On a scanner you sometimes need to be able to move the mirrors without a laser line being drawn. TTL blanking will turn the laser off.
An example, if you project a word in capital letters the blanking can be used to make sure that the letters are not joined together by a line, that part is blanked.
TTL modulation I think means to adjust the intensity of the beam rather than fully blanking it. On RGB laser projectors that would allow you to have a wider colour pallete.
"TTL" means Transistor-Transistor Logic. The term is a hold-over from the old days meaning a 0-5 volt discrete on-off signal. IE: TTL modulation means 0V = off, 5V = on (or vice-versa).
"Analog modulation" would mean a varying input signal would vary the intensity of the laser.