Problem:
300mW Mitsubishi 635nm laser diode has an extremely wide fast axis as compared to the slow axis. This results in a beam that look extremely wide when the slow axis is focused for infinity, not the nice round dot we come to expect from laser pointers.

Previous solutions:

- Single or double Anamorphic prism pairs - works well, but expensive, or very lossy because the cheap sources (surplus 473nm lasers) are AR coated for IR.

- Cylindrical lenses - Lenses with only one axis that operates as a lens. Works, but where to get them for cheap? Well I found the solution.

After a lot of experimenting I used a pair of cylindrical lenses that I had purchased years ago that came with some optical parts. One is a biconcave cylindrical lens, and also a few plano-convex cylindrical lenses.


The initial setup:


The above jury-rigged setup was the initial experiment and to measure losses of just the optics themselves. You can see the two lenses used. A bi-concave lens sits directly in front of the normal Aixiz-style lens, and a plano-convex lens sits a good distance in front of the bi-concave.

Power measurement:


A 94% transmission rate!

The uncorrected laser output power was initially tuned to 100mW. The above is the power measured after the laser beam passed through the two cylindrical lenses.


New optical setup:


The first setup worked, but was a big pain to get right because nothing was fixed to a stiff surface. So I constructed a more rigid setup with this half-assed "beam table" made of a plate, and some adjustable mirrors I bought some time ago. Note that the lenses were free moving, but at least the mirrors were fixed, as with the laser. Also, the losses were higher in this setup, down to 72%, from all the extra mirrors (despite the mirrors appearing to be coated for 633nm).

Beam shape measurements:


Here you can see the beam shape at various distances, and how it maintains a decent square shape. The beam appears to be corrected by a factor of five (5) in the fast axis.

Long distance measurements:


I brought the correction hardware to a different room to test beam shape at a "long distance" of 33ft. Here you can see that the beam is still quite small, and again, the factor of five reduction in the fast axis. Some distortion is present from the optics, but it is still quite good.

Measurement conclusion:

Definitely not perfect, but quite good nonetheless, and with very good transmitted power. Also cheap (see below).

Obligatory beamshot:


Somehow seeing a red beam is cooler than the other colors. The laser was running at 700mA, which is probably about 500mW I believe.



How much did the optics cost?

Wait for it....

FORTY DOLLARS.

And that's not just for lenses! You get a slew of other good stuff (see below).

Where to get these optics:

Meredith instruments.

Direct link.

Get them while they're hot! Only 44 sets left as of 12/09/2011 and I grabbed another two!

UPDATE: Search for the same sets on Meredith's eBay store for cheaper prices and shipping.

What do you get?

- 1x bi-concave cylindrical lens (coated for red)
- 2x plano-convex cylindrical lenses (each in a different axis, coated for red)
- 1x plano-convex lens (coated for red, different mount)
- 1x plano-convex lens (coated for red)

- 5x Multiple single-axis adjustable mirror mounts (the original reason I bought them). Attached to each respective mount: 2x 633nm dielectric mirrors, 1x 633nm dielectric long mirror, 2x front-surface mirrors (probably good for knife-edging!)

This means you can create your own "beam table" like I showed above! Note that I used some other optics, not the ones in the above link because I don't have any metric screws for them.

Again: $40. Get them while they're hot!

I got a set a few years back. I'll go try it out.

edit:

Replicated

I got about 4% loss. Magnification is around 3x. I tested divergence at 7 meters, but evidently 7 meters isn't long enough to test divergence. You end up focusing to that point instead of infinity. I was able to get it down to 0.14mRad which isn't possible I don't think 33ft will be much better. In theory it should be around 1-1.2. Advantages over Dr. Lava lenses: slightly cheaper, fits larger beam, already mounted, will potentially ship faster.

But the question is: considering the different focal points required and distance between the lenses, will this ever be possible to incorporate into a handheld?

Cyparagon: Try focusing only the slow axis down to infinity. That's the one I was aiming for. I would compare the size of the slow-axis at different distances to try and ensure it was focused, and then applied the lenses to the other axis. I'll see how other lenses work as well, though unfortunately the optics cause some visual artifacts in my sloppy "beam table".

Wolfman29: Not with these lenses. The focal lengths aren't short enough. However, I'll see if multiple convex lenses do much. Maybe you can stack them? Now that I have a "beam table" it's a lot easier to do.

Hmm. Interesting. I can see those being a good seller if you can create an Aixiz sized lens for these that would slow the fast axis, even on other diodes, like 445s.

crap i need 40$ ASAP

Ordered a set, if I can get this to work, I just need to figure out how to pbs 2 together for my new projector. 5-600mw of 635 sould go well with ~300mw of green and a 445 with drlava's lenses.

exactly what i need it for i really wish i had spare cash ATM

You can also try using knife-edging to combine beams; the set of mirrors in the kit could facilitate that. Stacking them up on the slow axis would widen it up somewhat and reduce the aspect ratio further.

Awesome work.

Nice find.

Sweet work.

This is Great. I was Just on there site too.

Well I ordered two sets. Yay more projects! heh.

they better not run out

I honestly wouldn't dally long.. however, the only real use for these would be people building projectors... Of which there aren't many of here. So I doubt they'll vanish 'over night' unless someone posts it over at PL too. heh.

i honestly have no money to spend right now and wont for atleast a month. looks like i out of luck...

I believe most diode lasers have short Rayleigh Lengths < 33ft. Therefore you should be good to go when you measure beam size a 33ft.

And who would do such a thing.

Just a little heads up; I have found these exact sets for sale at a cheaper price.

On the Meredith website, the sets are $39 plus ~ $16 shipping via UPS ground.
For 2 sets, shipping is ~ $18.

On Meredith's Ebay store, the same sets are $34.95 per set.
Shipping is $5 for the first set (USPS Priority Mail); free shipping each additional.

Here's the link to the ebay sale page for these optics sets:
LASER OPTICS LOT MIRRORS LENSES mounts optic dpss hene diode light show | eBay

I just bought 2 and there are 9 sets available as of this posting!!
Jump on 'em quick,guys!

Thats Meredith instruments on ebay. I wonder way they have it like that.

I always Wondered if that was them.

Well, the website and the ebay page have the same pictures and the same descriptions for the mounted optics set; word for word.

The company name and address are the same as well on both website and ebay page.

Sooo, I believe both pages are the same Meredith.

Wouldn't you think that they would charge more on ebay since all the fee's and stuff.

Nice find.

I thought so, as well.
But, to my surprise, it was a better deal.

Hey, I'm not gonna complain!

Me either. I just wish i seen that before i bought a set.

I had 2 sets in the cart, ready to checkout when I saw they had an Ebay page.
So, I almost bought them at the higher price as well...
Sorry I didn't find them faster.