Maximum voltage in series circuit
You have given no clue, part number or datasheet link.

If the laser module regulates the current in an analog fashion internally then the one with the lower current requirement will have a higher "resistance" and more than half the voltage will be dropped across it.

If the laser module regulates the current using some sort of PWM then the current waveform will follow the PWM and alternate between low and high. Since both are in series and not synchronised they will choke off current to each other when the PWM is off.


  Does this damage the modules or is the voltage shared evenly between the modules?


The voltage is unlikely to be shared equally. Damage is likely.