The video you posted shows a polycrystaline mass being produced, you want a monocrystal. Typically these are obtained by seeding a saturated or supersaturated solution under controlled temperature and pressure. The seed crystal, at a lower temperature than the suolution, is brought into contact with the surface of the solution and withdrawn at the growth rate of the crystal. A super saturated solution will provide faster growth, convection and controlled heating of the solution provide for continuous growth of the crystal. Calcium fluoride optical blanks are available from Corning Glass. If you really want to grow your own there are many ways to go about it, my suggestions are only that. You would need to do a fair amount of trial and error to find a method that works for you. FWIW calcium flouride crystals are usually either grown from molten calcium flouride at about 630F or produced by fusion forgeing something you probably won't be able to DIY.