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  Two-level
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Linear Absorption & Beer-Lambert Law
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Weak probe pulses and continuous-wave fields in a two-level absorber.
Demonstrates Beer-Lambert attenuation, the role of spontaneous decay, and
how increasing optical depth reshapes the transmitted pulse.

.. toctree::
   :maxdepth: 1

   mbs-linear-absorption

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Self-Induced Transparency & Optical Solitons
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Strong resonant pulses whose area exceeds π can form area-conserving solitons
via self-induced transparency (McCall–Hahn). 2π solitons propagate without
loss; larger areas break up into multiple solitons. Odd-π inputs are unstable
fixed points of the area theorem.

.. toctree::
   :maxdepth: 1

   mbs-sit-area-theorem

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Photon Echo & Coherence Time ($T_2$) Measurement
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A π/2 pulse followed by a π pulse creates a photon echo at $t = +\tau$ in an
inhomogeneously broadened (Doppler-broadened) medium. The echo amplitude decays
as $e^{-2\tau/T_2}$, allowing the **homogeneous** coherence time $T_2$ to be
measured even when the lineshape is dominated by inhomogeneous broadening.

.. toctree::
   :maxdepth: 1

   mbs-two-photon-echo