IR filter power loss

[ZapU]

Just tried this experiment with an IR filter.




There is a 18% reduction (131mW) on a Arctic G2.
Should I assume 18% non IR power loss at different frequencies (532nm)?

I got 43mW out of a green pointer.
With filter it measures 29mW.
18% = 7.74 round to 8mW for glass loss.
That would give me 6mW IR and 37mW 532nm.

 

[Cyparagon]

Should I assume 18% non IR power loss at different frequencies (532nm)?

No. Test it with a green that's already IR filtered to determine the loss at 532nm. I can guarantee it will be different.

 

[Hemlock_Mike]

Use an 808 nM laser to check the filter as part of your calibration.

HMike

 

[ZapU]

This is getting expensive. I need a filtered 532 and a 808, neither one I have.


I assume then any power loss on a IR filtered 532 would just be the glass loss?

If I use a 808 (IR), supposedly no mW would get through? How do I use 808 to test?

The 445 and 405 put out no IR, so the power loss should just be the glass reducing the beam.

I do have a 405, it tested at 46mW without and 37mW with the filter. (about 19%). Pretty close to the 18% from the 445 test.

 

[Hemlock_Mike]

OOPS -- I misread.
HMike

 

[Benm]

You need 2 identical IR filters to make an exact measurement of the loss.

Take 3 measurements of a green laser:

1 - no filter
2 - one filter
3 - both filters

The ratio between 2 and 3 gives you the loss of green in the filter. Lest assume values like these:

1: 150 mW
2: 100 mW
3: 90 mW

This indicates that the filter drops 10% of the green light, meaning that measurement 2 consists of 111 mW of green, and 39 mW of infrared.

Given the size of the filter you have, you could probably carefully break it into 2 pieces to get 2 identical filters.

 

[ZapU]

You need 2 identical IR filters to make an exact measurement of the loss.

Take 3 measurements of a green laser:

1 - no filter
2 - one filter
3 - both filters

The ratio between 2 and 3 gives you the loss of green in the filter. Lest assume values like these:

1: 150 mW
2: 100 mW
3: 90 mW

This indicates that the filter drops 10% of the green light, meaning that measurement 2 consists of 111 mW of green, and 39 mW of infrared.

Given the size of the filter you have, you could probably carefully break it into 2 pieces to get 2 identical filters.

Thanks Benm, I'll give it a try. :beer:

 

[ZapU]

You need 2 identical IR filters to make an exact measurement of the loss.

Take 3 measurements of a green laser:

1 - no filter
2 - one filter
3 - both filters

The ratio between 2 and 3 gives you the loss of green in the filter. Lest assume values like these:

1: 150 mW
2: 100 mW
3: 90 mW

This indicates that the filter drops 10% of the green light, meaning that measurement 2 consists of 111 mW of green, and 39 mW of infrared.

Given the size of the filter you have, you could probably carefully break it into 2 pieces to get 2 identical filters.

I broke my filter into 2 pieces and tried again.

Measured a modded 5W green.
Without a filter it stabilized at 61mW
With one filter it was 45mW, 16mW drop
With 2 filters it was 36mW. 9mW is a 20% drop, not much different than the 18% I got measuring a non IR laser with larger numbers. So let's use 18%.

So I figure I have 55mW green and 6mW IR.
Not bad for a $10 laser.

 

[Benm]

That sounds about right. Those filters can cause considerable losses in green light, especially if they are not AR coated.

I think you result is fairly typical of a decently designed green laser too - the IR contribution in total output power is only 10%. I'd consider that a very normal value, and nothing to worry about.

The really bad lasers put out more IR than green, but it seems like those are disappearing from the market