Very small working ranges

[m0sf3tz]

Hi, I am building a laser engraver and due to my mechanical ineptitude my base is somewhat wobbly, to get around this I need to use a very small working distance of ~ 1cm.

I'm hoping to use a 445nm 2 watt laser (DTR's 2W M140 445nm). However, I am a bit stumped on the optics. I was hoping to go for a 405-G-2 Glass Lens with an EFL of ~4mm.

However, I'm guessing this focal range is assuming that the laser beam is collimated. I plan to use laser.

I don't know much about optics. I know diode lasers have really bad outputs, but if I go ahead and assume that the beam is collimated and leave it as is... how terrible would the spot be? I was hoping for a spot that is on the order of .1mm (or less).

am I SOL?

 

[micheal rosen]

i don't know why this was never answered... anyways, with the multimode blues, you might be, but the 16x BDR-209 has an output of ~900mW plus the dot can easily get into the submillimetre range. you might want a 3-el lens if you don't mind the power loss, for a smaller spot, otherwise go for a G-2 lens for max output and slightly decreased beam specs.

 

[marcuspeh]

you might want a 3-el lens if you don't mind the power loss, for a smaller spot, otherwise go for a G-2 lens for max output and slightly decreased beam specs.

Use G2 for higher output but i wouldn't recommend using G2 for an engraver. For the engraver, you would need the beam dot as small. Lets say laser with 3 element dot has a surface area of about 0.13mm^2 (using 0.2mm diameter), a laser with G2 dot would a surface area of about 0.79mm^2 (using 0.5mm diameter). Assume that both put out 200mw, 3 element delivers 200mW/0.13mm^2 = 1538mW / mm^2 and G2 delivers 200mW/0.79mm^2 = 253mW / mm^2. Hence the 3 element would be more effective in this case.
Edit: Dont buy m140 for an engraver as it is multimode. Get a BDR-209 or similar monomode 405nm as they will make the dot smaller.

 

[DTR]

Check out this thread for a lot of great info on the subject.
CNC Laser Engraving 8bit Shades of Grey 445nm

The M140 and NDB7875 seem to be the most common diodes I sell for engravers and based on the feedback I have received and some of the testing info from the above thread the 405's will make a smaller spot but the engraving speed will greatly improve with the M140 or NDB7875. On the lens this one was confusing to me at first as well but the G-2 is the more commonly chosen optic. Over longer distances yes the G-2 will have much worse spot size compared to the three element lens but the most recommended distance I see from the aperture to the work is 30mm with these diodes and at that distance the G-2 will actually produce a smaller spot and give more power. The light with the G-2 is collected much closer to the diode so it actually exits the aperture smaller than the three element lens which the light is collected further away resulting in a fatter beam exiting the aperture. Over long distances the spread is less with the three element lens but at close distances the G-2 seems to be the winner.:beer:

Here is a quick picture I took to try and show what I mean.