This a simple circuit that allow the use of a standard laser dot as a Flash pointer.
The proposed circuit will turn off the laser dot when the circuit detects the flash light. A couple of photo-diodes BPW34 in reversed polarization detect the flash light.
The cathode of the series must be connected to the 1st pin of connector P1.
The driven laser led anode must be connected to the 1st pin of connector P4.
There are no protection resistors for the transistor in the circuit, because they are always included in the laser’s circuitry.
The same 4.5V battery of the laser dot could power the whole circuit. If the laser’s light intensity is too low (high voltage drop across the transistor) the voltage supply could be increased to 6V adding another button cell.
Remember to buy the chip (74HC123N) with the SMT container if you would like to use the supplied PCB layout (1:1 in the picture below), the PCB layout and schematic file are downloadable here in CIRCAD98 format This circuit is able to count the pre-flash from a digital camera and trigger a slave-flash only after a pre-set up number of pre-flashes.

Following the link it is possible to download the PCB and the schematic in CIRCAD98 format.

Disclaimer:
The circuit is : As Is.
Who decide to mount, test or modify it, will do at “own risk”. I will not be responsible about any kind of eventual damage derivate by the use of this circuit or any other present on this website.

Download here the sch/PCB in bitmap format