The 2 oscillator circuits below are appropriate for using crystal oscillators in sequence or parallel mode: Significant-repetition-rate and large-ability picosecond regenerative amplifier according to one bulk Nd:GdVO4 crystal A timing reference incorporating a single-crystal-silicon micromechanical resonator with a high quality issue of larger sized than one million as well as https://www.hxcrystals.com/seokeywords/bulk-crystal-oscillator.html