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

[neufer]

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.

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.)

Drawing of Newton dispersing light with a glass prism: Apic/Getty Images

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"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.

[Chris Peterson]

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.

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.)

Drawing of Newton dispersing light with a glass prism: Apic/Getty Images

---

"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!

[neufer]

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:

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.

[Chris Peterson]

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:

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.

[neufer]

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

[JohnD]

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

[Chris Peterson]

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.

[neufer]

Click to play embedded YouTube video.

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.

[JohnD]

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

[NGC3314]

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.

[neufer]

Click to play embedded YouTube video.

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.

[JohnD]

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

[Chris Peterson]

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.