flashcards_lasers_wave_optics
What is the coherence time of the Sun, LEDs, and pulsed lasers?
Sun: Very short coherence time (~10-14 seconds) due to random photon emission over a broad spectrum. LEDs: Short coherence time (~10-12 to 10-9 seconds) due to broad spectral width. Pulsed Lasers: Longer coherence times, on the order of nanoseconds to microseconds depending on pulse duration and spectral width.
How is light produced in a laser?
Light in a laser is produced via stimulated emission, where an excited atom or molecule releases a photon that stimulates other particles to release photons of the same energy, phase, and direction.
How does light from a normal lamp differ from laser light?
Light from a normal lamp is incoherent, emitted in all directions, and has a broad spectrum. Laser light is coherent, monochromatic, and highly directional.
What is the steady state in a laser?
The steady state in a laser occurs when the rate of photon production through stimulated emission balances the losses, resulting in a constant output power.
What are the microscopic and macroscopic Maxwell equations?
Microscopic Maxwell Equations: Describe electromagnetic fields at the microscopic level considering individual particles. Macroscopic Maxwell Equations: Include material properties like permittivity and permeability, averaging the microscopic fields over a volume.
How is the Helmholtz equation derived from Maxwell’s equations?
By assuming time-harmonic fields (e.g., E(r, t) = E(r) e<sup>iωt</sup>) and substituting into Maxwell’s equations, the wave equation reduces to the Helmholtz equation: ∇<sup>2</sup> E + k<sup>2</sup> E = 0, where k is the wave number.
Explain Ray optics, Wave optics, Electromagnetic optics, and Quantum optics.
Ray Optics: Light as rays, applicable in geometrical optics (e.g., lenses). Wave Optics: Light as waves, explaining diffraction and interference. Electromagnetic Optics: Light as electromagnetic waves using Maxwell’s equations. Quantum Optics: Light as quantised photons, explaining absorption and emission in quantum mechanics.
What are the assumptions made to solve macroscopic Maxwell equations?
Assumptions include linearity, homogeneity, isotropy, and neglecting quantum effects. Constitutive relations depend on material properties, such as D = εE.
What are the rate equations in lasers?
Rate equations describe population dynamics in a laser’s energy levels, accounting for the pumping rate, spontaneous and stimulated emission rates, and loss mechanisms.
What is mode selection in a laser and active medium?
Mode selection determines which spatial or longitudinal modes of the electromagnetic field dominate in the laser cavity, influenced by the gain medium and resonator design.
What are the finesse and quality factor of a resonator?
Finesse: The ability to resolve different frequencies, defined as the ratio of free spectral range to linewidth. Quality Factor (Q): Indicates the sharpness of resonance and energy storage efficiency.
What elements are required to create a laser?
Key elements include a gain medium, a pump source, and an optical cavity with at least two mirrors.
What are the stability conditions of a resonator?
Stability conditions ensure light remains confined within the resonator, typically defined by the geometry of the mirrors and the Rayleigh range of the beam.
What is the expression for the longitudinal modes in a resonator with 3 mirrors?
The longitudinal modes are determined by the round-trip phase condition: mλ = 2L, where L is the effective optical path length of the cavity.
What are pulsed lasers, and what are their advantages?
Pulsed lasers can be created via Q-switching, mode-locking, or cavity dumping. Advantages include high-intensity applications such as precision cutting, medical surgery, and spectroscopy.
