Some questions

[Soren]

I have a few questions that I couldn't resolve through searching.

1.) Why is the lasing threshold for 445nm diodes so high? Is it because of resonator losses? If that is so, why can we have low power diodes like PHRs?

2.) How do you get YAG or YVO4 to lase at different wavelengths (for blue and yellow DPSS)? I understand that it has to do with the energy difference between the excited and ground state, but how exactly does one achieve that?

3.) How does resonator length contribute to the output wavelength?

:thinking:

 

[Cyparagon]

1) Yes, it is because of resonator losses. The die is larger than that of a PHR so it takes more energy to excite it. A helicopter takes more fuel than a lawn mower to idle.

2) Changing the coatings to reflect and transmit different wavelengths. If a wavelength is reflected, it goes through the medium again and gains intensity. If a wavelength is transmitted, it is just lost as spontaneous emission.

 

[Soren]

:thanks:
So YAG and YVO4 naturally emit a range of wavelengths when excited?
But why then do exotic DPSS lasers cost so much? If it's just a matter of slapping a few coatings on the gain medium and throwing some LBO in front of it, then why am I paying exorbitant prices for 473 or 589?

Do you have an answer for question 3?

 

[DrSid]

The other colors are much weaker then green. So you need stronger pumping for same output. Also the alignment must be a lot better.

 

[Cyparagon]

LBO isn't cheap; the scale of production for these niche products isn't cheap; the coating process isn't cheap; the beefier pump isn't cheap...

589 isn't doubled either, it's sum frequency generation which involves two lines lasing simultaneously. That can be tricky when the 1064 line tries to hog all the gain.