Crystal oscillators are loosely divided because of the frequency they do the job at and whether or not they are essential oscillators—work in the frequency marked within the can or at even multiples of that (overtone oscillators). Superior-repetition-amount and large-energy picosecond regenerative amplifier based on only one bulk Nd:GdVO4 crystal https://www.hxcrystals.com/seokeywords/bulk-crystal-oscillator.html