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10 bucks via PP to the individual who calculates this for me...

Alaskan

Alaskan

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I will ppal 10 bucks to someone who can calculate both the theoretical as well as give a good opinion on the likely divergence this diode will have when expanded to 100mm diameter using a PCX lens, any takers?

http://www.junktronix.com/ebay/proddocs/54xxdiodelaser_ds_cl_ae.pdf

Money to be paid upon confirmation the figures are good :p so please show me how you derived it. I will pay 15 dollars if you just want me to donate it to the forum instead.
 
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There are some useful hints in the spec sheet for this:

Emitting dimensions W x H – 3 x 1 – – 3 x 1 – µm
and

Parallel to junction θ// – 9 – – 9 – degrees
Perpendicular to junction θ⊥ – 30 – – 30 – degrees

These figures are actually quite close for either axis, 30 degrees at a beam width of 10 uM or 9 degrees of beamwidth at 3 uM. Lets take the figure of 30 degrees at 10 uM to work on, forgiving the 10% difference with the other axis.

You will expand this beam from 1 uM to 0.1 meters, a factor of 100.000. If you used ideal optics that would reduce the divergence by the same factor, from 30 degrees to 0.0003 degrees, equivalent to 5.24 uRad.

This is a very small divergence, but it's what you could achieve from this diode with perfect optics (and a rather fat 10 cm beam). I doubt it is practially possible, but this would be your theoretical limit to aim for.
 
have any body solved this yet??? if it not solve i'm joining in!!!!
this is similar to my physic homework for the Photonic/Lens& Optic/ Divergence Chapter.
 
Besides the factor of finding the perfect lens, a much bigger issue is the moisture in the air.

Any visible or near IR beam of light will be influenced by atmospheric conditions, the longer the distance the more energy loss and beam disruption.

I remember watching a documentary on our military laser development and they talked briefly about this issue, the short of it was what they sent out didn't look like a focused beam at all, but it impacts as a focused beam.

I know microwave towers are used for a lot of our aerial communications, but the bandwidth is much less than IR light, I wonder about the usefulness of mid to far IR?

Someone pm me a clue about a 4500nm diode, I wonder what difference in real world variable conditions this would make?

I know we are talking communications, but mil applications use the same principle, speaking of which the 4th gen HELLADS is now being tested, it's a direct type emitter unlike the firestrike that was a stackable set of plate amplified boxes to boost a seed beam, HELLADS is the read deal, I wonder what wavelength it is, oddly enough I can't find that info lol. Just a basic announcement.

Hellads Laser Completes Development | General Atomics Aeronautical Systems News & Media
 
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RedCowboy said:
Besides the factor of finding the perfect lens, a much bigger issue is the moisture in the air.

Any visible or near IR beam of light will be influenced by atmospheric conditions, the longer the distance the more energy loss and beam disruption.

I remember watching a documentary on our military laser development and they talked briefly about this issue, the short of it was what they sent out didn't look like a focused beam at all, but it impacts as a focused beam.

I know microwave towers are used for a lot of our aerial communications, but the bandwidth is much less than IR light, I wonder about the usefulness of mid to far IR?

Someone pm me a clue about a 4500nm diode, I wonder what difference in real world variable conditions this would make?

I know we are talking communications, but mil applications use the same principle, speaking of which the 4th gen HELLADS is now being tested, it's a direct type emitter unlike the firestrike that was a stackable set of plate amplified boxes to boost a seed beam, HELLADS is the read deal, I wonder what wavelength it is, oddly enough I can't find that info lol. Just a basic announcement.

Hellads Laser Completes Development | General Atomics Aeronautical Systems News & Media
Click to expand...

1 - 2.4 um per the AirForce Institute of Technology.
The PDF File here

It looks like the used 1.07uM for this study though. It has to do with the Aerosols in the atmosphere.
 
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Good info fellas, rep TK254, Alaskan I owe you a rep again LOL

For those reading who don't know 1um = 1000nm

Everything I keep finding favors 1550nm for free space and open air as well as fiber optics.

There may be a good value in surplus in this range as well.

Also 1550nm is a lot more eye safe from what I have been reading, but bandwidth will be less, it's an interesting study, I am very interested in the emitter/junction size and divergence, a compact eye safe leaf burner with a tight beam could be fun. Safety first as always.
 
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Laser Diode 1310nm Sumitomo Laser Diode | eBay

There is so much stuff available, this says single mode, same kind of thing already mounted, I have also seen optics that are made to attach to fiber ends, I don't know if it would be less expensive though, I like to make my own everything as much as I can.
I may have to have some fun with some of this, but more power...always more power. :D

My other thought is background noise, a distant receiver won't need a perfect beam or as much signal strength if there is less background light of that wavelength. That may be another advantage of 1550 over 808.
But from what I have seen higher power 1550 is less abundant than 808.
Although emitter size being our point source matters more than output in this case, for data transfer LESS may be MORE.
 
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I don't know but it's by a power of 10, wow.

Another thought on using more power with a wider spot is your alignment wont have to be as critical.
In a walkie talkie or portable temporary set up type scenario you would want wide spots with higher powers for faster tune ins.
 
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Alaskan said:
:) Alex, when is your birthday, I can send 10 bucks then. Benm, do I have my decimal points wrong? I thought .1 meters divided by 1 um was a much larger number. Edit, nevermind you did write 100.000 I took that to mean 100 carried out three decimal places when you meant 100,000! Your figures are much lower than I had, where did I go wrong with these calculations for the 3 um fast axis?

My earlier calcs on another forum no one answered:



100mm divided by an emitter aperture of .000003 is 33,333. I took the 523 mRad (closer to 523.6) for the raw output angle and divided it by 33,333 to give .0156 mRad, did I calculate incorrectly? Any idea what the real world divergence would likely be with economy priced optics? I would be happy to achieve .1 mRad using a 100mm diameter PCX lens.
Click to expand...

This 0.0156 mRad figure is 3 times what i ended up with, which is understandable because i used the figure for the slow axis for the larger width, while he used the figure for the fast axis on the lower width.

I believe i am correct here though, and you perhaps verify this to some extent by looking at a 445 nm multimode laser. You can clearly see that when using an ordinary lens, close to the laser the beam is thinner in one orientation. Looking at the dot at some distance (say 20 meters) you will notice that things are now the other way around. If you started with a beam that looked like a vertical | at the lens, the projected 'dot' will look like [====] (horizontal bar).

As for the base principe of beam expansion: With perfect optics you can trade divergence for diameter. If you expand a beam to 10 times its diameter, you will reduce its divergence by 10 times. This can be carried to the extreme case of 100.000 to 1 here for theoretical calculations. You will never achieve this with even the slightest imperfection in the optics, but that is hard to caculate unless the error is known.

With real world optics and 10 cm output aperture i think you could get around 0.05 mrad from a single mode diode (dvd/bluray writer sourced). Normally you would first collimate to a beam of say 5 - 10 mm diameter and then place a 10x or 20x beam expander so it's easier to align the whole lot.
 
Alaskan said:
I haven't been having problems using a single long FL PCX lens to let the output expand and collimate my beams, so far, or am I not getting the best divergence that way?
Click to expand...

In theory it's absolutely no problem to use only one lens. Practially it is harder to get the diode the exact distance required from it and in the exact center position. A down side to a focus lens + telescope arrangement is that it produces more loss due to more elements in the path.

One problem with very low divergence lasers is how to actually align them: you can't really go for 'spot size across the room' or even reflected off a window giving you twice the size of the room (if your windows are reasonably flat, many are not).

A way about this for me is to use retroreflective traffic signs when there is noone on the road. Since i'm the 15th floor i have a view that gives me 100s of meters to about 1km away.


And for paypal donations: I'll accept one to go towards 'chinese laser roulette', if you seen any quirkily specced product on DX or such i'll give that a go to see what's going down!
 
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