445nm help

[sellersmd]

Hello. Long time lurker, first time poster here. I recently built a ~1.6W 445nm laser using a host, driver, lens, and focus adapter from jayrob and an M140 diode in a module from DTR. I've got my Eagle Pair glasses at the ready, and have read through all the good stickies about safety and what have you.

Equipment:
- c6 host from jayrob with copper heatsink
- whatever driver jayrob uses in his just-add-diode c6 18650 kit. (forgive my ignorance)
- 405-G-2 lens with focus adapter
- M140 445nm diode in 12mm module from DTR

Here's my question:

After putting my laser together, she lights up, she's bright, and she definitely burns things. BUT... I am concerned about beam divergence. I know the diode is multimode, so I won't get a nice, small dot and should instead expect a rectangle. However, even with the focus adapter cranked down as far as I can get it, the beam is still probably 10 x 20 inches at even 25 feet. I don't think that much divergence is normal.

Any suggestions? Is the lens still not close enough to the diode, perhaps?

Thanks in advance for your help.

 

[oahu99]

To focus the laser you don't screw in the lens all the way.
Instead you just screw the lens in until the dot is the smallest.
Welcome to the forum!

 

[sellersmd]

Attempted but no success. The smallest beam was when the lens was screwed down as far as possible, and even then I get a big nasty spot. Other advice?

 

[oahu99]

Do you have the top of the module flush with the top of the heatsink?
Because if the module were recessed, then the lens wouldn't thread in all the way.
You could also try taking off the focusing ring to get the lens to thread deeper.

 

[KrowBar]

Yeah - it sounds like you aren't able to get the collimating lens close enough to the emitter. This could be due to the diode not being pressed completely into the module, mucked up threads in the front of the module/back of the lens barrel, or possibly a g-2 lens that is not close enough to the back of the barrel for some reason. Where is your glass in relation to the barrel?

Finally, you may just never be satisfied with the beam using that lens. A 3-element lens is quite cheap, but will give you a noticeably better beam with that diode. Also, it has a longer focal length so it will not need to get as close to the diode face still possibly allowing correct focus even if you are suffering from one of the above mentioned problems.

Finally, pictures always go a long way in helping diagnose problems, as well as helping others identify if they have a similar problem. We all like beam shots. Let's see that spot.

 

[sellersmd]

Thanks for the responses, guys. Sorry in advance for my sideways pictures, not sure why the iphone/tinypic decided to do that.

Do you have the top of the module flush with the top of the heatsink?
Because if the module were recessed, then the lens wouldn't thread in all the way.
You could also try taking off the focusing ring to get the lens to thread deeper.

As a matter of fact, I was afraid of that very thing, so I have about 2-3mm of the module sticking out of the front of the heatsink:

And with focusing ring cranked down:

I wish I were able to unscrew the focusing ring from the barrel, but I can't. When I put the thing together and tried to screw it down to focus it, the barrel kept getting stuck and the focusing ring alone would come unscrewed from the barrel. To remedy this, I glued the focusing ring to the barrel. So taking the focusing ring off the barrel isn't likely. Unless you have a good plan for getting superglue out of little tiny threads:

(This is some left over thread tape in the threads, NOT super glue)

Yeah - it sounds like you aren't able to get the collimating lens close enough to the emitter. This could be due to the diode not being pressed completely into the module, mucked up threads in the front of the module/back of the lens barrel, or possibly a g-2 lens that is not close enough to the back of the barrel for some reason. Where is your glass in relation to the barrel?

Finally, you may just never be satisfied with the beam using that lens. A 3-element lens is quite cheap, but will give you a noticeably better beam with that diode. Also, it has a longer focal length so it will not need to get as close to the diode face still possibly allowing correct focus even if you are suffering from one of the above mentioned problems.

Finally, pictures always go a long way in helping diagnose problems, as well as helping others identify if they have a similar problem. We all like beam shots. Let's see that spot.

In regards to the diode not being pressed all the way into the module, I don't know if it is or not. I bought the diode/module from DTR because of his reputation, so I hope that isn't it.

The threads in the module and the threads outside the barrel are both very smooth. As far as I can tell, the barrel threads completely into the module all the way until the focusing ring is flush with the module.

The lens is about 3mm from the back end of the barrel. How close is it supposed to be?

Here are some shots. The first two I am approximately ten feet from the wall (standard exterior door for scale) and the laser was rotated 90 degrees between the images. The third photo is from about 6ft.

I may have to just suck it up and buy a new lens/barrel. Do I need the longer barrel? What lens would you guys suggest for minimizing beam divergence? I don't mind if I lose a bit of power. Any other suggestions guys? Thanks in advance!

 

[ChaosLord]

If you do go with a new lens/lens barrel, I would suggest the extended barrel. I noticed that the 9mm 445 diodes require the lens to be closer to the diode than most other diodes I've dealt with.

The extended barrel will allow you to fully focus (and even over focus) it. I've come to prefer them, especially with a focus adapter, in order to get a full range of focus.

 

[KrowBar]

IIRC the flat part of the g2 lens should be very close to the back of the barrel. I think you might have the lens backward - just from seeing where the flat-head notch is. This is actually a somewhat easy mistake to make, so you wouldn't be the first. Are you sure it is facing the right way? The collimated beam should be exiting the curved side of the lens.

[edit] I just looked back at you OP and saw that you got the lens from Jayrob. I think he does put them in a flipped around barrel so the notched side will be toward the diode as you have it. Still worth checking which way the curved side faces though, just in case.

[edit2] Also, I just thought to ask, are you focusing while the laser is on, or turning it off between adjustments? I didn't see that mentioned so I'm not going to assume. It is very hard to get good focus by the latter method. Does slowly unscrewing the lens from the all-in position while the laser is on result in a slowly widening beam?

If it is in correctly and the focus ring gets flush with the module, then it sounds like it is keeping you from getting the lens close enough to the diode. Either way this would require removing the focusing ring. You could try soaking it in boiling water or acetone (not boiling acetone) to "unstick" the superglue. Or possibly heating it with a hair dryer/heat gun.

The 3-element lens with its longer focal length will give a rounder dot with less divergence, but not insignificant power loss (as much as 30%) It is only 8 or 10 dollars in a barrel, so you should get one even if it's just to help determine your preference.

 

[IsaacT]

Hey man, you have your lens in backwards. That is why it isn't working for you. Try to use a vice and some leather maybe to hold the focus adapter, and use a screwdriver to turn the lens via the notches on the top of the lens.

Hopefully you can get it out. As I recall that Focus Adapter is 24 dollars.

 

[sellersmd]

Well the glue wasn't too cooperative. Cracked the lens. new one on the way.

 

[IsaacT]

Better a new lens than a new focus adapter. Just make sure this time that the big grooves are facing away from the LD.

PS - as far as mistakes go that one isn't terrible, the only bad part was the glue. I have done much more costly mistakes so don't let it get you down.