Hi Matthijs,
You are right - cooling is not a big problem on the 658nm diodes.
As long as the mount has a reasonably low thermal resistance to chassis (and is electrically isolated).
The diodes are usually rated for 70degrees C operation. You can tell they must be designed to run hot by the small size of the original heatsink in DVD writers.
From the couple of data sheets I have seen which include wavelength vs temperature for 658nm diodes the tempco was 0.15 to 0.17 nm/DegC. (808s are usually circa. 0.27nm/DegC.) So cooling a 658 by 20C only gains you a 3nm shift.
Anyone out there measured shift on the Mitsubishis?
Yes - A 2W TEC would let you shift one Watt over a 30C gradient (or 800mW over a 40C gradient) The 2W rating of a 2W TEC is pumping power over a zero gradient.
You do not really need a TEC for a dual diode set up but for more diodes you do get the secondary benefit of thermal stability of your mechanics if you TEC everything.
Good luck with the dual.
Best regards,
Robin
Lasers and beer don't mix. After 2 beers I lose coherence.