Optics Flashcards
(33 cards)
Fermats principle of least time
The optical path length of the ray between two points is stationary with respect to small changes of the path
Light travels in _ in uniform medium
Straight lines
Law of relfection
The reflected ray lies in the plane of incidence, with the angle of reflection equal to the angle of incidence
Law of refraction
The refracted ray lies in the plane of incidence, with the angle of refraction related to the angle incidence by Snells law.
Positive R means
C is to the right of the lens
Negative R means
Its to the left
Positive lenses
Thicker in the middle than the edges. f is positive. (Bulge out more than they cave in). Always tries to make rays converge more than they did to start with
Real images form
After the lens
Virtual images form
Before the lens
Negative lenses
Thinner in the middle than the edges, they ‘cave in’ more than they ‘bulge out’ . Makes rays diverge more than they did to start with
Chromatic abberation
Focal length depends on refractive index, which depends on wavelength, so different colours get focused at different points, leading to fringing
Spherical aberration
Spherical lenses deviate from the “thin and paraxial” approximation. Light further from axis is focused closer to the lens than light closer to the axis, so light is not focused at a single point
Chromatic aberration mitigation
Use curved mirrors instead of lenses
Spherical aberration mitigation
‘Aspheric’ lenses
Superposition Principle
The disturbance, at any point in a linear medium is the algebraic sum of the separate constituent waves
Coherence
Two waves are coherent if they have:
-a well defined (relatively stable) relative phase
- have the same frequency, and
-split off from the same source
-delay between waves must be small compared to coherence time
Interferometers
An experiment of device that makes use of interference. Light from a single source is split into two or more waves that are made to interfere.
Types of interferometer
Wavefront-division interferometer
Amplitude division interferometer
Types of Amplitude division interferometers
Michelson, Mach-Zehnder, Sagnac
Fabry perot interferometer
A precisely parallel pair of such mirrors, with a cavity of width d between
Finesse measures
The interferometer’s performance as a spectrometer
Full width half maximum (FWHM)
The width between where the transmission is half its maximum value
Free spectral range. (FSR )
Separation between fringes
Huygens Fresnel Principle
Every point on a wavefront serves as a source of secondary wavelets. The disturbance at a point beyond is the superposition of all these wavelets
