Question about using a LPM

[sopark4000]

Ok if I'm testing a 3W 445nm laser on a LPM that is only rated to 2W using a 50/50 beam splitter will I still get an accurate reading? (give or take the absorption by the splitter)

 

[kiyoukan]

some what you are better off using a ND filter rating 2.
its a 50% filter with a cube you could have alot of losses.

 

[MegaWattson]

Okay, the first thing you need to know is EXACTLY what your optics are doing to your beam. In other words......You absolutely cannot assume that your 50/50 BS is actually 50/50. There are VERY FEW beam splitters that are flat across any real range of wavelengths (and they are VERY expensive).

There are also a whole host of other factors involved with anything you put between your laser and your power meter. The best advice I can give you is to leave the beam path clear, OR, if you have to attenuate the beam power (as you indicated here), then you need to use a KNOWN and MEASURED element in your beam path (whether it be a ND filter, beamsplitter, or other optic).

SO......


If you have a lower powered laser at the same wavelength as your 3W unit (one within the range of your meter), then you can measure the attenuation of any optic you want to use between your laser and your power meter.

Then, you can apply that loss factor to your measurement of the 3W laser.

This is a handy way of "extending" the range of a power meter. As long as you know the real attenuation of a given optic at your wavelength, you can use it to measure power levels beyond your meter's range.

But, you need to be aware that you are also introducing errors into your measurements here. (nothing comes for free) It all depends on just how accurate you need to be......

AND you also need some standard to begin with. Meaning...some MEASURED standard on which to base your comparisons.

But for the moment, I need to go. I'm sipping my favorite bourbon, and watching my girlfriend undress in front of me, so .......you know ....i gotta go...



-mega

 

[lasersbee]

Okay, the first thing you need to know is EXACTLY what your optics are doing to your beam. In other words......You absolutely cannot assume that your 50/50 BS is actually 50/50. There are VERY FEW beam splitters that are flat across any real range of wavelengths (and they are VERY expensive).

There are also a whole host of other factors involved with anything you put between your laser and your power meter. The best advice I can give you is to leave the beam path clear, OR, if you have to attenuate the beam power (as you indicated here), then you need to use a KNOWN and MEASURED element in your beam path (whether it be a ND filter, beamsplitter, or other optic).

SO......


If you have a lower powered laser at the same wavelength as your 3W unit (one within the range of your meter), then you can measure the attenuation of any optic you want to use between your laser and your power meter.

Then, you can apply that loss factor to your measurement of the 3W laser.

This is a handy way of "extending" the range of a power meter. As long as you know the real attenuation of a given optic at your wavelength, you can use it to measure power levels beyond your meter's range.

But, you need to be aware that you are also introducing errors into your measurements here. (nothing comes for free) It all depends on just how accurate you need to be......

AND you also need some standard to begin with. Meaning...some MEASURED standard on which to base your comparisons.

But for the moment, I need to go. I'm sipping my favorite bourbon, and watching my girlfriend undress in front of me, so .......you know ....i gotta go...



-mega

EXACTLY..... I concur 100%....:gj:

Jerry

 

[MegaWattson]

Hey, thanks for the kudos, Lasersbee. :yh:

I have a few things to add (I was a bit distracted last night).

If you have two of those beamsplitters, then you don't really need a second, lower powered laser at all.

You just use one of them to cut the beam power so that it is within the range of your detector. At this point, you don't need to know what your first B/S is doing, because we're only taking relative measurements.

Whatever the power is with the first B/S in your beam, write it down.

Now, without disturbing your setup (leave the first B/S where you had it), place the other B/S into your beam path between the first B/S and your detector, and write down that reading. Now you can easily calculate the attenuation factor of the second B/S. Remember though, that this number is only valid for that wavelength and angle of incidence.

And once you know that, you can measure your laser, and the other B/S.

Very important: Be consistent regarding the angle of your B/S and the rotation of your beam. Both will affect your measurements. This is especially true if your beamsplitter is of the multilayer dielectric coated type.

The rotational position of your laser is important because the output of a diode laser is inherently polarized, and when you pass your beam through a B/S at, say, a 45° angle of incidence, the split ratio (reflected/transmitted) of your beamsplitter will change as you rotate your laser beam.

You'll see what I mean when you try it. Good luck-


-mega

 

[sopark4000]

Thanks for the help guys. These are exactly the tips I needed.

 

[rhd]

I'm sorry, can I ask the simple question here?

- Who sold you a "3W" 445?

Unless you bought one of those knife-edge rigs (that are really two lasers combined into one beam) made by a clever member here in the forum, I would question anyone who marketed a "3W" 445.

 

[sopark4000]

Wow just realized I put in 445. Tired when I posted this. I meant to write 532. The laser I am talking about is actually a 2.5W Laserglow bench top and the LPM I am working with has a limit of 2W so I rounded the numbers just to simplify the question. I should have posted that in the original post. But yea the laser I have is this

http://www.laserglow.com/R53#

 

[Plyman44]

Holy crap...did I read that right 1mw to 20w of 523nm?!

20w of green must be ridiculous!

3w huh? That's some serious dough!

 

[sopark4000]

It's actually a 2.5W I bought about 2 years ago. I don't think they sell it anymore. It's funny because the same laser in 2W power costs like 5,000 dollars now but back when I got the 2.5W it was less than half the price of there current 2W. I really like laserglow tech they truly stand behind there product, to this day I can still get help from them with my laser. Unfortunately they are overpriced but they are extremely helpful from questions you might have before ordering to questions or service you might need after you have owned your laser for a year.

 

[Plyman44]

Never the less... 2.5w of 532 is amazing to us "pointers only" people. I would love to see that beam in person. Bet it is impressive and has nice ir filtering!

Lab style tinkering still down the road for me, but soon enough.

Thanks for the info on laserglow.

Regards,
Patrick

 

[sopark4000]

When I get a chance I will take some nice beam shots. Unfortunately I don't currently have a quality camera but next time my friend dan comes over I am going to have him bring his camera.

 

[lasersbee]

When I get a chance I will take some nice beam shots. Unfortunately I don't currently have a quality camera but next time my friend dan comes over I am going to have him bring his camera.

I hope that is not the same DAN as the MOD from
WL... :crackup:

Jerry

 

[sopark4000]

i hope that is not the same dan as the mod from
wl... :crackup:

Jerry

absolutely not

 

[madog]

I'm sorry, can I ask the simple question here?

- Who sold you a "3W" 445?

Unless you bought one of those knife-edge rigs (that are really two lasers combined into one beam) made by a clever member here in the forum, I would question anyone who marketed a "3W" 445.

I had the same question.

So the lucky buyer of wannaburns' masterpiece remains anonymous?