www.LaserFreak.net

Hi,

400nm is UV-A radiation and can go through the epidermis (upper skin layer) to the dermis.
There it can cause short lasting changes of the skin colour, like tan.
Much more dangerous is the fact, that UV-A may cause skin cancer by indirect DNA damage .
But I think, with a Class 4 laser the risk ...

Hi:

Is it physically-possible to design and build a 400 nm laser that is
directly-"pumped" by aneutronic nuclear fusion and in which the active
lasing medium/gain-medium is a rare-earth crystal?

The "pump" is the part of the laser that excites the atoms in the laser
medium.

Hydrogen-Boron fusion ...

Hi:

What hazards -- other than thermal burns -- does a 400-nanometer-wavelength continuous [i.e. non-pulsed] laser of Class 4 intensity pose to human skin?

As far as I know, 400 nm is the longest wavelength classified as "black light".

Class 4 laser: http://en.wikipedia.org/wiki/Laser_safety ...