Using ND filter to dim a 60-70mw laser

[Nuguns]

Experiment success! There's been no melting on the 12$ Amazon go pro ND filter and id love to see someone come out with a stronger laser and try a darker filter. If you're afraid of melting, try getting multiple filters and stack them from ND4 next ND8 next ND16. I consider this a great alternative to multimode lasers especially since those give tons of divergence on them as a downside, yet to be proven.

Onto my laser ND8 is super glued to a 25$ rubber and plastic rifle scope cap I drilled a hole with a knife in and placed at an angle for reflections. When I close the cap with the laser on, it still flashes too bright and could be hazardous. Design flaw that. It also reflects the beam onto the host surface instead of back into the laser, idk if it would be a problem, it definitely isn't here now.

Math says 70 divided by 8 is 8.75 so I'm gonna guess and say my laser is reduced to 10mw an ND16 should reduce it to less than 5mw.

Fun and bright still to play with and I can make it full power with ease.

No melting issues unlike the first batch of cheap NDfilters in a pack, melted almost immediately only noticable by dot divergence.

It would be cool to see someone take a stronger laser and reduce to a lower or safe level with this design. AND I consider this to be a great alternative to multimode lasers.

 

[Nuguns]

Photos

 

[RA_pierce]

It's better that the reflection is directed away from the laser aperture. Reflecting a beam back onto the diode can damage it.

ND filters are not ideal for high power lasers. The beam, unless it's expanded first, is intense enough that it can damage the thin coating, diminishing the effect of the filter (I know this from experience). Plastic filters may melt.

If you have some old, useless DVD or Blu-Ray burners laying around, rip them apart. There are lots of nice optics inside, including dichroic mirrors that can be used in a similar fashion to reduce the output of a laser by reflecting a large percentage of the beam. Just be aware of where the reflection is being directed. Ideally it will be sent to a dark, matte, heat resistant surface.

 

[WizardG]

You use the term 'multimode lasers' a couple of times. I think you mean multimode drivers. A multimode laser is one that does not have a nice, clean, single mode gaussian beam. The increased divergence of multimode diodes has nothing to do with whether or not the driver will operate at more than one power level. The divergence of a multimode laser will not be changed by ND filters.

 

[Nuguns]

It's better that the reflection is directed away from the laser aperture. Reflecting a beam back onto the diode can damage it.

ND filters are not ideal for high power lasers. The beam, unless it's expanded first, is intense enough that it can damage the thin coating, diminishing the effect of the filter (I know this from experience). Plastic filters may melt.

If you have some old, useless DVD or Blu-Ray burners laying around, rip them apart. There are lots of nice optics inside, including dichroic mirrors that can be used in a similar fashion to reduce the output of a laser by reflecting a large percentage of the beam. Just be aware of where the reflection is being directed. Ideally it will be sent to a dark, matte, heat resistant surface.

Ah dang, well after i read this I checked my filter and so far it's ok and un damaged. I wonder when I'd need to replace the filter or if ever being that the laser is under 70mw

Also awesome that I pointed the beam to a dark matte surface on a guess I was worrying that it could damage the diode.

And now I gotta tear apart a DVD player somehow to find out what to do with those optic panes hiding in there. thanks dude

 

[Nuguns]

I started thinking and with common sense, you wouldn't use a over powered laser to play with, with no glasses. So there must be some kind of threshold where the beams brightness begins to degrade a normal ND filter. Someone could use a 200mw laser or something off the top of my head and try to dim it to a safe level. From what I've seen the filter tends to let more light in than you'd think so I'd assume that 200mw would be reduce to 15-20mw on the bright end, this is already relatively safe. Although it could be true to it's rating. My laser may be at 9mw when darkened by ND8 from 70mw at it's highest potential.

What strength will the filter begin to degrade its properties, because the darker it is the more light it will absorb and such is the brighter laser more dangerous. Then would begin the idea to start with ND4 and stack them darker as little as possible ideally.

 

[kecked]

I think you could do better with a pair of glass polarizers if the diodes are polarized. In the least they will be partially polarized so you can use a less extreme nd filter. Why not just turn the drive current down?

you can also pass it through a microscope slide and beam block the straight beam. This will cut down to like 1mw. I use this to sample beams all the time. The reflection is also polarized. You will get two beams as the reflection is off the front and back of the glass. If you don’t like that use a beam cube. That I’ll be likely 50/50. If you use a polarized cube you can rotate the cube and dial in whatever you like.