L21 90% not exam relevant (non-linear optics)

Question 1

Nanowire laser components

Answer 1

Main components of a nanowire laser:

• Gain medium (nanowire)
• Resonator (end facets of the nanowires as mirrors)
• Pump (electrical current between Si and Ti/Au electrode).

Question 2

Lasing threshold

Answer 2

At the lasing threshold, the gain exceeds losses, and photons stimulate the emission of other photons with the same wavelength.

Question 3

Nonlinear optics definition

Answer 3

Nonlinear optics: phenomena where the optical properties of materials change with light irradiation. Requires high optical intensities.

Question 4

Two-photon absorption

Answer 4

Two-photon absorption: simultaneously absorbing 2 photons, a process predicted by Maria Goeppert-Mayer in 1931.

Question 5

1960 First Laser

Answer 5

First laser by Theodore Maiman in 1960 using a flash lamp on a ruby rod.

Question 6

Second-harmonic generation

Answer 6

First second-harmonic generation measurement in 1961 by Franken et al., using a ruby maser through crystalline quartz.

Question 7

Nonlinear optics applications

Answer 7

Applications include generating new colours and laser eye surgery. High power consumption and low conversion efficiency are challenges.

Question 8

Quadratic χ(2) materials

Answer 8

For quadratic χ(2) materials: Induced Polarization P = ε₀χ(1)E + ε₀χ(2)E².

Question 9

Second harmonic generation

Answer 9

Second harmonic generation involves doubling the frequency (ω) to 2ω, requiring a non-zero χ(2).

Question 10

Third harmonic generation

Answer 10

Third harmonic generation involves tripling the frequency (ω) to 3ω, using χ(3).

Question 11

Non-Centrosymmetric materials

Answer 11

Examples of Non-Centrosymmetric materials: Gallium arsenide (GaAs), Barium titanate (BaTiO₃), Lithium niobate (LiNbO₃).