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The beam in the cavity and the output beam of the laser, when travelling in free space ( or a homogenous medium ) rather than waveguides ( as in an optical fiber laser ), can be approximated as a Gaussian beam in most lasers ; such beams exhibit the minimum divergence for a given diameter.
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beam and cavity
Depending on the design of the cavity ( whether the mirrors are flat or curved ), the light coming out of the laser may spread out or form a narrow beam.
In a few situations it is possible to obtain lasing with only a single pass of EM radiation through the gain medium, and this produces a laser beam without any need for a resonant or reflective cavity ( see for example nitrogen laser ).
The latter is called the output coupler, because it allows some of the light to leave the cavity to produce the laser's output beam.
In order to increase the purity of the isobaric beam, laser ionization can take place inside the ionizer cavity to selectively ionize a single element chain of interest.
When illuminated by a radio beam from a remote location, the cavity would return a frequency modulated signal.
Alternatively, when the modulator is in its low-Q state, an externally-generated beam can be coupled into the cavity through the modulator.
This can be used to " seed " the cavity with a beam that has desired characteristics ( such as transverse mode or wavelength ).
* Cavity dumping: The cavity end mirrors are 100 % reflective, so that no output beam is produced when the Q is high.
Instead, the Q-switch is used to " dump " the beam out of the cavity after a time delay.
The cavity Q goes from low to high to start the laser buildup, and then goes from high to low to " dump " the beam from the cavity all at once.
Electro-optic modulators are normally used for this, since they can easily be made to function as a near-perfect beam " switch " to couple the beam out of the cavity.
The modulator that dumps the beam may be the same modulator that Q-switches the cavity, or a second ( possibly identical ) modulator.
A dumped cavity is more complicated to align than simple Q-switching, and may need a control loop to choose the best time at which to dump the beam from the cavity.
This beam is then passed through an input cavity.
RF energy is fed into the input cavity at, or near, its natural frequency to produce a voltage which acts on the electron beam.
In the two-chamber klystron, the electron beam is injected into a resonant cavity.
While passing through the first cavity, the electron beam is velocity modulated by the weak RF signal.
This is because the electron beam must produce the bunched electrons in the second cavity in order to generate output power.
In the reflex klystron ( also known as a ' Sutton ' klystron after its inventor, Robert Sutton ), the electron beam passes through a single resonant cavity.
beam and output
The output mirror of the laser is an aperture, and the subsequent beam shape is determined by that aperture.
Hence, the smaller the output beam, the quicker it diverges.
Another development is the availability of electron accelerators with extremely high power output, up to 1, 000 kW beam.
Spatial coherence typically is expressed through the output being a narrow beam which is diffraction-limited, often a so-called " pencil beam.
The resonator typically consists of two mirrors between which a coherent beam of light travels in both directions, reflecting back on itself so that an average photon will pass through the gain medium repeatedly before it is emitted from the output aperture or lost to diffraction or absorption.
Some applications of lasers depend on a beam whose output power is constant over time.
In effect, all three incident beams interact ( essentially ) simultaneously to form several real-time holograms, resulting in a set of diffracted output waves that phase up as the " time-reversed " beam.
All operations are synchronised with the output of the video beam.
The power per thrust required for a perfectly collimated output beam is 300 MW / N ( half this if it can be reflected off the craft ); very high energy density power sources would be required to provide reasonable thrust without unreasonable weight.
In the transmitted direction the beam is split and then combined and focused into the output collimator.
The electron beam of the output display is then commanded to move from vertex to vertex, tracing an analog line across the area between these points.
Q-switching, sometimes known as giant pulse formation, is a technique by which a laser can be made to produce a pulsed output beam.
In the United States, ANSI in 2009 published voluntary standard FL1 Flashlight basic performance standard, which standardizes the test procedures for total light output, beam intensity, working distance, impact and water resistance, and battery running time to 10 % of initial light output.
This is used to make a round beam from the elliptical output of a laser diode.
In laser physics and engineering the term " continuous wave " or " CW " refers to a laser which produces a continuous output beam, sometimes referred to as ' free-running '.
Some use the KT88 / 6550 beam power tubes in the output stage.
beam and laser
Laser Doppler anemometers use a beam of light from a laser that is divided into two beams, with one propagated out of the anemometer.
Particulates ( or deliberately introduced seed material ) flowing along with air molecules near where the beam exits reflect, or backscatter, the light back into a detector, where it is measured relative to the original laser beam.
Optionally, an atom probe may also include laser-optical systems for laser beam preparation, targeting and pulsing, if using laser-evaporation methods.
As with digital photocopiers and multifunction printers ( MFPs ), laser printers employ a xerographic printing process but differ from analog photocopiers in that the image is produced by the direct scanning of a laser beam across the printer's photoreceptor.
A laser beam reads the CD and is reflected back to a sensor, which converts it into electronic data
The polycarbonate disc contains a spiral groove, called the " pregroove " ( because it is molded in before data are written to the disc ), to guide the laser beam upon writing and reading information.
The pregroove is molded into the top side of the polycarbonate disc, where the pits and lands would be molded if it were a pressed ( nonrecordable ) Red Book CD ; the bottom side, which faces the laser beam in the player or drive, is flat and smooth.
For example, the expanding profile of a laser beam, the beam shape of a radar antenna and the field of view of an ultrasonic transducer can all be analysed using diffraction equations.
Diffraction of red laser beam on the hole
The way in which the profile of a laser beam changes as it propagates is determined by diffraction.
Paradoxically, it is possible to reduce the divergence of a laser beam by first expanding it with one convex lens, and then collimating it with a second convex lens whose focal point is coincident with that of the first lens.
It is a result of the superpostion of many waves with different phases, which are produced when a laser beam illuminates a rough surface.
The upper half of this image shows a diffraction pattern of He-Ne laser beam on an elliptic aperture.
In the basic version of the experiment, a coherent light source such as a laser beam illuminates a thin plate pierced by two parallel slits, and the light passing through the slits is observed on a screen behind the plate.
In the double-slit experiment, the two slits are illuminated by a single laser beam.
In the free electron laser ( FEL ), a relativistic electron beam is passed through a pair of undulators containing arrays of dipole magnets, whose fields are oriented in alternating directions.
* English laser and Scottish Gaelic lasair ( light beam, flame )
This glowing plasma is excited and then acts as the active laser medium | gain medium through which the internal beam passes, as it is reflected between the two mirrors.
The gain medium of a laser is normally a material of controlled purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission described above.
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