Optical Knowledge
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Instantaneous Frequency
1/15/2024
Definition:
The differential of the oscillation phase with time divided by 2π.
When describing non-monochromatic signals, instantaneous frequency needs to be used, and its definition is:
That is, the differential of the oscillation phase φ with respect to time. (Removing the factor 1/2π gives you the instantaneous angular frequency.) Unlike the Fourier frequency, the instantaneous frequenc...
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Collimated beams
1/7/2024
Definition:
A laser beam with a small divergence angle.
A collimated beam is a beam (usually a laser beam) that has a small beam divergence angle so that the beam radius does not change significantly after a certain propagation distance. The simplest and most common case is a Gaussian beam, which means that the Rayleigh length is longer than the assumed propagation distance.
A Shack-Hartman...
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Lenses
1/3/2024
Definition:
It is a transparent optical device that affects the wavefront curvature of light.
Figure 1: Focus and defocus of a lens.
Optical lenses contain a transparent medium through which light enters from one side and exits from the other. The function of a lens is to change the wavefront curvature of light, that is, to focus or defocus the light. For example:
A collimated...
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Infrared light
12/25/2023
Definition:
Invisible light with wavelengths between 750nm and 1mm.
The wavelength of infrared light is greater than 700-800nm, which is the upper limit of the wavelength of visible light. The boundary between the two is not very clear, and the responsivity of the eye decreases very slowly in this area. Although the responsivity is already very low at 700nm, it can still be seen at a wavelengt...
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Laser beams
12/17/2023
Definition:
A beam of light traveling in one direction.
In most cases, the light radiated by a laser is a laser beam. That is, the radiation beam propagates in a specific direction, and the optical power is concentrated on a small area of several square millimeters.
The laser beam is very close to the Gaussian beam. The cross-section of the Gaussian beam intensity can be described by the Gaus...
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Optical Spectrum
12/11/2023
The spectrum (or radiation spectrum) of a light source or some light beam contains information about the distribution of energy and power in different wavelengths. It is usually expressed in the form of a graph, giving a curve of the power spectral density versus wavelength or optical power. Figure 1 is an example, showing the numerical simulation spectrum of a supercontinuum light source. The spe...
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Types and applications of waveplates
12/4/2023
The most common waveplates are quarter-waveplates (λ/4 plates) and half-waveplates (λ/2 plates), in which the phase retardation differences in the two linear polarization directions are π/2 and π respectively, and the corresponding phase propagation The distances are λ/4 and λ/2 respectively.
Here are some important conclusions:
If the beam is linearly polarized and the polarization direction ...
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Some basic properties of mirrors
11/28/2023
Mirrors have some basic properties:
Reflectance is the percentage of reflected light power. Usually it is related to wavelength and angle of incidence, but also to polarization direction.
Reflection phase is the phase shift of reflected light, that is, the phase change of light before and after light reflection. Phase shift is related to wavelength and polarization direction. If the phase...
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Dispersion
11/23/2023
Definition:
The effect of light frequency or propagation mode on phase velocity in a medium.
There are many types of dispersion, which all involve the phase velocity or phase delay of light in a medium or device and are related to certain parameters:
Chromatic-dispersion, phase velocity is related to light frequency or wavelength. Possibly from frequency dependence of refractive index, or ...
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Optical density
11/23/2023
Definition:
Abbreviation: OD Logarithmic value of power attenuation.
Optical density is generally considered to refer to the absolute value of the base 10 logarithm of the optical attenuator power transmission factor. For example, an optical density of 3 represents a power attenuation factor of 103 = 1000. The corresponding attenuation coefficient is 30 dB.
If several attenuators form a ...
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Chromatic dispersion effect of optical components
11/9/2023
Chromatic dispersion can also be defined as the dispersion in the optical element rather than in the medium. At this time, it is necessary to perform Taylor expansion on the total phase delay of the component (rather than on the wave number, that is, the phase delay per unit length), and then obtain the total group delay dispersion (units are seconds squared), instead of unit length as mentioned a...
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