# Improving the Laser Dot Rendering in The Refraction Simulator

#### Mick West

Staff member
Something I'd like to improve is the rendering of the laser when it hits the camera. Currently what is being rendered is the diffuse beam (i.e. the beam light that is scattered by the air.) But when that beam covers the camera, there should be a very bright spot of light at the position of the laser source.

I did a few experiments in daylight, shining a laser at a tree about 330 feet (100m) away.

From this distance, it was just visible to the naked eye. Up close there was a visible spot 2-3" across

Iphone X camera looking back at the laser shows a clear bright light that grows and shrinks as you move in and out of the dot.

So I kind of need something like this in the simulator.

Last edited:

#### Mick West

Staff member
Got a dot overlay that looks similar. Now to make it appear in the right spot.

#### Mick West

Staff member
THinking about the spread of the beam raises some interesting things. Here I added three laser beams to the simulation, one angled up slightly at -0.056° (the green one) and then two that are just 0.001° on either side of this.
https://www.metabunk.org/refraction...0Front~multiple~0~gap~0))~localDefault~true)_

If we remove refraction:

So the refraction is causing the beam to diverge a LOT more than you would expect, which in turn makes it a lot more visible from a wider variety of positions.

The spread I observed was about 2" in 330 feet, so about atan(2/(330*12)) = 0.029° spread. Say 0.03° If we Stick that in for the upper and lower blue beams, we get:

The top edge now being 60 feet above the center with refraction

Without refraction, the divergence is far less, about the 20 feet I estimated earlier.

#### Mick West

Staff member
Early morning experiments for better light:

Right next to the laser, the beam is about 1mm, but there's plenty of scattering quite widely.

330 feet (100m) away

Laser's perspective

Target's perspective

Size of dot (card is 12.5 inches, 32cm across)

The colors are:
• Solid white
• mixed solid white and solid green
• solid green
• scattered green
Which you don't see with the naked eye, but are really artifacts of the camera.

Looking back at the laser, with the camera exposing video for the dim light, we get more intense "dots"

#### Mick West

Staff member
Using some laser safety glasses allowed me to see the size of the business portion of the beam more easily.

[compare]

[/compare]

#### Mick West

Staff member
Of nerdy interest, on the target the solid white center has a ring of cyan (green+blue) between it and the solid green

But a few seconds later in the same shot, facing the laser, it's a ring of yellow. (green+red)

This must be something sensor specific, to do with how the red, green, and blue sensors in the camera get overloaded. In reality, it's all green.

#### Mick West

Staff member
So, I think for the improved rendering, I need to trace a center ray, and a top and bottom ray, and then see where they hit the plane of the camera, then interpolate (and possibly do a binary search to refine) to get the incident angle of the direct path, and hence the position of the center of the dot

In the above, the camera is on the left. The laser is on the right, the green line is the nominal center of the laser, and the red and blue indicate the spread.

The orange line (with the mouse cursor) is the line of sight from the camera to the laser, this will need a binary search to narrow down. This involves narrowing the extents of the beam depending on which half it is in. So here I'd cast a new laser ray midway between green and blue, and then see which side of that ray the camera is on. This process will also give me the angle from the center beam, and hence a more accurate basis for brightness.

#### Mick West

Staff member

Other sources:
https://www.quora.com/What-is-realistically-the-least-possible-beam-divergence-of-a-laser
mRad seems to be the most common unit for giving beam divergence. Here's a bunch of
https://www.wickedlasers.com/laser-tech/laser_beam_comparison.html

Similar here, mostly 0.5 to 1.5, so I think a default of 1.0 is good. I'll make it editable.
http://www.lasersafetyfacts.com/resources/FAA---visible-laser-hazard-calcs-for-LSF-v02.png

Since I was measuring in daylight, I got too small a value. Looking at the dawn shots, it was probably three times as much, or 1.5 mRad (0.08°).

My laser is a generic 301 green laser (532nm). The beam can be focussed, and I had it on the tightest beam. This review says that's about 1mRad, consistent with my observations.

Last edited:

#### Mick West

Staff member

Replies
43
Views
15K
Replies
10
Views
2K
Thread starter Related Articles Forum Replies Date
ATFLIR and range information (RADAR/LASER/Passive range?) UFO Videos and Reports from the US Navy 15
Flat Earth Claim: "The Greatest Laser Experiment In History" - FECORE Flat Earth 11
Plasma Laser Hologram as a possible UFO sighting Explanation UFO Videos and Reports from the US Navy 6
Claim: UFO performs sharp maneuver after laser pointer directly hits craft UFOs and Aliens 20
Why Flat Earth Laser Tests are Misleading Flat Earth 16
Demonstrating How Refraction Helps You See Over The Horizon Flat Earth 32
Lasers vs. Flashlights vs. Daylight for Observing the Curve of the Earth Flat Earth 12
Measuring the distance to the moon with laser reflections and the speed of light Flat Earth 5
Greenwich Meridian Laser - Can it Demonstrate Curvature? Flat Earth 20
Lake Balaton Laser experiment to determine the curvature of the Earth, if any. Flat Earth 1027
Upcoming Laser Experiment Flat Earth 3
Pilot laser sightings Contrails and Chemtrails 3
Debunked: Chemtrail "Laser Line" and 4 UFOs Contrails and Chemtrails 1
Laser could trigger rain and lightning UCF College of Optics & Photonics General Discussion 5
Reward to catch people who point lasers at planes General Discussion 21
Laser attacks on airplanes continue Contrails and Chemtrails 11
British Pilot's Association Reporting 5 Laser Attacks/Day, Calls for Laser Ban Contrails and Chemtrails 35
Related Articles