  We report the first demonstration to our knowledge of a continuously tunable
picosecond laser operating around 1 MHz. The emission can be tuned from 640 to
685 nm and the repetition rate from 200 kHz to 1 MHz with a pulse duration of
less than 200 ps. The system is based on a Nd:YVO4 passively Q-switched
microchip laser providing a few tens of nJ per pulse. Two cascaded stages of
amplification are then used to increase the pulse energy to several microJ .
The frequency doubled radiation is then used to pump a
periodically-poled-niobate-lithium (PPLN)-based optical parametric generator in
an all-solid-state architecture. 20 nJ of tunable signal radiation are
obtained. We also demonstrated 300-ps pulses generation in the UV (355 nm) at 1
MHz.
