Coating Linearity (White Uncoated TECs)

[WizardG]

One other problem with using a 0.5mm Plate glued to a
TEC that I can see is that it greatly increases the time
to get a stable reading due to the additional mass in
front of the TEc's ceramic plate.

Another problem I can see is the melting temperature
of the solder used to assemble the TEC... Going over
that will destroy the TEC and it's characteristics.

Jerry

Yeah, I get it that the additional thermal mass of the plate would be an issue, but I think it will be a while before I have any lasers that could heat the TEC to destruction.

But wouldn't a plate distribute the heat a bit more evenly making it harder to damage the TEC though, in addition to being a 'coating' that would be highly resistant to damage?

 

[paul1598419]

For higher power lasers, using a large surface area to spread the beam across would seem to be the way to go. The calorimeter for my Scientech weighs 1.5 lbs. and has a surface 25mm in diameter. It was made to take high energy pulses and the meter measures these in Joules. It can take 20 watts, though it wasn't meant to read powers that high. It is very well heat sinked.

 

[Benm]

It's a bit of a materials science nightmare designing these coatings, as you want several properties that are hard to combine:

- good linear absorption of light (i.e. being black/gray across a wide wavelength rate)
- good thermal conductivity (so a small spot doesn't make a burn as it would on say plastic)
- low thermal mass (to prevent slowing down the readings)

These things are very hard to combine in ordinary materials really. There are various materials that are good at 2 out of the 3 criteria, but looking at all 3 it will always be a compromise.

 

[lasersbee]

Again... For example...

The diameter of a Lasers beam is crucial...

Our LaserBee AX3 Thermolpile Sensor Coating
refered to in the 1st Post has a non destructive
broadband coating that can handle 5.2 watts
at a beam diameter of ~3mm.
That is ~173 W/cm2 or if you increase the beam
diameter for example to the full 15mm diameter
available on the 15mm X 15mm Active area of that
coated sensor you could in effect apply 265 W of
Laser Power without damage of the coating.

The problem is that users of Laser Power Meters
are not all experts in their use. So we state a
Minimum acceptable Laser Beam Size and a
Maximum Power in the User Instructions to make
sure our coatings are not abused or damaged.


Jerry