need help on lasers hw please

3.18. Is the cavity shown below stable? Demonstrate the logic of your answer by (a) con- structing a unit cell starting at the flat mirror, (b) finding the ABCD matrix for that cell, and (c) applying the stability criteria. (d) What are the circumstances under which the quantity [AD - RC] can be different from 1? Why is AD - BC always equal to 1 for a cavity? R1 = DO d = 100 cm R = 100 cm d = 100 cm R = 50 cm