matrix formalism, which uses a vector to represent the polarization state of light and a matrix to represent the linear transformation of a wave plate or polarizer."

I hold that a half-wave plate mirrors the polarization about the extraordinary axis. Assume a vertical extraordinary axis: if the vertical component of light passes unchanged, then the horizontal component will be retarded by half a wavelength and will negate the horizontal component. This mirrors the polarization vector about the vertical axis. The action of a fixed half wave element is a mirror and not a rotation: if the incident linear polarized light is rotated in one direction the outcoming polarization will rotate in the opposite direction, hence it is a mirror and not a rotation. If I understand a halfwave plate correctly that is. —Preceding unsigned comment added by 78.21.47.52 (talk) 22:52, 4 January 2010 (UTC)

You may be right. I don't have time to think about this right now, though. Either way, the description needs to be supported by a reference.--Srleffler (talk) 04:46, 5 January 2010 (UTC)

This point of view is supported by the fact that a half wave plate converts one handedness of circularly polarized light to the other. Dave3 (talk) 20:12, 11 April 2010 (UTC)

Image

Not necessarily a waveplate.

Regarding the image that was just added (and deleted by me): It's not clear that it shows a wave plate. If you put an ordinary polarizer at 45° between two crossed polarizers, you will get transmission. No wave plate needed. No quantum mechanics either; it's purely classical optics. The comments on Commons about the image showing a wave plate were not put there by the original poster but were added as speculation by another editor. I have removed them, and added a note explaining the situation.--Srleffler 07:09, 3 November 2006 (UTC)

Note that RealD_3D, for example, uses glasses with circular polarizing filters, normally made from a linear polarizer and 1/4 wave plate. So, the glasses might have a wave plate, depending on viewing side. Gah4 (talk) 00:12, 4 September 2019 (UTC)

Gamma

The units of gamma are missing. Is phase in radians? — Preceding unsigned comment added by 192.249.47.176 (talk) 16:20, 1 November 2011 (UTC)

Yes. When an angle appears in an equation outside of a trigonometric function, it is always in radians.--Srleffler (talk) 16:48, 1 November 2011 (UTC)

Zero-order waveplate

I thought this bit came out of nowhere and was confusing rather than illuminating:

Waveplates are thus manufactured to work for a particular range of wavelengths. The phase variation can be minimized by stacking two waveplates that differ by a tiny amount in thickness back-to-back, with the slow axis of one along the fast axis of the other. With this configuration, the relative phase imparted can be, for the case of a quarter-wave plate, one-fourth a wavelength rather than three-fourths or one-fourth plus an integer. This is called a zero-order waveplate. — Preceding unsigned comment added by VSohn (talk • contribs) 13:34, 28 October 2013 (UTC)

Error in Phase

This line:

For a single waveplate changing the wavelength of the light introduces a linear error in the phase.

Doesn't define what error in the phase means. I assume it's a phase shift between wavelengths that are within the recommended range of wavelengths for the waveplate, but this isn't clear and the rest of the paragraph becomes less insightful because of this ambiguity. — Preceding unsigned comment added by VSohn (talk • contribs) 13:40, 28 October 2013 (UTC)

Tilt

Can someone define tilt/provide a picture indicating its use in this paragraph?

Tilt of the waveplate enters via a factor of 1/cos θ (where θ is the angle of tilt) into the path length and thus only quadratically into the phase. For the extraordinary polarization the tilt also changes the refractive index to the ordinary via a factor of cos θ, so combined with the path length, the phase shift for the extraordinary light due to tilt is zero.

This is seeming too technical for the first heading (Principles of Operation). It is especially difficult without a picture. — Preceding unsigned comment added by VSohn (talk • contribs) 13:41, 28 October 2013 (UTC)

The effect of tilt is that the effective length is longer, which you can see from geometry. Quadratic comes from the second order term in the Taylor series for cos(). Gah4 (talk) 23:53, 3 September 2019 (UTC)

way to technical for a general encylopedia

the intro and how it works is ok, but the half wave part is way way wayyyyyyy to complex for a genreal encylopedia or, at least, that sort of complex stuff should be after simple stuff (u can grade your general intellignec with this comment: if you focus on the typos instead of the content, u fail) — Preceding unsigned comment added by 50.245.17.105 (talk) 17:58, 3 February 2016 (UTC)

Wikipedia is not just a general encyclopedia. We cover both general knowledge and more technical detail, sometimes in the same article. Articles should generally start with the simple stuff and then move into more complex material. I'm sorry that you did not find that to be the case here. What information would you like to see covered, before the article dives into the technical details?--Srleffler (talk) 18:22, 3 February 2016 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Waveplate/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

== Hyphenation and this term == Sometimes on sees the term "half wave plate" hyphenated in this manner: "half-wave plate", but since "half" does not modify "wave" but rather "wave plate" then the term should not be hyphenated at all. Is isn't 1/4 of a wave plate. That would be 1/4 of a plate, like a slice of pie. The plate is retarding the light by a 1/4 of a wave. Thus 1/4-wave plate is correct. — Preceding unsigned comment added by 192.249.47.176 (talk) 16:26, 1 November 2011 (UTC)

Substituted at 22:05, 26 June 2016 (UTC)

common applications in optics?

It would be nice for the article to mention:

• common applications in optics tables e.g. using quarter-wave plates in interferometers of various sorts
• common applications in optical astronomy
• common applications in radio astronomy
• common applications in communications (cell towers, microwave towers, radar)
• materials and construction: for light, for centimeter radio, for sub-millimeter radio
• what happens to unpolarized light going through waveplate?

Basically, there's neat stuff you can do with birefringent crystals (well, ok so old-school polarizers) and waveplates, and other neat stuff, and I can't quite remember what those are... I'm also unclear on quite exactly how they work for radio astronomy and microwaves in general. 67.198.37.17 (talk) 06:04, 16 April 2019 (UTC)

plastic

The article mentions quartz and mica as birefringent materials, but does not mention plastic. As far as I know, for some plastics if you stretch them at an appropriate time during production, the molecules will line up in the stretch direction. That gives them a different index of refraction in that direction. This is also much cheaper than polished quartz or mica. Consider the circular polarizers used for reflection reduction in some places, where they are large and must be produced for low prices. The article should also mention plastic. Gah4 (talk) 23:57, 3 September 2019 (UTC)

See, for example: RealD_3D which uses circular polarizers in (almost) disposable glasses. (They normally reuse them, but I suspect that many walk out the door.) Gah4 (talk) 00:11, 4 September 2019 (UTC)

Edmund sells plastic achromatic wave plates. Gah4 (talk) 02:28, 4 September 2019 (UTC)

References

green light

In the section Full-wave, or sensitive-tint plate it mentions using green light of 540 nm. I could be wrong, but I imagine that the mercury arc green line of 546 nm is most probably what is meant. It is a small difference, but I believe it is better to be correct. I have never used this technique, but perhaps someone with knowledge of the apparatus could comment or correct the mention if I am right. AJim (talk) 04:42, 23 January 2023 (UTC)

I can't imagine why you would assume that. The article describes the procedure in some detail, and gives no reason to suppose the plate is designed to match a mercury line. Looking at vendors of these plates online, it appears clear that the exact wavelength is not all that important. It's somewhere between 530 and 570 nm. --Srleffler (talk) 04:59, 23 January 2023 (UTC)

I agree the exact wavelength does not matter much. I was just thinking about convenient sources of narrow band green light. Today I imagine 532 nm might be a good choice. So maybe a better wording would be: green light (wavelength near 540 nm). It was the equal sign that bothered me.--AJim (talk) 05:42, 23 January 2023 (UTC)

Read the description of how the plate is used again. It's clear that one would not want a narrowband light source that matches the waveplate for this technique, but rather a broadband source—perhaps an incandescent lamp. A narrowband green source would be absolutely useless.--Srleffler (talk) 22:41, 28 January 2023 (UTC)

c-plate? a-plate?

What do these terms mean? I often come across them, but it's hard to find a straight definition of them anywhere. 162.246.139.210 (talk) 17:56, 21 July 2023 (UTC)