Using ND filter to dim a 60-70mw 488nm-492nm 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.

 

[Nuguns]

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.

The only other option Im willing to currently eplore is potentiometer adjustment and I took it apart which there was none on the driver.

What a wealth of ideas o_0

Im happy with what Ive got, its nice to have those ideas here for the taking on our thread.

 

[Nuguns]

I found with this laser to remove the spring in the lenses. Ive been trying to align the dot for months and never got it right fully, there was always some kind of artifact or wideness and if it managed to get it aligned by tapping the culmination lens slightly, it moves by the smallest touch back and forth and up and down because its held up by a spring.

When you take off the lens cap, use some pliers to unscrew the main brass casing for the lenses and youll find on the main outside protective glass, 2 O-rings, one on the outside then glass then on the inside. Its useful to clean it by doing this. Screw in the outside facing brass part so its well into the casing and then screw in the culmination lens so they are a really tight fit. Now you have a new variable to adjust the the beam with the brass casing. The first time I got it aligned the bow tie shape was mostly gone with the dot holding all the brightness, and now its shaped like a oblong bar eggplant shape bar dot.

I also had issues with reflections off the outside facing screw in thing creating large circles or half circles to the side of the dot, eventually its possible to get rid of all of it. Adjust the brass lens case itself as well as the lens until you find a sweet spot.

The picture of the dot is from about 50ft away at 8mw-ish

Last two images taken are readjusted for a rounder and smaller spot, the bowtie is back, im sticking with this. I have it placed where I have to unscrew it slightly to get such a small spot. whatever good enough

Ok it bothered me again after one day, I got the bar back and reduced the bowtie again only its more centered than last time. The greener pictures taken at night show the color more true to the eye, Ive done a lot of looking around and determined my laser is a 492nm, I welcome skepticism on this (my computer screen makes it more greenshifted than my phone, its much more pale). The first green shifted blurry dot is now from 85ft ish feet away on white surface and its shaped rather oddly, its got two arms coming out in opposite directions from the bowtie and the top left is brighter than the bottom right saturated into white.

AND I went back on my idea about tightening the culmination lens tight with the top screw in thing, Thread locker is the new solution, I used liquid super glue to make the threads grind and stick After drying. Turns out that the top piece blocks out some of the square reflection and if you take it out the dot gets bigger but that square gets twice as bright, so I moved it back to the top until the reflection circle was generally less present

god this took a lot of work for a long time............ It feels good using it now, no pesky issues anymore :T