Optical chopper on:
[Wikipedia]
[Google]
[Amazon]
An optical chopper is a device which periodically interrupts a
Optical choppers, usually rotating disc mechanical shutters, are widely used in science labs in combination with
An optical chopper is a device which periodically interrupts a light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...
beam. Three types are available: variable frequency rotating disc choppers, fixed frequency tuning fork
A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs ( tines) formed from a U-shaped bar of elastic metal (usually steel). It resonates at a specific constant pitch when set vibrating by striking it agains ...
choppers, and optical shutters. A rotating disc chopper was famously used in 1849 by Hippolyte Fizeau in the first non-astronomical measurement of the speed of light.
Use in science laboratories
Optical choppers, usually rotating disc mechanical shutters, are widely used in science labs in combination with lock-in amplifier
A lock-in amplifier is a type of amplifier that can extract a signal with a known carrier wave from an extremely noisy environment. Depending on the dynamic reserve of the instrument, signals up to a million times smaller than noise components, p ...
s. The chopper is used to modulate the intensity of a light beam, and a lock-in amplifier is used to improve the signal-to-noise
Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal (electrical engineering), signal to the level of background Noise (signal processing), noise. SNR is defined as the ratio ...
ratio.
To be effective, an optical chopper should have a stable rotating speed. In cases where the 1/f noise
Pink noise or noise is a signal or process with a frequency spectrum such that the power spectral density (power per frequency interval) is inversely proportional to the frequency of the signal. In pink noise, each octave interval (halving ...
is the main problem, one would like to select the maximum chopping frequency possible. This is limited by the motor speed and the number of slots in the rotating disc, which is in turn limited by the disc radius and the beam diameter.
Examples
Optical incremental rotary encoders are a form of choppers. These are used in many industrial machines. Some early anti-lock braking systems used rotary encoders for wheel speed sensors. Late 20th century opto-mechanical computer mice used two encoders for X-Y position measurement. Optical linear encoders also exist.LCD television
Liquid-crystal-display televisions (LCD TVs) are television sets that use liquid-crystal displays to produce images. They are, by far, the most widely produced and sold television display type. LCD TVs are thin and light, but have some disadvantag ...
s use millions of LCD shutters paired with red, green or blue filters to control the color of the pixel
In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device.
In most digital display devices, pixels are the ...
s on the screen.
Movie cameras use an optical shutter to record individual frames of the movie. Movie projectors use an optical shutter synchronized with the movie frames to produce the effect of apparent motion on the movie screen.
Liquid crystal shutter glasses
An active shutter 3D system (a.k.a. alternate frame sequencing, alternate image, AI, alternating field, field sequential or eclipse method) is a technique of displaying stereoscopic 3D images. It works by only presenting the image intended for th ...
are used in conjunction with a synchronized display screen to create the illusion of a three-dimensional image.
Light signals are sent at sea and at airports using a signal lamp
Signal lamp training during World War II
A signal lamp (sometimes called an Aldis lamp or a Morse lamp) is a semaphore system using a visual signaling device for optical communication, typically using Morse code. The idea of flashing dots and da ...
with a hand-operated shutter.
See also
*Stroboscope
A stroboscope, also known as a strobe, is an instrument used to make a cyclically moving object appear to be slow-moving, or stationary. It consists of either a rotating disk with slots or holes or a lamp such as a flashtube which produces br ...
References
{{reflist External links Frequently asked questions
on optical choppers.
Optical metrology