Re: Laser aimer arrested

From: Larry Dighera (LDighera_at_att.net)
Date: 01/09/05 

Date: Sun, 09 Jan 2005 00:33:45 GMT

On 8 Jan 2005 14:19:01 -0600, Andrew Sarangan
<asarangan@yahoo-nospam.com> wrote in
<Xns95D89B7CF36A3asaranganyahoocom@38.119.71.61>::

>Larry Dighera <LDighera@att.net> wrote in
>news:8chpt09a1n731pbgj3taor318532s61fod@4ax.com:
>
>> On Wed, 5 Jan 2005 23:30:57 -0500, "Happy Dog" <happydog@sympatico.ca>
>> wrote in <ea3Dd.42444$P%3.1760523@news20.bellglobal.com>::
>>
>>>"Larry Dighera" <LDighera@att.net> wrote in message
>>>news:vrdpt0tuq95fk4fgiht5bv0enduas1nrs9@4ax.com...
>>>> On Thu, 06 Jan 2005 03:52:02 GMT, Jose <teacherjh@aol.nojunk.com>
>>>> wrote in <CB2Dd.10686$by5.448@newssvr19.news.prodigy.com>::
>>>>
>>>>>There may not be that many photons involved, but
>>>>>they are all coming from the same direction, and that does count for
>>>>>something.
>>>>
>>>> If I'm not mistaken, coherent laser light is all in phase. Doesn't
>>>> that cause it to have more energy?
>>>
>>>No. The energy is measured in watts like any other kind of power
>>>source.

Of course, power is measured in watts. That was not what I was
referring to. Without the knowledge of the specific terms involved,
I'm finding it difficult to express my thoughts coherently. The point
I was trying to make was that for a given brightness, coherent (in
phase temporally) light will affect the surface it strikes greater
than light whose waves/particles arrive at random times.

>>
>> I was referring to the phenomenon of light coherence. There's an
>> explanation of it here:
>> http://whatis.techtarget.com/definition/0%2C%2Csid9_gci214527%
>2C00.html
>>
>> And my point was that because the light of a laser is coherent (in
>> phase), it will provide more energy than an equally bright light
>> source whose radiation is out of phase. At least this is what I was
>> told by an EE.
>>
>
>Coherence comes in two flavors. Spatial coherence add temporal
>coherence. Spatial coherence is a measure of how well we can focus the
>light into a small spot.

That is the first time I have heard coherence used to refer to spot
size.

>Temporal coherence is a measure of how narrow the frequency (color) is.

Yes. But it's more than that. Like it says here
<http://whatis.techtarget.com/definition/0%2C%2Csid9_gci214527%2C00.html>,
"Coherent electromagnetic waves have identical frequency, and are
aligned in phase." I am referring to the _in-phase_ aspect of
coherent light that permits a 0.005 watt light source (laser) to
illuminate its target significantly brighter than a light source whose
electromagnetic waves are not aligned in phase.

>Both are responsible for how it can damage the
>eye. However, I doubt that a 5mW laser can cause much damage. I work
>with these lasers all the time, but I have never looked at the beam
>directly.
>

My guess is that the US military possesses laser weapons for blinding
the enemy, and fears that something similar may be used by terrorists.
So the fellow who was charged under the Patriot Act provided a
convenient vehicle for the government to flex its might publicly in
the vane attempt to impress the populace with its prowess for which we
are paying dearly. Instead, it displays the government's ruthlessness
in dealing with citizens now that it is no longer constrained by
judicial due process. (I suppose much of that went away on January 2,
2005.)

Like you, I would not expect a Class III laser to be capable of
inflicting permanent physical damage. But that doesn't make it a good
idea to aim one at aircraft.

Relevant Pages

  • Re: Why cant waves cause the photoelectric effect
    ... >> measure the coherence length. ... > Does this imply that even light from incoherent sources, ... > coherence lenght of white light from an incoherent source. ... laser, but hardly any light will pass! ...
    (sci.physics)
  • Re: IS IT A LASER?
    ... Since the acronym laser means Light Amplification by Stimulated ... generated, not to it's coherence, brightness, divergence, etc... ... > beam properties such as power, divergence, wavelength, spectrum, ... Sed quis custodiet ipsos Custodes? ...
    (sci.optics)
  • Re: IS IT A LASER?
    ... laser has been labeled with "highly" ... about the coherence of the light source. ... > emitting laser beams. ...
    (sci.optics)
  • Re: Coherence length of yellow, green, blue lasers?
    ... for the laser but I'd think that a HeNe laser should be acceptable. ... yellow or green HeNe lasers shouldn't be significantly ... >> There may be long coherence length blue DPSS lasers and etalon stabilized argon ion lasers. ... please use the feedback form on the S.E.R FAQ Web sites. ...
    (sci.optics)
Quantcast