Question on combining beams and more!

[Stryker295]

if power density is the key to burning... is there really much of a difference between colors?

also, if there was and it was measurable/noticeable, then wouldn't that show up on LPMs? like if I got a multimeter calculated that something with a 'low power density' (to use the term) was using exactly 1W, and the same but with something with a 'high power density', wouldn't that show up as different readings on an LPM?

 

[Bionic-Badger]

Well a watt is a watt is a watt, but you first need to be able to absorb that light before you can do anything with it (i.e. convert it to heat). If you're not absorbing any light at a particular wavelength most of the light will simply be reflected away. So yes, the absorption spectrum (i.e. the "color") is important.

For LPMs, ideally the LPM will utilize a surface that will absorb all wavelengths equally. That's why the surfaces of thermopile-based LPMs have a black matte surface. The LPM should also be able to provide the same reading regardless of the power density. This can be facilitated by using a material that spreads out the absorbed heat, or with multiple sensors spread over a large area (which you integrate the output over). TEC-based LPMs use the latter approach. They read the same output regardless of the density of the energy because a large beam spot will cover multiple P-N contacts, while a smaller spot of the same power will affect few contacts but each will have an increased output. In that manner the reading will (ideally) be the same.

 

[Stryker295]

Well a watt is a watt is a watt, but you first need to be able to absorb that light before you can do anything with it (i.e. convert it to heat). If you're not absorbing any light at a particular wavelength most of the light will simply be reflected away. So yes, the absorption spectrum (i.e. the "color") is important.

For LPMs, ideally the LPM will utilize a surface that will absorb all wavelengths equally. That's why the surfaces of thermopile-based LPMs have a black matte surface. The LPM should also be able to provide the same reading regardless of the power density. This can be facilitated by using a material that spreads out the absorbed heat, or with multiple sensors spread over a large area (which you integrate the output over). TEC-based LPMs use the latter approach. They read the same output regardless of the density of the energy because a large beam spot will cover multiple P-N contacts, while a smaller spot of the same power will affect few contacts but each will have an increased output. In that manner the reading will (ideally) be the same.

That's good to know.