Laser diode efficiency

[Marco]

Calorimeters are finnicky, ask the cold fusion guys. Measuring the temperature rise for an absorber with a known Rtha seems easier to me than building an isolated box with a window for the laser light.

[npelov]

I measured my 2.5W laser and it draws about 15W. So this might just be a 5W laser.

To mark steel you need higher energy light. I think (correct me if I'm wrong) they use blue or UV for cutting steel.

Even with 5W blue laser you can mark stainless steel (does not work on non-stainless, aluminium or brass):

[Kleinstein]

For coarse steal cutting they normally use CO2 lasers (10.x µm) - not because of the wavelength, but because they are relatively cheap at high power (several kW). For fine parts (e.g. < 0.1 mm) or marking it is more about blue or maybe pulsed NIR (1064 nm) from laser diodes or solid state lasers - they have less power, but are easier to focus to a very small area and thus get a comparable power-density.

[LaserSteve]

Home made laser power meters are typically made with a modest size Peltier Thermoelectric cooler ran in reverse as a calorimeter.  Graciously heat sink one side, and either glue on a thin piece of black anodized aluminum or paint with a high carbon, high temperature flat black engine paint (Krylon high temp grill paint or engine paint is 98% carbon black in the US) .  If you can machine graphite, a thin graphite panel works well, but is highly reflective if your not careful with the surface finish. "Black Velvet" paint from Nextel / 3M is the old, preferred, improvised coating, but it costs a fortune.

 I've had good luck when I was a college kid with  fine carbon black and clear nail polish or potassium silicate solution (floor sealer, hardware store) as the binder. These days I use a carbon nanotube mix for blackening sensors.  However these days I also have a considerable collection of professional LPMs that outperform the home made gear.

Run it into a variable gain op-amp, with a gain from 10-100 or so and read it with a volt meter.

Real thermopile power meters use a custom absorber material, and an array of specially designed ultra thin  Peltier elements.

Home calibration is done with a thin, flat coil of resistance wire of known characteristics (usually around 30-40  ohms) and a bench power supply.  No where near as accurate as a commercial model, but should get you +/- 5% across the visible range  if your  black surface  has a flat adsorption spectrum.

Be aware, that the quality difference between a home made one and a commercial unit is considerable.  The commercial unit will compensate for a lot of technical  factors, have an anticipator circuit to speed the reading. It will be able to take much, much more beam energy.

  Even on commercial units, we spread the beam out across the sensor with a lens some times to avoid surface damage.

As I often tell laser hobbyists, nothing comes close  to a commercial laser power meter when doing comparison measurements or when tuning the laser.

 PS< Most of the  older Coherent OEM  LPM heads on Ebay output .40 mV per Watt. 

Steve