# What is Optical: Definition and 696 Discussions

Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.Most optical phenomena can be accounted for by using the classical electromagnetic description of light. Complete electromagnetic descriptions of light are, however, often difficult to apply in practice. Practical optics is usually done using simplified models. The most common of these, geometric optics, treats light as a collection of rays that travel in straight lines and bend when they pass through or reflect from surfaces. Physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be accounted for in geometric optics. Historically, the ray-based model of light was developed first, followed by the wave model of light. Progress in electromagnetic theory in the 19th century led to the discovery that light waves were in fact electromagnetic radiation.
Some phenomena depend on the fact that light has both wave-like and particle-like properties. Explanation of these effects requires quantum mechanics. When considering light's particle-like properties, the light is modelled as a collection of particles called "photons". Quantum optics deals with the application of quantum mechanics to optical systems.
Optical science is relevant to and studied in many related disciplines including astronomy, various engineering fields, photography, and medicine (particularly ophthalmology and optometry). Practical applications of optics are found in a variety of technologies and everyday objects, including mirrors, lenses, telescopes, microscopes, lasers, and fibre optics.

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1. ### A What is the correct form of the Berry curvature formula?

I am studying Berry curvature for a specific material and faced different types of the Berry curvature formula. Some papers use only valence eigenstates (u1) like this i∗(<(∂U1/∂kx)|(∂U1/∂ky)>−<(∂U1/∂ky)|(∂U1/∂kx)>) and someone uses summation on all the conduction and valence bands like this...
2. ### Who is the Optical Engineer from Italy?

Hello, I'm an optical engineer from Italy
3. ### I How can I model squeezed states in 3D optical modelling software?

I would like to model squeezed light and its evolution (such as when passing through lenses after being generated) using optics software such as OptiFDTD or ZEMAX. However, I don’t see any way to make such states…my plan was to simulate an Optical Parametric Amplifier to generate these states...
4. ### I Why do we use low-coherence light in Optical Coherence Tomography?

Hello , I study the principles of optical coherence tomography, where we emit light and by the refraction that we detect we reconstruct and image, but I don't understand why we use low coherence light , if i want to measure the refracted light i would prefer to have coherent light so that the...
5. ### A Confused about reflected signal in a bow-tie optical cavity

Hello! I am building a bow-tie optical cavity, of finesse about 10,000. When I measure the transmitted signal out of the cavity, after aligning it, I see clear peaks, significantly higher than the background and pretty much single mode. I do see 2 other peaks, probably from other modes, but much...
6. ### A What’s the meaning of decay rate in optical Bloch equations?

i have some questions about decay rate. 1：why do we need decay rate in these equations? 2：is it a constant for a specific medium? 3：it can be changed with respect to some conditions like temprature or pressure? 4：how can i know the decay rate of some energy levels in 85Rubidium
7. ### Evaluate the outgoing radiation from an optical fiber on a surface

The geometric configuration that I am adopting is the following, I hope you understand. The optical fiber is positioned relative to the bottom surface at a height ##a## and an angle ##\alpha## with respect to the y-axis in the yz-plane with x = 0. ##b## is the distance between the origin and...
8. ### Why optical pyrometer gives a low reading?

From my knowledge, the optical pyrometer determines temperature of a body based on the visible part of the heat radiation spectrum emitted by a body. Now the iron piece was red hot inside the furnace as well as outside the furnace, so it is emitting heat radiation in the visible part both while...
9. ### A How are quantum optical experiments designed? ;)

inspiration: How does one predict the effects of small modifications (ordering of optical devices etc)? https://www.physicsforums.com/threads/the-experiment-of-kim-et-al-1999-with-small-modification.1047803/ In chapter 5 and 6 of A Guide to Experiments in Quantum Optics, the authors deal with...
10. ### I Interesting Optical Phenomenon

The lines have a slight purplish hue to them (at least reflected from leaves) and are about 2 feet apart. Here are images of the lines and the sun through the tree.
11. ### I Light coupling from optical fiber to glass?

Hey everyone, I am trying to couple light from an optical fiber connected to an LED (365nm) into a small glass capillary which is pulled on one end and should be used as a small light source. The idea is to use the glass as a light guide. Has anyone tips for efficient incoupling of the light? I...
12. ### B Multimode optical fiber, physics beginner help :D

Hello ! I have a problem understanding how light works in multimode optical fiber. What do I mean in single-mode optical fiber there is single light which contains information. In multimode there can be multiple lights with multiple information. Like here 1st picture contains multiple...
13. ### Solid State Researching Gold Thin Films: Electrical & Optical Properties

Hi Physics folks,I am currently collecting resources for my senior seminar project at my university and would like to ask if anyone has any good references for gold thin films. I am planning on focusing primarily on the electrical and optical properties of gold thin films. I appreciate any...
14. ### Absorption coefficient and Linear Optical Susceptibility

##\alpha## is considered to be the absorption coefficient for a beam of light of maximum intensity ##I_0##. It's related to the complex part of the refractive index as we have shown above. Now, I have a doubt. Should I solve for ##k## from the quadratic equation in terms of the linear optical...
15. ### I Huge farsightedness/nearsightedness lens

Hello guys, I have a question for optics experts, is there any possibility to produce a farsightedness/nearsightedness lens in big dimmensions, without distorting the obsjects or anything else you watch through that lens. Thank you!
16. ### Optical power of Smartphone (Galaxy S20) torch

In doing a project on phototransistors I am using my smartphone as illumination source. In order to find the responsivity of the induced current from the light, I need to know the surface power density, which I could estimate, if I knew the effective optical power of the light from the...
17. ### I Find the interference function for different emission modes

Homework Statement:: Find the interference function ##I(\delta)## where The emission is analyze by a Michelson interferometer. Relevant Equations:: ##I(\delta) = \frac{1}{2} \int_{-\infty}^{\infty} G(k) r^{ik \delta} dk## ##I(\vec{r}) = I_1 + I_i + 2 \sqrt(I_1 I_i) cos (k\delta)## I have 5...
18. ### Finding Total Number of Optical Field Modes for Visible Light

ρ_kdk = k^2/π^2 dk is the density of field modes (what we are trying to solve for here), and as ρ_kdk = ρ_λdλ, and k=2π/λ, we can rearrange this to get ρ_λdλ = 8π/λ^4dλ This is where my confusion lies. I am not sure what to do next. I know this equation physically means the number of modes per...
19. ### Medical Error measuring glucose optical sensor

Hello We have designed an optical sensor to measure glucose. But we do not have the same changes for different concentrations. What do we need to do to be able to observe different Lifetime concentrations? In our sensor test, we used phosphorescence and glucose oxidase technology. The sensor...
20. ### Find the Best Zemax Textbook for Professional Optical Engineers

Summary:: Hi all, does anyone know a good Zemax textbook? I’d like to learn. Hi all, does anyone know a good Zemax textbook? I’d like to learn. I am a professional looking to move into the optical engineering field.
21. ### I Optimizing Sensor Thickness for Efficient Optical Wavelength Detection?

When creating sensors to record images from much larger wavelengths of radiation, must the sensor be at least as deep as the wavelength, or is there a way to make it more compact?
22. ### Optical qualities of prism sheet and glass substrate (LCD screen)

Hi! I am an electronics engineer and I would be very grateful for some help and suggestions with my problem. I am experiencing severe discomfort when working with almost any LCD screen (smartphones, laptops, monitors). Ophthalmologists say that I am completely healthy and they cannot understand...
23. ### Optical vs Static Dielectric Constant for E-field Simulation

I am just learning about e-field simulations and I came across two different types of dielectric constants: optical and static. I'm unsure which to use and in which cases. I would like to simulate e-field intensity to help ensure I'm always below the dielectrics breakdown strength.
24. ### I Optical proprieties of sulfur dioxide in the gaseous state

Hi, I am a first-year university student in engineering and for this year I have to do a presentation( with related experience ) about the physical implication of geoengineering methods. The theoretical aspect seems quite understandable, my principal problem is to find a clear experience with...
25. ### Engineering Recommended book for Optical Engineering graduate

I am a recent Optical Engineering graduate, It's easy to forget about concepts that I learned, so I would like to have a book to that can help me while preparing for job interviews, a book to help me remember the most important concept in Optics and Optical Engineering. Can anybody recommend...
26. ### I Software for optical simulation with interference

I would like to simulate both double-slit and Mach-Zehnder interference, with some other common optical components such as lenses, beam splitters, mirrors, and wave plates. Is there something online for this or a program that can be downloaded and run on either Linux or Windows? Thanks, Erik
27. ### Crosstalk Algorithm - Optical system

I have a camera that take pictures of square boxes that are really close to one another. There is a light that is Illuminating the boxes but when I try and isolate a single but in my picture, I am reading higher values then what I should be. If I remove the other boxes and only do one box, I am...
28. ### I What is the size and shape of single optical photon?

Optical photon is produced e.g. during deexcitation of atom, carrying energy, momentum and angular momentum difference. So how is this energy distributed in space - what is the shape and size of single photon? Looking for literature, I have found started by Geoffrey Hunter, here is one of...
29. ### Optical versus digital reflections

This is allegedly (part of) a bona fide photo of a critter, staring at its own reflection in the water. I am skeptical. I am almost certain that the highlight in the reflected image is provably digitally reflected. To-wit: If the virtual image in the water were a true reflection off the water...
30. ### Engineering Optical Fibres: Wavelength for Zero net Dispersion

Hi, I was working on the problem below: Question: An optical fibre transmission system uses a step-index multimode optical fibre which has a core refractive index of 1.49 and a cladding refractive index of 1.48. The fibre is also subject to material dispersion which is a function of wavelength...
31. ### I Optical spectrum analyzer related

Can anyone explain why optical spectrum analyzer plots are in negative dB
32. ### Material index formulas for optical clarity and Ashby charts

Hello:) i need some help trying to find some formulas that i can retrive the material index from at the end of simplification to use with an ashby chart to select materials. here is an example of deflection equation from a sphere used for a spherical cap and what material index we used to find...
33. ### Engineering Optical Fibres: Spectral Width Calculation

Hi, I was working on this problem that I think should be quite simple, but I cannot seem to get the correct answer. Question: A pulsed laser operates at 850 nm wavelength. Under pulsed conditions there are several lasing modes present separated in frequency by ## \Delta f = c/2nl ## where...
34. ### Brockenspectre - foreboding optical illusion in misty mountains

Brockenspectre - foreboding optical illusion in misty mountains. Interesting account: https://www.livescience.com/dark-watchers-california-optical-illusion.html
35. ### Question on Optical Systems and Lenses

Hi everybody and very glad to be here. I am given a small piece of lens which is tightly sealed and there are two lenses at the end and I do not know what is in between. My question is as follow. If I design a small apparatus of object and get the image then will I be able to design a similar...
36. ### Magnetic permeability and optical impedance

Hi, It's given that an electromagnetic wave (5.10^14 Hz) traveling in an environment with the index n = 1,33, where the magnetic permeability (μ) is equal to the magnetic permeability in a vacuum (μ0). The optical impedance (Z) is given by the formula : Z = μ . c/n. I tried to turn μ into μ0 to...
37. ### Classical Recommendation for a primer on optical system design/optomechanics?

I am looking for a textbook or handbook on optical system design. I would prefer one that actually derives equations rather than just slapping down rules of thumb, although I would take the latter. My problem is that I've done a ton of bench top optic setups, but my skills are kind of capped at...
38. ### What is the definition of Unit Optical Depth?

$$\chi = n \sigma$$ Where Chi is the Opacity, n is the number density of absorbers (constant), and $\sigma$ is the cross section(given). We define the optical depth is just the number of photon mean-free paths in a given physical step, i.e. if we consider a...
39. ### DIY large aperture optical comparator

Hi. In machine shops optical comparators have been used for a really long time to measure and inspect complex and usually small parts. But they are usually for small parts and they are usually really expensive machines. How can i do this for cheap for larger parts like for example for making...
40. ### Optical Problem: drawing the reflected wave

That is the diagram of the question. How is the reflected going to be?
41. ### Can you calculate optical density from permittivity and permeability?

Does electric perm and magnetic perm give you enough info to work out OD? Thanks in advance
42. ### What Causes Molecules to Aggregate Over a Fiber in Optical Trapping?

I poured a droplet that has 1.55 refractive index (RF) over a fiber that has core and cladding with (RI) 1.45 and 1.4 respectively, and I the molecules aggregated over the fiber, known that because the refractive index of the liquid is higher than of than of the core or the cladding a leakage of...
43. ### Elliptical facet cylindrical optical fiber - Mathieu equation

Let's say I have three modes in a fiber that is elliptical cylinder shaped (cylinder with elliptical facet), as in the image below (the source:Optical Engineering, 46(4), 045003 (2007)) so what is the equations that describe these fields..
44. ### Topological insulators and their optical properties

I have tried to write down the boundary conditions in this case and looked into them. As conditions i) and ii) were trivial, i looked into iii) and iv) for information that I could use. But all I got was that for the transmitted wave to have an angle, the reflective wave should also have an...
45. ### Strange optical phenomenon: lighting a candle in front of a TV screen

I observed a strange optical phenomenon when lighting a candle in front of a tv screen, in the dark (attached picture). There seems to be two lines forming an 'X' figure with a colored pattern (of diffraction, I suppose). I think it must be related to the material structure of the TV screen...
46. ### Optical depth using Bremsstahlung emission coefficient

Equations I think may be relevant:

48. ### Which is the correct solution for Optical Image Overlap?

[Moderator's note: Moved from a technical forum and thus no template. Own effort in next post.]
49. ### Trapping stiffness of optical tweezers

I read in some articles that the force in optical tweezers can be written as: F=kx, with no minus because the force will increase as the distance increased and the particle moves to the source..., This I can understand, but what I can not understand if I make integral (it is conservative force)...
50. ### Evanescent and Gradient force on an optical waveguide

Let's say that on the surface of the cladding we have evanescent field due to the total internal reflection between the core and the cladding. The refractive indices of the the core is 1.45 and the refractive index of the cladding is 1.4, and I want to use the gradient force of the evanescent...