Injection seeders are devices that direct the output of small "seed"
laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...
s into the
cavity of a much larger laser to stabilize the latter's output. Most seed lasers are stable,
single-frequency lasers that emit within the
linewidth
A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used ...
of the larger laser's
gain medium
The active laser medium (also called a gain medium or lasing medium) is the source of optical gain within a laser. The gain results from the stimulated emission of photons through electronic or molecular transitions to a lower energy state from ...
. The single frequency encourages the larger laser to lase in a single
longitudinal mode
A longitudinal mode of a resonant cavity is a particular standing wave pattern formed by waves confined in the cavity. The longitudinal modes correspond to the wavelengths of the wave which are reinforced by constructive interference after man ...
, and the seed laser can also improve the laser's spatial profile and improve the
M2 parameter.
Seed lasers can be
continuous
Continuity or continuous may refer to:
Mathematics
* Continuity (mathematics), the opposing concept to discreteness; common examples include
** Continuous probability distribution or random variable in probability and statistics
** Continuous ...
or pulsed. Seeding a pulsed laser can reduce variations in the output energy and timing (
jitter
In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a signifi ...
) from pulse to pulse, and smooth out temporal variations within the pulse. Many commercial lasers use a
laser diode
file:Laser diode chip.jpg, The laser diode chip removed and placed on the eye of a needle for scale
A laser diode (LD, also injection laser diode or ILD or semiconductor laser or diode laser) is a semiconductor device similar to a light-emittin ...
as a seeding source.
See also
*
Laser construction
A laser is constructed from three principal parts:
*An energy source (usually referred to as the ''Laser pumping, pump'' or ''pump source''),
*A ''gain medium'' or ''Active laser medium, laser medium'', and
*Two or more mirrors that form an ''o ...
*
Q-switching
Q-switching, sometimes known as giant pulse formation or Q-spoiling, is a technique by which a laser can be made to produce a pulsed output beam. The technique allows the production of light pulses with extremely high (gigawatt) peak power, much h ...
*
Mode locking
References
Spotlight: Injection Seeding, Technical University of Darmstadt
Bibliography
*
*
Laser science
{{Optics-stub