Questions on fat beam lasers...

[Externet]

Seems that if a laser beam is bigger than about 2 mm diametre it is not a laser any more ?  Or is it still a laser even if the beam is 1 metre diametre ?

How is that accomplished ? Diverging lens and collimator after ?

 

The danger of vision impairment persists or is it greatly reduced as the light 'density' is a much smaller figure ? 

Which wavelength shows the beam brighter at night ?  To achieve 1Km range on a 10cm fat beam at night, what power would be needed by educated guess ?

 

[swansont]

Laser implies a certain source (stimulated emission). There may be issues of coherence of the light and beam quality with beams, but I’ve used 50mm beams without any issues. Still able to do laser cooling and trapping. We expanded the beams using lenses.

I can’t see your embedded image

Vision impairment is an intensity issue, which is made worse by having a collimated beam

The eye is most sensitive in the green (555 nm), ~5x more sensitive in green than red (~650 nm). this shifts a little toward shorter wavelengths if your eye is dark-adjusted

https://www.ncbi.nlm.nih.gov/books/NBK11513/figure/ch24psych1.F10/

The effective range is going to depend on the beam’s divergence. If it’s 10 cm at the target, a few mW should be visible.

[Sensei]

17 hours ago, Externet said:

To achieve 1Km range on a 10cm fat beam at night, what power would be needed by educated guess ?

Distance depends on air polution, humidity, fog, dust etc. Water and other particles disperse light in the all directions randomly.

In vacuum there is not enough particles to scatter photons thus we can see light from distant stars..

Edited March 25, 2021 by Sensei

[Area54]

17 minutes ago, Sensei said:

In vacuum there is not enough particles to scatter photons thus we can see light from distant stars..

On a clear day you can see all our yesterdays.

[Externet]

10 hours ago, swansont said:

...I can’t see your embedded image...

...The effective range is going to depend on the beam’s divergence. If it’s 10 cm at the target, a few mW should be visible.

Thank you.  The failed embedded image was just a generic one like :

 

What if possible could be the way to obtain one Km long 10cm diametre fat beam as close as possible from start to end ?

These are outdoors

---> https://www.youtube.com/watch?v=RmcQNiNHemc  -

---> https://www.youtube.com/watch?v=uYKERtq_L5M

 

Edited March 26, 2021 by Externet
changed text

[swansont]

All lasers eventually diverge; most can be described by gaussian profiles, so they have a minimum spot size (“waist”) at some distance from the laser. Making the beam fat actually improves the divergence issues.

The laser used for the moon ranging measurement diverged to be ~2 km across by the time it got to the moon (the atmosphere’s changing density played a part in this); the beam started out several meters wide

https://tmurphy.physics.ucsd.edu/apollo/basics.html

We use the telescope as a gigantic (3.5 meter wide) laser pointer and also as a signal receiver.

Staying close to 10 cm over 1 km would seem to be possible with good optics+optomechanics and the right laser (for example, laser diodes, such as ones found in laser pointers, have horrible inherent divergence issues)

 

 

[Externet]

Thank you sir, +1

12 hours ago, swansont said:

Making the beam fat actually improves the divergence issues.

What is "improve" ?  Makes it less or more diverging?

[swansont]

28 minutes ago, Externet said:

Thank you sir, +1

What is "improve" ?  Makes it less or more diverging?

less divergence.