DIY beam stop/dump

[clansley]

After researching beam stops I decided to make one, but weren't sure of the finer details so have been experimenting. This thread covers my process so far, and will be updated until I have my final beam dump. UPDATE: The completed beam stops are in later posts.

There were two types I was interested in: one made from a stack of razors or one made from a cone.

Parts
Here's the parts I have so far:

• High temperature deep matt spray paint - Found this to be hard to work with as it needed heating to cure (used on cone beam dump).
• (not in image) Rust-Oleum Heat Resistant Matt Black Spray Paint - Much easier to work with (used on razor beam dump).
• 100mmx50mmx50mm 1.5mm thick Aluminium box section
• (not in image) 150mmx50mmx50mm 1.5mm thick Aluminium box section (used on razor beam dump)
• double edged razor blades
• 50mm box section caps
• Plumb bob

Results so far (summary)

• a stack of unpainted razors does a fine job (better than painted ones using the paint above)
• Using a candle to coat the razors in carbon helps a bit
• an unpainted cone does a fine job (still to test painted cone)
• Using a flame to coat the razors in carbon can damage the paint :-(

Tips

• Avoid touching the razor blade sharp edge and/or resting the sharp edge on anything - minor damage can reduce their effectiveness.

Tests
All test images are zoomed in so to more clearly see the reflected amount of light - clicking on them will show the full photo such as this:

All photos were taken in near darkness, with the same settings in manual mode and made as close to what I was actually seeing. The beam stop was close to the lasers focus point (+/- 2cm). The laser was a 50mW 520nm and 65cm from the beam stop. The beam stop was 1 meter from the wall.

Black matt card - reflects a lot back:


The plumb bob had a screw in the top which I removed, I drilled a hole in one of the box section end caps and screwed it to the end of the plumb bob (so when the end cap is placed in the box section the cone was securely held up).
Unpainted cone - huge improvement over the card:


Stack of unpainted razors - slightly better than the unpainted cone (although debatable as there is more light on the wall but less on the table):


Painted razors - slightly worse than unpainted:


Razors that have had a candle flame run over them until they go black - slightly better than unpainted:

 

[gozert]

Looks good, could you post a picture of the finished beam stop?

 

[clansley]

Looks good, could you post a picture of the finished beam stop?

Sure will - I just have to run some more tests to decide if razors or a painted cone are best and then to begin constructing the final item. If razors win then I will be drilling two holes through the box section to hold the razors, if the cone wins then I will need a metal end cap as the plastic end cap is unlikely to cope with high powers.

 

[Smeerworst]

Maybe it works better when you have the beam stop at a angle... like up or down... and move it further inside the tube.

 

[clansley]

Decided to make both the cone based and razor blades based ones. Here's the cone one (will take a while to complete the razor one):

Plump bob bolted to a 50mmx50mm square washer. All parts sprayed matt black with heat proof BBQ paint:


Fully assembled:


Side view 52mW 520nm then 1W 445nm:



Internal view:



Wondering if using a candle to cover the internals in carbon would improve it further.

 

[clansley]

Seems beam stops don't excite many...

I've completed the razor based beam stop but have damaged the external paint when I used a flame to coat the blades in carbon. The paint got soft with the heat and then stuck to my gloves. :-(

These were the steps I did to create this:

• Unpack and stack 470 razors! (each 0.1mm thick)
• blot them together using m5 machine screws
• put glue down the sides of the razors (this was just to make it easier to insert them as one whole thing)
• drill holes for screws in the box section,and spray black
• remove machine screws, insert razors into box section and insert the machine screws
• cut off the excess screws
• use a flame to blacked up (not really needed)
• add some sticky rubber feet

The large one is the razor based one, the other being the cone based one. The damaged paint is clear to see. The bolts are holding the razors inside the box section:


Here's a close up of the razors (with a flash pointing into it):


Here's both, they both look very dark in normal lighting. A little light leaks above and below the razors as they are shorter than 50mm:


Beam shots






Comparison
How to test how effective each is? Tried a few ways and ended up using my camera on it's least sensitive settings (ISO 200, 1/4000 s, F/36).

To give you an idea what that means I've taken a picture using the above settings of a 50W halogen downlighter which would normally be painful to look at:


And shining a 52mW 520nm and a ~1W 445nm on to:

"Control"/matt black surface (Side of razor beam dump):


Cone based beam stop:


Razor based beam stop:


Both cone and razor solutions seem much better than a matt black surface. But the cone appears to be overall winner. If I had to make another I would go for a cone based one as it was cheaper and easier to make.

 

[o_DEATH_ANG3L_o]

That's actually really genius. Way to go!!!!!!!

 

[djQUAN]

How about making a cover with a smaller aperture just enough to let the light beam in but small enough to block the reflected light coming back out?

 

[clansley]

How about making a cover with a smaller aperture just enough to let the light beam in but small enough to block the reflected light coming back out?

Yeah not a bad idea - but it would be a lot harder to aim the laser. I found even a 40-50mm square target hard to aim for from a few meters away. Maybe aim lasers and then switch them off, put something in front (paper/wax?), switch on lasers and then let them burn a hole in it! Everything improves once the hole is burnt.

 

[gozert]

I'm amazed by how it worked out. Definitely worth a +rep. Thanks a lot for sharing!