at theoretical perspective, if the X-Y plane can be addressed with 16-bit DAC by controlling laser deflection. then to seek any data with in a 4GB address space will have typical latency of 300us with the latest laser scanning technology.

I am not aware any laser scanning technology that can do 16-bit accuracy that has no moving part. so, fundamentally, this is a storage technology with mechanical addressing.

laser can be scanned by acoustic wave, but that itself lack the beam pointing accuracy. the ultrasonic drive frequency will limit how fast is can deflects the laser beam.