flashcards_second_half_lasers_wave_optics
How does a planar and dielectric waveguide work?
A planar waveguide confines light in one dimension, while a dielectric waveguide uses total internal reflection to guide light in two or three dimensions within a dielectric medium.
What is a waveguide and what are the types of waveguides?
A waveguide is a structure that guides electromagnetic waves. Types include optical fibre waveguides, planar waveguides, and metallic waveguides used in microwave systems.
What are dispersive waveguides?
In dispersive waveguides, the phase velocity of light depends on the frequency, leading to dispersion effects that affect signal propagation, particularly in optical fibres.
What are evanescent waves and their applications?
Evanescent waves are non-propagating fields that decay exponentially outside the waveguide. Applications include near-field microscopy and coupling light between waveguides.
What is the diffraction pattern of a square aperture in near and far field?
In the near field (Fresnel diffraction), the pattern is complex and changes with distance. In the far field (Fraunhofer diffraction), the pattern forms a series of bright spots corresponding to the square’s geometry.
How is diffraction used to measure the size of small particles?
The diffraction pattern of light passing around a small particle can be used to determine its size by analysing the angular spread and intensity distribution of the diffraction rings.
What is the intensity profile of a wave propagating in a waveguide?
The intensity profile of light in a waveguide typically shows a confined mode structure, with the highest intensity at the centre and decaying towards the edges.
What is the intensity profile of aligned point sources and the effects of spreading them out?
Aligned point sources produce an interference pattern. Spreading them out increases the distance between interference fringes and can reduce contrast.
What are Fraunhofer and Fresnel approximations?
The Fraunhofer approximation applies to far-field diffraction, where the wavefronts are approximately planar. The Fresnel approximation applies to near-field diffraction, where the curvature of the wavefront must be considered.
What are Jones vectors and the Poincaré sphere?
Jones vectors represent the polarisation state of light using complex amplitudes for horizontal and vertical components. The Poincaré sphere visualises polarisation states, with points corresponding to different polarisations (linear, circular, elliptical).
What is birefringence and its applications?
Birefringence occurs when a material has different refractive indices along different axes, causing polarised light to split into two rays. Applications include wave plates and polarisation controllers.
How are wave retarders made?
Wave retarders are made by introducing birefringent materials with a specific thickness, causing a phase shift between orthogonal polarisation components of light.
What are the different methods of linear polarisation?
Linear polarisation can be achieved using wave retarders (e.g., half-wave plates), magneto-optic effects (Faraday rotation), or optically active materials (rotating the polarisation plane).
What are metamaterials and their applications?
Metamaterials are artificially structured materials that exhibit unique electromagnetic properties not found in nature, such as negative refractive index. Applications include superlenses and cloaking devices.
What photon processes occur in a 2-level system?
In a two-level system, photons can be absorbed, causing an electron to jump to a higher energy level, or emitted through spontaneous or stimulated emission when the electron returns to a lower energy state.
