how do power meters measure power

[f22warzone]

Hi
I was wondering how power meters measure power. Do they measure the W/cm2 or just all the green light added up together.
Ok say I have a 100mw laser with a divergence of 1 and I hold it one meter away from the power meter now say I have another 100mw laser but with a divergence of 2 and it am held one meter away from the power meter. They both have a beam diameter of 1 when they leave so the 1mrad laser will have 2mm diameter on the power meter head and the 2mrad laser will have a 3mm diameter on the power meter but they both still read 100mw..... Now let’s say I focus them down with a magnifying glass to .5mm on the power meter head. Will the lasers still read 100mw or will they read 100+mw and if that is the case will the 2mrad laser have more power then the 1mrad laser?

I am just wondering this because if you buy a 400mw laser with a 1.2mrad divergence does it put out more green lights then say a 400mw laser with an .8mrad divergence and do they have the same W/cm2?

 

[likewhat]

The output power is how many Watts there are. If you have a 100 mW laser then you have 100 mW of power, that is how much green or red or whatever color light you have. The intensity, measured in W/cm^2, has Watts over area. So if you have a 100 mW laser then you put 0.1 W in the top and if the beam is 5mm big then you put Pi*(.25cm)^2 in the bottom and do the math and get whatever that equals to.

So if you want higher intensity you make the beam smaller which will make the fraction bigger. You win pretty fast when you make the beam small because the bottom is squared.

Power meters measure power, that means that they measure Watts. It doesnt matter how big or small your 100 mW laser is it is still 100 mW and that is what the power meters measure.

 

[f22warzone]

ok thats what i figured i just was just making shure i was right
thank you

 

[BlueFusion]

They do not measure per surface area but total power. It makes no difference if a 100mw laser covers 1mm or 10mm on the sensor. it still reads as 100mw because it's total output over the sensor that matters.