What if I Don't Have an LPM?

[ARG]

what about testing like ballistics gel?

take a worldwide available candle (wax) with a special colour eg brown (mass coloured-not surface), slice 2cm piece
and lay it on a light (neon or led-should be cold) to see trough a bit...shine on 30seconds with your lp from above and measure the depht and the diameter of the fresh molten pond and multiply them
depht will be more when focused,diameter will be more with non focus lp

what you think ?

If I understand you correctly I don't believe this would work because results would vary with power density.

 

[Javalin]

If I understand you correctly I don't believe this would work because results would vary with power density.

Not only this but ambient temperature would alter the results dramatically as the wax would melt at a different rate. What if you don't have an LPM you ask?:

http://laserpointerforums.com/f70/now-over-60-listed-list-lpf-members-lpms-locations-81288.html

Or Just buy an LPM for yourself.

 

[ARG]

Not only this but ambient temperature would alter the results dramatically as the wax would melt at a different rate.

That too, there's lots of reasons it wouldn't work correctly. Wavelength absorption of the material would be a factor as well.

 

[hakzaw1]

The last post (before all the new ones) was more than 7 months old- maybe NOT 'necro' old but still, guys-- if this member has not yet figured out what he 'deal' is posting now seems to be pointless- let this thread DIE-- Dave has said it all so nothing more needs to really be added. posting is bumping and WHY would you want to bump this thread???

hak

edit update- missed the fact that this thread has been stickied- sorry
I missed that--+5 to The Duke for setting me straight!! TY

 

[TheDukeAnumber1]

The thread's stickied, it's not really a bump.

 

[hakzaw1]

oops YOU are correct-- my bad

 

[starlight]

How important is having the laser focused before you measure the power with a LPM? Can results vary out of focus?

 

[ARG]

How important is having the laser focused before you measure the power with a LPM? Can results vary out of focus?

NEVER FOCUS YOUR LASER ON THE LPM SENSOR.
Please, never do this. It is the fastest way to damage your sensor.


Before shining the laser on the LPM sensor unfocus the laser so that it will cover the entire LPM sensor area without spilling over, then shine the laser on the sensor.

Results should not vary with focus as long as the entire beam is on the sensor. (I'm assuming you're using a TEC based LPM.)

 

[starlight]

I do not have a LPM. I've been thinking about this for a couple of days looked around the forum but couldn't find any explanation on how to perform a test with a meter. I'm getting close to buying a meter and glad I asked because my impression was having it focused would give the highest reading. Thanks

 

[ARG]

You can download the Radiant X4 user manual from their website which has guidelines on how to measure power with a LPM. The basic concepts are the same for every TEC based hobby meter.

Sent from my SM-N900W8 using Tapatalk

 

[Marco Polo]

Check out my thread in this section about using a Crooke's radiometer as a sort-of LPM. It does work, to an extent.

 

[john_lawson]

You got to have a meter

 

[Bionic-Badger]

As long as you've got the entire beam on the surface of the sensor, you should spread the beam out as much as you can across the sensor's surface for a reading. This avoids damaging the surface of the sensor. Ideally, the sensor will pick up the same amount of power across its entire surface and sum all those components up for a reading, producing the same reading as if the beam were focused in a single spot.

 

[Enchilada]

Certainly an old thread, but since its sticky and just hanging there in necrofileland, still room for own approaches.

I dont own an LPM.. been thinking about jumping on one for some years, and patrtically since they TEC-based-ones, seems to be acces-able from around 70US (certainly attractive pricelevel)

but still, to some extend still in no-mands land in lack of some of the praised OPhir heads as to relaying on TECs, so been in doubt if I should go all in from an relative hobbyperspective and get an amp. Ophir head and suit it up with own DMM hence v=w with sep. 9v power, but still here anno 4q16 they are certainly in another price-ballpark in lack of relative few out there.

Im a noob' as they come, and also enjoy my lasers from time to time here at home, and enjoying ´the different wavelength and bouncing them on multiple small mirrors to get the beam going and thrue prismes and simply enjoying this leveraging of massless-particles there takes place and there charistica,- and in lack of an LPM also wonder about alternatives just to measure and enjoy these lasers..

but from household items, I mostly been using multimeters with an cheap 0.70US pearl-thermocouple fx attached with an small thin matblackcolored cobber-heatsink attached to catch the beameffect, and checking what the temp-reaches, while having an eye on what ampcurrent the diode takes..

it doesnt tell me anything usefull to put into mW, for that i need an trustworthy LPM for simply grasping an benchmark and being able to put it into context and what temp equals what on wich <nm but still.)
but for the time being its been better then nothing, just to use an multimeter with an pearlthermocouple (pic attached) and taking the temp on an infinity beam setup close-by, while looking at the graph on my computer from the bluetooth-DMM connection and how the heat goes to the thermopearl and when it seems to flat out on the computer graph..

the cheap laser-graving-labby that cost around 65US containing NDB7775.. that one i took the plunge at around a little year ago for 65US shippped (that model are being labeled as high as 2.5w at fx BG) but that clock in at around +700 degrees.. the lesser 1.4w comes in around 400degrees as i remember.. its been some time since i did the measurements, but in lack of an LPM..I did love fiddling with that and seeing the charistica & temp graphing out while an eye on the amp, ewen thow i cant use it for jack-shit in regards to put solid MVnumbers on my stuff, but im an rookie on this field an learning a lot' as i go..-

Do got got an peltier in house, but its an massive 3x3cm optained from aliE some years back, for around 1.5US shipped and wont do any favors in taking the temp, and been checking for some of the smaller ones, but are certainly on foreign ice.. as to knowledge on this subject.

been purchasing some expensiv-diodes lately from sale (7675,NUBM08,500mitP73,900*16x), and do need an LPM to sense when they flat out, and not just take it by the amp and my own-sense of beam-light..(reckon it will be cheaper in the long run)

as for some of the more tested diodes, and in lack of an LPM and just getting an rough-idea of mW-effect' could comparing the ampcurrrent-level draw suited with an site like DTR testphotos on that partically diode, - that give an rough indication where your at, if it aint an freak or an cousin3..

 

[lasersbee]

Yes... It's a Sticky...
You could have also opened a new Thread as well.

There was a discussion on using a temperature sensing
approach to making an LPM with all the Pros and Cons....
http://laserpointerforums.com/f70/can-tmp36-lpm-meter-sensor-98267.html

The main problem in building an LPM from scratch is and
has always been "What to use to calibrate it to accurately".

A recently calibrated NIST traceable commercial LPM like
our Coherent FeildMax II with matching 30watt head or our
Newport 1825C LPMs are very expensive for a one time
calibration.

A calibration source must be accurate to have the numbers
of your LPM comparable to others.

Of course if you only want a reference point to know which
laser is more powerful than another without really knowing
it's actual power output then a temperature sensor may
be useful enough for your needs.

BTW... you will get different temperature reading from the
same laser on the same sensor if the focus of the laser is
different (Power Density).


Jerry

 

[_Wim_]

Hi hope it is ok to post here as it is a sticky thread but quite old?


For higher power lasers (>250mW) you should be able the measure the power reasonable accurate with a piece of aluminium and a temperature sensor (for example the thermocouple from your multimeter or some low cost temperature sensor module from Ali-express) This is done by making a crude LPM with these 2

This would be the approach:

- take a piece of aluminium (+-30g) and drill a hole in it so the temperature sensor can be fitted tightly (use some thermal grease if available)
- measure the weight of the piece of aluminium
- light a candle and hold the piece of aluminium in the flame to deposit lots of black soot from the flame. This creates a dark coating that is really unreflective (this coating is however fragile and wipes easily off). Let the piece of aluminium cool down before continuing
- take some scrap Styrofoam and cut a hole in it to fit the piece of aluminium (ideally the entire piece of aluminium is covered in Styrofoam apart from where we will shine the laser on).
- record the start temperature as accurate as possible (remark: absolute accuracy is not important, we only need to measure the relative temperature increase, but preferable in as high resolution as possible)
- turn the laser on and point it on the exposed blackened aluminium in the styrofoam
- record for example every minute the increase in temperature
- calculate the laser power as explained below

Laser power calculation:

Laser power (Watt)= ("weight of aluminium piece" x "specific heat aluminium" x "temperature increase") / "time laser was on (in sec)
(Specific heat aluminium: 0.91J/g.C°)

Example:
Weight piece of aluminium = 30g
Start temperature = 20.1°C
End temperature = 25.1°C
=> 5°C temperature increase
Time between start en end = 120 sec
=> laser power = (30 x 0.91 x 5) / 120 => 1.14 Watt

This will under estimate the true power of the laser due to heat loss to the surroundings, but the Styrofoam should provide a reasonable thermal isolation. While for sure not as accurate as a calibrated meter, it will be much more accurate than trying to determine laser power based on the damage it can make.