Take a1% Nd:YAG rod of 6cm length & 6mm Diameter and by side pumping exposed length by Laser diode is 4cm . Does the unexposed area also participate in gain, extraction energy etc . How does it involve in lasing?
I believe by and large the lasing will be confined to the irradiated region. Depending on teh beam divergence of the diode laser there may be some lasing action just outside the main irradiated region of the Nd:YAG crystal
We have to pay attention that Nd:YAG is 4 -level laser system. In opposite 3-level dye or ruby system no absorption laser emission takes place on the case. In the same way no gain exist without pumping pumping of this part of laser element. But output energy from laser decreases because last one is proportional of pumped volume. Similar conclusion results from the main oscillation condition: gain should be equal or more than losses.
My best regards!
You should look at thermal effect too like thermal lensing what would change your mode size. I remember lamp pumped lasers with un-dopted-end rods.
Unexposed portion of laser rod will not provide any lasing action. However it may produce some absorption. Finally the laser output may be same or less than the expected intensity.
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