Round-trip loss: Difference between revisions

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In [[laser physics]], the   '''round-trip loss''',  or '''background loss''' <math>~\beta~</math>, determines what part of the energy of the [[laser field]]  
In [[laser physics]], the '''round-trip loss''' or '''background loss''' <math>~\beta~</math> determines how much of the energy of the [[laser field]]  
becomes unusable at each round-trip; it can be absorbed or scattered.
becomes unusable during each round-trip. The loss can be due to some of the laser-field energy being either absorbed, scattered, or both.


The round-trip loss is an important parameter of a laser that affects the [[self-pulsation]]. The self-pulsation may take place while the gain takes some time to respond to the variation of number of photons in the cavity and the number of photons in the cavity, in its turn, takes some time to respond the variation of gain. Within the simple model, the round-trip loss and the [[output coupling]] determine the
The round-trip loss is an important parameter of a laser that affects the [[self-pulsation]]. The self-pulsation may take place while the gain takes some time to respond to the variation of the number of photons in the cavity, and the number of photons in the cavity, in its turn, takes some time to respond to the variation of gain. Within the simple model, the round-trip loss and the [[output coupling]] determine the
period of pulsations and their relaxation. These are  
period of pulsations and their relaxation. These are the main parameters
main parameters
<!--its damping; in particular, the [[damping parameter]]s !-->
<!--its damping; in particular, the [[damping parameter]]s !-->
of the equivalent  [[oscillator]]<ref name="oppo">{{cite journal|url=http://worldcat.org/issn/0722-3277| author=G.L.Oppo|coauthors=A.Politi|title=Toda potential in laser equations|
of the equivalent  [[oscillator]]<ref name="oppo">{{cite journal|url=http://worldcat.org/issn/0722-3277| author=G.L.Oppo|coauthors=A.Politi|title=Toda potential in laser equations|
Line 21: Line 20:
}}</ref>.  
}}</ref>.  


At the steady-state operation, the round-trip gain <math>~g~</math> exactly compensate both,
At steady-state operation, the round-trip gain <math>~g~</math> exactly compensates both the output coupling and the losses:
the output coupling and losses:
<math>~\exp(g)~(1-\beta-\theta)=1~</math>.
<math>~\exp(g)~(1-\beta-\theta)=1~</math>.
Assuming, that the gain is small (<math>~g~\ll 1~</math>), this relation can be written as follows:
Assuming that the gain is small (<math>~g~\ll 1~</math>), this relation can be written as follows:


  <math>~g=\beta+\theta~</math>
  <math>~g=\beta+\theta~</math>


Such as relation is used in analytic estimates of the performance of [[laser|lasers]]
Such a relation is used in analytic estimates of the performance of [[laser|lasers]]
<ref name="uns">{{cite journal
<ref name="uns">{{cite journal
| author=D.Kouznetsov
| author=D.Kouznetsov
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| doi=10.1364/JOSAB.22.001605
| doi=10.1364/JOSAB.22.001605
}}</ref>. In particular, the  
}}</ref>. In particular, the  
round-trip loss <math>~\beta~</math> may be one of important parameters which limit the
round-trip loss <math>~\beta~</math> may be one of the important parameters that limit the
output power of a [[disk laser]]; at the power scaling, the gain <math>~G~</math> should be decreased
output power of a [[disk laser]]; at the power scaling, the gain <math>~G~</math> should be decreased
(in order to avoid the [[exponential growth]] of the [[amplified spontaneous emission]]), and the round-trip gain
(in order to avoid the [[exponential growth]] of the [[amplified spontaneous emission]]), and the round-trip gain
<math>~g~</math> should remain larger than the  background loss <math>~\beta~</math>;
<math>~g~</math> should remain larger than the  background loss <math>~\beta~</math>;
this requires to increase of the thickness of the slab of the [[gain medium]]; at certain thickness, the
this requires increasing the thickness of the slab of the [[gain medium]]; at a certain thickness, [overheating]] prevents efficient operation
[[overheating]] prevents the efficient operation
<ref name="kouz06">{{cite journal| author=D. Kouznetsov|coauthors= J.-F. Bisson, J. Dong, and K. Ueda| title=Surface loss limit of the power scaling of a thin-disk laser| journal=[[JOSAB]]| volume=23| issue=6| pages=1074–1082| year=2006| url=http://josab.osa.org/abstract.cfm?id=90157| accessdate=2007-01-26| doi=10.1364/JOSAB.23.001074}}</ref><ref name="kouz08">{{cite journal
<ref name="kouz06">{{cite journal| author=D. Kouznetsov|coauthors= J.-F. Bisson, J. Dong, and K. Ueda| title=Surface loss limit of the power scaling of a thin-disk laser| journal=[[JOSAB]]| volume=23| issue=6| pages=1074–1082| year=2006| url=http://josab.osa.org/abstract.cfm?id=90157| accessdate=2007-01-26| doi=10.1364/JOSAB.23.001074}}</ref><ref name="kouz08">{{cite journal
|author=D.Kouznetsov
|author=D.Kouznetsov
Line 58: Line 55:
}}</ref>.
}}</ref>.


For the analysis of processes in active medium, the sum <math>~\beta+\theta~</math> can be also called
For the analysis of processes in an active medium, the sum <math>~\beta+\theta~</math> can also be called
"loss"
"loss"
<ref name="siegman">
<ref name="siegman">
Line 69: Line 66:
|id= ISBN 0-935702-11-3
|id= ISBN 0-935702-11-3
}}
}}
</ref>. This notation leads to confusions as soon as one is interested, which part of the
</ref>. This notation leads to confusion when one wishes to know how much of the
energy is absorbed and scattered, and which part of such a "loss" is actually wanted and useful output of the laser.
energy is absorbed and scattered, and how much of such a "loss" is actually wanted and useful output of the laser.


==Notes==
==Notes==
{{reflist}}
{{reflist}}

Revision as of 12:40, 28 January 2022

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In laser physics, the round-trip loss or background loss determines how much of the energy of the laser field becomes unusable during each round-trip. The loss can be due to some of the laser-field energy being either absorbed, scattered, or both.

The round-trip loss is an important parameter of a laser that affects the self-pulsation. The self-pulsation may take place while the gain takes some time to respond to the variation of the number of photons in the cavity, and the number of photons in the cavity, in its turn, takes some time to respond to the variation of gain. Within the simple model, the round-trip loss and the output coupling determine the period of pulsations and their relaxation. These are the main parameters of the equivalent oscillator[1] [2] with an anharmonic potential as proposed by M. Toda[3].

At steady-state operation, the round-trip gain exactly compensates both the output coupling and the losses: . Assuming that the gain is small (), this relation can be written as follows:

Such a relation is used in analytic estimates of the performance of lasers [4]. In particular, the round-trip loss may be one of the important parameters that limit the output power of a disk laser; at the power scaling, the gain should be decreased (in order to avoid the exponential growth of the amplified spontaneous emission), and the round-trip gain should remain larger than the background loss ; this requires increasing the thickness of the slab of the gain medium; at a certain thickness, [overheating]] prevents efficient operation [5][6].

For the analysis of processes in an active medium, the sum can also be called "loss" [7]. This notation leads to confusion when one wishes to know how much of the energy is absorbed and scattered, and how much of such a "loss" is actually wanted and useful output of the laser.

Notes

  1. ↑ G.L.Oppo; A.Politi (1985). "Toda potential in laser equations". Zeitschrift fur Physik B 59: 111–115. DOI:10.1007/BF01325388. Research Blogging.
  2. ↑ D.Kouznetsov; J.-F.Bisson, J.Li, K.Ueda (2007). "Self-pulsing laser as oscillator Toda: Approximation through elementary functions". Journal of Physics A 40: 1–18. DOI:10.1088/1751-8113/40/9/016. Research Blogging.
  3. ↑ Morikazu Toda (1975). "Studies of a non-linear lattice". Physics Reports 18 (1): 1-123. DOI:10.1016/0370-1573(75)90018-6. Research Blogging.
  4. ↑ D.Kouznetsov; J.-F.Bisson, K.Takaichi, K.Ueda (2005). "Single-mode solid-state laser with short wide unstable cavity". JOSAB 22 (8): 1605–1619. DOI:10.1364/JOSAB.22.001605. Research Blogging.
  5. ↑ D. Kouznetsov; J.-F. Bisson, J. Dong, and K. Ueda (2006). "Surface loss limit of the power scaling of a thin-disk laser". JOSAB 23 (6): 1074–1082. DOI:10.1364/JOSAB.23.001074. Retrieved on 2007-01-26. Research Blogging.
  6. ↑ D.Kouznetsov; J.-F.Bisson (2008). "Role of the undoped cap in the scaling of a thin disk laser". JOSA B 25 (3): 338-345. DOI:10.1364/JOSAB.25.000338. Research Blogging.
  7. ↑ A.E.Siegman (1986). Lasers. University Science Books. ISBN 0-935702-11-3. 
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