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lamedust

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Hello all! These seem like great forums!
So, I was wondering if you could lend me a hand. I'm the creater of the 50 dollar laser cutter hack:
instructables.com/id/Laser-cutter-start-slicing-stuff-for-under-50-dol
and I have a question I think someone here knowledgeable in optics and wavelengths can help me with.

In essence it's about frequency absorption. I'm using a 200+ mW red diode to do the cutting right now. My objective material is black construction paper. I have a 3W IR laser diode (fiber optic with no pigtail collimator) and I'm looking into a green laser. So, which will the black paper absorb most of the light from, the red frequency, the green, or the IR? It's black, right, so it should be absorbing all frequency ranges, but I'm sure it makes a difference which laser color?

Thanks for your help, and if you like my project you can send me flowers, diodes, or vote for it so I win the 25W laser cutter here: instructables.com/forum/lamedust---Universal-Laser-Cutter-Finalist/

-Bilal Ghalib
 

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lamedust

Probably the best way of determining this would be for someone to check the reflection from your medium with a power meter. You could setup your paper at 45 degrees to your laser and your LPM at 45 degrees to that and measure the intensity of the reflection at a set range.

Swap out for both lasers and that should give you your result. It would be hard to tie the figures down exactly since the power output and focus etc of both lasers will be markedly difference, but it would be a start.

I have often thought that it would useful to have a database of this type on this site, especially for IR lasers, as IR doesn't always reflect off stuff the way you might expect and for safety reasons it would be useful to know which materials reflect IR least/most.

/tuppence added
 
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Oh, and is anyone else on this site hoping to with the 25W cutter on instructables. Perhaps some organised voting is in order to secure this valuable item.

And btw - verrry nice instructable!
 

lamedust

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Sweet experiment setup idea thekanester! I too think it would be a great resource to have that information, perhaps someone here knows if it's been done before. Especially since I do not have, nor do I know where to get something that could measure reflection. Is a power meter exencive?

Could I take the average brightness of a camera still taken in a controlled environment (darkness) for a reflection from both diodes to make a sort of make shift power meter?

Also the ranking has ended for instructables, so the people in the finalist position are: instructables.com/group/laserfinalists/ check and see if you recognize any of the screen names. Maybe the fresnel lens project might be of special interest to you all! I'm exteremly luckt to have gotten on that list.

Thanks for the quick info!
-Bilal Ghalib
 
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Using the camera and measuring the average brightness within your controlled environment sounds like a good start to doing this and especially if you have no other tools.

The only problems I can forsee with this method is that the camera sensor will have a variable frequency response so might be better at picking up green than red say. It may also do post-processing of the image that'll skew your results.

I was wondering and perhaps someone else could add to this...would a standard lux meter be of any use in this. You can get them very cheap here:

http://www.dealextreme.com/details.dx/sku.5100

It seems possible to me that If you had a number of lasers of KNOWN output could you determine the output of other lasers based on your known results.

Does this make sense? Has anyone tried this?
 

Switch

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I'd still be using the 3W IR diode.I'm guessing it's 780 or 808.So it doesn't really matter if red is reflected 1% more than green, or IR reflected 2% more than red or whatever, at 3W that baby will cut black paper like no other. :p
 

lamedust

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Ah, but the problem is more fully explained in the optics post I submitted. My IR laser has no collimating lens and burns a 2mm wide "tear" rather than the neat cut I get with the red diode. I still can't find the right pigtail accepting collimating lens and even if I did, would need help on installation.
-bg
 
L

likewhat

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black absorbs everything optical pretty much the same. Black powdercoated pieces of metal are used all the time as beam dumps for TiSaph, YAG, and CO2 lasers.

If you want to collimate your fiber laser you need to know the core diameter of the fiber and then it is really easy to calculate what focal length lens you need and where you need it. I will post how to do it if you want.
 

lamedust

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Hey likewhat, sure I'd love some help, thank you!
So info about the fiber:
From:
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
psplc.com/datasheets/jdsu/JU6300Series_041802.pdf
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
Fiber core diameter – – – – – – – – 104 – [ch956]m
Fiber numerical aperture NA – – – – – – – 0.22
Fiber cladding – – – – – – – – 125 – [ch956]m
Fiber buffer – – – – – – – – 250 – [ch956]m
Connector Option
Fiber sheath – – – – – – – – 900 – [ch956]m
(when connector ordered)
Connector type – – – – – – – – SMA –

Laser pigtail is pushing light out through an 18 degree cone (the pigtail Numerical Aperture is .16 and the arc-sin of that is 9.2 degrees x 2 ((each side of the cone))= ~18 degrees full angle).

Is anything from here going to be useful?
thorlabs.com/Navigation.cfm?Guide_ID=27&visNavID=333
 

Tektryx

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thekanester said:
I was wondering and perhaps someone else could add to this...would a standard lux meter be of any use in this. You can get them very cheap here:

<URL to meter page>

It seems possible to me that If you had a number of lasers of KNOWN output could you determine the output of other lasers based on your known results.

Does this make sense? Has anyone tried this?
<Had to remove URL to meter page as I am too new and can't use links yet :) >

This meter is set up for a 'photopic' response, that is, the human eye response (the CIE Photopic Curve mentioned at the web page). The filter that forces this response very likely cuts the NIR around 600nm. I suppose one could remove the filter, but then the calibration will be all out of whack, so for IR laser work, it's probably not worth it. As a general lab tool for visible light reflecting from a surface (Lux is a measurement of luminosity, like lumens , not intensity, like candellas) it looks like a pretty interesting deal.

Comparing unknown against known is a common metrology technique and yes, it will work as long as all variables are constrained for both the standard and the device under test. In other words, do the exact same measurement using the same instrument. So, take your known standard laser, measure it with your meter, record the output, then do the same exact measurement (keeping all geometry the same) with the unknown.

Laura
 

Tektryx

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Ahh, one more thing... by 'standard', I mean the laser of known output that serves as the baseline or 'standard' that you are measuring against (just to clarify should the term 'standard' be mistaken for "ordinary')

And, the 'meter' that is used for measuring is used in the generic sense. For instance, you could use electrical tape as a 'meter', by measuring how long it takes to burn a hole through the tape with the standard and then time how long it takes with the laser of unknown power. Just keep all the conditions of the tests the same for both. Back in the day, they measured lasers in 'Gillettes'... the number of razor blades the laser would punch through. Using electrical tape as described, I suppose the unit of measure would be, 'time-to-puncture-electrical tape' or TTPET's (T-PETS)... "My laser does .3 T-PET's on a single layer of 3-M Scotch Super 88!" (actually, the time should be divided by 1 so the number gets bigger with shorter times- .3 becomes 3.333, .2 is 5, and so on). Or, stack up layers and lase for a set time... in which case the measure would be in 'tapes'. :)

Laura
 

Tektryx

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lamedust said:
Hey likewhat, sure I'd love some help, thank you!
So info about the fiber:
From:
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
psplc.com/datasheets/jdsu/JU6300Series_041802.pdf
\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
Fiber core diameter – – – – – – – – 104 – [ch956]m
Fiber numerical aperture NA – – – – – – – 0.22
Fiber cladding – – – – – – – – 125 – [ch956]m
Fiber buffer – – – – – – – – 250 – [ch956]m
Connector Option
Fiber sheath – – – – – – – – 900 – [ch956]m
(when connector ordered)
Connector type – – – – – – – – SMA –

Laser pigtail is pushing light out through an 18 degree cone (the pigtail Numerical Aperture is .16 and the arc-sin of that is 9.2 degrees x 2 ((each side of the cone))= ~18 degrees full angle).

Is anything from here going to be useful?
thorlabs.com/Navigation.cfm?Guide_ID=27&visNavID=333
Does it have the SMA connector on it or is it a raw end? If the connector is there, several of the collimators at Thor will work- look for those with the SMA connector, an NA the same or larger than your pigtail, and AR coatings that work for the wavelength of the laser. Pretty spendy items though. Have you tried using an ordinary convex lens (of short focal length, like say an inch... the lens will be pretty steeply curved, though not a sphere (which might work if you want to focus the output real close to the lens)). You will need some sort of jig to align the fiber on axis with the lens. This is easier if the pigtail is terminated in a standard connector. If the connector is there, you'd need to get the mating part of it and mount it to some sort of lens holder. If it isn't, a V-block to hold the fiber rigid and on axis to the lens is a common approach. There are many variables to be considered, so the more flexible your set-up is, the easier to experiment with different lenses.

BTW, how are you imaging the IR beam?

Finally, don't be afraid to call Thor for advice. Ask to speak to an applications engineer and tell them what you have and what you want to do. Most of these companies are more than happy to lend advice. Even if you don't buy, you may gain some useful information! :)


Laura
 




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