Can you use a 555 to modulate a laser
The actual laser element in a typical "keyring laser" or toy laser is a laser diode, and for most purposes behaves pretty much like a conventional LED, with some minor differences:


The laser diode is a bit more sensitive to over-current than the cheap indicator LEDs, hence needs a constant current driver of some sort: Even a current limiting resistor works for most low power laser diodes.
Some laser diodes have a sensing element, to allow the support circuitry to determine how much actual LASER intensity is being produced, and regulate the driving current accordingly. The cheap toy lasers I've seen don't seem to have this, so that's a good thing for you.


However, toy lasers typically have a constant current driver in them, one that would also contain a capacitor to buffer supply dips. If this is so, and depending on how much capacitance there is, the device will be limited in the pulse rate you can achieve in driving it from a timer circuit. 

For low pulse rates, inexpensive laser modules such as this one can be driven directly off a 555 timer's output, keeping in mind the drive voltage, of course. I'm able to achieve about 180 pulses per second (40 Hz) with one such module I have. Beyond that, the laser doesn't turn on at all.

Slightly more expensive laser modules are sold, which have a separate TTL control input, independent of the supply line. Notice the third wire in the photo below:



These can be pulsed to much higher frequencies, by wiring the TTL control pin from the timer circuit's output. This example accepts modulation up to 20 KHz on the yellow wire.