L18 Flashcards
What are the types of line broadening?
- Homogeneous broadening (from individual atoms): Lifetime broadening, Collision broadening.
- Inhomogeneous broadening (from aggregate of atoms).
What is the lifetime of an atomic energy level?
- Each atomic energy level has a lifetime τ
- the inverse of the rate at which its population decays.
What is the probability of photon emission related to?
Related to the time for the decay from state 2.
Describe the lineshape with Lorentzian profile.
The radiated light is a sequence of wavepackets emitted at random times, resulting in random (partially coherent) light whose power spectral density is the Lorentzian function.
What is the significance of the absorption cross-section?
The absorption cross-section is represented by σ and is critical in photon-atom interactions.
how many photons intercepted by atom in time dt
What causes Doppler broadening in gaseous laser systems?
- Occurs due to the different velocities of atoms
- Causing a shift towards lower frequencies if observed from a stationary position.
What are the key points about three-level lasers?
- Require pumping to a high energy state
- Relaxation to a metastable state where lasing occurs
Describe population inversion.
Population inversion occurs when the number density of atoms in the excited state (N2) exceeds that in the ground state, enabling net gain.
What is gain saturation?
Occurs when the gain coefficient decreases as the photon-flux density increases, limiting the amplification.
What is the laser threshold condition?
Laser oscillation occurs if:
- amplifier gain exceeds losses
- total phase shift in a round trip is a multiple of 2π.
What is the function of a Fabry-Pérot resonator in lasers?
- Filters out unwanted frequencies
- Forces photons to travel through the active medium multiple times, enhancing stimulated emission.
Collision broadening
tbd
Lifetime Broadening
tbd
sill missing
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