Status of Cheap DIY Laser Power Meters?

[seoguy]

Looking for how to build a homemade laser meter was how I found this forum, and I was wondering what the current status on DIY Power Meter design approaches was here now?

Some of the ideas I've read about include -

* The thermopile DIY Laser Power Meter - this appears to have been based on a sensor that was scavenged from some surpl. circuit boards on eBay, and which are apparently no longer available. Can anybody that has one of these things tell us the manufacturer and P/N of the sensor, or of the device it came out of - perhaps we can find another source?

(Christ, I just saw a pic of the innards of that sensor - is that a manufacture date of 1975??!)

* The DIY i/f board - from what I've read, this was a proprietary design, neither the source code (even sans libraries) nor the PIC microcode was ever released : by the author, who has now disappeared? :-? It also uses old RS-232 (vs. USB), and was designed to hook into the "part no longer available" DIY design above, so it's basically a lost cause now, is that correct?

* Various photodiode/solar-cell versions on the Sam's Laser FAQ site. Two issues with this approach appears to be max power levels (but can use an attenuator/ND filter), and the fact that the response curve on some of these devices can get a bit squiggly. But given we can't get any more of those low-cost eBay thermal sensors, perhaps this approach deserves a closer examination?

* The Benm diode-based design. This one is still a little rough around the edges, but got me to thinking about ideas for possible enhancements. Anyone using this, and how does it compare with the old thermopile design?

Did I miss anything? What do you all think is the best option right now for building a low-midrange (0.1mw to <5W) inexpensive homemade laser power meter?

 

[lasersbee]

Hi.... and welcome to the Forum...

It is refreshing to see new members that actually read the Threads/Posts
on LPF... [smiley=thumbsup.gif]

The DIY LPM project has died due to lack of the cheap used Coherent Thermal
Heads. You can still get New ones for around $700.00. The Thermal heads were
calibrated at coherent.. and only required a precision Op Amp to get a useable
output.
Yes.. the Source code belonged to the member that designed it... The PIC was
not required unless you wanted data logging...
You can get an RS232 to USB Converter cable for a few bucks that solves your
"old RS-232 (vs. USB)" issues..

With the different wavelengths of lasers we use here... we have found that
Optical Sensor LPM... are not the best way to go... (if you want precision)

The Benm LPM Gauge is one of the latest ideas that has some potential as
a cheap DIY LPM design...

You will not get a better LPM than a Thermopile based Laser Power Meter... IMHO

Here are 2 links to inexpensive LPMs...

(small 120mW optical)
http://www.bauer-electron.com/eby/ebayhlpm.htm

(1 Watt Thermopile)
http://www.bauer-electron.com/eby/eby1wlpm.htm

Jerry

 

[ndrew2505]

there are still ways to make them but like jerry said its just to expensive to justify trying now unless you find a real deal on the heads. jerry's laserbee lpm1 w/ datalogging is what i use and its almost dead on with more expensive meters. the only difference ive seen is ~1-2mw which is perfectly acceptable for a hobbyist lpm...

 

[691175002]

I have built one of the diode based power meters and while it takes a while to get somewhat accurate readings, I would put it +- 15%, perhaps even better.  Its nothing super precise, but it gives me a general idea of what my diodes are putting out which is all I really wanted.  I am considering plugging the output into a pic or something and sticking it in a box with an LCD so it looks fancy.

You could build one for under 5$ if you have resistors and such laying around so if you are good with electronics its always worth a shot.

 

[Kenom]

You can also find an occasional Thermal head on ebay that can easily be put together with the opamp circuit into a fully functional meter. The problem with putting together a meter with a sensor purchased on ebay is sometimes you have no clue what the mv/mw is and can't determine it unless you have another meter to accurately measure your lasers output against the new head. Coherent sells a few that are specifically calibrated to 1mv/mw so literally all you have to do is power it up and hook it to a DMM.

 

[lasersbee]

I agree... there are deals for those who look for them...but you could get a
damaged Thermopile head like we already saw in the DIY project...
And after many years of use the Sensors can become uncalibrated from the 1uV/mW..
I had one dated 1975..
And you really don't know if someone played with the factory calibration in the head..
I had a Coherent Head that was far from 1uV/mW..

But like Kenom said.... occasional you can find a good Thermal Head on ebay.
You just need to be vigilant...

Jerry

 

[seoguy]

It is refreshing to see new members that actually read the Threads/Posts on LPF...

Thank you!

The DIY LPM project has died due to lack of the cheap used Coherent Thermal Heads...

That's kinda what I figured.

You can still get New ones for around $700.00.

I have also seen used heads on eBay for ~400 - that's still ridiculous! :

I think prices for many things in this marketplace are artificially inflated, due to the industrial/government clients they typically sell to.

For example, want a pen "greenie" to impress your friends? Forget about DX, check out these from XADS...

http://www.washingtonpost.com/wp-dyn/content/article/2005/08/23/AR2005082301227.html

What, you don't think $1,100 each is a fair price? The Pentagon did!

I believe that if I told someone I wanted to measure radiant energy from a pizza oven, rather than from a laser beam, the quoted prices would be orders of magnitude less!

You can get an RS232 to USB Converter cable for a few bucks that solves your "old RS-232 (vs. USB)" issues..

No port problem here!...just pointing-out one of the reasons that his "proprietary": interface board design likely wasn't worth trying to resurrect anyway.

With the different wavelengths of lasers we use here... we have found that Optical Sensor LPM... are not the best way to go... (if you want precision)

That may be an overly broad characterization, I'm not convinced of that (yet), I think it may depend on the sensor device in question.

For example, I have read that they can be more sensitive, and (if properly calibrated), more accurate, for low-power measurements? The specs of those commercial products you linked to demonstrate that as well (the optical one is listed as 50x as sensitive, and 10x better precision/resolution than the thermal one!)

Worse-case, a really squirrelly response curve on a sensor could easily be handled by a look-up table, and I have read that some thermal devices are also not linear. For different spectral sensitivity, a wavelength range switch could be utilized, indeed, I have seen such switches on fancy commercial meters for that very purpose.

On the other hand, the spectral range of some optical sensors may not be as good as others. For example, the specs on the optical product you linked to seem to indicate that the sensor being used in that particular product does not have an adequate visible spectrum range to accurately handle either a DPSS Blue (473nm), or the popular blue-violet diodes (~405nm).

However, as you point-out in your second post, thermal heads can get knocked out-of-wack also! In fact, given their construction and method of operation (compared with purely photoelectronic devices), I would think they would be more prone to drift over time, and perhaps less precise unless regularly recalibrated?

I think the performance really depends on the specific variety of optical sensor device being used.

The Benm LPM Gauge is one of the latest ideas that has some potential as a cheap DIY LPM design...

I agree. I'm thinking it could perhaps benefit from an improved sensor arrangement.

You will not get a better LPM than a Thermopile based Laser Power Meter... IMHO

I believe that approach has a lot of benefits. However, after looking at that picture of the innards of the archaic device being used in that eBay DIY design, I think that thermal sensors have come a long way since then!

The first ones were based on the ancient thermocouple bimetal design, but I have read that the semiconductor-based P-N devices can now provide much better performance.

They are also now doing some really nifty things in applying semiconductor miniaturization technologies, for example, fitting an entire thermopile (> 100 junctions, compared to 30 in that ancient eBay sensor), inside of a small TO-5 transistor case!

By the way, that heat sink/sensor pic in the thermal-based meter you linked to is an excellent example of the kind of quality DIY head I was talking about! What make/model thermopile device is that using?

Here are 2 links to inexpensive LPMs...

The tiny shrink-wrapped optical one (I could swear I've seen that on eBay before???) is not really sufficient for my needs (like you pointed-out, it can't even handle blue-ray!) And the second link is the other extreme, too much horsepower (and $$$) for my needs.

That's why I'm looking for a DIY solution. A hobbyist-level homebrew meter, something sufficient for my needs, but not so fancy that I have to spend hundreds of dollars, or feel I need to be wearing a lab coat in order to use it!

 

[seoguy]

its just to expensive to justify trying now unless you find a real deal on the heads

drew, I think that is the problem - $700 for a thermal sensor attached to a big heatsink is ridiculous! Our options may have been limited way back in 1975 (the hot thing back then was the toggle-switch & LED, MITS Altair 8800), but technology has advanced quite a bit since then! There is no reason why we can't come up with a reasonably priced sensor alternative that is good enough for our needs; it makes no sense for us to still be paying Pentagon $2,500-toilet-seat prices for name brand!

The fact that he was selling these old relics for not much more than scrap ($35 w/shipping), indicated what he felt they are worth today. It's like those old $2,000 DVD players, sure, they used to be worth that much, but now??? :-?

Kenom, thanks for the information! But while you guys got a great bargain on those surpl. ones, that deal is long gone, and the few heads I have see are nowhere near what I would call reasonable.

And like you said, you may not even know what the response curve may be for a different model head from eBay.

Finding that one "diamond in the haystack" is also not a practical solution for the group as a whole. I would think that it would be much preferable, if we could come up with an inexpensive DIY approach with easily available components that anyone could build!

 

[seoguy]

I have built one of the diode based power meters and while it takes a while to get somewhat accurate readings, I would put it +- 15%, perhaps even better.

691175002, I have given a lot of thought (and research) to the accuracy issues on the diode meter, and have come up with a few ideas on how we may be able to improve that; I also came up with a neat improvement for this design, based on a state-of-the-art ap note I read on a related topic!

I look forward to sharing these with the group, once I've had a chance to refine them a bit.

 

[lasersbee]

691175002, I have given a lot of thought (and research) to the accuracy issues on the diode meter, and have come up with a few ideas on how we may be able to improve that; I also came up with a neat improvement for this design, based on a state-of-the-art ap note I read on a related topic!

I look forward to sharing these with the group, once I've had a chance to refine them a bit.  

Hey seoguy...
I'm sure when you come up with the ultimate cheap DIY LMP... the members here will
jump on it like hungry dogs.. In the mean time we're all ears... keep us posted of your progess..

PS..
what "archaic device" were you referring to when you quoted....

"However, after looking at that picture of the innards of the archaic device being used in that eBay DIY design, I think that thermal sensors have come a long way since then!"

Jerry

 

[Th0ughts]

Realize those greenies are from 4 years ago.

 

[Swordofsalvation]

wow, the USA paid that much!!! does the article mention output power? im guessing 10mws-20mws....

 

[seoguy]

I'm sure when you come up with the ultimate cheap DIY LMP... the members here will
jump on it like hungry dogs.. In the mean time we're all ears... keep us posted of your progess..

Thanks, Jerry!

PS..
what "archaic device" were you referring to...

Something like this? -

 

[seoguy]

wow, the USA paid that much!!! does the article mention output power? im guessing 10mws-20mws....

Swordofsalvation, the article didn't specify directly - but it did leave us a clue...

Near the end, it mentions he is negotiating on a new version of XADS's dazzler for the military & police -

The PD/G-105 is a souped-up laser that would be twice as powerful as the ones Bitar sold at the Burger King back in January.

The PD/G-105 has a rated power of 105mw, so assuming the prediction on the increased power was correct, I'm guessing ~50mw?

Given that the eye is most sensitive to green light, it does raise the question if it is a really good idea to be shining 50-105mw of green laser into the eyes of an oncoming driver at a checkpoint?!!

And if it's a DPSS, I'm wondering how much of that power is actually green vs. IR? For a weapon designed to temp blind people, would the military even care about filtering? :-/

And when deliberately pointing a laser weapon into people's eyes, where do you draw the line between temporary and permanent blindness/damage? Apparently, even the military is starting to express safety concerns! According to the article -

Gayl, the Pentagon official who has supported Bitar's work, cautions now that he is concerned that some companies, including XADS, are making lasers so intense that they would permanently blind the people they target. The XADS lasers "are way out of line," Gayl said recently.

Given that they are also selling the high-power models to law enforcement, however, my greatest concern is that of some overzealous cop using 105mw of green laser light as a sobriety test! Gives a whole new meaning to being "blind drunk"!

 

[goamarty]

In some article I read about "dazzler" weapons" with 500mW of 532nm. Its probably just a question of distance to call this "non permanent" blinding.
But as a sobriety test he can just project a green line on the floor and tell you to walk along - spares the chalk And then its all a question of his calm hand, so the line does not dance around.

 

[sk8er4514]

Hi.... and welcome to the Forum...

It is refreshing to see new members that actually read the Threads/Posts
on LPF... [smiley=thumbsup.gif]

The DIY LPM project has died due to lack of the cheap used Coherent Thermal
Heads. You can still get New ones for around $700.00. The Thermal heads were
calibrated at coherent.. and only required a precision Op Amp to get a useable
output.

I like to see posts like this, I'm thinking of buying LOTS of COHR (Coherent) stock very soon I already have like 3/4 of all my stock market money in DYSL which makes bad ass optics for lasers. I want to invest in lasers themselves though and Coherent was the only company that I could find that I've actually heard of and like.

<end random ramblings>

You probably won't be able to make your own LPM for cheaper than you can buy them... You should try posting on the BST section that you want to buy a power meter and see if anyone is selling. I have one but really love it and am keeping it

good luck,
Kendall