Beam expander with >1w 445nm?

[Dogs Best Friend]

I am in the process of putting together a laser which will be include an M140 diode driven by a Mohgasm 1.62mA driver.

I already have this Melles Griot 10x beam expander:

LBM Precision Laser Beam Expanders

I would love to integrate this into this laser, but I can't find any information about their compatibility. Mounting it will not be a problem as I will machine threads into the heatsink around the lens to mount it directly.

It seems that everyone uses beam expanders on 532nm lasers only. Is there an obvious reason for this that I am not aware of? The coating on the MG BE is their HEBBAR coating. The reflectance curve for this coating is bimodal with two valleys where reflectance is <0.5%; one at 450nm and one at 650nm, so I can't see reflectance of 445nm being an issue. The input is 2.5mm, but optimized for 1mm diameter.

So, my questions are: Has anyone ever tried this? -and- Am I being stupid for considering it?

 

[DrSid]

It is meant to work on collimated beam right ? In such case the input size will be a problem. If you use common module with common lens to get collimated beam, the output is usually about 4x1mm in size, or even bigger. If the expander has some kind of its own focus, you could focus the laser closer, to obtain smaller beam (at some point) and the feed it into the expander, which would then have to compensate the different input divergence.

 

[Dogs Best Friend]

It does have it's own focus, but I don't know if it would have enough range to compensate for a focused beam in order to focus it back to infinity.

I haven't used a M140 diode before, I was not aware that they were 4mm on the long axis. This measurement is at the lens?

Even so, I suppose It may still work while clipping the beam. I would lose a lot of power, but it would still be functional... unless the direct beam on the edge of the aluminum housing would become a problem?

 

[Cyparagon]

If you didn't think the 445 dot looked like a bar before, you sure will after a 10x expansion. You'd be better off correcting the fast axis, then using a 3x expander or something like that.

Build, don't buy. There's no sense paying $400 for something you can make yourself for <$40.

 

[Dogs Best Friend]

Build, don't buy. There's no sense paying $400 for something you can make yourself for <$40.

I already have the expander. There's no sense building something for <$40 that I already have sitting on the table in front of me.

If you didn't think the 445 dot looked like a bar before, you sure will after a 10x expansion.

I am not all that concerned with the shape of the beam close up. The reason I am interested in using it is to reduce the divergence over a longer distance. I will take it off unless I really want to reach out there. Will the fast/slow axis cause some unwanted effect at a distance?

 

[DrSid]

As for the beam profile. The most common lens we use for collimation, ie. lens fitting AiXiz module or similar, already act as a beam expander in a way. The lens are constructed so the output element is filled with the beam, so the beam is as wide at the output as possible. If you could somehow not use such lens, it would be different. For thin beam you would need rather strong convex lens, or better planoconvex, with flat side toward the more diverged side ie diode. it would have to be very close to diode, and the strength of the lens should be so the focal point is at diode chip. Ie for distance from diode 10mm, the focal length should be 10mm, ie the strength should be 100 diopters. It also should be coated, and it better be heat-sinked well.

Other trick could be using AiXiz lens, focus it for close .. then use concave lens to collimate the beam and thinner diameter. Those small concave lens used as first element in green lasers should work fine .. but then they are not coated for 445 and there could be trouble with cooling too. On the other way, if you ever broke some cheap green pointer (I did many times), you could have some at hand.

I was trying to use old photographic telescopic lens earlier. But I was feeding it directly from diode, not with collimated beam. But that was different problem all together. The lens have 20mm input, and the beam must be about 40 degrees divergent to obtain good focus at the output. So it fitted the raw beam rather well.
The output diameter was 80mm. The beam was SUPER badass thick, focusable into pinhead on any distances I could test inside my house. The power was not. My 1.5W barely burned CD case at 5m. I guess there was some clipping inside, as the beam did not show shape of the raw beam, it filled the output lens evenly. There also had to be some losses on the optics, on the other hand the lens are reflector type, with only 1 glass element, the rest are mirrors, so the losses should be rather low. Will do some more tests with it and make some pictures.

 

[Dogs Best Friend]

Thanks for the info. Optics are fun to play with... even more fun when shooting an unnatural amount of single wavelength light through them

I'm still going to see what happens with the 445nm and the expander, only because I have it already. I'm not going to go out of my way (cylindrical correction lenses etc.) at this point. I guess if I feel like it would be worth the effort, I can build the next one to fit.