Portable FAP Red

Hemlock_Mike · May 14, 2016

Cyparagon --
My new PCX diverter is -30 mm FL. My mounting puts it
about 16 mm from the fiber. If I read your above message
correctly, I should have no problems --- right?
HMike

Hemlock_Mike · May 18, 2016

Blue Fiberman is sending me a few new fiber jumpers. SUPER ----
I tried an expander with a -30 FL lens and a PCX lens and it's a POS.
Seems that the divergent quality of the beam needs two +FL lenses.
That seems to get the beam under control -- FIRE -- I will order more lenses from Thor Labs.
HMike

Cyparagon · May 18, 2016

The beam is already diverging rapidly after exiting the fiber. Why are you using a convex lens to make matters worse? What is your actual goal here?

If you're just trying to get a usable beam, a convex lens is enough. You just need to chose it based on initial beam characteristics, and desired final output beam diameter.

Hemlock_Mike · May 18, 2016

Cyp --- Be patient with me here!!! I have built many expanders using -FL followed by a +FL lens to keep the expander short. This is my first attempt with a real divergent beam.
I want to make an expander (focusable) which will burn at short range but serve as an illuminator at distance for IR photos. That's a big menu ! The +25 mm lens I'm using now is useless but with another PCX lens, I have control of the beam.
I now have +15 mm and a +75 mm less coming (NIR coated) to try.
Hey -- if you have suggestions -- I'm listening
Thanks -- HMike
I'm thinking now of using a +50 mm objective lens to cut it to about 3X magnification.

Cyparagon · May 18, 2016

If you're insisting on using a concave to keep the expander shorter, you need a convex with a VERY short focal length. Two lenses might also work, but might also introduce unforeseen aberrations.

What is the divergence of the raw fiber output? What lenses do you have at the moment (type, diameter, and focal length)? What is your final target beam diameter?

Hemlock_Mike · May 19, 2016

CYP -
I currently have a -30mm x 1/2" and a +75 mm x 1". Not good.
I have a +15 mm x 1/2 coming from ThorLabs. A short FL objective would give little magnification but I'll try it. As I said, I'm experimenting looking for a small spot at 3 to 10 feet but adjustable for say 100 yard illumination for night vision.
HMike

Cyparagon · May 19, 2016

You forgot to mention the divergence of the raw fiber output. That matters a lot.

half inch isn't big enough diameter either. I'm not even sure 1 inch is.

Hemlock_Mike · May 19, 2016

I've never tried to measure it but the specs are beam dia: 810 microM and divergence is shown as <0.14 Num Aperture.
HMike

Cyparagon · May 20, 2016

.14NA is 16 degrees (280mRad) by my calculations. Going with basic inverse relation from diameter/divergence, best case: when you expand the beam from 0.8mm to 25mm (~1 inch), divergence goes down to 9mRad in theory. 2 inches at 4.5mRad, 4 inches at 2.2mRad etc.

-30FL .5" is another 24 degrees if my trig isn't too rusty (2arctan((12.7/2)/30)) for a total of around 40 degrees. This means it will expand ~7.3mm for every cm of travel. A 75mm FL convex would need to be at least 55mm wide to collimate the beam, and even larger to focus it.

The 15mm FL 12mm dia convex you have coming should be able to collimate and "focus" the beam. But the collimation would have a divergence of ~20mRad, which will not make for a small point at 1-3 meters. The fiber size is what makes this hard - 810 microns is very large. To get a small point at 1-3 meters, you'd need an obscenely large lens. Think a foot or two.

Hemlock_Mike · May 20, 2016

Cyp -- I thought I had expanders figured out ...... Now I have to do some more figuring based on your info. Damn this is getting nasty!!
I got three more fibers today but one is uncoated -- maybe another project for it.
Thanks again -- HMike
I'd like to give +rep but I can't. You still get my + rep.

Hemlock_Mike · May 24, 2016

I find this company -- Micro Laser Systems, Inc.-- Has what I think
I am trying to make for my FAP laser. They look short and sweet !!!
Any ideas what they are doing in these ??
HMike

Cyparagon · May 24, 2016

Same as we all do with diode lasers, except they charge 3-4 figures for their products... Using a convex lens to collimate the beam.

It's really that simple. Short experiment I did (with a TOSLINK cable and a lens from an old camera) a few years back:

But again, you're running into problems because your fiber is so large, so you can only tame it with a very large lens.

Alaskan · May 25, 2016

Cyparagon said:
.14NA is 16 degrees (280mRad) by my calculations. Going with basic inverse relation from diameter/divergence, best case: when you expand the beam from 0.8mm to 25mm (~1 inch), divergence goes down to 9mRad in theory. 2 inches at 4.5mRad, 4 inches at 2.2mRad etc.

That's why I'm planning on using at least a 7 inch diameter lens for my FAP800, maybe as large as 12.

What I am wondering now is how much should the diameter of the beam of a 40 watt output FAP800 be expanded to keep from being a eye hazard? Time to do power density calc's, will be working on it.

Edit: Looks like 300mm diameter for one watt of VIS laser energy is close to be safe, but not going to be anywhere near safe at 40 watts with a ~12 inch/300mm diameter lens for 800nm if directly viewed much under a mile distant.

See: https://upload.wikimedia.org/wikipedia/commons/2/28/IEC60825_MPE_W_s.png and: http://www.ophiropt.com/laser-measu...ergy-meters/services/power-density-calculator - Anyone willing to check my figures? Next I need to figure what focal length I need for a 300mm diameter lens with the raw output from a FAP800, need the info for a quote on having one made for me, or at least, to know if I can afford one at 1/2 wavelength accuracy. Cyp., can you tell me if is that accurate enough for a BE?

.
.

Hemlock_Mike · May 26, 2016

Chris -- Glad to see you made it home -- I hope.
HMike

Alaskan · May 26, 2016

I'm still in Afghanistan, will be here for a long time to come, I think. I figured out what I need to do for the big lens, I'm forced to use an expander with it because the FAP beam only expands to about 3 to 4 inches after 15 feet without one.

Hemlock_Mike · Jan 8, 2017

I'm still around :wave::wave:
It's amazing how much there is to do after retirement.....
That PLUS cataract replacements.

WHERE IS ALASKAN. I can't PM him.
H Mike

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