A diagram has two vertical lines (left = ket, right = bra). Time goes up. Arrows point toward the molecule (absorption) or away from it (emission).
If your signal is weak, use a boxcar geometry (beams at three corners of a square). The signal goes out the fourth corner. No fancy optics required.
In linear spectroscopy (absorption), you poke once, the polarization wiggles, and you measure the wiggle decay. Boring. A diagram has two vertical lines (left = ket, right = bra)
That new light is your signal .
Confusing ( T_1 ) (population lifetime) and ( T_2 ) (dephasing time). Fix: ( T_2 ) = ( 1/( \textlinewidth ) ). ( T_1 ) = how long excited state lives. Always ( T_2 \le 2T_1 ). If your ( T_2 ) is shorter than ( 2T_1 ), you have pure dephasing. If your signal is weak, use a boxcar
When you poke with three beams (wavevectors ( k_1, k_2, k_3 )), the polarization emits light in specific directions. The most famous is the :
Ignoring the rotating wave approximation (RWA). Fix: The RWA means you drop terms that oscillate at optical frequencies (they average to zero). Without RWA, you will cry. With RWA, you get simple exponentials. In linear spectroscopy (absorption), you poke once, the
But here is the dirty secret of experimentalists: