Note that a very small gain or loss difference for the two polarization directions can be sufficient for obtaining a stable linear polarization, provided that there is no significant coupling of polarization modes within the laser resonator.

Adolescents and teens in general are exposed to LED lights sources for long periods of time, spending time on their phones, tablets and computers, and they may also be exposed to new LED light sources, like virtual reality headsets, where the screen is very close to the eyes. The luminance of the light source in virtual reality headsets is very low, however, and the exposure limits are not likely to be exceeded. Manufacturers give guidance on the maximum duration of use for these types of headsets. While the scientific evidence does not show any increased risk to the eyes, there may be other effects, like disrupting normal sleep and wake patterns, which might be particularly important for this age group.

Unpolarizedlight

On the other hand, the polarization state of the laser output can be disturbed e.g. by random (and temperature-dependent) birefringence, such as occurs e.g. in optical fibers (if they are not polarization-maintaining or single-polarization fibers) and also in laser crystals or glasses as a result of thermal effects (→ depolarization loss). If the laser gain is not polarization-dependent, small drifts of the birefringence may lead to large changes in the polarization state, and also a significant variation in the polarization state across the beam profile.

Jones vectors can be used only for fully defined polarization states, not for unpolarized or partially polarized beams (see below) having a stochastic nature.

Political polarization

The degree of linear polarization is often quantified with the polarization extinction ratio (PER), defined as the ratio of optical powers in the two polarization directions. It is often specified in decibels, and measured by recording the orientation-dependent power transmission of a polarizer. Of course, the extinction ratio of the polarizer itself must be higher than that of the laser beam.

In many respects, light can be described as a wave phenomenon (→ wave optics). More specifically, light waves are recognized as electromagnetic transverse waves, i.e., with transverse oscillations of the electric and magnetic field.

In many cases, the output of a laser is a linearly polarized laser beam. Different mechanisms can be responsible for that:

Circular polarization

I would have been glad to finally remove a serious mistake, but I believe my equations are correct. They agree with those in various textbooks and e.g. also in Wikipedia. Your argument concerning energy swapping back and forth between the electric and magnetic fields looks somewhat plausible but is not accurate.

Fully polarized states can be associated with points on the so-called Poincaré sphere. Partially polarized states correspond to points inside that sphere; unpolarized light is represented by the point at its center.

A radially polarized laser beam may be generated from a linearly polarized beam with some optical element, but it is also possible to obtain radially polarized emission directly from a laser. The advantage of this approach, applied in a solid-state bulk laser, is that depolarization loss may be avoided [4]. Furthermore, there are applications benefiting from radially polarized light.

As explained above, a waveplate or other birefringent optical element may rotate the direction of linear polarization, but more generally one will obtain an elliptical polarization state after such an element. True polarization rotation, where a linear polarization state is always maintained (just with variable direction), can occur in the form of optical activity. Some optically active substances such as ordinary sugar (saccharose) can produce substantial rotation angles already within e.g. a few millimeters of propagation length. Optical activity can be accurately measured with polarimeters.

The polarization state of light often matters when light hits an optical surface under some angle. A linear polarization state is then denoted as p polarization when the polarization direction lies in the plane spanned by the incoming beam and the reflected beam. The polarization with a direction perpendicular to that is called s polarization. These indications have a German origin: s = senkrecht = perpendicular, p = parallel.

Shalom EO also offers other optical crystal materials, including: nonlinear crystals, laser crystals, and electric-optical and acousto-optic crystals.

This summary of the scientific Opinion on 'Potential risks to human health of Light Emitting Diodes (LEDs)' by the Scientific Committee on Health, Environmental and Emerging Risks (SCHEER) covers some of the Opinion's key points and goes more in depth than the one-page factsheet on the same topic, also available on this website. An abstract and a shorter but more technical summary are also included in the scientific Opinion itself. Information about data and methodology and the science behind LEDs and eye and skin optics are also found in the Opinion and are not covered here.

A circular polarization state can mathematically be obtained as a superposition of electric field oscillations in the vertical and horizontal direction, both with equal strength but a relative phase change of 90°. Effectively, this leads to a rapid rotation of the electric field vector – once per optical cycle – which maintains a constant magnitude.

In the previous cases, the direction of the electric field vector was assumed to be constant over the full beam profile. However, there are light beams where that is not the case. For example, there are beams with radial polarization, where the polarization at any point on the beam profile is oriented in the radial direction, i.e., away from the beam axis.

EKSMA Optics has various kinds of birefringent crystal materials including various nonlinear crystals, some of our laser crystals and Raman crystals and polarizing optics crystals.

Circularly polarizedlight

In simple cases, one has a polarization direction along one of the axes of the crystal lattice. One may then call this c polarization, for example, if it is along the crystal's c axis. (Unfortunately, for one type of crystal, there are sometimes different ways of labeling the crystal axes.)

Using our Advertising Package, you can display your logo, further below your product description, and these will been seen by many photonics professionals.

There are also azimuthally polarized beams, where the electric field direction at any point is tangential, i.e., perpendicular to a line through the point and the beam axis.

While optical activity usually results from the presence of chiral molecules, with a concentration difference between the two possible enantiometers, it can also be induced by a magnetic field in a substance which is not naturally optically active. That is called the Faraday effect, and is exploited in Faraday rotators and Faraday isolators.

Linearly polarized light can be depolarized (made unpolarized) with a polarization scrambler, which applies the mentioned random polarization changes, or at least quasi-random changes.

In the simplest case, a light beam is linearly polarized, which means that the electric field oscillates in a certain linear direction perpendicular to the beam axis, and the magnetic field oscillates in a direction which is perpendicular both to the propagation axis and the electric field direction. The direction of polarization is taken to be the direction of the electric field oscillations (i.e., not the magnetic ones). For example, a laser beam propagating in ($z$) direction may have the electric field oscillations in the vertical (($y$)) direction and the magnetic field oscillations in the horizontal (($x$)) direction (see Figure 1); it can be called vertically polarized or ($y$)-polarized. In a different perspective, this is also shown in the second part of Figure 2.

For the mentioned phase-matching scheme, which is denoted as XY oo-e, the pump wave has ordinary polarization, while the second-harmonic wave has extraordinary polarization. There are also cases with type II phase matching, e.g. the scheme XY oe-e, where the pump wave has both an ordinary and an extraordinary polarization component.

Shalom EO offers various birefringent materials, including: MgF2 crystals, LiNbO3 and alpha-BBO crystals, quartz crystals, calcite crystals, and YVO4 crystals. The crystals exhibit excellent properties when used to make waveplates, Glan and Thompson polarizers, and other optical components. Crystal ingots, blanks, and polished and coated optical elements made of birefringent crystals are offered according to your request.

All light affects the circadian rhythm, which is the body's 24-hour internal clock that alternates between sleepiness and alertness at regular intervals and is also known as the sleep/wake cycle. Most people naturally dim or turn off the lights to sleep; darkness is a cue for the brain and body to rest.

Children have a higher sensitivity to blue light and although emissions may not be harmful, light from blue-emitting LEDs may be very dazzling for young children. Some LED emission spectra may cause light-induced retina damage, which is a concern especially for children below about three years of age. There is, however, a European standard for electronic toys that limits the emission of optical radiation from toys.

The polarization state of monochromatic light is often described with a Jones vector, having complex electric field amplitudes for ($x$) and ($y$) direction, if propagation occurs in ($z$) direction. That Jones vector may be constant over some area across the beam, or it may vary, for example for a radially polarized beam (see above). The effect of optical elements such as waveplates, polarizers and Faraday rotators can be described with Jones matrices, with which the Jones vectors can be transformed by multiplication. (One assumes a linear relationship between input and output amplitudes.) A whole sequence of such optical elements can be described with a single Jones matrix, which is obtained as the product of the matrices corresponding to the components.

Of course, the polarization can have any other direction perpendicular to the beam axis. Note that a rotation of the polarization by 180° does not lead to a physically distinct state.

Some LEDs emit a narrow but concentrated band of light in the UV or ultraviolet range – UV LED. Although UV-LEDs are not widely used by the general public for their UV output, they are being used for their UV properties by the cosmetic industry, both by nail studios and for home use, which are increasingly opting to use UV LED gel lamps rather than UV gel discharge lamps because of their efficiency. Neither type of nail lamp appears to significantly increase the risk of non-melanoma skin cancer. However, there is insufficient data on the possibility of premature skin ageing and the risk to the eyes of professional operators. This topic is reviewed in the 2012 Opinion 'Health Effects of Artificial Light', produced by the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR).

As people age, they may experience more difficulties with blue light sources. Some LED lights that pulse, result in phantom images when someone turns their head or if the eye is moved quickly. These effects can be distracting, and in some cases, older eyes might perceive lights to be blurred, which might cause difficulties, for example when the lights are used on destination displays on the front of buses. Older people also tend to experience glare more often, while younger people seem to experience flicker more often than their elders.

polarization中文

As good lighting practice, high luminance LED lights should be diffused or shielded from being looked at directly to avoid glare. Some LED street lights have exposed LED elements that can be seen by road users within their normal field of view, such as when they are looking ahead. This may make viewers instinctively look away from the light source if it is too bright or have difficulty seeing the area near the light source.

Linear polarization

Studies show that the radiance from screens is less than 10% of the maximum amount that would be within safe limits to still protect the retina from photochemically-induced injury, so the short answer is no. The general public does not risk getting eye injuries from optical radiation exposure from LED screens in normal use. The longer answer, however, is that evaluating the risk is not as simple as it might seem because of the many variables that have to be taken into account. The type of LED light used in screens, toys and car lighting contains blue light, and evaluating the risk of blue light damaging the retina requires considering the integrated radiance of the retinal image from the light source (the reflected glow of the light source seen in the eye itself), or the flux of radiant energy per unit area per unit solid angle. This changes, depending on if the light is looked at momentarily, with the eye looking directly at it for a brief time, or if it is viewed over extended time, when the retinal image is spread out over an increasingly large area of the retina because the eye will not remain fixed and staring at it, but will move around. So in fact, looking at lights longer does not necessarily pose a greater risk, because the eye will normally roam and blink, reducing the radiant energy that reaches each part of the retina.

By submitting the information, you give your consent to the potential publication of your inputs on our website according to our rules. (If you later retract your consent, we will delete those inputs.) As your inputs are first reviewed by the author, they may be published with some delay.

Vehicle LED lights, particularly daylight running lights and headlights, can be a source of glare. They might also produce more glare when it is foggy. Glare occurs when light is scattered in the eye and it is more common when light sources emit high levels of blue light. This may make it difficult to see things that are near to the light source, especially for older eyes. When glare is so intense that vision is completely impaired, it is sometimes called disabling glare.

Frequently, however, one requires a propagation direction which is not aligned with one of the crystal axes – for example, in the context of critical phase matching. The article on critical phase matching contains an example case for type I phase matching of frequency doubling in LBO, where the pump and second-harmonic beams propagate within the XY plane with an angle ($\varphi$) against the X axis). In this situation, polarization can be either ordinary or extraordinary:

When light propagates in a non-isotropic medium, such as a nonlinear crystal, the direction of polarization relative to the crystal axes is relevant. This is not the direction of beam propagation, but rather perpendicular to that.

There are also partially polarized states of light. These can be described with Stokes vectors (but not with Jones vectors). Further, one can define a degree of polarization which can be calculated from the Stokes vector and can vary between 0 (unpolarized) and 1 (fully polarized).

Feel free to contact us for assistance. Our experienced staff is only too pleased to help you with the decision process.

Polarization

Please do not enter personal data here. (See also our privacy declaration.) If you wish to receive personal feedback or consultancy from the author, please contact him, e.g. via e-mail.

Linearly polarizedlight

Your first plot shows the magnetic and electric field in phase – which is wrong. The magnetic field is made from the changing electric field. The two fields swap energy back and forth. Hence the magnetic field is at a maximum when the electric field has the largest rate of change, that is, at zero E field. The magnetic field zeros in strength when the electric field rate of change is zero, at it's peak. These are a simple consequence of Maxwell's Equations and is covered in most any text on E&M. The worst error I have found in years of use of your marvelous resource!

Here you can submit questions and comments. As far as they get accepted by the author, they will appear above this paragraph together with the author’s answer. The author will decide on acceptance based on certain criteria. Essentially, the issue must be of sufficiently broad interest.

If the oscillations of the horizontal and vertical electric field vector do not have the same strengths, one has the case of an elliptical polarization, where the electric field vector, projected to a plane perpendicular to the propagation direction, moves along an ellipse.

There is some evidence that normal use of LEDs or screens illuminated by LEDs during the evening can affect the circadian system influencing sleep quality. However, the influence of different wavelengths of light on the circadian system is not completely clear yet. In addition, the activity being carried out on phones and tablets and computers also plays a role – watching an exciting movie or reading a thriller, for example, may hinder someone's ability to drift off to sleep.

The blue light component of the optical emission of LED lights is similar to an incandescent lamp, but the infrared emission will be greatly reduced or absent. This might influence the normal bioprocesses in humans and is still being investigated.

There are cases where polychromatic light can be described with a single Jones vector, since all its frequency components have essentially the same polarization state. However, the polarization state is substantially frequency-dependent in other cases.

A light beam is called unpolarized when the analysis with a polarizer results in 50% of the power to be in each polarization state, regardless of the rotational orientation. Microscopically, this usually means that the polarization state is randomly fluctuating, so that on average no polarization is detected. Note that such fluctuations are not possible for strictly monochromatic light.

Many street lights and other street fixtures now use LED lighting, mainly because it is energy efficient. However, poor quality LED lighting can appear harsh or can induce glare or scattering effects. The brightness of lighting should be appropriate to its use, and LED street lights do not need to be so bright as to replicate daylight, but should provide soft lighting for security and safety. Motorways might require brighter lighting than residential roads as well. The blueness of an optical radiation source like LEDs is often measured by its correlated colour temperature (CCT). The higher the CCT, the more blue-rich it is and the harsher and brighter it appears. However, this metric can provide misleading results for some LED sources.

The widespread use of LEDs is relatively recent. Therefore, only a small number of studies have looked at the effects of LEDs versus traditional light sources on circadian rhythms. It is important to note that LEDs do not fall into one homogenous class; their influence on the circadian system depends on their specific properties.

One distinguishes left and right circular polarization (see Figure 2). For example, left circular polarization means that the electric (and magnetic) field vector rotates in the left direction, seen in the direction of propagation. For an observer looking against the beam, the rotation of course has the opposite direction.

Note that radial or azimuthal polarization state requires a zero electric field strength and thus also a vanishing optical intensity on the beam axis; it is not compatible with a Gaussian beam, for example. Radially polarized beams frequently exhibit a kind of donut profile.

We offer a wide range of polarizers and polarization optics for many different uses. Choosing the right polarization optic for your application can be a bewildering task, as we offer a wide range for many different uses.