Diode laser cutter focusing

Hello,

I'm currently working on a laser cutting extension for my Prusa i3 to cut thin material (paper or balsa sheets). For that purpose I ordered a 445nm M140 laser diode (2w) with a G2 lens. (link). I already created a constant current driver which delivers about ~1.65A with an electronic on/off control; my questions are about focusing the laser diode beam.

1) What is the distance to set up between the surface and the laser module ?
2) I suppose there is a manual adjustment to be done on lens by (un)screwing the "lens ring"; how to adjust that ring to optimize the beam precision knowing that I wear laser goggles preventing to see it?
- 2.a) Do I need to create a smaller laser driver with very low output current to be able to safely calibrate the beam without going blind?
- 2.b) What is the safe current level (10mA as for normal LEDs ?)
3) How to deal with the relationship between 1) and 2). Distance vs Focusing.

Thanks in advance.

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[vvinch.blogspot.com] - [vvinch-diy.blogspot.com]

... the minimum current needed to start the laserbeam is called 'threshold current' and is stated in the datasheet of the diode ... should be something around 100mA with the 1W(2W)-diodes ... below the threshold current the laserdiode emits blue light like a conventional LED, so the position of the spot is visible, but not with the correct focus diameter.

For setting/measuring the focus distance/diameter I'm adjusting the lens with activated laser at lowest possible power (see 'threshold') and blow fume into the beam or beam into water with a small amount of milk mixed in.

The focal distance adustment is best made with black paint on a white tile and engraving lines with different distances ... the thinnest lines (around 0.03mm) are burned with the exact distance. Then make a measure with this distance to adjust the Z-height with objects of different heights ...

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Viktor
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Thanks a lot!

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[vvinch.blogspot.com] - [vvinch-diy.blogspot.com]

I notice that you have the one with the current-limiting driver built in, so you could limit your current going in to get a minimal beam. I got a similar 3W diode laser [www.ebay.com] and still putting together my heat sink and driver circuit.

I got cheap red laser safety goggles for doing low-power focusing. It was pretty easy to focus a low-power beam well enough to get about a 0.2mm burning beam. For testing I've just been using a current-limited bench power supply. My threshold current is around 80mA.

Thanks @vdx for the suggestion about black paint on a white tile for getting a more precise focus!

Sorry, my link is wrong. I didn't noticed it was the version with a driver included. In fact I have the same item, but without the driver.
I'm currently building a smaller driver without electronic on/off control for delivering a test current of about 250mA (seller said me the threshold is 200mA to get a laser beam).

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[vvinch.blogspot.com] - [vvinch-diy.blogspot.com]

I am using 1.7W 445 laser diode rig from Jtech
diode is driven at 2 amp
There is a gold ring below diode that I twist to adjust lens
and focus laser.
Laser light only hurts close to focus point. (still have all my fingers -- unburned)
I use a set of red glasses (made for Blue laser) I can still see quite well