do you mean pulsed wave?

Dear Zhuxiao Gu , may be I´m completely wrong, but are you asking for a paused or pulsed laser source?

In the case of pulsed laser souces, I think the following information from Ansys-Lumerical knowledge base could be useful:

https://support.lumerical.com/hc/en-us/articles/360034383094

If you want create the pulsed source from scratch, something less common you can follow this explanation:

https://support.lumerical.com/hc/en-us/articles/360034383114-Creating-a-custom-source-time-signal-for-an-FDTD-source

Hope it helps.

By default, all sources in Lumerical emit a short pulse, since autoshutoff would never trigger otherwise and your simulations would take very long. What are you trying to do that doesn't work well this way?