Chinese DPSS - Migration from 2 TEC to one TEC - Why?

[dave]

I think I pretty much summed it up in the title.

Whilst not so long ago it was typical to see a diode tec and a tec on the crystals, but now I am only seeing one TEC in a lot of products.

Whats the reason here? Just to save a buck? Or are today's diodes less likely to shift wavelength with temp?

[kl79]

Don't know exactly why, but you are true..I think with only one tec, they are able to mount all crystals and diode on a solid base plate, as is, there is no movement of the parts, the quality and the power is more stable ?

Oh and for sure, it's less expensive !

[sbk]

Viasho always had only one TEC as far as I know. Furthermore it can only cools. And you really notice it as a bad thing, as the output takes a long time before reaching its max power after being on standby.
That's not an accident if there is *3* separate TEC for an OPSL head

[planters]

The YAG type of laser needs tight 808nm diode wavelength control and that is accomplished by temperature tuning the diode's wavelength to compensate the manufacturer's variations. The vanadate type of DPSS has a fairly broad pump wavelength absorption band and so here the diode only needs good heat sinking to prevent overheating, but fixed, active control is not necessary. Thermal control of the KTP is necessary to tune for maximum conversions irrespective of the gain medium and so I assume the TECs are driven to "control " the KTP and the crystal rides along and benefits from the extra heat removal.

[polishedball]

Viasho always had only one TEC as far as I know. Furthermore it can only cools. And you really notice it as a bad thing, as the output takes a long time before reaching its max power after being on standby.
That's not an accident if there is *3* separate TEC for an OPSL head

Yep it is a real bummer trying to use my green in ambient temps in the 50's.

[mixedgas]

Yep it is a real bummer trying to use my green in ambient temps in the 50's.

If it was for the reason it was supposed to be, ie pump diodes with internal Bragg gratings, newer materia;s with broader pump adsorption, life would be good.
But Alas, I suspect not...

Steve

[planters]

If it was for the reason it was supposed to be, ie pump diodes with internal Bragg gratings, newer materia;s with broader pump adsorption, life would be good.
But Alas, I suspect not...

No. I disagree. I think the vanadate solves this. With its broader absorption width in moderate power DPSS lasers where higher A.% doping will not lead to Fx I think life is pretty good.

And ambient temps in the 50's are lethal at least to humans. If these temps are just within the enclosure then some fans should help here.

[buffo]

And ambient temps in the 50's are lethal at least to humans.

I thought he (polishedball) was referring to his green failing when running at around 50 degrees F, not C. Which in that case meant that the KTP got cold, and doubling efficiency dropped way off.

It wouldn't make sense if it failed at 50 C, because as you've already pointed out, Vanadate has a wide absorption band so the temp of the pump diode (and thus the output wavelenth) is not nearly as critical, and the KTP actually prefers to be warm vs cool.

For what it's worth, I have the exact same thermal problem when running my Lasever blue (473) outside in cold weather. The BBO doubling crystal gets cold, and the output falls to less than 10% of spec. I actually had to install a switch to kill the case fans to solve the problem. With the fans off, the heat from the scanner amps is just enough to warm the inside of the projector housing so that the blue runs normal.

Adam

[planters]

F and not C that makes sense. But, the KTP does not actually like to run warm. Rather, It needs to run at the general temperature for which it was cut. In these low power lasers that means approx RT. However, once it is installed and adjusted in tip, tilt and rotation then it needs to be held closely to the temperature at which the adjustments were made. This is why the temperature is stabilized and if the controller is not bi-phasic then running warm (and adjusting warm) avoids the problem of cooling. At 50F the TEC probably just can't keep up.

[Things]

I suspect as you said it was a cost cutting measure, as it means 2 less cables they have to run, 1 less thermistor, less driver circuitry and less complexity in alignment. I guess they figured the diode required temp tuning more than the crystals - suppose it makes sense in that it'd prolong the diodes lifetime a bit more too.