laser

Laser is light rays that are coherent and monochromatic (i.e. of a single frequency). As such, the energy of a laser beam can be concentrated to a small cross-sectional area.

laser系monochromatic(成個light source同1個frequency,得1隻色)
laser比普通light ray強好多

2010-06-23 17:56:31 補充：
laser 同 light ray其實系同1種光

Light is coherent and has the same frequency in laser but not in common light beam.

For example, one could shine a laser beam through a double slits comparable to the wavelength to get an interference pattern on a screen behind the slits. This would not be the case if one uses a common light source even with a fixed frequency.