Electric polarization

The simplest designs are usually called ‘achromat objectives’ and contain only a front lens and a couple of achromatic doublets to correct for aberrations. On the other hand, we have Apochromat microscope objectives in which several apochromatic doublets are used, in addition to some achromats for a better image quality. For a better explanation of the difference between achromatic and apochromatic lenses, please read the linked articles.

Note regarding glare and sunglasses and the Brewster angle: You have pointed out that unpolarized light incidence at (or near) the brewster angle will be filtered and (mostly) s-polarized upon reflection. If the surface under consideration is horizontal (asphalt on the road, or standing water, for example) then we know that s-polarized light is h-polarized light. Thus if we want to filter this out using sunglasses for example we should make the sunglasses eliminate h-polarized light. Polarizing sunglasses are designed to eliminate h-polarized light when the wearer is standing upright and holding their head in the usual way. If they tilt their head, however, then their sunglasses will now let in more h-polarized light and allow in more v-polarized light. The angle of the sunglasses defines a new coordinate system. Note also that if the surface is vertically oriented (such as the rear window of the car in front of you) then since sunlight is typically coming from above, the s-polarized reflected light will again be mostly horizontally polarized. This means that generally polarizing sunglasses are good and reducing glare from all sorts of objects assuming the sunlight is coming from above. However, during sunrise and sunset the sun is lower in the sky so the reflected s-polarized light may now have large components in the vertical direction so the sunglasses will not work as effectively.

Another specification can be “Plan Fluor” for fluorite and “APO” for apochromatic. Next we have the magnification, numerical aperture, and the immersion medium. As mentioned before, dry objective lenses usually have a NA no larger than 0.95, but that number can be considerably higher in immerse objectives. We next have an infinity symbol, meaning that the lens is infinity corrected.

Political polarization

Objective lenses can have just a couple of lens elements, (an achromat and simple lens, for example) or multiple groups of elements. Even two microscope objectives with the same magnification can have a completely different design, as shown in Figure 1.

Finally to unite all of these concepts. We see that horizontal and vertical polarization refer to the direction of polarization compared to the direction of gravity and s and p-polarization refer to the direction of polarization compared to the plane of incidence. If the surface normal is pointing either in the direction of gravity (as implied by the figure in the OP) or perpendicular to the direction of gravity (a surface which is vertical like a mirror in the restroom) then there is a relationship between s and p-polarized and horizontal and vertically (h and v) polarized light.

The microscope objective will show the manufacturer (not shown in the figure), followed by the type of aberration correction; in our image, we have a “Plan Achromat” which produces a flat surface at the image plane and achromat for the type of chromatic aberration.

\begin{align} p\text{-polarized} & = \text{vertically polarized}\\ s\text{-polarized} & = \text{horizontally polarized} \end{align}

S-polarization

In cases where the objective is not meant to be used in infinity corrected microscopes, there will be a number, usually 160) referring to the length of the microscope tube. Some microscope objectives will show the letters “DIN” which stands for “Deutsche Industrial Normen.” that sets a length of 160 mm.

s and p polarizations are different from horizontal and vertical polarizations. As described above, horizontal and vertical usually refer to the direction of the electric field with respect to gravity. s and p polarizations are instead defined with respect to a reference frame which is related to the surface with which the light is interacting. The surface can be oriented in an arbitrary direction with respect to gravity so we see that s and p are unrelated to horizontal and vertical polarization.

If the electric field is directly incident on the surface the propagation direction and surface normal are parallel so we cannot define a plane of incidence. In this case all polarizations "lie flat" in the plane of the material surface so it is sort of like all polarizations are "s-polarized". This is comparable to the case when light was travelling directly upwards against gravity and all polarizations looked like horizontal polarizations so it didn't make sense to talk about horizontal and vertically polarized light anymore. In this case we must introduce a new different reference frame if we want to talk about the polarization of the light field.

If that's the case then sunlight (unpolarized light) will be reflected as horizontally polarized so to reduce glare effects the polarizing sunglasses must block the horizontal direction of polarization, right?

Polarization

In conclusion, microscope objective lenses are an essential part of a microscope and are used to magnify the specimen being observed. They consist of several components that work together to produce a clear image, and their magnification can vary depending on the intended use of the microscope.

So an unpolarized electromagnetic wave as light when incident on an interface air-water will be reflected as an "s" polarized light at the Brewster angle. This means it oscillates on a plane perpendicular to the plane of incidence, hence parallel to the surface? If yes, then can we say that an s-polarized light is equivalently said to be horizontally polarized?

The magnification of the objective lens can vary, depending on the intended use of the microscope. For example, objective lenses for biological applications typically range from 4x to 100x, while those used for metallurgical applications can range up to 200x or more [1].

polarization中文

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In previous entries, we have talked about the design of scanning microscopes, infinity corrected microscopes, confocal microscope design, and Koehler illumination systems-a common illumination system in microscopes. The most essential microscope element in a borescope design is the objective lens.

H and V polarization usually refer to some arbitrary reference frame. This reference frame is usually defined by the direction of gravity (call this $\hat{z}$ direction). If light is travelling "horizontally" (meaning perpendicular to the direction of gravity, for example in the $\hat{y}$ direction) then we can talk about horizontally and vertically polarized light. For vertically polarized light the electric field is parallel to the direction of gravity so it is in the $\hat{z}$ direction. For horizontally polarized light the electric field is perpendicular to the direction of gravity, that is in the $\hat{x}$ direction. Note that in both cases the electric field is perpendicular to the direction of light propagation.

My doubt comes from a discussion we had in class about the Brewster angle, glare effect produced by the reflection of sunlight on water and polarizing sunglasses.

In the previous calculation, I assumed an angle of acceptance of 72-degrees with a reasonable upper limit when working with air (that angle gives us a NA of 0.95). However, by immersing the sample and microscope in oil or another liquid, it is possible to have a larger NA. This affects not only the resolution of our image but also its brightness (the brightness is calculated as the square of its NA).

Where R is the resolution, ? is the light wavelength, n is the refractive index, and θ is the half angle of the acceptance light cone (NA is the numerical angle defined as sin(θ)). For example, a microscope objective that works with visible light, with air surrounding the sample, and an acceptance half-angle cone of 72-degrees, will have a minimum resolution of 256 nm. If we surround the sample in a liquid with a refractive index of 1.5, our resolution will improve to 171 nm.

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However, imagine a beam travelling directly upwards from the ground in the $\hat{z}$ direction. In this case the polarization lies in the $\hat{x}$, $\hat{y}$ plane. It doesn't make sense to me to call either of these vertical polarization. Rather, we would be better served calling them "East-West" and "North-South" polarized, for example. The key point here is the geometric and coordinate dependent nature of how we call polarizations.

Circularly polarized light

p-polarized light is light where the electric field vector lies in this plane of incidence. s-polarized light is light where the electric field vector is perpendicular to this plane of incidence. If you think about this in terms of the material surface you can see that the electric field vector either pokes in or out of the material surface for p-polarized light while it "lies flat" in the plane of the material surface.

There are three design variables that can help us calculate the microscope objective resolution: the system wavelength, the light cone captured by the objective (also known as numerical aperture), and the refractive index between the first lens of the objective and the sample. This can be expressed by the following formula:

Most off the shelf microscope objectives have several body markings to better identify them. Typical markings can be seen in Figure 2.

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Objective lenses for microscopes typically have several components, including the front lens, the rear lens, the aperture, the lens barrel, and the thread. Each component plays an important role in determining the objective’s performance. For example, the aperture determines the resolution and depth of field of the objective lens, while the thread allows the objective to be attached to the microscope.

This definition of horizontal and vertical polarization also makes sense for light travelling at some reasonable angular deviations from the horizontal plane. We can talk about polarizations which mostly don't have components in the $\hat{z}$ direction, horizontal polarizations, and polarizations which mostly do have components in the $\hat{z}$, vertical polarizations.

*However for the case of light which is shining directly incident onto a material surface the two vectors are parallel and no plane is defined. I'll discuss this case shortly.

I put the tilde on the p to v comparison because for glancing angles (where the light is travelling almost horizontal, large angle of incidence) it makes sense to talk about vertical polarized light but if the light is travelling more and more perpendicular to the surface (smaller angles of incidence) it makes less and less sense to talk about vertically polarized light.

Microscope objective lenses are a crucial part of a microscope, responsible for magnifying the specimen being observed. They are used to gather light from the object being observed and focus the light rays to produce a real image. The objective lens is one of the most important parts of a microscope, as it determines the microscope’s basic performance and function [3].

s and p are defined with respect to the plane of incidence as described in the Wikipedia article. The plane of incidence is defined by two vectors. One vector is the normal vector to the surface (the vector which points out of the surface). The other vector is the direction of propagation for the light under consideration. Often these two vectors are not parallel and thus they describe a plane*. This plane is called the plane of incidence.