Ursula Keller invented a type of these objects that adds a layer of saturable absorber on top of alternating layers of materials with different indices of refraction. For 10 points each:
[10e] Interferometers often use the “half-silvered” type of what objects as beam splitters? In Cassegrain and Newtonian telescopes, these objects have a parabola shape.
ANSWER: mirrors [accept reflectors or distributed Bragg reflectors or (semiconductor) saturable absorber mirrors; prompt on SESAMs or SAMs by asking “what does that stand for?”]
[10m] Passive mode locking replaces one of the mirrors in these devices with a saturable absorber mirror. These devices can use a ring-like arrangement of mirrors to avoid creating standing waves.
ANSWER: optical resonators [or optical cavities or resonating cavity or cavity resonator; prompt on lasers]
[10h] On the other hand, active mode locking uses one of these devices to periodically vary the intracavity loss. These devices usually operate by either an electro-optic or an acousto-optic physical mechanism.
ANSWER: modulators
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