I got it from one of these guys. Check out the 'Laser Pro Shop' section of this forums, there should be 3 makes, namely Kenometer, nospin, and Radiant.
Kenometer is using real thermopile with measurement range up to 5Watts. Running on batteries, charger included. It has data logging features and it makes it portable. Price range is higher.
nospin is using real thermopile too like above. But running on AC adapter. There is an option for an external battery pack for portability but with an extra price. No graph or data logging features. Lower price than the above.
I don't own a Radiant but I read it's using sensors with TEC instead of real thermopile. Very affordable price, but rather high in demand, so you got to wait.