I'm after a clean beam - what to look for?

[PatchEdward]

After having a lot of fun with <5mw red lasers, I recently put together a focusable high power blue laser. Sad to say, I was disappointed in the properties of the beam, with the spot at ~10mm by 25mm at only three meters at its best focus.

It seems I need more information before acquiring a new laser.

What options are available for beams with the smallest diveregence within the visible spectrum?

Within those options, are there common pitfalls to watch out for as power levels increase (e.g., Laserglow's Polaris line doubling divergence when going over 500mw)?

Ultimately, I'd like to try mounting a new laser in a handheld host. Are there handheld hosts that have available adapters to mount additional optics on (such as beam expanders), or recommendations for enterprising individuals who have created third-party adapters?

 

[bdgreenb]

SINGLE MODE! <--- that term is your best friend. Single mode diodes produce round dots, as opposed to bars. High power 445s and most 635s have terrible spots. But LPC-826 red diodes have a nice round red dots and tight beams. The tightest divergence i've ever had was on my glp-589, but that is rather pricey. I would recommend the lpc826 as a nice easy build with a durable diode that will give you a tight beam and dot. Although the 0sram 450 single mode diode will give you a much brighter beam, but its a bit more moolah.

 

[chipdouglas]

In my opinion the best diode beam comes from a 405nm laser. You could easily build a 12x and get a beautiful beam profile and have over 600mw,

Michael

 

[HitShane]

Are we talking beam or dot profile? My 445nm looks great with a stock 9mm lens...@2watts...

Edit: the thinnest I have seen is from a 532...

 

[Shakenawake]

Optotronics RPL 532nm lasers have divergence ratings better than 1mrad or even .9mrad, but even a 300mw is over $700. 1.5mrad is common, and much better than 2mrad, the worst divergence I have seen on a 532nm. A few companies sell green lasers with 1.2mrad, which would be very good, probably the best option for divergence short of the optotronics RPLs. I am talking 532nm only here, as others noted many wavelengths of red(not 638 or 635 or whatever) and violet (405) have excellent divergence. If a laser you are considering lists this attribute, get the smallest number you can in front of the mrad part.

 

[PatchEdward]

Dot profile is what I'm specifically looking to improve; the beam looks tight and narrow when viewing a picture of it (I can't see the beam when wearing my safety goggles), but the power of the beam is diffused throughout its "large" cross section/dot at three meters.

I may just need to start throwing optics in front of the laser, as after digging around through the forums, it seems I'm more interested in being able to have a lot more control over the the focal point than having a picture-perfect beam from the get-go. I'd like both, but that doesn't seem to be an option right now for >1 watt and <$1,000.

Next stop: custom machinists!

 

[Shakenawake]

the better the divergence, the smaller the dot, the two correlate directly, in fact, measuring the size increases of the dot at different distances from the laser is how divergence is measured

 

[Bionic-Badger]

It seems like you're concerned about the divergence moreso than a clean or round dot. The divergence will determine how the beam expands over distance. Divergence is inversely proportional to the size of a beam; so a small beam at aperture (such as a DPSS green laser's beam at 1.5mm) will have a worse divergence over distance than something like a diode laser with a 3mm beam. I have a nice CNI green laser with a tiny beam at aperture, but at 20-30ft or so, the spot is over 1cm in diameter.

If you want a well-collimated beam over long distances, you'll need a beam expander. The beam will be widened, but as a result, the divergence will be improved. At long distances the dot will ultimately be smaller than it would with a smaller beam at the aperture.

You can make your own beam expanders with telescope parts (look up the term "beam expander" to learn more), but often that's not very compact, and the optics may not be coated and laser quality. Instead, you should probably buy a beam expander made for lasers. They're relatively expensive ($200-$1000), but sometimes you can find some cheaper ones ($50 or so). Try contacting Hakzaw1 on the forum and see if he has any available from JetLasers. Otherwise, you can buy one from JetLasers directly.

 

[bdgreenb]

you can look into getting machined parts from members to add on to your custom beam expanders(or make parts for) to allow hook up to your own builds. Mcrouse and his dad do AMAZING work for custom machining, but i think he's about to be AFL(away from lathe) for a bit. Good Luck!

 

[PatchEdward]

Thanks for all the advice!

I've got a 3-element lens coming to try with the 445nm build, as well as a focusable beam expander to enable projecting the focal point out quite a bit farther.

I sense a new 405nm build with a single-mode bluray diode is probably not too far off, either!

 

[chipdouglas]

You will not easily clean up a 445 beam. But you best hope at cleaning up the beam profile is to use anamorphic prisms. Member cyparagon cleaned up a 445 dot the best I've seen, and its still far from perfect. Multimode diodes suck for this. If blue is what you have to have, I believe if you set the 445 driver just high enough to lase, then it will be single mode.

Good luck
Michael.

 

[ZeroLaser]

When i use a 3 element lens with a 445nm diode, I get a halo. Is that something inherent in the combination of 3 element lens and a multi-mode diode?

 

[PatchEdward]

ZeroLaser, I can't say for sure as I haven't taken photos of the dot from my 445nm laser with the 3-element lens and my safety goggles may be blocking the light from any halo. However, that should mean that the halo is faint and not a significant loss from the main beam.

Even with the loss of some beam power, the 445nm beam sure looks nice from a 3-element lens. I'm hoping that with the addition of a beam splitter, I can have my cake (great-looking dot) and eat it too (pop ballons at 10, 20, 30 meters)!

 

[ZeroLaser]

Patch,
you are right the halo isn't significant, but a clean beam is always desirable. Are you using one of my lasers?

ZeroLaser, I can't say for sure as I haven't taken photos of the dot from my 445nm laser with the 3-element lens and my safety goggles may be blocking the light from any halo. However, that should mean that the halo is faint and not a significant loss from the main beam.

Even with the loss of some beam power, the 445nm beam sure looks nice from a 3-element lens. I'm hoping that with the addition of a beam splitter, I can have my cake (great-looking dot) and eat it too (pop ballons at 10, 20, 30 meters)!

 

[PatchEdward]

ZeroLaser, no, I purchased my parts from another vendor.

 

[ZeroLaser]

Any idea where the optics came from?

ZeroLaser, no, I purchased my parts from another vendor.