APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Comments and questions about the APOD on the main view screen.
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neufer
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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by neufer » Thu Feb 11, 2021 10:32 pm

neufer wrote:
Thu Feb 11, 2021 8:04 pm
neufer wrote:
Thu Feb 11, 2021 8:04 pm

Each laser delivers 22 watts of power — about 4000 times the maximum allowed for a laser pointer — in a beam with a diameter of 30 centimetres.
Chris Peterson wrote:
Thu Feb 11, 2021 6:50 pm
Yes. Your point?
  • 22 watts of eye sensitive yellow light (= 15,000 lumens) shouldn't be sneezed at.
    (And it is not clear to me that the ground atmospheric sodium is entirely negligible.)
Chris Peterson wrote:
Thu Feb 11, 2021 8:08 pm

"22 watts" is meaningless without considering the density. Every square meter of ground is receiving around 1000 watts in the middle of the day. So what?
A beam with a diameter of
30 centimetres = .0707 m2

So 311 watts per square meter
in the middle of the night.
Art Neuendorffer

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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by Chris Peterson » Thu Feb 11, 2021 10:39 pm

neufer wrote:
Thu Feb 11, 2021 10:32 pm
neufer wrote:
Thu Feb 11, 2021 8:04 pm
neufer wrote:
Thu Feb 11, 2021 8:04 pm

Each laser delivers 22 watts of power — about 4000 times the maximum allowed for a laser pointer — in a beam with a diameter of 30 centimetres.
Chris Peterson wrote:
Thu Feb 11, 2021 6:50 pm
Yes. Your point?
  • 22 watts of eye sensitive yellow light (= 15,000 lumens) shouldn't be sneezed at.
    (And it is not clear to me that the ground atmospheric sodium is entirely negligible.)
Chris Peterson wrote:
Thu Feb 11, 2021 8:08 pm

"22 watts" is meaningless without considering the density. Every square meter of ground is receiving around 1000 watts in the middle of the day. So what?
A beam with a diameter of
30 centimetres = .0707 m2

So 311 watts per square meter
in the middle of the night.
Yes. So what? Why is that any health or safety concern? You'd be far worse off encountering a 20 mW laser beam of typical 1 mm diameter!
Chris

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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by neufer » Fri Feb 12, 2021 2:13 am

Chris Peterson wrote:
Thu Feb 11, 2021 10:39 pm

Yes. So what? Why is that any health or safety concern? You'd be far worse off encountering a 20 mW laser beam of typical 1 mm diameter!
This long thread has NOTHING to do with any health or safety concern :!:

Rather, I was simply ADDING to your own response to John's question:
JohnD wrote:
Thu Feb 11, 2021 6:09 pm

Now, please explain why they are visible? So very visible!
The beam from a milliwatt hand held pointer is invisible, unless in a smoke filled room.
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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by Chris Peterson » Fri Feb 12, 2021 4:57 am

neufer wrote:
Fri Feb 12, 2021 2:13 am
Chris Peterson wrote:
Thu Feb 11, 2021 10:39 pm

Yes. So what? Why is that any health or safety concern? You'd be far worse off encountering a 20 mW laser beam of typical 1 mm diameter!
This long thread has NOTHING to do with any health or safety concern :!:

Rather, I was simply ADDING to your own response to John's question:
JohnD wrote:
Thu Feb 11, 2021 6:09 pm

Now, please explain why they are visible? So very visible!
The beam from a milliwatt hand held pointer is invisible, unless in a smoke filled room.
Well, as this whole long thread STARTED with questions about safety, perhaps you can understand the confusion.
Chris

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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by neufer » Fri Feb 12, 2021 2:46 pm

Chris Peterson wrote:
Fri Feb 12, 2021 4:57 am

Well, as this whole long thread STARTED with questions about safety,
perhaps you can understand the confusion.
  • No mind.
When I'm not doing pratfalls for cheap laughs
I'm mostly trying to educate myself by arguing a case.

I found this one was very ilLUMENating :!:
Art Neuendorffer

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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by JohnD » Fri Feb 12, 2021 5:23 pm

Neufer,
I was concerned, and matbe started this thread down this route, but Chris' answers have reassured me!

Chris, I'm sorry if my concern - idle, because I'm on the other side of the planet! - gave you a hard time. Thanks again for your patient education!
John

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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by Chris Peterson » Fri Feb 12, 2021 5:33 pm

JohnD wrote:
Fri Feb 12, 2021 5:23 pm
Neufer,
I was concerned, and matbe started this thread down this route, but Chris' answers have reassured me!

Chris, I'm sorry if my concern - idle, because I'm on the other side of the planet! - gave you a hard time. Thanks again for your patient education!
John
It was a reasonable question. Anybody who has worked around lasers at all knows that a 22 W laser is dangerous. But we're not usually accustomed to encountering them in the form of 30 cm diameter beams. That can distort our intuition.
Chris

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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by neufer » Fri Feb 12, 2021 8:04 pm

Click to play embedded YouTube video.
Chris Peterson wrote:
Fri Feb 12, 2021 5:33 pm
JohnD wrote:
Fri Feb 12, 2021 5:23 pm
Chris, I'm sorry if my concern - idle, because I'm on the other side of the planet! - gave you a hard time. Thanks again for your patient education!
It was a reasonable question. Anybody who has worked around lasers at all knows that a 22 W laser is dangerous. But we're not usually accustomed to encountering them in the form of 30 cm diameter beams. That can distort our intuition.
Art Neuendorffer

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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by JohnD » Wed Feb 17, 2021 5:30 pm

I am now reassured that the people who use the lasers at Paranal, do so responsibly.
However there may be others who do not. I just came across this video. Do NOT try this at home!
https://youtu.be/WAI7Lu4UFi4

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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by NGC3314 » Wed Feb 17, 2021 7:12 pm

Sites with visible-light AO systems use human plane spotters to avoid accidentally flashing a pilot's vision, with some work in progress on automated systems to first augment, and eventually replace, the spotters. (I am told that UV lasers such as the Robo-AO setup do not need this step). And at least for US systems, there is also a requirement for coordination with (IIRC) NORAD to avoid illuminating sensitive satellites. It is widely believed that NORAD will occasionally insert a fake satellite-avoidance zone to avoid advertising the orbits of satellites they want to protect, but it's not like amateur observers worldwide don't do a good job of tracking most of their orbits anyway.

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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by neufer » Wed Feb 17, 2021 9:01 pm

Click to play embedded YouTube video.
NGC3314 wrote:
Wed Feb 17, 2021 7:12 pm


Sites with visible-light AO systems use human plane spotters to avoid accidentally flashing a pilot's vision, with some work in progress on automated systems to first augment, and eventually replace, the spotters.
Best for all involved that planes avoid any observatories in the Andes.
Art Neuendorffer

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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by JohnD » Sun Feb 21, 2021 11:08 am

Just for comparison, I read that the US Army is developing a TUPLARP, Tactical Ultrashort Pulsed Laser for Army Platforms, that will deliver fentosecond pulses in the Terawatt range! The average power will be only 20-50 Watts, but in such short pulses will vaporise the target. If it hits it.
See: https://www.sbir.gov/node/1654485

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Re: APOD: Firing Lasers to Tame the Sky (2021 Feb 10)

Post by Chris Peterson » Sun Feb 21, 2021 2:19 pm

JohnD wrote:
Sun Feb 21, 2021 11:08 am
Just for comparison, I read that the US Army is developing a TUPLARP, Tactical Ultrashort Pulsed Laser for Army Platforms, that will deliver fentosecond pulses in the Terawatt range! The average power will be only 20-50 Watts, but in such short pulses will vaporise the target. If it hits it.
See: https://www.sbir.gov/node/1654485
The ability to do damage largely comes down to energy density.
Chris

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