Ultrafast optical evidence of coexisting density waves in bilayer nickelate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>La</mml:mi> <mml:mn>3</mml:mn> </mml:msub> <mml:msub> <mml:mi>Ni</mml:mi> <mml:mn>2</m

Utilizing ultrafast optical pump-probe spectroscopy, we investigate the coexistence and competition of electronic orders in the bilayer nickelate ${\mathrm{La}}_{3}{\mathrm{Ni}}_{2}{\mathrm{O}}_{7}$. Our results reveal two coexisting density waves that can be selectively manipulated with light. We directly identify a spin-density wave (SDW) with electronic nematicity emerging below ${T}_{\mathrm{SDW}}$ $\ensuremath{\approx}140$ K by measuring its spin dynamics, and discover a distinct, nonmagnetic charge order appearing below ${T}_{\mathrm{DW}}$ $\ensuremath{\approx}115$ K. The central finding is the demonstration of differential optical control: the charge order is fragile, completely suppressed by a pump fluence of approximately 40 $\textmu{}\mathrm{J}/{\mathrm{cm}}^{2}$, while the SDW is remarkably robust, persisting to 200 $\textmu{}\mathrm{J}/{\mathrm{cm}}^{2}$. This work establishes a clear hierarchy in the stability of competing electronic orders and provides a powerful method for disentangling their interplay in quantum materials.