Is there a theoretical reason that a sufficiently-gigantic ultrafast pulse laser with a sufficiently-massive lens couldn't put enough photons at the focal point?
Which is about 3e34 joules, or the total energy output of our sun over 2.5 years.
The longer the wavelength, the more energy you need.
You have to also make sure they're timed precisely enough to all be within the (target) horizon at the same time.
IIRC there's also a quantum mechanical limit on energy density distributions (I have a lower confidence feeling that this is Heisenburg uncertainty?), but I don't know enough about it to get Wolfram Alpha to calculate it for me.
Interesting! I didn't have a good intuition for how rapidly the density of a black hole grows as its event horizon shrinks. Now I do! Clearly nano-black-holes are much, much heavier than I thought.
If your photons are 1 nm wavelength, you're making a black hole of at least 3.37e17 kg:
http://www.wolframalpha.com/input/?i=0.5nm%20%2A%20c%5E2%20%...
Which is about 3e34 joules, or the total energy output of our sun over 2.5 years.
The longer the wavelength, the more energy you need.
You have to also make sure they're timed precisely enough to all be within the (target) horizon at the same time.
IIRC there's also a quantum mechanical limit on energy density distributions (I have a lower confidence feeling that this is Heisenburg uncertainty?), but I don't know enough about it to get Wolfram Alpha to calculate it for me.