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What if I Don't Have an LPM?

ArcticDude

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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
Here is good LPM (price/quality) ;)

 



_Wim_

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Hi, I agree this one has for sure a good price/quality ratio, but still think many people find 350$ quite expensive., and wanted to describe a very low cost alternative (can be done with 15$ and some scrap materials when using a temperature sensor like this: "PT100 digital display LED digital thermometer thermometer Temperature high precision waterproof Sensor 12V 24V" on Ali-express)

I personally have a couple of good quality laser power meters (for low power lasers, as this is my main interest), and if I need to measure a higher power version, I use a neutral density filter in front.

Remark: due to my low post count, I am apparently not allowed to post a link, hence only the search term for Ali-express...
 

Giannis_TDM

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Hi, I agree this one has for sure a good price/quality ratio, but still think many people find 350$ quite expensive., and wanted to describe a very low cost alternative (can be done with 15$ and some scrap materials when using a temperature sensor like this: "PT100 digital display LED digital thermometer thermometer Temperature high precision waterproof Sensor 12V 24V" on Ali-express)

I personally have a couple of good quality laser power meters (for low power lasers, as this is my main interest), and if I need to measure a higher power version, I use a neutral density filter in front.

Remark: due to my low post count, I am apparently not allowed to post a link, hence only the search term for Ali-express...
There a lot of problems that I will answer once I get some sleep but the main things are:
1) You need a stable measured laser as a calibration source, The method of yours has too much Inaccuracy due to having so many set values needed for its cal, at best +-20 - 30 %
2) That carbon coating won't have anywhere near a good spectral response across WLs
3) The temp transfer efficiency from the coating to the TEC won't be good.
 

skijohn

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Here is good LPM (price/quality) ;)

I'm seriously looking at getting one of these!

Thanks!

Has anyone here bought one of these?
 

_Wim_

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There a lot of problems that I will answer once I get some sleep but the main things are:
1) You need a stable measured laser as a calibration source, The method of yours has too much Inaccuracy due to having so many set values needed for its cal, at best +-20 - 30 %
2) That carbon coating won't have anywhere near a good spectral response across WLs
3) The temp transfer efficiency from the coating to the TEC won't be good.

I fully agree with the points you made above. But an accuracy of 20-30% (which will typically be minus due to inefficient coupling and heat loss to the surrounding) is in my opinion still way more accurate than trying to estimate laser power based on how fast it will light a match or burn stuff, which was the topic being discussed earlier in the thread. And as many pointed out, this method is problematic due to beam focusing differences.

I am not claiming that you can get the above method to within 5% or so without having some calibration equipment. It is not a replacement for an LPM if you can afford one. But if you are on a tight budget and bought one of those Ali-express diode laser modules claiming to output 5 or 10 "Watts" and what to test what it actually puts out on a tight budget, this is in my opinion the cheapest was to get a reasonable result.
 

FAP

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You can estimate the power output by the type of diode and known average power output at the current level the diode is pulling, but to do that, you would need to measure the current output at the driver output, not input to the driver. If you are talking about a DPSS laser, well, that isn't nearly as straight forward, they can vary all over the map due to different efficiencies for a particular pointer.
 

hakzaw1

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remember
using the method of comparison--1) RESULTS may be very wrong if you are comparing with a diff. nm.
405 looks 'tame' BUT of the $3 RGV pointers , while looking low power, is actually, most often the most powerful.. The WORST danger is mistaking a 405 to be 'weak' our eyes see green & red much better.
2) it is not easy to compare even with the same nm.
I remember reading a fresh post about someone getting a 'trio' and since they 'thought' the 405 was weak--SO HE WROTE that he gave it to his kids TO PLAY WWITH OMG-- I PMed asap and the buyer replies quick and thanked me--NO LASER is child safe except one that does not work.

not even the red pet toy laser..READ and HEED
GET A METER-
they are very easy to sell later-- think of buying more like 'renting'
your 'investment ' will not be much. The Hyperion IMHO is the best choice--Barrnet has them at EEKBAY- I have a few to sell soon.(better price-and FREE delivery at SELEM 2021) ( 1st week in Aug from Monday to friday) << more on this in another thread--READ IT!!
 
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_Wim_

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If you need an LPM to know a laser is dangerous, then I think it is better to just not buy lasers at all...

I think the main reason people that do not want to buy and LPM but do want to "measure" power is to perform a single measurement of their new toy, and evaluate if they have been ripped off or not. For this kind of use, I think it is still valuable to list alternative methods and describe their trade offs.

I agree however that investing in an LPM if your in this hobby is a very good idea, as it is useful for so much more that only determining the max power of your laser once. I currently own 3 Advantest tq8210, which I have bought over the years for around 50$ a piece (some of them broken, but the only fix was was to install a new battery, as these do not charge without a working battery installed).

Why multiple? It lets me check their accuracy. If all 3 show an identical value, I am probably ok, and this is currently still the case. But it is also very have during alignment of a more complex setup to have multiple simultaneous measurements. They do top out at 50mW, but can measure to 1nW. For higher powers I use ND-filters, for which I first test its actual attenuation at lower power (lower power can be achieved by placing another ND filter in front of the laser).

If you are into low power fiber lasers, it is always good to look on Ebay for HP8152A & HP 8153A modules+mainframe. These regularly also appear sub 100$, and are extremely accurate (measure down to pW, but can only take a couple of mW). I own quite a bit of 8153A hardware, which I have collected over the years for very low prices.

For high power LPMs however, it does indeed seem that new units like the Sanwu are one of the better alternatives, certainly because many of the high power LPM on Ebay look to have been abused severely, so accuracy is at least questionable.
 




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