[Laser] laser optics questions

[Garnier Yves]

Hi Tim
Coherence is not realy a bandwidth question.
A coherent ray comes with a defined phase for all the equidistant points from its source.
Lasers and LEDs give very different lights.
Laser are oscillators like in radio because it uses resonnator (Pery Fabrot) to amplifie a define very accurate "photons energy vibration".
A perfect laser should not have bandwith and should provide a pure monochromatic radiation.
The LED effect into a laser diode give only the primary light to provide the pumping energy to maintain the amplification between the two mirrors resonnator.
LEDs give a melting of frequency without common phase and in radio one can say it is a noise generator followed by a filter that define a bandwidth :o) 
Yves F1AVY
http://f1avyopto.wifeo.com

-- En date de : Dim 21.3.10, Tim Toast <toasty256 at yahoo.com> a écrit :

> De: Tim Toast <toasty256 at yahoo.com>
> Objet: Re: [Laser] laser optics questions
> À: laser at mailman.qth.net
> Date: Dimanche 21 mars 2010, 14h27
> Hi all,
> I just want to be clear, i'm not trying to argue one method
> is 
> better than some other here. From what i've read about all
> this 
> so far, it looks like most, if not all, of the de-coherence
> noise 
> is generated in the first kilometer or two as the spatial 
> coherence of the laser is being destroyed by passage
> through 
> the atmosphere. The de-coherence process has, in effect, 
> modulated the beam in amplitude and so the beam carries
> this 
> noise with it to the detector. 
> 
> I suspect an LED still suffers from some scintillation
> because of 
> its narrow bandwidth. Both the laser and LED have a finite
> 
> bandwidth and so both have a degree of "coherence" which
> shows up 
> as the noise and scintillation on both signals - the LED
> having 
> less because its bandwidth is greater and has less temporal
> 
> coherence. (Not because it has None) In the real world, no
> 
> light source can be made "non-coherent" or infinite
> bandwidth.
> 
> I pick a random point in the discussion and run with it
> now... 
> I don't think a fresnel lens would scatter laser light any
> more 
> than it does with LED light. It may be that it is just more
> notifiable with a laser because it is a sharply defined 
> reflection or scatter (caustic?). The LED light gets
> scattered 
> just as much but its reflections are fuzzy and diffuse due
> to 
> the wider bandwidth.
> 
> -toast
> 
>  
> 
> 
> 
> 
> 
>       
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