Light and Entropy

[energia]

let's see if anyone can answer the question of why c (lightspeed) a universal unyealding constant does not violate the laws of thermodynamics - especially entropy

from what energy source do free photons in space draw the limitless power to travel at 299792458 m/s and no other speed?

what causes the apparent optical illusion of light slowing down 25% to 225000000 m/s in a tank of water - apparently losing energy (since c is constant it must be an illusion after all) and returning to 299792458 m/s upon leaving the tank? (apparently gaining energy)

what causes electromagnetic signals to slow down due to gravitational drag (http://www.geocities.com/newastronomy/animate.htm) especially since gravity is supposed to propagate at lightspeed
(since c is a constant this must be an illusion as well)

why is light not able to escape a black hole?
if lightspeed is a constant and gravity propagates at the speed of light
why should light be stopped or slowed by gravity?
causing it to be blue or red shifted

if light is a wave how does it propagate in a vacuum?
if light is a particle, why does it behave like a wave, causing interference patterns in Thomas Young's double slit experiment (http://micro.magnet.fsu.edu/primer/java/interference/doubleslit/) ?

if a laser injected a single precisely perpendicular pulse between 2 parallel mirrors (assuming one mirror was a 2 way mirror) would the beam reflect for infinity at the speed of light - producing a perpetual floating light beam?
(according to entropy the beam must lose energy)

why does light travelling through a transparent solid cause the solid to heat up? as if the light were losing energy to the solid

if light (a photon) has no mass how can it push a solar sail?

[ZapperZ]

let's see if anyone can answer the question of why c (lightspeed) a universal unyealding constant does not violate the laws of thermodynamics - especially entropy

from what energy source do free photons in space draw the limitless power to travel at 299729458 m/s and no other speed?

It doesn't draw any energy. Via conservation of mass-energy, it has ALL of its energy in h\nu. If it draws any more energy, this conservation will be violated.

what causes the apparent optical illusion of light slowing down 25% to 225000000 m/s in a tank of water - apparently losing energy (since c is constant it must be an illusion after all) and returning to 299792458 m/s upon leaving the tank? (apparently gaining energy)

If you study a bit of a field of physics called optical conductivity, you will learn that photons do NOT lose speed in a dispersive material. The scattering-absorption-reemission of the material is what appears to slow down light in matter. It is the GROUP velocity that is measured, and it is this velocity that is found to have slowed down in matter.

what causes electromagnetic signals to slow down due to gravitational drag (http://www.geocities.com/newastronomy/animate.htm) especially since gravity is supposed to propagate at lightspeed
(since c is a constant this must be an illusion as well)

why is light not able to escape a black hole?
if lightspeed is a constant and gravity propagates at the speed of light
why should light be stopped or slowed by gravity?
causing it to be blue or red shifted

Gravity warps spacetime metric. Light travels along such lines. Blackholes are thought to bend these spactime lines into itself. Thus, light follow these lines and never escape.

if light is a wave how does it propagate in a vacuum?
if light is a particle, why does it behave like a wave, causing interference patterns in Thomas Young's double slit experiment (http://micro.magnet.fsu.edu/primer/java/interference/doubleslit/) ?

Why would there be a problem of propagation whether it is a wave or a particle? It would be more unusual if something in free space doesn't move. What would make it THAT special that it shares the same reference frame with us?

if a laser injected a single precisely perpendicular pulse between 2 parallel mirrors (assuming one mirror was a 2 way mirror) would the beam reflect for infinity at the speed of light - producing a perpetual floating light beam?
(according to entropy the beam must lose energy)

I deal with a high powered Ti-Sapphire laser with roughly 8 ps pulse length. If you can find a "perfect" mirror that can do 100% reflectivity, give me a call.

why does light travelling through a transparent solid cause the solid to heat up? as if the light were losing energy to the solid

Because it does! Solids ALWAYS have phonons, which is partly responsible for what makes something transparent, and something else opaque.

if light (a photon) has no mass how can it push a solar sail?

Hint: solar sails works most efficiently if it has a metallic surface. Hint 2: how would you know there isn't another definiton of "momentum" that doesn't involved mass? p=hbar*k. Look that up.

Zz.

[energia]

I deal with a high powered Ti-Sapphire laser with roughly 8 ps pulse length. If you can find a "perfect" mirror that can do 100% reflectivity, give me a call.

let's start with this one...

assuming 100% reflectivity were possible
would you have a perpetually reflecting beam without a source?

[ZapperZ]

let's start with this one...

assuming 100% reflectivity were possible
would you have a perpetually reflecting beam without a source?

1. How would you have a beam already without a source?

2. By simply allowing reflectivity, it implies an interaction of the light with the plasmon states of the metallic surface. Unless you want to insist that (i) electrons should have zero mass and (ii) they don't scatter of each other and the phonons within the material, then we can't just weely-neely assume 100% reflectivity, because those are the two things that have to happen FIRST for you to have that.

Zz.

[energia]

you're not doing so well on this test

maybe you should review your physics books a bit before taking on the question



the question is...

assuming 100% reflectivity (hypothetically) and a pre-injected perfectly perpendicular laser pulse between 2 perfectly parallel reflectors
would (after this initial pulse) there be a perpetual beam reflecting between the mirrors without a subsequent source?

it's not such a hard question, even a child should be able to answer it

[swansont]

you're not doing so well on this test

maybe you should review your physics books a bit before taking on the question



the question is...

assuming 100% reflectivity (hypothetically) and a pre-injected perfectly perpendicular laser pulse between 2 perfectly parallel reflectors
would (after this initial pulse) there be a perpetual beam reflecting between the mirrors without a subsequent source?

it's not such a hard question, even a child should be able to answer it

Yes, if you had a perfect reflector you would get a perpetual beam.

You might get further if you drop the patronizing tone.

[ZapperZ]

you're not doing so well on this test

maybe you should review your physics books a bit before taking on the question



the question is...

assuming 100% reflectivity (hypothetically) and a pre-injected perfectly perpendicular laser pulse between 2 perfectly parallel reflectors
would (after this initial pulse) there be a perpetual beam reflecting between the mirrors without a subsequent source?

it's not such a hard question, even a child should be able to answer it

What do you think is a "reflectivity"? Light BOUNCING of a surface? If that is all that is, then why doesn't light bounces off ALL surfaces? Why does it bounce off metallic surfaces BETTER than dielectric surfaces? It is the interaction of the conduction electrons that participate in the retransmission of the incoming light AND the rest of the lattice recoiling via the phonons to preserve the conservation of momentum that ALLOWS for what you call "reflection" to happen! For there to be 100% reflectivity, you WANT zero electron mass, and for the object to be at 0K for there to be ZERO losses via the phonons.

Unless you live in a different physical reality than I do, I haven't seen both of those criteria ever being fulfilled.

If a child can answer your question, then why can't you answer it yourself?

Zz.

[Gokul43201]

In other words, you can not have your 100% reflectivity, unless you violate your favorite entropy law.

"If I only had a little humility, I'd be perfect." - Ted Turner

[energia]

since you can't just answer the question with a simple yes or no

I will answer it for you

the answer is: NO

it is not possible for a perpetual beam to reflect between 2 mirrors without a constant source

it violates the law of thermodynamics

there - that wasn't so hard was it?

You might get further if you drop the patronizing tone.

the patronizing nature of my tone is directly proportional to that of the tone I respond to - ZapperZ set the tone many posts ago

I will go back to my normal tone....

Now

[jcsd]

since you cannot just answer the question with a simple yes or no

I will answer it for you

the answer is: NO

it is not possible for a perpetual beam to reflect between 2 mirrors without a constant source

it violates the law of thermodynamics

that wasn't so hard was it?



the patronizing nature of my tone is directly proportional to that of tone I respond to

something to think about

whatever goes around comes around

It violates the law of thermodynamics, so what do we conclude about perfect refelectors then?

[energia]

the question was very hypothetical, since it would not be possible in reality

it was as much a question of logic as of entropy


it seems everytime a simple hypothetical question is asked

for example: if a 200KG piano is accelerating through space at 1 g at what speed does the piano's relative mass reach 400KG?

some brilliant physicist jumps in to enlighten us to the fact that pianos cannot accelerate through space (wow! who would have guessed?)

Yes, if you had a perfect reflector you would get a perpetual beam.

respectfully - no, you would not get a perpetual beam

this violates entropy since you cannot draw more energy out of a system than goes into it

and it takes considerable energy for a laser beam to even exist
perfect reflectors or not

this is an excellent example of the difference between the modern scientific approach, and the classical (Natural Philosophy) approach

the modern approach relies almost exclusively on a set of accepted paradymes
and leaves logic out in the cold

the classical approach relied heavily on logic and reason - as well as experimental trial and error

which explains why the most prolific scientists lived centuries ago

[Gokul43201]

respectfully - no, you would not get a perpetual beam

this violates entropy since you cannot draw more energy out of a system than goes into it

and it takes considerable energy for a laser beam to even exist
perfect reflectors or not

this is an excellent example of the difference between the modern scientific approach, and the classical (Natural Philosophy) approach





What ????????????????????

[energia]

have you more to add to the discussion besides... what????????????

[Gokul43201]

Okay, so even if you had 100% reflectivity, you don't get a perpetual beam ! Either the clauses in this sentence contradict each other, or I'm missing something. Where does the lost energy go ?

[energia]

the energy would be lost as soon as the laser source were cut off
we must remember how a laser works

Light Amplification by Stimulated Emission of Radiation

this is not just a beam of light, it's amplified light
which requires a high energy source (an inductor coil) to drive it

as soon as this source is cut off, the laser beam is also cut off
perfect reflector or not

there is nothing for free according to entropy

[Doc Al]

Are you claiming that the laser beam, having left the laser, still requires an energy source to continue to propagate?

[GRQC]

from what energy source do free photons in space draw the limitless power to travel at 299729458 m/s and no other speed?


I generally find that anyone who must explicitly give the speed of light down to an integer value doesn't have a solid argument.

[energia]

Are you claiming that the laser beam, having left the laser, still requires an energy source to continue to propagate?

to propagate.. no

to perpetually reflect...yes

I generally find that anyone who must explicitly give the speed of light down to an integer value doesn't have a solid argument.

oh? perhaps you think it's better (or maybe safer) to use the term 'c' rather than a precise value, since c can be any value we like within an equation

299792458 m/s leaves nothing to interpretation, and forces accountability

I was not even offering an argument, it was a question
and just for the record, I never start an argument without a solid basis

accepting something to be true as a paradyme does not make a solid argument, that approach is for the most timid and conservative scientists
and it's a shortcut to thinking

[Doc Al]

I asked:
Are you claiming that the laser beam, having left the laser, still requires an energy source to continue to propagate?
You answered:
to propagate.. no
Then what was all this about?
the energy would be lost as soon as the laser source were cut off
we must remember how a laser works

Light Amplification by Stimulated Emission of Radiation

this is not just a beam of light, it's amplified light
which requires a high energy source (an inductor coil) to drive it

as soon as this source is cut off, the laser beam is also cut off
perfect reflector or not

there is nothing for free according to entropy

to perpetually reflect...yes
Why?

[energia]

first of all it violates the laws of thermodynamics

secondly it violates common sense

and if these are not enough for you... perfect reflectors do not exist and cannot exist


perhaps you should attempt the experiment yourself
and report the results

the best metallic mirror absorbs a certain amount of light instead of reflecting. for focusing a laser beam, that's a serious problem. metallic mirrors reflect almost all wavelengths of light; for lasers you only want to reflect specific wavelengths

there's another kind of mirror that doesn't share these shortcomings. "Dielectric" mirrors use materials that selectively conduct electricity, stacked in a layer. If they're layered just right, they'll reflect almost all of a particular wavelength or wavelengths. Until recently, unfortunately, they've had one big drawback: they only reflect light that hits them at specific angles.

but for this experiment dielectric mirrors would work just fine

but you will have to inject the laser beam through a hole in one of the mirrors
and very quickly shift the hole in the mirror to one side before the light is reflected back, which means that these 2 mirrors must be a great distance apart

[krab]

to propagate.. no

to perpetually reflect...yes


Energia, you are quite wrong. Take an enclosed container with perfectly conducting walls. and a photon inside. This photon will bounce around forever. Experimentally, we come very very close to this situation. We have designed and built such cavities, by making the walls superconducting. Upwards of 10 billion bounces have been demonstrated. For normal conducting cavities, only 10000 or so is possible. Moreover, the finite number of bounces is consistent with the departure from ideal reflectivity.

[energia]

were not talking about free photons
were talking about a laser pulse (BIG DIFFERENCE!)

try to bounce a single laser pulse for a sustained period at it's initial energy level in your reflective superconducting cavity and tell us about the result

[Integral]

were not talking about free photons
were talking about a laser pulse (BIG DIFFERENCE!)

Really? What would the difference be?

[Doc Al]

first of all it violates the laws of thermodynamics
How's that?
secondly it violates common sense
It's your thought experiment.
and if these are not enough for you... perfect reflectors do not exist and cannot exist
But you're the one who said:
assuming 100% reflectivity (hypothetically) and a pre-injected perfectly perpendicular laser pulse between 2 perfectly parallel reflectors
would (after this initial pulse) there be a perpetual beam reflecting between the mirrors without a subsequent source?


And you go on to say:
were not talking about free photons
were talking about a laser pulse (BIG DIFFERENCE!)
Please tell us the difference.

[energia]

the quick answer

photons exist free in nature and require no outside energy source to propagate

laser pulses do not exist free in nature... and do require an outside energy source to become amplified

[Doc Al]

the quick answer

photons exist free in nature and require no outside energy source to propagate

laser pulses do not exist free in nature... and do require an outside energy source to become amplified
The amplification takes place within the laser cavity. Once the pulse leaves the laser, it is just like any other set of photons. (Except for coherence, of course.)

[energia]

initially yes, but as soon as the source is removed the photons are on their own
and subject to dispersal after reflecting

what you would end up with a a bunch of scattered free photons
and not a perpetually fucused laser beam at a constant energy level

which would be impossible

imagine 2 dielectric reflectors, spaced 149864729 mm apart
mirror A is the source location - mirror B is the distant reflector location

a high powered laser pulse is injected towards mirror B
within 0,8 milliseconds mirror A is lowered into the path of the beam - in effect cutting it off and creating a secondary reflector

by this time the initial pulse has already been reflected off mirror B
and is near it's start point

after 1 millisecond the pulse has returned to mirror A after reflecting off mirror B 0,5 milliseconds earlier

at this time the laser source has been cut off by mirror A which is waiting to reflect the laser beam back to mirror B, and so forth, etc....

however as soon as the pulse is reflected it loses coherence
and there is no further laser source to refresh the losses in the intitial reflected pulse, so the pulse becomes more and more diffused
until it's photons disperse, and the beam vanishes

[Doc Al]

initially yes, but as soon as the source is removed the photons are on their own
and subject to dispersal after reflecting
As soon as the photons leave the laser cavity, they are on their own and the source is irrelevant.

[Antonio Lao]

My understanding of Light and entropy is the same as between order and disorder. The energy in entropy is useless (disorder and wasted) energy. The energy in a light beam such as a laser is highly ordered energy. Light waves of a laser are monochromatic and in phase although the linewidth still cannot be exactly zero.

Since the natural tendency of nature is toward higher entropy, toward higher disorder, laser lights are not found in nature, these lights have to be created by artificial process which requires high energy input at the outset.

[energia]

I've already made my points very clear
if you read them point by point and still don't follow the logic

then don't take my word for it

do the experiment...

and then watch your jaw drop in amazement as the laser pulse vanishes almost as quickly as it's interrupted by mirror A

because that's exactly what will happen
whether you like it or not
whether it agrees with whatever you've been taught or not

[krab]

I've already made my points very clear
if you read them point by point and still don't follow the logic

Still that patronizing tone... maybe you are getting defensive.

try to bounce a single laser pulse for a sustained period at it's (sic)initial energy level in your reflective superconducting cavity and tell us about the result

Type "fabry-perot" into google. Here's a good site

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/fabry.html

It's an interferometer whose operation depends exactly on the feature you claim is impossible; many reflections between two mirrors. As an undergraduate, I did these experiments with white light and also laser light.

[energia]

if you look at the link you posted
you will see at the lower left where it illustrates an incident light source

now take away the incident laser light source and see what happens

[energia]

now please go and produce a perpetually reflected laser pulse bewteen 2 mirrors
removing the incident laser source after the initial pulse
and let me know how long the beam hangs there at a constant intensity

when you've done that - then come and report your results

[krab]

So it is your position that if you suddenly turn off the light source, the light that is already between the plates will no longer continue as before, reflecting and partially transmitting at each mirror, but instead will suddenly what? evaporate?

[swansont]

I've already made my points very clear
if you read them point by point and still don't follow the logic

then don't take my word for it

do the experiment...

and then watch your jaw drop in amazement as the laser pulse vanishes almost as quickly as it's interrupted by mirror A

because that's exactly what will happen
whether you like it or not
whether it agrees with whatever you've been taught or not

The experiment that starts with "assuming 100% reflectivity were possible"?

You are arguing two sets of conditions. If you assume 100% reflectivity, you get one answer. If you do a real experiment you get a different answer.

Nobody's jaw would drop in amazement, since what you describe would not happen. It violates conservation of energy, for one. And the behavior you deny has been observed (as noted in another post), whether you like it or not.

[energia]

perhaps someone can find a link to such an experiment somewhere

meanwhile, I will do my best to come up with a better explanation


if all of you don't follow my thought experiment

then I have to blame myself :confused:

it's obvious you all have a good working knowledge of photonics
so it's just to find the right expression

[Gokul43201]

perhaps someone can find a link to such an experiment somewhere

meanwhile, ... if all of you don't follow my thought experiment.


Here's where the problem lies : You propose a "thought" experiment - one that can not be duplicated in practice because of the non-existance of 100% reflectors - and then support your argument with claims that a "real" experiment will not work because of your "entropy philosophy". Do you see the inconsistency ?

A photon has a certain energy, no matter where it came from. To make the energy disappear is a violation of energy conservation. In reality, the photon does disappear, but it's energy goes into the mirrors. This is not allowed by your 100% reflectors. So, in your thought experiment, there is no place for the energy to go. Hence, the beam lives forever !

[russ_watters]

Here's where the problem lies : You propose a "thought" experiment - one that can not be duplicated in practice because of the non-existance of 100% reflectors - and then support your argument with claims that a "real" experiment will not work because of your "entropy philosophy". Do you see the inconsistency ? That appears to me to be precisely the problem: energia, you won't accept any experiment given to you, only one that matches your criteria, criteria which you specificy to make the experiment imposssible to conduct in reality. And even then, every now and then you make a mistake and suggest one that is possible to do or has even already been done, then you change your requirements to correct that.

energia, whether you like it or not, the experiments that have been done fit the theories we use. Period. You can't ask anything more from a theory.

[energia]

b*tch :devil:



haha just kidding - you're absolutely right of course, the conditions for my argument have been allowed to morph into obscurity ..I apologize :rolleyes:

I've been trying to design a thought experiment that would test the 100% reflectivity premise for a perpetual laser beam pulse with no incident source

logic suggests that it's not possible to have a hanging laser beam with no laser tube to power it - the beam should vanish as soon as the source is cut off since a beam of photons scatter without being amplified and focused
perfect reflector or not

now do you see what I'm suggesting?

bouncing photons don't violate entropy since electric fields and magnetic fields balance each other out

however a laser beam is highly focused and amplified
and it's the continuity of the highly focused and amplified state that I'm calling into question

[russ_watters]

logic suggests that it's not possible to have a hanging laser beam with no laser tube to power it - the beam should vanish as soon as the source is cut off since a beam of photons scatter without being amplified and focused perfect reflector or not

now do you see what I'm suggesting? I'm not sure at all what you are trying to prove here. A laser beam continues independent of its source for the duration of its existence, fancy experimental setup or not.

How about just turning off the laser before the beam hits/bounces back from the target? In the lunar ranging experiments, the time lag between the beam being turned off and reflected back would be noticeable on a human scale (3sec or so, IIRC).

Is that all you're interested in?

[energia]

Is that all you're interested in?

no, not exactly

but let me ask you a more specific question
since you work with lasers (yes?)

lets say that we use the world’s most powerful laser: the 60-beam Omega
at LLE which draws energies in the 300 TeraWatt range during a
1 nanosecond pulse

and we use mirrors equal to the reflectivity of those used on the Hubble Space telescope (the most reflective that exist)

these are technologies which exist in the real world

assuming a near perfect vacuum (let's say in a 150 m EM shielded tube)

the mirrors are adjusted perfectly parallel
the mirror nearest the laser is synchronized to rotate 180o in such a way that a hole on 1 side of the circular mirror is aligned with the pulse at the precise moment

so when the 60-beam Omega fires a 1 nanosecond pulse
1 microsecond later the pulse has returned and is again reflected
this time by the mirror nearest the laser, with it's hole now rotated away

the question is...

how long will this 300 TeraWatt pulse reflect (unchanged) between the 2 mirrors?

that is precisely what I''m intersted in

[Gokul43201]

The beam intensity decreases geometrically with each reflection as

I = Io*R^n, where R is the reflectivity.

If the distance between mirrors is d, then the time taken for each traversal is d/c = T, say.

Then n=[t/T],
So I = Io*R^[t/T]

This tells you the change in beam intensity as a function of time.

[energia]

The beam intensity decreases geometrically with each reflection as

I = Io*R^n, where R is the reflectivity.

If the distance between mirrors is d, then the time taken for each traversal is d/c = T, say.

Then n=[t/T],
So I = Io*R^[t/T]

This tells you the change in beam intensity as a function of time.


thank you for brilliantly illustrating my point

so, as you can see the laser pulse does not reflect for infinity at it's original intensity, but in fact decreases geometrically with each reflection

entropy wins again

[russ_watters]

thank you for brilliantly illustrating my point

so, as you can see the laser pulse does not reflect for infinity at it's original intensity, but in fact decreases geometrically with each reflection

entropy wins again That's it? Couldn't you just have come out and said that before? We already know this (several people have explained it already). So what?

And btw, this is also quite different from your assertion that a photon from a laser behaves any differently than any other photon when emitted.

[energia]

a single photon (as I stated before) does not behave differently from any other single photon

however a high energy laser beam is not a single photon

it's a focused and amplified bundle of photons - which should lose coherence after the beam is broken

that's my main argument

[Integral]

it's a focused and amplified bundle of photons - which should lose coherence after the beam is broken

Just what do you mean by focused here? How is a laser beam broken? Once again your terminology does not lead one to believe that you have depth of knowledge in these matters. It is not clear that you fully under stand the term "amplification" when applied to a laser.

[energia]

perhaps you should read my earlier post....

we must remember how a laser works

Light Amplification by Stimulated Emission of Radiation

this is not just a beam of light, it's amplified light
which requires a high energy source (an inductor coil) to drive it

a basic solid state laser assembly consists of:

1. a polished aluminium reflecting tube (laser tube)
2. a 99. 9% reflective mirror
3. a 95% reflective mirror
4. a quartz flash tube (the photonic inductor coil I mentioned)
5. a ruby crystal (natural or glass)
6. a power supply

theory of operation:

first: a high voltage power supply causes the photonic inductor coil (quartz flash tube) to emit an intense burst of light, exciting atoms in the ruby crystal to higher energy levels

above a critical energy level, these atoms emit (initially unfocused) photons. travelling in all directions

the photons from one atom stimulate emission of photons from more atoms and the light intensity is geometrically amplified

the 2 mirrors reflect these photons, resulting in stimulated emission and amplification

the photons reach a critical excited and amplified state and finally are ejected out the 95% reflective mirror - in the form of a laser beam

besides solid state lasers, there are also gas, liquid, and semiconductor lasers

the most powerful lasers are solid state
the 60 beam Omega is a solid state laser


so, do you still question my knowledge of lasers?

I've built a laser myself - have you?

It is not clear that you fully under stand the term amplified

it is not clear that you understand the meaning of the terms 'focused' or 'amplified' since you question their meaning

I design and build amplifiers professionally - I know the meaning of term 'amplified' better than you will ever dream of knowing it

[swansont]

a single photon (as I stated before) does not behave differently from any other single photon

however a high energy laser beam is not a single photon

it's a focused and amplified bundle of photons - which should lose coherence after the beam is broken

that's my main argument

Then how is it possible that a pulsed laser works? That's a bunch of "broken" beams.

[energia]

Then how is it possible that a pulsed laser works? That's a bunch of "broken" beams.

this is the area of misunderstanding

you are refering to propagation
and I am refering to reflection

[Integral]

What you posted sounds as if it were copied from a High school text book.

This (http://www.cohr.com/products/index.cfm?fuseaction=Interfaces.Part&PCID=23&PLID=34&PDID=300&PTID=DPSS0002) is what I work with every working day. I am responsible for the maintenance of 18 of these things. The only barely resemble your description. Lasers come in many different varieties your general description is every much wrong as it is right. Further it still does not convey any true understanding, on your part, of how a laser operates.

[swansont]

this is the area of misunderstanding

you are refering to propagation
and I am refering to reflection

I think an area of misunderstanding is that you keep changing the question. But a pulsed laser can be reflected, and is, inside of the laser - the gain medium is just a small section of the overall device - and yet it seems to work just fine.

[Integral]

I design and build amplifiers professionally - I know the meaning of term 'amplified' better than you will ever dream of knowing it

Does this mean you are an Electrical Engineer?

If so that explains a lot right there.

Simply because you build amplifiers does not mean that you understand or even know the basics of LASER operation. The fact that you claim a laser beam is "focused" means that you do not understand laser beams. The fact that you somehow separate the the beam from the generation means that you do not understand lasers.

The fact that you seem to think that reflection is somehow different for lasers then any other source of light means that you do not understand light. It does not appear to me that you understand enough of these topics to carry on a meaningful converstion. And that explains alot right there.

[energia]

my description of laser operation was given at it's most basic level
I don't need to write an essay on the operational theory of all lasers

since you work with lasers - you must understand the energy states of the electrons that make them work

lasers are possible because of the way light interacts with electrons
the photoelectric effect

(btw. Einstein was awarded the Nobel prize in 1921 for his theory on the photoelectric effect )

the electrons of each atom and molecule exist at specific energy levels
which orbit a nucleus

outer orbital electrons are at higher energy levels than inner orbital eletrons

the energy levels of electrons can be AMPLIFIED by the injection of photons

as an electron drops from an outer to an inner orbit, it loses energy in the form of light

the wavelength (colour) of the emitted light is relative to the amount of energy released. specific wavelengths of light are absorbed (exciting the electrons) causing specific wavelengths to be emitted as soon as the electrons return to their original energy level

and that's how a laser operates - any laser, whether solid state, gas, liquid, whatever

and yes I'm an electronics engineer - with a firm foundation in Maxwell equations and semiconductor physics

if physicists think they're somehow above engineers - let me remind you that it's engineers who provide the means to take physics from theory to reality
and many engineers are also physicists

[energia]

now back to the point

I'm suggesting that - at the moment of reflection, the photoelectric effect occurs between the striking photons and the electrons orbiting the nuclei of the atoms of the reflector, resulting in a net energy loss (entropy)

now do you see my point?

[swansont]

the energy levels of electrons can be AMPLIFIED by the injection of photons


:confused:

The "Amplification" is the increase in the number of photons, from stimulated emission. That is, one photon induces an atom to de-excite and emit a photon (in phase), so now you have two photons. You have amplified the light signal.

[Integral]

Obviously you have not had even basic Quantum Theory. You need to stop lecturing about things outside of your expertise and start asking questions. Your knowledge of the fundamental functionality of lasers is woeful.

I am sorry the photoelectric effect is not the place to start.

my description of laser operation was given at it's most basic level
I don't need to write an essay on the operational theory of all lasers In reality your description did not get anywhere near the core of the physics of a laser.
the energy levels of electrons can be AMPLIFIED by the injection of photons

as an electron drops from an outer to an inner orbit, it loses energy in the form of light

the wavelength (colour) of the emitted light is relative to the amount of energy released. specific wavelengths of light are absorbed (exciting the electrons) causing specific wavelengths to be emitted as soon as the electrons return to their original energy level
This also describes a light bulb. Or even a reflection off of a wall. What is different in a laser? You did not mention population inversion, nor did you touch the idea of stimulated emission. These are the keys to a laser, the rest is window dressing.

[Integral]

now back to the point

I'm suggesting that - at the moment of reflection, the photoelectric effect occurs between the striking photons and the electrons orbiting the nuclei of the atoms of the reflector, resulting in a net energy loss (entropy)

now do you see my point?

The photoelectric effect does not enter into this. In the photoelectric effect an electron is IONIZED, simply not the case in common reflections.

Give this up, I would like you to change your approach, rather then assuming that you have a full understanding, assume that you have only a partial understanding and attempt to ask questions to help us guide you to a better understanding. As long as you maintain the delusion that you understand this field you will find it impossible to learn.

[energia]

You did not mention population inversion

you want to discuss population inversion? fine

first we create two photons from one
then an amplifier must produce millions of photons
adding increasing numbers of atoms to the upper metastable state
and holding them long enough to store energy and allow the production of lorry loads of stimulated photons

the longer lifetime states allow the rate at which atoms are raised into one of these states to exceed the rate at which they leave

atoms can be excited into and held in the upper state leaving an almost empty state below them

atoms can stay in this metastable state without de-exciting while the population is being raised

a population inversion occurs when more atoms are in a higher state of excitation than in the lower state

NOTE: this violates entropy



nor did you touch the idea of stimulated emission

we must remember how a laser works

Light Amplification by Stimulated Emission of Radiation

this is not just a beam of light, it's amplified light
which requires a high energy source (an inductor coil) to drive it



here is my quote again

as you can see i've already stated the process with these terms alone

"Light Amplification by Stimulated Emission of Radiation"

notice the terms "Stimulated Emission of Radiation"


and i've had far more than basic QED (Euler-Lagrange equations) thank you

[energia]

in any case...

i've already demonstrated my point - which is that a laser beam cannot be sustained indefinately between 2 reflectors without a constant source

not using current technology - not even using emerging technology


why can't you just admit that it can't be done (?)


the whole argument is that it can't be achieved because it violates entropy

[swansont]

this topic has become tiresom

i've already demonstrated my point - which is that a laser beam cannot be sustained indefinately between 2 reflectors without a constant source

not using current technology - not even using emerging technology


why can't you just admit that it can't be done (?)


the whole argument is that it can't be achieved because it violates entropy

What the? Who has disputed this, if you use real mirrors?

What has been disputed is the notion that laser photons somehow know whether the laser is still on or not.

[energia]

The photoelectric effect does not enter into this. In the photoelectric effect an electron is IONIZED, simply not the case in common reflections

this was a personal theory of mine - it has nothing to do with accepted theory

accepted theory violates entropy which is why I decided to attack it in the first place