This extension set comes with a Nd:YAG rod coated for the operation at 1330 nm, the mounted KTP crystal and a KG5 filter. The KTP crystal is cut for optimum conversion efficiency from 1330 nm to 665 nm. The crystal is mounted in a disk which is inserted into a „click“ - holder which itself is clicked into a kinematic adjustment holder which is adjustable in the X and Y direction and in two orthogonal angles. Furthermore the crystal can be rotated around its central axis to fulfil the phase-matching condition for optimum conversion efficiency. The KG5 filter block the pump as well as Nd:YAG radiation of 808 nm and 1064 nm respectively. It is used to measure only the "red" power to demonstrate its quadratic dependence on the power of the fundamental radiation at 1064 nm. The power of the fundamental radiation is controlled by the injection current of the pump laser diode.
Energy level diagram of diode pumped Nd:YAG laser
The "red" KTP crystal is located inside the cavity formed by the mirror M1 and M2, close to the smallest beam waist (diameter) of the fundamental wave. The Nd:YAG rod (M1) as well as the mirror M2 are coated for the operation at 1330 nm. The pump radiation at 808 nm is focused by the lens L1 into the Nd:YAG rod. In addition the mirror M1 of the Nd:YAG rod has also a high reflectivity at 665 nm, thus the red radiation will leave only via the MIrror M2 the Nd:YAG laser cavity.