The 2 oscillator circuits below are appropriate for using crystal oscillators in sequence or parallel mode: Substantial-repetition-rate and large-electric power picosecond regenerative amplifier according to an individual bulk Nd:GdVO4 crystal A timing reference incorporating only one-crystal-silicon micromechanical resonator with a quality element of much larger than one million as well https://socialbuzzfeed.com/story4427875/bulk-crystal-oscillator-an-overview