Tagged Questions

Optics is the study of light, and its interaction with matter. It includes topics such as imaging systems, fiber optics, lasers, quantum optics, and more.

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7
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2answers
935 views

Do all light rays from a point passing through a thin lens converge at the image?

I have often seen diagrams, like this one on Wikipedia for a thin convex lens that show three lines from a point on the object converging at the image. Do all the other lines from that point on the ...
9
votes
2answers
793 views

Quantum shot-noise and the fluctuation dissipation theorem

Classically, shot noise observed in the signal generated by a laser incident on a photodiode is explained as being due to the quantization of light into photons, giving rise to a Poisson process. In ...
4
votes
2answers
1k views

What does Lijun Wang's experiment about supraluminal speed of light in a medium mean?

This is a summary from Physics World of the paper: L J Wang et al. 2000 Nature 406 277-- "Wang and colleagues begin by using a third continuous-wave laser to confirm that there are two peaks in the ...
4
votes
2answers
262 views

Visibility of moon-based laser from Earth

If someone (or some robot) on the moon were to point a laser at the Earth, how many watts would the laser need, to be easily seen with the un-aided eye from Earth? Obviously this depends on a number ...
2
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2answers
3k views

What happens when you cut a biconvex lens in half?

Specifically, does the focal length change? How can this be rationalized?
8
votes
5answers
5k views

Interference of polarized light

Does polarized light interfere?
2
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3answers
217 views

Will watering tea down make it clearer?

If I poured water into my tea, would I see more or less of the bottom of the tea-cup? Intuitively, there would be as many particles blocking as many photons, and so I'd see the bottom just as clearly ...
0
votes
1answer
206 views

Interaction of polarized beam to optical active substance

Kostyas question for angular momentum and half wave plates Half wave plate and angular momentum made me think a little bit. It took me some seconds to "swallow" the answer. :=) Then I started to ...
5
votes
2answers
625 views

Half wave plate and angular momentum

Given: A half wave plate freely floating in space. Circularly polarized light, falling perpendicularly to it. The plate changes polarisation of the beam to the opposite one. Therefore it ...
18
votes
4answers
2k views

Newton's rings: What causes the other rings?

This is from an experiment we did in physics class. We shone a sodium light at a convex lens on top of a sheet of glass - and this image was captured by a USB microscope. I know what causes the main ...
2
votes
3answers
971 views

Reconciling refraction with particle theory and wave theory

I have searched the web for good answers to why refraction occurs when light moves from one medium to another with different density. I have limited background in physics and want to know if there is ...
7
votes
4answers
5k views

Eyes open under water

Yesterday I looked underwater with my eyes open (and no goggles) and I realized I can't see anything clearly. Everything looks very, very blurry. My guess is that the eye needs direct contact with air ...
9
votes
7answers
5k views

Why is a 1mW laser dangerous?

In our Physics lab we have a 1 milliwatt (0.001W) helium neon laser. Despite the low power, we were cautioned not to even look at reflections of the beam as it could cause permanent eye damage - why ...
6
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2answers
4k views

How does the Kinect device work?

Some explanations of the device base it on a simple echo of light: "The camera transmits invisible near-infrared light and measures its “time of flight” after it reflects off the objects. ...
12
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2answers
4k views

Why is a plastic bag transparent in infrared light?

This is a classic trick to do with a IR camera: Bu why is the plastic bag transparent, while the glasses aren't? I've also heard that water is not transparent in IR light. What causes this ...
6
votes
2answers
1k views

Converting between brilliance, intensity, and flux

This one should be a bit of a softball, but I can't find it explicitly stated anywhere on the internet, and my basic unit analysis doesn't seem to work. Suppose you have a beam of synchrotron ...
4
votes
2answers
7k views

Why do things that are far away seem smaller?

As you see things that are far smaller, a funny question about this: Imagine there are many people in a row (all are same height) ...
5
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4answers
764 views

Optical explanation of images of stars?

Very often when viewing pictures of the cosmos taken by telescopes, one can observe that larger/brighter stars do not appear precisely as points/circles on the image. Indeed, the brighter the light ...
5
votes
4answers
457 views

How would you design an experiment to grok optical phenomena?

I've been toying with the idea of making a 3D scanner that uses an IR distance sensor to find position vectors of an object in space and then translates that into a 3D computer model. One of the ...
18
votes
3answers
76k views

Virtual vs Real image

I'm doing magnification and lens in class currently, and I really don't get why virtual and real images are called what they are. A virtual image occurs the object is less than the focal length of ...
3
votes
3answers
475 views

How bright can we make a sun jar?

A sun jar is an object that stores solar energy in a battery and then releases it during dark hours through a led. Assume: a $65cm^2$ solar panel a 12h/12h light/dark cycle insolation of ...
12
votes
4answers
426 views

Do high/low pass lenses exist?

For an experiment I will hopefully be soon conducting at Johns Hopkins I need two different lenses. The first needs to allow all wavelengths above 500 nm to pass (thus a high pass filter) and cut off ...
13
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3answers
1k views

Aspherical lenses

It's known that single spherical lens cannot focus parallel beam of monochromatic light into single point. Could you suggest how should aspherical lens look like to be able to focus in single point ...
2
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3answers
860 views

What does the optical zoom in telescopes do?

How does the optical zoom works.. Does it brings the light closer to the object... Or Does it just enlarges the picture of the object. In other words... Suppose I have telescope with 1 light-year ...
2
votes
3answers
1k views

Why does light refract if photons are not bound by an axle?

In the classic metaphor, a light beam bends for the same reason that a wagon getting one wheel stuck in the sand does...the wheels travel at uneven speeds, and the wheel on the smoother surface ...
8
votes
1answer
567 views

How are classical optics phenomena explained in QED (color)?

How is the following classical optics phenomenon explained in quantum electrodynamics? Color According to Schroedinger's model of the atom, only particular colors are emitted depending on the type ...
21
votes
2answers
3k views

How are classical optics phenomena explained in QED (Snell's law)?

How is the following classical optics phenomenon explained in quantum electrodynamics? Reflection and Refraction Are they simply due to photons being absorbed and re-emitted? How do we get to ...
11
votes
1answer
498 views

Formulation of Transformation optics using a Material Manifold

Dear Community, recently, Transformation optics celebrates some sort of scientific revival due to its (possible) applications for cloaking, see e.g. Broadband Invisibility by Non-Euclidean Cloaking ...
2
votes
1answer
152 views

Reflected and refracted wave sphased

When we derive refraction and reflection laws for a generical plane wave on a surface, we say that reflected and refracted must be in phase with the incident wave. Why a medium cannot do a sphased ...
2
votes
3answers
141 views

Can a multipass x-ray absorption cell be constructed?

I've been trying to understand the various concepts behind x-ray optics compared to standard visible/IR optics like mirrors and such. However, the x-ray mirrors I've been finding typically have ...
13
votes
2answers
5k views

How does a photon travel through glass?

This was discussed in an answer to a related question but I think that it deserves a separate and, hopefully, more clear answer. Consider a single photon ($\lambda$=532 nm) traveling through a plate ...
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2answers
1k views

What does an atom radiate: a wave packet or a single photon?

What does an atom radiate: a wave packet or a single photon?
1
vote
1answer
138 views

How much can a laser's position be fine-tuned?

Suppose you wanted to do a time-resolved experiment with a molecular beam traveling at, say, 300 m/s involving a mobile excitation (pump) laser that scans across the length of the molecular beam and a ...
13
votes
4answers
696 views

Nonlinear optics as gauge theory

the widely used approach to nonlinear optics is a Taylor expansion of the dielectric displacement field $\mathbf{D} = \epsilon_0\cdot\mathbf{E} + \mathbf{P}$ in a Fourier representation of the ...
15
votes
1answer
2k views

Why does my watch act like a mirror under water?

I have a digital watch, rated to go underwater to $100 \rm m$. When it is underwater it can be read normally, up until you reach a certain angle, then suddenly, it becomes almost like a mirror, ...
9
votes
2answers
742 views

How “How to See Without Your Glasses” works?

If you see through small enough aperture, you can see things without glasses. How does this trick work?
3
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3answers
5k views

How do contact lenses work?

I understand how telescope, microscope and glasses work. But how do contact lenses work?
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7answers
2k views

Is it possible to blur an image in such way that a person with sight problems could see it sharp?

If someone has short or long sight, is it possible to tune image on a computer monitor in such way, that a person could see it sharp as if they were wearing glasses? If not, will 3d monitor make it ...
18
votes
4answers
2k views

Is it possible to observe interference from 2 independent optical lasers?

It seems that if the coherence length of a laser is big enough, it is possible to observe a (moving) interference picture by combining them. Is it true? How fast should photo-detectors be for ...
7
votes
8answers
2k views

Is it possible to make glasses that make everything brighter, but do not magnify or focus?

Corrective glasses are usually intended to help focus light on your retina. Supposing I had good vision already, but simply wanted more light, could I make glasses that would send more light into my ...
2
votes
3answers
239 views

Material resistency to lasers beam

Keeping the average power constant, why some materials are more eager to be damaged by pulsed laser with respect of C.W. lasers, or viceversa? When i talk about pulsed lasers i think for examples of ...
18
votes
5answers
4k views

Why can you have shiny black objects?

Knowing black is supposed to be the "color" (I don't want to get into the color/hue/shade debate, please) that absorbs light. how does one manage to have shiny black surfaces? I know about "gloss ...
4
votes
2answers
554 views

In interferometry, what is the origin of the name “Airy function”?

In interferometry (specifically, in the domain of Fabry-Perot cavities), the function $$f(\phi) = \frac{1}{1 + F \sin^2 \phi}$$ , which describes the shape of the resonant structure of the cavity, is ...
6
votes
3answers
711 views

How can we describe the polarization (of light) coming from an arbitrary angle?

In an optics lab, where all optical beams pretty much reside in a plane, it is fairly simple to describe (linear) polarizations as vertical or horizontal (or s and p). When we start talking about ...
13
votes
7answers
3k views

What is a general definition of impedance?

Impedance is a concept that shows up in any area of physics concerning waves. In transmission lines, impedance is the ratio of voltage to current. In optics, index of refraction plays a role similar ...
4
votes
2answers
274 views

In optics, how does the vacuum state compare to thermal radiation?

In quantum optics, a perfect absorber of light is said to emit the "vacuum field". In practice, any beam dump will be at finite temperature, so it will emit blackbody radiation. How do these fields ...
8
votes
1answer
7k views

The principle behind door peepholes

Hotels usually install peepholes in their doors so that a person inside a suite can see who is at the door without having to open it. I understand that there should be a convex lens within the ...
6
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3answers
3k views

How can I determine transmission/reflection coefficients for light?

When light rays reflect off a boundary between two materials with different indices of refraction, a lot of the sources I've seen (recently) don't discuss the relation between the amplitude (or ...
15
votes
4answers
2k views

What ways are there to measure the local polarization of a laser beam?

Measuring the polarization of a laser beam is a simple enough task if the polarization is the same everywhere. You can even buy commercial polarimeters. How do you go about it if the light beam has ...
8
votes
3answers
850 views

How is squeezed light produced?

Ordinary laser light has equal uncertainty in phase and amplitude. When an otherwise perfect laser beam is incident onto a photodetector, the uncertainty in photon number will produce shot noise with ...