Laser slow motion

Question

Something really strange happen and I was hoping someone could shine some light on this. I always play around levelers with red lasers. I decided one day to shine a laser through a magnifying glass (projected onto a white wall) and recorded it with a canon 60D at 1920x1080 at 30 fps. I took this footage, put it into Apple Motion editing software and slow it down to 25%. What I saw after the video rendered was really strange. While playing the footage back I noticed the halo of the laser light surrounding the center portion of the laser light was moving like a gas (such as smoke). What was even more weird was that the laser light would flash really quick. When stopping the video play head over the blip the attached picture is what I saw. Everytime it blips is shows a different pattern. I ensure the laser was not affected by vibrations I know this is going to sound crazy but it looks like a wormhole. What is this?

https://www.youtube.com/watch?v=sRA-rQI9TeU&feature=youtu.be

Answer 1

The laser leveler is using a pulsing technology, which is most often associated with distance measurements. The halo is due to scattering of the laser light off of dust particles. The motion you are seeing is that of the dust particles.

Video of laser scattering off chalk dust

If it is laser speckle, as Peter Shor mentioned, the pattern will randomly move, but it is pinned to the wall, where the laser beam strikes:

Laser speckle on a digital camera image from a green laser pointer.

Based on your description, scattering from dust seems most likely; as Daniel Sank said, seeing the video would result in a definite diagnosis.

Answer 2

Slow movements in the beam profile of a laser are usually the result of temperature variations inside the laser - it tends to warm up gradually. Temperature changes lead to two effects:

1. The laser cavity gets slightly misaligned, causing the divergence of the laser beam to change and possibly the mode as well. Usually, an ideal laser beam has a smooth Gaussian beam profile, but it can become less smooth if the cavity is misaligned.

2. In particular with laser diodes, the wavelength spectrum of the laser can be temperature-dependent. The speckle pattern that you see is highly sensitive to the exact wavelength spectrum. In particular laser diodes (your red laser likely is one) may drift in wavelength. Green laser pointers (532 nm) are typically more stable in wavelength.

In a laser, thermal drift may be subject to a feedback mechanism. As the laser crystal heats up, it becomes initially more efficient because it was originally aligned at full power. But more efficiency means more power going out and less power is left behind in the laser, counteracting the warming up. In some circumstances, the internal temperature of the laser may oscillate slowly, so that it never stabilizes.

As for the flashing: I didn't catch it on the video clip (not patient enough to sit it all the way out), but it could be an extreme case of temperature instability.

As for the hypothesis of dust blowing through the laser beam path: this would generally lead to much faster fluctuations in the speckle pattern, unless the laser beam travels through tubes with very little air circulation.