If I have a picosecond laser how would that be expressed in terms of zeptoseconds? In terms of petaseconds?

Picosecond = 10 ^ - 12 seconds.

Zeptosecond = 10^ - 18 seconsds

Petaseonds = 10^15 seconds

To express Picoseconds into any of other two, you have to divide 10^-12 by the power index of the one in question

1Picosecond : 10^-12 / 10^-18 = 10^ (-12 - 18) = 10^ (-12+18) = 10^6 zeptoseconds

1Picosecond : 10^-12 / 10^15 = 10^ (-12-15) = 10^-27 Petaseconds.

1Picosecond = 10^6 zeptoseconds

1Picosecond = 10^-27 Petaseconds