能量密度

Or the universe might even recollapse if dark energy density falls to a negative value.

当然宇宙也有可能因为暗能量密度降为负值，而再度塌。

Satellite retroreflector is used as laser ranging cooperative target to improve the intensity of reflected beam, which has close relationship with processing parameters of the retroreflector.

角反射器作为激光测距系统中的合作目标, 其主要作在于提高地面接收机范围内反射光束的能量密度。