An injection seeded single frequency Nd:YAG Q-switched laser with precisely controllable laser pulse firing time

Abstract

We have realized a single frequency Q-switched Nd:YAG laser with precisely controllable lasing time and thus enabled synchronization of multi-laser systems. The use of injection seeding to the slave ring oscillator results in unidirectional Q-switched laser oscillation with suppression of bidirectional Q-switched oscillation that otherwise would be initiated from spontaneous emission if the seeding laser is not present. Under normal condition, the cavity is high in loss during the pumping period; then a Pockels cell opens the cavity to form the pulse build up, with a second Pockels cell to perform cavity dumping, generating the Q-switched pulse output with optimized characteristics. The two Pockels cells can be replaced by a single unit if an adjustable gated electrical pulse is applied to the Pockels cell in which the pulse front is used to open the cavity and the falling edge to dump the laser pulse. Proper selection of the pump parameters and Pockels-cell gating enables operation of the system in a mode in which the Q-switched pulse can be formed only under the seeding condition. The advantage of the realized regime is in stable laser operation with no need in adjustment of the seeded light wavelength and the mode of the cavity. It is found that the frequency of the Q-switched laser radiation matches well to the injected seeded laser mode. By using two-stage amplifiers, an output energy better than 300 mJ has been achieved in MOPA configuration without active control of the cavity length and with pulse width adjustability from several nanoseconds to 20 ns. The Q-switched oscillator operates not only at precisely controlled firing time but also can be tuned over wide range. This will enable multi-laser systems synchronization and frequency locking down each other if necessary.