Propagating solutions to Maxwell’s equations in classical electromagnetism and real photons in quantum electrodynamics. A superset of thermal-radiation.

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How can a laser pointer have range of several kilometers in atmosphere?

Laser pointers manufacturers claim that some pointers have range of several kilometers. Okay, they use a powerful laser, but that powerful laser usually has power less than one watt. Okay, the laser ...
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1answer
4k views

Why are lasers inefficient?

Why are lasers inefficient? Is it because of the heat lost during lasing? Why couldn't there be thermocouples or turbines in parts of the cooling circuits to extract something out of that heat?
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Is there a reason for photodynamic therapy to not cause cancer if mobile phones might?

I don't want to open a debate about whether cell phones can cause cancer, I read the thread: Could cell-phone radiation cause cancer? For the sake of this question let's assume there's a chance for ...
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1answer
144 views

Does a slide in a projector act as a diffuser?

I was wondering whether or not a slide in a slide projector acts as light diffuser? So when I have a light source that does not have a parallel beam on the slide can I expect that the other side of ...
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1answer
337 views

Is there a limit to the visual information a photon can carry?

As photons bounce around and finally find their way into our eyes, are they continually relinquishing the information of the previous thing they "bounced off of"? Is this the reason why we receive a ...
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181 views

range of infrared light

I notice in the EMS chart that only half of the IR range will travel through the earth's atmosphere. So in the range of frequencies that penetrate the atmosphere what frequency travels farthest?
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854 views

Light Energy Absorption In Mirror

Let the amount of energy in one pulse of (laser) light be $E$, and the wavelength be $\lambda$. This pulse goes straight to the mirror, and it is reflected by the mirror. Let the reflectivity of ...
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What does an electromagnetic wave look like at a fixed moment in time?

I am curious what the electric and magnetic field's of light look like when time is stopped. A "photograph" or illustration/description of these fields at a moment in time is what I desire. Also, ...
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What happens to light in a perfect reflective sphere?

Let's say you have the ability to shine some light into a perfectly round sphere and the sphere's interior surface was perfectly smooth and reflective and there was no way for the light to escape. If ...
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Why is electricity not transmitted wirelessly?

Why is electricity not transmitted wirelessly such that we don't need to span cables on the earth's surface? As in: electricity is transmitted wirelessly from the power plant to the household.
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Solar chamber trapped light

Was wondering if trapping light in a reflective chamber could heat rods sufficiently enough to heat water? Trying to think of new ways in which we can utilise solar energy.
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803 views

Could cell-phone radiation cause cancer?

It is very crucial that I ask whether it ``could'' and not whether it does. I do not mean to be the least controversial. To my surprise, having read ``Physics for Future Presidents'' by Richard ...
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3answers
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Could we enable ourselves to send messages to and receive messages from the future?

Based on John Isaacks' question, "If you view the Earth from far enough away can you observe its past?" and the responses, it appears that we could use mirrors to see into the past. Using Vintage's ...
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If you view the Earth from far enough away can you observe its past?

From my understanding of light, you are always looking into the past based on how much time it takes the light to reach you from what you are observing. For example when you see a star burn out, if ...
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1answer
249 views

Why electromagnetic waves propagating along x transfers to electron momentum along z?

Why EM waves having only x momentum transfers to electron z momentum? Electron begins oscillating along z, so will not radiate EM waves along z direction, to compensate its z momentum. It seems that ...
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3answers
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Batman spotlight in the sky

I have noticed that obstructing a spotlight typically results in a blurred shadow unlike the crisp batman symbol in the comics of batman. Is there a way to create a spotlight with a crisp batman ...
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1answer
303 views

Linear polarizer and the angle of incidence

It is known that when a beam of lineary polarized light falls perpendicularly on a linear polarizer, the intensity of polarization changes according to Malus' law and the direction of polarization ...
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2answers
721 views

vander waals and casimir forces

Does one need to invoke quantum mechanics to explain casimir force or vander waals force. I see that textbooks show derivation of vander waal force with no QM but casimir force is typically described ...
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3answers
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What other shielding material than lead is effective against gamma rays?

As the question in the title states I am wondering what material can be effectively used to shield gamma rays apart from lead? I believe concrete is often used, but it is nowhere near as effective as ...
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2answers
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How do you calculate the intensity of light around the focal point from a focused collimated beam of light?

Problem/Purpose of me asking this question to you people who know more than me: So I'm doing a science project where I'm collimating a beam of light to a focus point in a light medium (water vapor or ...
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Where does light energy go when the electric and magnetic components equal zero? [duplicate]

Possible Duplicate: Popular depictions of electromagnetic wave: is there an error? The electric and magnetic components of light increase and decrease at the same time, pass through zero ...
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3answers
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Distant bodies emitting photons

This comes from a discussion forum, where a friend of mine asked the following: We can see objects in space billion of light years away, right? I started wondering about that. If you take 2 ...
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2answers
303 views

Effect of gravitation on light

Einstein predicted that the gravitational force can act on light. This was verified in one solar eclipse that light from a star near to the sun's disc bent due to Sun's gravity as predicted. Since ...
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1answer
173 views

Will the sun cool and produce a disrupting EMP?

Scientists say rare drop in sunspot activity could cause global cooling http://www.globalpost.com/dispatch/news/business-tech/science/110615/science-news-solar-flares-sunspots-global-warming ...
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Polarization and mirrors

When a light beam reaches a dielectric surface, the incident and reflected beams have different intensities depending on polarization. For the so-called Brewster's angle, the reflected light is ...
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430 views

How long do reflections take?

How long does it take for a photon to be reflected? Starting with the photon being absorbed by some atom to the point it's reemitted? And what's the same point with pressure waves, like sound?
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Michelson rotating mirror experiment

Could someone explain the calculation required to answer this question. It is from a text book and the answer is recorded as 585Hz but I cannot replicate the answer. In 1931 Michelson used a ...
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1answer
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Adverse Health Effects of Strong Radio Waves

A while ago, I was hiking near the Hollywood Sign in Los Angeles. When I got to the sign, I found out it was fenced off; with several signs and a security camera promising prompt enforcement. As I was ...
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3answers
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How do laser rangefinders work when the object surface is not perpendicular to the laser beam?

I find the functioning of a laser rangefinder confusing. The explanation usually goes like this: "you shine a laser beam onto the object, the laser beam gets reflected and gets back to the device and ...
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3answers
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Explain how (or if) a box full of photons would weigh more due to massless photons

I understand that mass-energy equivalence is often misinterpreted as saying that mass can be converted into energy and vice versa. The reality is that energy is always manifested as mass in some ...
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0answers
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EM Field having simultaneously minimum divergence and minimal transversal extension

I read that the field that have simultaneously minimum divergence and minimal transversal extension is the fundamental Gaussian mode. What are the good references in this subject, to prove the ...
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1answer
412 views

Light travels a straight line write down the principle in which this is manitested [closed]

Light traveles a straight line write down the principle in which this is manifested.
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1answer
301 views

future light cones and light paths

I understand that an event, in a four dimensional space-time, produces a light cone. As time increases the cones gets larger on either side of the event (past and future). For example the if the sun ...
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2answers
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How does reflection work?

In Newton's model of light as being composed of particles, it's easy to imagine reflection as being the rebounding of individual corpuscles off a surface. However, since light can also behave like a ...
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2answers
520 views

“Optically performed” Fourier Transform

This article says that they are only able to achieve such extremely high fiberoptic data rates because the multiplex light and then use a Fourier Transform to split it up again. But they say that ...
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260 views

What stochastic process is associated with spontaneous electromagnetic radiation?

Imagine one have an ideal sensor, which can convert the emission to some kinds of signal (typically, voltage, and suppose no noise at all), then what process can describe the measure data? Is it ...
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999 views

Can the speed of light become complex inside a metamaterial?

The speed of light in a material is defined as $c = \frac{1}{\sqrt{\epsilon \mu}}$. There are metamaterials with negative permittivity $\epsilon < 0$ and permeability $\mu < 0$ at the same time. ...
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1answer
603 views

A new idea on unifying sound and light [closed]

Got a new idea regarding the unification of light wave and sound wave into a single entity , may be probably a wave. Is it possible to proceed in that manner,and has it been done previously,like i ...
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4answers
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How to get Intensity over a range of wavelengths from a Total Intensity

This is a theory vs experiment problem for me I think in that - as usual - I think I know the theory, but when it comes time to run an experiment, I can't actually extract squat. So, here is my light ...
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387 views

Do and can phone signals come inside AC car which is glass-packed

Can phone signals penetrate glass, so can I expect phone signals to come if I am sitting inside a closed AC car. Thanks,
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2answers
304 views

Very High Power Light Beams

Consider a collimated light beam in a vacuum (I am being unspecific about the frequency, anything from radio to gamma). If the beam power/cross section was increased indefinitely would new phenomena ...
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1answer
170 views

Merge different wavelength rays

Let's say an array of rays of light is given. Each ray has a specific wavelength (in the range of visible light). Example: ...
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2answers
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Lots of little questions about radiation of LC circuits

I'm trying to get a more intuitive understanding of resonant inductive coupling. It's supposed be a more efficient way to transfer electrical energy wirelessly, because the coils are only coupled by ...
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3answers
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Does opening or closing the window in a non-AC car in the summer affect how much heat is felt inside?

This will perhaps look like a very basic and trivial question. But I find it confusing. As an experience, when you are travelling in non-AC car in summer, have people felt if putting on or putting off ...
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3answers
319 views

Can one see radioactive substances with an X-ray detector?

I was wondering the other day an X-ray detector (like the ones used at airports) can detect gamma-rays lets say from a sample of uranium. I know its all electro-magnetic waves but I'm really unsure ...
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3answers
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UV reflective surfaces

Do surfaces that reflect visible light efficiently also reflect UV light? If not, are there surfaces that do? (I have a large array of UV LEDs that I need to make larger and more diffuse, so I'm ...
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1answer
669 views

The Interactions of Light and Matter

So basically, I was trying to find a good answer to the question of how light interacts matter. Namely on the quantum level what causes matter to appear transparent, reflective, opaque, etc I came ...
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1answer
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Light waves and Schrödinger probability waves

Ok, bearing in mind that I only have a brief understanding of quantum mechanics (no formal education, only from reading about concepts in books), so I could be way off here, I have a question ...
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4answers
597 views

Isn't wave particle duality of light actually cheating?

When answering questions about light, I see that we conveniently shift between wave and particle nature of light to match the answer-- isn't this really cheating? Or, is it the principle that the ...
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1answer
470 views

Where does the energy go, when light is blocked by polarisation

I've been looking around about LCD monitors, and how they polarise light. When a pixel needs to be black, the light is "twisted" so that it can't go through the polarising sheet in front. What happens ...