Round dot needed for 1.1 W 445 nm laser

[drummerdimitri]

Hey guys, i have received my blue laser not long ago, and have been wondering if it is possible to turn the line dot into a round one. I've read about Dr.Lava's correctives optics, but those are from what I know only used in non-portable lasers. Do you know if it is possible to get a lens that produces a round dot with good divergence? Please let me know!

Thanks!

 

[ElektroFreak]

That's actually quite a complicated topic, but the simplest way I know of to get a truly round beam with good divergence is to couple the diode's output into a short piece of singlemode optical fiber and then collimate the fiber output with whatever set of lenses gets you the characteristics you desire. Anamorphic prisms will get you a square beam, but not round.

 

[JLSE]

That's actually quite a complicated topic, but the simplest way I know of to get a truly round beam with good divergence is to couple the diode's output into a short piece of singlemode optical fiber and then collimate the fiber output with whatever set of lenses gets you the characteristics you desire. Anamorphic prisms will get you a square beam, but not round.

Actually I just finished up a labby with anamorphic prism pair, and so far the dot
is quite nice.

I have only viewed it at 20ft, and approx 30% loss... But the dot is more oval
than square.

DrLava's optics should yield less loss, but am not sure about shape comparison
until my sets arrive.

His sets will be better suited to a portable application, the prism pairs are much larger.

 

[drummerdimitri]

That's actually quite a complicated topic, but the simplest way I know of to get a truly round beam with good divergence is to couple the diode's output into a short piece of singlemode optical fiber and then collimate the fiber output with whatever set of lenses gets you the characteristics you desire. Anamorphic prisms will get you a square beam, but not round.

That might work. I will try feeding the diode's output to a fiber optic cable and then place the Aixiz glass in front of it and see what this gives me. Although it wont be a portable laser anymore! I think Aixiz should really consider making a specially designed lens that turns the line into a dot. Thanks for the suggestion anyway!

 

[ElektroFreak]

@wannaburn: the dot is quite nice with prisms, but by round I assumed the OP was looking for output as close to TEM00 as possible. Single mode fiber gives a nearly perfectly circular flat-top profile, with the power distribution being even across the diameter of the spot. TEM00 of course exhibits a bell-shaped power distribution curve across the profile, with power being greatest at the center of the spot.. so fiber is very close, but even then it's still not quite true TEM00. It is the closest I've seen to it from multimode diodes though. There are losses, but that's an issue no matter what solution you try. With prisms and lenses the power distrbution can be uneven and splotchy. For laser show apps that's no problem, but if one wants/needs something akin to TEM00 from a multimode diode it's usually not quite enough.

That might work. I will try feeding the diode's output to a fiber optic cable and then place the Aixiz glass in front of it and see what this gives me. Although it wont be a portable laser anymore! I think Aixiz should really consider making a specially designed lens that turns the line into a dot. Thanks for the suggestion anyway!

Unfortunately it's not quite as simple as making a lens.. unless fiber is used, evening out the beam shape
requires multi-element optics, not all of which are lenses. Even then the beam is not truly circular, but square or oval as above.

 

[JLSE]

Makes sense...

Though with the 445's ive noticed it is much easier to manipulate the beam,
where if trying with a c-mount red... forget it as far as prisms go.

I bought that Melles 672nm pump module from ebay that was posted in a thread.
Even with the stock setup the 'dot' was an ugly square with really bad divergence.

I tried a pair of uncoated prisms and the 445, the divergence is amazing, and with the
aid of a tunnel like aperture, I was able to get the beam damn near perfect.

In this setup, the losses are ridiculous. 900mW out from the LD and 350mW after
all optics and aperture.

Without the aperture it came in just under 600mW. But the beam isnt as nice..
Clipping the edges and the prisms is good if you dont mind the losses. But the LD
has to work hard if those numbers are to come up.

Ive also noticed with the 445's that there is anomalies surrounding the beam.
I tried 4 different collimators, and nothing, still there.

Id like to try the fiber op, but only have ones that can handle that kind of
power rated for 1W 850nm.

Quite the battle to tame this wavelength...

 

[ElektroFreak]

Ive also noticed with the 445's that there is anomalies surrounding the beam.
I tried 4 different collimators, and nothing, still there.

Same here.. there seems to be some light emitted around the edge of the die itself, you can see a rectangular halo around the main spot.. also, with every collimator I've tried there's speckle surrounding the dot, not a lot but enough to be noticeable. I'm not complaining though.. they're great for everything I use 'em for.

 

[drummerdimitri]

Does anyone know why the beam of the 445 diodes come out to be rectangular? I just don't see why all other lasers could come in TEM00 but that's just not the case with 445 diodes. I guess there is no solution to rounding the line of my portable laser without great losses, at least that is what I can conclude from your input.

 

[ElektroFreak]

It's not just 445nm diodes. It's because these diodes are multimode as opposed to singlemode diodes which give an oval spot that could be compared to TEM00. Multimode diodes allow for much higher power levels than would be possible with singlemode designs. These are actually some of the nicest looking multimode diodes.. just think how you'd feel with this coming out of your laser:

(pic by FrothyChimp)
This is a multimode 650nm red laser. Many multimode diodes produce this kind of output which yields far worse divergence, so you can see that these 445nm are actually not all that bad.

Yes, you are correct that there is no way to easily correct the output of your portable 445nm laser without heavy losses. This is the only build I've seen that comes anywhere close:
http://laserpointerforums.com/f65/445ld-anamorphic-prisms-jayrob-diy-52334.html

 

[Coherent Light]

It has to do with the shape of the Laser's Cavity + Waveguide, and that's control by the Junction where the Photons are produced.

 

[lasersbee]

Here's a drlava pic of the 445nm beam profile at 17 meters or ~56 feet
using drlava's GB lenses...

Jerry

 

[drummerdimitri]

Here's a drlava pic of the 445nm beam profile at 17 meters or ~56 feet
using drlava's GB lenses...

Jerry

That's really good divergence for such a laser. Too bad there are no schematics or instruction on how to set up Dr.Lava's corrective optics into my portable laser. Hope someone can actually help by providing me with such information.

 

[ElektroFreak]

drlava would probably be the guy to ask.. it's his kit after all.

 

[drummerdimitri]

drlava would probably be the guy to ask.. it's his kit after all.

You're right. I'll send him a PM right now regarding this subject. Thx!

 

[JLSE]

It's not just 445nm diodes. It's because these diodes are multimode as opposed to singlemode diodes which give an oval spot that could be compared to TEM00. Multimode diodes allow for much higher power levels than would be possible with singlemode designs. These are actually some of the nicest looking multimode diodes.. just think how you'd feel with this coming out of your laser:

(pic by FrothyChimp)
This is a multimode 650nm red laser. Many multimode diodes produce this kind of output which yields far worse divergence, so you can see that these 445nm are actually not all that bad.

Yes, you are correct that there is no way to easily correct the output of your portable 445nm laser without heavy losses. This is the only build I've seen that comes anywhere close:
http://laserpointerforums.com/f65/445ld-anamorphic-prisms-jayrob-diy-52334.html

Another thing to consider, is that most LD's we use around here are from optical drives.
That in mind, the beam has to be of decent quality. The 405, 445, 650 and even 780's
are meant to read an write to disc. I cant say 100%, but my guess is that a multimode LD
would not perform very well in these applications.

So we are kind of limited on what powers are availible depending on what the
current optical drives can provide.

The only other hope I think will be LD's taken from TV projectors that emit the
actual laser light, rather than fluorescing a phosphor disc like the Casio LD's.


All in good time, and fingers crossed while we wait...