Another Simple Laser Power Meter

[lasersbee]

The Problem with Chris is.... he does not respond to PMs or E-Mails or
eBay messages until you open a Dispute or lodge a complaint... too bad....

I tried multiple times to get Info on his stuff in the past and have now
given up doing any more business with him in the future... I don't need
to be ignored...

BTW... you are correct in your evaluations of the TECs available and their
prices in general... Not to mention a minimum quantity order when dealing
with a distributor/manufacturer....


Jerry

 

[billg519]

Well, it looks like this meter, and my DMM to LPM adapter are only going to be useful to those who win the "TEC Lottery" and manage to find one somewhere along the way. Just don't expect to do anything more with a large TEC other than prove that a laser beam on a big TEC can generate a few mV's as long as you are willing to use up half your laser's battery waiting for the TEC to stabilize. Large TEC's also tend to have a thick ceramic layer. All of this is bad for sensitivity to the laser beam. I did an example of a large TEC, 40x40x4mm in my other LPM thread.

 

[StardustSprinkles]

I want a handheld power meter, I can point my laser at it once and it says how many mWs hit it. That is all. Simple. I would really be impressed and I'd buy one for sure...

 

[Eudaimonium]

...

Eudaimonium - have you read up on electronics theory? You seemed to be pretty lost last time I talked to you about your microcontroller based LPM idea.

HAHA dude, don't worry! I learned to read since then! I haz improoved.
:beer:

 

[Krutz]

ah, i feared that, that it will be tough to find such tiny TECs. will keep my eyes open..
thanks for the info!

manuel

 

[lasersbee]

I want a handheld power meter, I can point my laser at it once and it says how many mWs hit it. That is all. Simple. I would really be impressed and I'd buy one for sure...

It looks like you are looking for a LaserCheck LPM...
It is the only truly Portable LPM pen.....
But it is an Optical LPM and must be adjusted to the wavelength of the
Laser being tested... and it has been posted that it is not too accurate
at 405nm..

The other down side is the $395.00USD + Shipping cost...

Coherent Inc. : LaserCheck


Jerry

 

[billg519]

I have a Coherent Lasercheck as well. If I am going to measure a laser at home or the shop, my Laserbee or my Coherent 210 get used. If I need to take an LPM with me somewhere, the Lasercheck goes with me. The Lasercheck also has trouble with green lasers that leak IR. Set the Lasercheck to 532nm, and the IR throws the reading off from what a thermal LPM will show. Here's an example : An IR leaking DX green pen reads 97mW on my Laserbee thermal LPM. This same IR leaking pen measures 286mW on the Lasercheck set at 532nm. Maybe those cheesy ebay pen resellers use a photodiode based LPM to measure their greens ...

 

[HIMNL9]

^ Common problem ..... all the photodiodes are MUCH more sensitive to IR than to visible light (except the ones specifically filtered with front matched dichros, ofcourse)

Otherwise, you need an Ag/p-InP/p-InGaAs schottky photodiode, like this one, as example (but i don't think they are too cheapy ..... )

 

[brtaman]

Thermal meters really are the way to go.

Great project, billg!

However, if we want to make something like a DIY thermal meter viable, a group buy of sorts would be in order. We find a TEC supplier, with TEC's that fit our needs, work out the price at the lowest quantity at which they are willing to deal with us, then see if there is enough interest. I think it could be pulled off, especially due to the forums size.

Personally I would be in for ~5 tiny TEC's, depending primarily on the price we can get.

 

[Krutz]

thermal sensors are the way to go, definitely. except for really low powered lasers, under 10mw perhaps. but who would want such lasers, and want to measure those anyway? ;-)
(yellow and blue lasers come to mind, though)

someone likes to do a feeler in groupbuys for tiny TECs? they must be relatively cheap in larger numbers. if interest is high enough..?
if we get nice ones, it could open the way for a whole new class of diy "pointers". with one (or more) TECs inside, temperaturestabilized, or cooled down for even lower wavelength (635nm!). no more dutycycle, no more kinks, powerfluctuations and the like! thats what my next laserproject will be.

manuel

 

[brtaman]

thermal sensors are the way to go, definitely. except for really low powered lasers, under 10mw perhaps. but who would want such lasers, and want to measure those anyway? ;-)
(yellow and blue lasers come to mind, though)

someone likes to do a feeler in groupbuys for tiny TECs? they must be relatively cheap in larger numbers. if interest is high enough..?
if we get nice ones, it could open the way for a whole new class of diy "pointers". with one (or more) TECs inside, temperaturestabilized, or cooled down for even lower wavelength (635nm!). no more dutycycle, no more kinks, powerfluctuations and the like! thats what my next laserproject will be.

manuel

While they would be great for LPMs, I wrote a rather lengthy post as to why they are not as useful as it first seems for pointers, I will try and find it and post it up.


EDIT, found it:

"That was one of the inherent flaws of the Spyder II laser (dunno about spyder III). The peltier would keep the crystals (or diode, dunno what they decided to cool...probably both) cool for a bit of time, but the problem is the sinking.

After a limited amount of time the laser itself would overheat (remember reading long ago some user mention the laser getting HOT quick), due to a lack of thermal mass. The heat itself cannot be radiated fast enough.

When the hot plate of the TEC becomes to hot, the effectiveness of the peltier drops significant, with the "microcontroller" not being able to hold a temperature due to an inherent lack of sinking mass, the stability goes out the window. (Hercules uses active cooling, allowing complete thermal stability over time)

Though these 8X 5,6mm diodes do radiate less heat than a DPSS laser, their need for temperature stability is nowhere near that of a tuned DPSS system.

Another thing to consider is that a peltier is 5-10% efficient and will result in extra heat being dumped into the host (it is not a magical device that teleports heat to a distant black hole), effectively shortening the "duty cycle", very counter-productive.

In our case, limited thermal mass and passive cooling, adding a peltier which would admittedly add a "cool" factor to a host, is not justifiable from an engineering point of view, imo."

 

[Benm]

I concur with the above on the usefulness of TEC in laser pointers. If you want to have a pointer that can be run continously, its heat resistance to ambient should be low enough to sustain an acceptable rise in temperature.

Thermal mass is not really important in itself, but larger hosts will usually have larger thermal mass AND larger surface areas resulting in lower thermal resistance to ambient. To illustrate the difference:

Lets make 2 hosts of identical size and shape, one from copper, the other from aluminium. The copper one is much heavier, and much larger heat capacity ('thermal mass'), but will still reach exactly the same temperature after infinite ontime.

The only thing TEC will do is -move- heat, and generate a whopping lot of extra in the process. Its useful if you need something to be cold (pump diode, crystal) but only if you can afford to dissipate the heat to ambient at some point (i.e. bulky host).

 

[HIMNL9]

Fixed ..... sorry, just kidding, but, sometimes i can't resist :crackup:

 

[Benm]

Hehe... some of those cheap green pens are so unstable you'd want to do exactly that

 

[Krutz]

brtaman:

very true!
i wouldnt want to tec-cool a high-power laser (8x or dpss) in a tiny host. my idea here is to cool a 20mW 635nm diode to (or below) roomtemperature, for lower wavelength (instead at 40° with passive cooling). with a maximum of 100mW heat from the diode, the heat from both the diode and the tec should easily be dissipated in any host.

remember, the higher the temperature-difference, the more effective the heat transfer! so a hot host will get rid of the heat better. if then the diode is even cooled down by a tec, it might be quite effective! sure, again, the tec doesnt like it hot..

manuel

 

[brtaman]

brtaman:

very true!
i wouldnt want to tec-cool a high-power laser (8x or dpss) in a tiny host. my idea here is to cool a 20mW 635nm diode to (or below) roomtemperature, for lower wavelength (instead at 40° with passive cooling). with a maximum of 100mW heat from the diode, the heat from both the diode and the tec should easily be dissipated in any host.

remember, the higher the temperature-difference, the more effective the heat transfer! so a hot host will get rid of the heat better. if then the diode is even cooled down by a tec, it might be quite effective! sure, again, the tec doesnt like it hot..

manuel

Oh, then yes a TEC is a good way of cooling...good luck with the project, though I would suggest using 635nm diodes.

A long time ago, right when I joined to forums, I used my phase-change CPU cooling system (r-402a, left over from my overclocking days) and cooled the diode down to ~-50ish C, there was a slight change in the wavelength comparing to a room temperature diode, though it really wasn't enough to turn it "orange". Maybe the thread is still around...?

So if you do go through with your experiment a 635nm diode is a must. :beer: