determining IR (Infrared)

Hey folks,
I've been mulling this over in my head for a few days (as well as searching)
and can't quite figure it out.....

Lets say you have an un-IR-filtered 532nm laser that measures 200mw on an LPM.
You install an IR filter and then it measures 150mw. Without knowing the efficiency of a particular filter, how can you know how much 532nm v/s IR there is?

I just ordered 5 of these....
One piece IR Filter

But really, I'm just taking the sellers/manufacturers word in determining how effective the filter really is. I wouldn't know a true BG39 filter if it bit me.:yh:

Is there a way for the hobbiest to really be certain of exactly how much IR v/s 532nm you have?

Or am I just being "too anal" about it.

Thanks,
Rod

Several people here have take high od glasses that block 532mn and put them between the laser and the power meter.

I would guess that the green and the IR have different divergence, so by moving the laser further away from the meter and checking with and without filter you could get an idea of whether the filter is 99% or 10%.

I think I'm really trying to be TOO accurate for a hobby scenario.
I just see people saying that thier particular IR filtered laser is xxxmw and wonder how much of that is STILL really IR instead of 532.
Like I said, I'm probably trying to over analyze for a hobbyist type application.

I would just like to be able to accurately say how much 532 I have compared to infrared.
At least reasonably be accurate.

BTW....Toke,
Have you ever lived in the US?
I KNOW I've seen you somewhere but I can't remember when or where

Udanis...That might work to give a pretty close idea.
Thanks

Those little filters from snoctony are pretty good actually and they're AR coated. Due to this coating the losses at 532 to 473nm are very small. Subtract the output after filtering from the output before and you have your IR content to within a mW or two.. BG-39 blocks the VAST majority of 808nm and 1064nm IR, with around .1% of it still being allowed through. Not enough to be significant..

Well, the obvious way of measuring needs two criteria to be met:

- the ir filter will block the ir almost completely
- the ir filter will block the 532 to some extent

The solution to this, is to get 2 identical ir filters. First you measure the laser without any filer, then with one filter in the beam, and then you measure it with both filters in the beam.

Lets say this gives measurements like these:

- no filter: 100 mW
- one filter: 80 mW
- two filters: 78 mW

From the latter two you can conclude that the filter loses 2.5% of the green. You then know that you must increase the measurement with one filter by that factor to get the real green power output, which in this case would be 82 mW, with 18 mW of IR mixed in.

RoDnSuE said:

BTW....Toke,
Have you ever lived in the US?
I KNOW I've seen you somewhere but I can't remember when or where

Click to expand...

I have been years since I visited the US, LA and NY, but I use the same avatar on several forums.

Another way for see if your IR filter left pass them, can be to use an IR-pass filter after it.

Place the IR filter in front of your green laser, and get a measure with an LPM, then place in the path an IR-pass filter (that must block all except IR), and if you still read something on the LPM, this part is the IR that your anti-IR filter left pass.

Thanks everyrone.:wave: I think I got a handle on it now.
I appreciate the ideas and responses.
When my filters get here, I should be able to figure it out now.

@Toke...I might be remembering your avatar from another forum somewhere. I can't recall where I've seen your face before. Maybe America's Most Wanted??:eg::crackup::crackup::crackup::crackup:

ir and 532 have different index of refractions so you could use a prism to separate them