Coherent addition (or coherent combining) of
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" is an acronym for "light amplification by stimulated emission of radiation". The firs ...
s
is a method of
power scaling Power scaling of a laser is increasing its output power without changing the geometry, shape, or principle of operation. Power scalability is considered an important advantage in a laser design. this means it can increase power without changing outs ...
. It allows increasing the output power and brightness of
single-transversal mode laser.
Usually, the term coherent addition applies to
fiber laser
A fiber laser (or fibre laser in British English) is a laser in which the active gain medium is an optical fiber doped with rare-earth elements such as erbium, ytterbium, neodymium, dysprosium, praseodymium, thulium and holmium. They are re ...
s. As the ability of pumping and/or cooling of a single laser is saturated, several similar lasers can be forced to oscillate in phase with a common coupler.
The coherent addition was demonstrated in
power scaling Power scaling of a laser is increasing its output power without changing the geometry, shape, or principle of operation. Power scalability is considered an important advantage in a laser design. this means it can increase power without changing outs ...
of
Raman laser A Raman laser is a specific type of laser in which the fundamental light-amplification mechanism is stimulated Raman scattering. In contrast, most "conventional" lasers (such as the ruby laser) rely on stimulated electronic transitions to amplify ...
s.
Limits of coherent addition
The addition of lasers reduces the number of longitudinal modes in the output beam; the more lasers are combined, the smaller is the number of longitudinal modes in the output. The simple estimates show that the number of output modes reduces exponentially with the number of lasers combined. Of order of eight lasers can be combined in such a way.
[D. Kouznetsov, J.F. Bisson. A. Shirakawa, K.Ueda ]
Limits of Coherent Addition of Lasers: Simple Estimate
" Optical Review
''Optical Review'' is a bimonthly peer-reviewed scientific journal that was established in 1994 and is published by Springer Science+Business Media in partnership with the Optical Society of Japan. The editor-in-chief is Masahiro Yamaguchi. The jo ...
Vol. 12, No. 6, 445–447 (2005). (Als
) The future increase of number of combined lasers requires the
exponential growth
Exponential growth is a process that increases quantity over time. It occurs when the instantaneous rate of change (that is, the derivative) of a quantity with respect to time is proportional to the quantity itself. Described as a function, a ...
of the spectral bandwidth of gain and/or length of partial lasers.
The same conclusion can be made also on the base of more detailed simulations.
[
A.E.Siegman. Resonant modes of linearly coupled multiple fiber laser structures.
Preprint of the Stanford University, 2005, 25 pages;
http://www.stanford.edu/~siegman/coupled_fiber_modes.pdf
] Practically, the combination of more than ten lasers with a passive combining arrangement appears to be difficult. However, active coherent combining of lasers has the potential to scale to very large numbers of channels.
[Leo A. Siiman, Wei-zung Chang, Tong Zhou, and Almantas Galvanauskas,]
Coherent femtosecond pulse combining of multiple parallel chirped pulse fiber amplifiers
Optics Express
''Optics Express'' is a biweekly peer-reviewed scientific journal published by Optica. It was established in 1997. The journal reports on scientific and technology innovations in all aspects of optics and photonics. The Energy Express supplement ...
20 (2012) 18097-18116
Nonlinear coherent addition of lasers
Nonlinear interactions of light waves are used widely to synchronize the laser beams
in multichannel optical systems. Self-adjusting of phases may be robustly achievable in binary-tree array of beam-splitters and degenerate four-wave mixing Kerr
Phase conjugation Phase conjugation is a physical transformation of a wave field where the resulting field has a reversed propagation direction but keeps its amplitudes and phases.
Description
It is distinguished from Time Reversal Signal Processing by the fact th ...
in
Chirped pulse amplification
Chirped pulse amplification (CPA) is a technique for amplifying an ultrashort laser pulse up to the petawatt level, with the laser pulse being stretched out temporally and spectrally, then amplified, and then compressed again. The stretching and ...
extreme light facilities.
This phase-conjugating Michelson interferometer increases the brightness as
,
where
is the number of phase-locked channels.
Talbot coherent addition
Constructive interference due to Talbot self-imaging forces the lasers in the array to
transverse mode locking. The
Fresnel number
The Fresnel number (''F''), named after the physicist Augustin-Jean Fresnel, is a dimensionless number occurring in optics, in particular in scalar diffraction theory.
Definition
For an electromagnetic wave passing through an aperture and hitti ...
of the one-dimensional
element laser array phase-locked by
Talbot cavity is given by
For the two-dimensional
element laser array phase-locked by Talbot cavity Fresnel number
scales as
as well. Talbot phase-locking techniques are applicable to thin disk diode-pumped solid-state laser arrays.
[{{cite journal , title=Scaling of diode-array-pumped solid-state lasers via self-imaging
, journal=Opt. Commun., volume=99 , issue=5-6 , pages=350–354 , year=1993, last1= Okulov , first1=A Yu, doi=10.1016/0030-4018(93)90342-3]
See also
*
List of laser articles
This is a list of laser topics.
A
* 3D printing, additive manufacturing
* Abnormal reflection
* Above-threshold ionization
* Absorption spectroscopy
* Accelerator physics
* Acoustic microscopy
* Acousto-optic deflector
* Acousto-optic modul ...
References
Laser science