I am trying to build a laser security system and would want to add a 555 timer in my transmitter. I have had several long attempts on fixing this but I have to a conclusion that I am not capable of adding a 555 timer in the circuit. Will you guys please help me out or advise me what to do?

Thanks in advance.

I also have added an image of my circuit. Please take a look at it.

 

What do you want the 555 to do? Modulate the laser? Provide a timed output upon alarm trigger? Many details missing from your question need to be provided before any help can come your way.
There are many, many 555 circuits scattered throughout this forum. Have you done a search to see if any of them meet your needs?