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| {{distinguish|Laserdisc}}
| | Nice to meet you, my name is [http://www.mpp.com/warranty-plans/used-car-warranties.htm Araceli Oquendo] but I don't like when people use my complete name. Interviewing is how he supports his family but his promotion never comes. Years ago we moved to Arizona but my wife [http://www.dutchtaskforce.com/index.php?mod=users&action=view&id=46500 extended car warranty] desires us to move. Camping is extended auto [http://www.holzkunst-scholz.de/index.php?mod=users&action=view&id=7124 car warranty] something that I've carried extended auto [http://www.fcc.gov/guides/auto-warranty-scams warranty] out for years.<br><br>Also visit my weblog ... [http://sportshop-union.de/index.php?mod=users&action=view&id=13058 http://sportshop-union.de/index.php?mod=users&action=view&id=13058] |
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| [[Image:DiskLaserJPEG.jpg|200px|right|thumb|Fig.1. An optically-pumped disk laser (active mirror).]]
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| <!--[[Image:DiskLaser.png|200px|right|thumb|Fig.1. An optically-pumped disk laser (active mirror).]] !-->
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| A '''disk laser''' or '''active mirror''' (Fig.1.) is a type of [[solid-state laser]] characterized by a heat sink and laser output that are realized on opposite sides of a thin layer of [[active gain medium]].<ref>{{cite web| work=Encyclopedia of Laser Physics and Technology| url=http://www.rp-photonics.com/thin_disk_lasers.html| title=Thin disk lasers}}</ref> Despite their name, disk lasers do not have to be circular; other shapes have also been tried.
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| Disk lasers should not be confused with [[Laserdisc]]s, which are a disk-shaped optical storage medium.
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| Disk lasers should not be confused with
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| [[Power scaling#Fiber_disk_lasers|Fiber laser disk]]s,
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| which are a disk-shaped coils of a [[fiber laser]],
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| pumped from the side.
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| ==Active mirrors and disk lasers==
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| [[Image:ActiveMirror.png|right|250px|thumb|Fig.2. A disk laser (active mirror) configuration presented in 1992 at the [[SPIE]] conference.<ref name="Ueda">{{cite journal
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| |doi=10.1117/12.143686
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| | url=http://spiedl.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PSISDG001837000001000336000001&idtype=cvips&gifs=yes
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| | author=K. Ueda| coauthors=N. Uehara| title=Laser-diode-pumped solid state lasers for gravitational wave antenna| journal=[[Proceedings of SPIE]]| volume=1837| pages=336–345| year=1993}}</ref>]]
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| Initially, disk lasers were called ''active mirrors'', because the [[gain medium]] of a disk laser is essentially an optical [[mirror]] with [[reflection coefficient]] greater than unity. An active mirror is a thin disk-shaped double-pass [[optical amplifier]].
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| The first active mirrors were developed in the [[Laboratory for Laser Energetics]] ([[USA]]).<ref name="abate">{{cite journal|url=http://ao.osa.org/abstract.cfm?id=24598| author=A.Abate|coauthors=L.Lund, D.Brown, S.Jacobs, S.Refermat, J.Kelly, M.Gavin, J.Waldbillig, and O.Lewis|title=Active mirror: a large-aperture medium-repetition rate Nd:glass amplifier|journal=[[Applied Optics]]|volume=1837|pages=351–361| year=1981|doi=10.1364/AO.20.000351|issue=2|bibcode = 1981ApOpt..20..351A }}</ref>
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| Then, the concept was developed in various research groups,
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| in particular, the [[University of Stuttgart]] ([[Germany]])<ref>{{cite journal| author=A. Giesen| coauthors=H. Hügel, A. Voss, K. Wittig, U. Brauch and H. Opower| title=Scalable concept for diode-pumped high-power solid-state lasers| year=1994|
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| url=http://www.springerlink.com/content/n7350870q8q57324/?p=c874af0585094717b13bb41e3fc548da&pi=0|
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| journal=[[Applied Physics B]]|volume=58| issue=5| pages=365–372| doi=10.1007/BF01081875| bibcode=1994ApPhB..58..365G}}</ref> for Yb:doped glasses.
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| In the ''disk laser'', the heat sink does not have to be transparent, so, it can be extremely efficient even with large transverse size <math>~L~</math> of the device (Fig.1.).
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| The increase in size allows the [[power scaling]] to many kilowatts without significant modification of the design.<ref name="1kw">
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| {{cite journal
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| |title= A 1-kW CW thin disc laser
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| |author= C.Stewen
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| |coauthors= K.Contag, M.Larionov, A.Giesen, H.Hugel
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| |journal=[[IEEE Journal of Selected Topics in Quantum Electronics|IEEE J. of Selected Topics in QE]]
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| |year=2000
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| |volume=6
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| |pages=650–657
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| | issn= 1077-260X|id=NSPEC Accession Number 6779337
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| |doi= 10.1109/2944.883380
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| |issue=4
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| }}</ref>
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| | |
| ==Limit of power scaling for disk lasers==
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| [[Image:BouncingRay.png|right|thumb|Fig.3. Bouncing ray of [[Amplified spontaneous emission|ASE]] in a disk laser]]
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| <!-- {{Copyedit|date=March 2007}} !-->
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| The power of such lasers is limited not only by the power of pump available, but also by overheating, [[amplified spontaneous emission]] (ASE) and
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| the background [[round-trip loss]].<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| bibcode=2006JOSAB..23.1074K}}; [http://www.ils.uec.ac.jp/~dima/disk.pdf]</ref>
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| To avoid overheating, the size <math>~L~</math> should be increased with power scaling.
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| Then, to avoid strong losses due to the [[exponential growth]] of the [[Amplified spontaneous emission|ASE]], the transverse-trip gain <math>~u=GL~</math>
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| cannot be large.
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| This requires reduction of the gain <math>G~</math>;
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| this gain is determined by the reflectivity of the output coupler and thickness <math>~h</math>.
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| The [[round-trip gain]] <math>~g=2Gh~</math> should remain larger than the
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| [[round-trip loss]] <math>\beta~</math>
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| (the difference <math>g\!-\!\beta~</math> determines the optical energy,
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| which is output from the laser cavity at each round-trip).
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| The reduction of gain <math>G~</math>, in a given [[round-trip loss]] <math>~\beta~</math>,
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| requires increasing the thickness <math>h</math>.
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| Then, at some critical size, the disk becomes too thick and cannot be
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| pumped above the [[lasing threshold|threshold]] without overheating.
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| Some features of the power scaling can revealed from a simple model.
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| Let <math>Q~</math> be the [[active laser medium|saturation intensity]],<ref name="uns">{{cite journal
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| | author=D.Kouznetsov
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| | coauthors=J.F.Bisson, K.Takaichi, K.Ueda
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| | title=Single-mode solid-state laser with short wide unstable cavity
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| |url=http://josab.osa.org/abstract.cfm?id=84730
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| |journal=[[JOSAB]]|volume=22| issue=8| pages=1605–1619
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| | year=2005
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| | doi=10.1364/JOSAB.22.001605
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| | bibcode=2005JOSAB..22.1605K
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| }}</ref>
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| <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| bibcode=2006JOSAB..23.1074K}}; also at http://www.ils.uec.ac.jp/~dima/disk.pdf</ref>
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| of the medium,
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| <math>\eta_0=\omega_{\rm s}/\omega_{\rm p}~~</math> be the ratio of frequencies,
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| <math>R~</math> be the [[thermal loading]] parameter.
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| The key parameter
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| <math>P_{\rm k}=\eta_0\frac{R^2}{Q\beta^3}~</math>
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| determines the maximal power of the disk laser.
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| The corresponding optimal thickness can be estimated with
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| <math>h \sim \frac{R}{Q \beta}</math>.
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| The corresponding optimal size
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| <math>L \sim \frac{R}{Q \beta^2}</math>.
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| Roughly, the [[round-trip loss]] should scale inversely proportionally to the cubic root of the power required.
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| An additional issue is the efficient delivery of pump energy.
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| In low round-trip gain, the single-pass absorption of the pump is also low. Therefore, recycling of pump energy is required for efficient operation. (See the additional
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| mirror '''M''' at the left-hand side of figure 2.) For [[power scaling]],
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| the medium should be [[optical thickness|optically thin]], with many passes of pump energy required; the lateral delivery of pump energy
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| <ref name="uns">{{cite journal
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| | author=D.Kouznetsov
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| | coauthors=J.-F.Bisson, K.Takaichi, K.Uesa
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| | title=Single-mode solid-state laser with short wide unstable cavity
| |
| |url=http://josab.osa.org/abstract.cfm?id=84730
| |
| |journal=[[JOSAB]]|volume=22| issue=8| pages=1605–1619
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| | year=2005
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| | doi=10.1364/JOSAB.22.001605
| |
| | bibcode=2005JOSAB..22.1605K
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| }}</ref>
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| also might be a possible solution.
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| | |
| ==Anti-ASE cap==
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| [[Image:UndopedCapFig1.gif|right|300px|thumb|Fig.4. Uncovered disk laser and that with undoped cap
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| .<ref name="ase">{{cite journal| author=D.Kouznetsov| coauthors=J.F.Bisson| title=Role of undoped cap in the scaling of thin-disk lasers| url=http://www.opticsinfobase.org/abstract.cfm?URI=josab-25-3-338| journal=[[JOSAB]]
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| |volume=25
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| |pages=338–345
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| | year=2008| doi=10.1364/JOSAB.25.000338| issue=3|bibcode = 2008JOSAB..25..338K }}</ref>]]
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| In order to reduce the impact of ASE, an anti-ASE cap consisting of undoped material on the surface of a disk laser has been suggested.<ref name="pa1">{{cite journal
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| |author=Stephen A. Payne
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| |coauthors=William F. Krupke, Raymond J. Beach, Steven B. Sutton, Eric C. Honea, Camille Bibeau, Howard Powel
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| |title=High average power scaleable thin-disk laser
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| | url=http://www.patentstorm.us/patents/6347109.html
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| | journal=US patent
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| | volume=6347109
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| |year=2002
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| }}</ref><ref name="pa2">{{cite journal
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| |author=Beach; Raymond J. (Livermore, CA),
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| |coauthors=Honea; Eric C. (Sunol, CA), Bibeau; Camille (Dublin, CA), Payne; Stephen A. (Castro Valley, CA), Powell; Howard (Livermore, CA), Krupke; William F. (Pleasanton, CA), Sutton; Steven B. (Manteca, CA)
| |
| |title=High average power scaleable thin-disk laser
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| |journal=USA patent
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| | volume=6347109
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| | year=2002
| |
| |url=http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=13&f=G&l=50&co1=AND&d=PTXT&s1=6347109&OS=6347109&RS=6347109
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| }}</ref>
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| <!-- It seems, at least two different sites have published different patents (they differ with order of authors) with the same title and number. I keep both until anybody provides a reference indicating that one is wrong. Dima.!-->
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| Such a cap allows spontaneously emitted photons to escape from the active layer and prevents them from resonating in the cavity. Rays cannot bounce (Fig.3) as in uncovered disk. This could allow an order of magnitude increase in the maximum power achievable by a disk laser
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| .<ref name="ase"/> In both cases, the back reflection of the ASE from the edges of the disk should be suppressed. This can be done with absorbing layers, shown with green in Figure 4. At operation close to the maximal power, a significant part of the energy goes into ASE; therefore, the absorbing layers also should be supplied with heat sinks, which are not shown in the figure.
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| [[Image:DiskLaserScalingLimit.gif|right|300px|thumb|Fig5. Upper bound of loss <math>\beta</math> at which the ouptut power <math>P_{\rm s}</math> of a single disk laser is still achievable. Dashed line corresponds to uncovered disk; thick solid curve represents the case with undoped cap.<ref name="ase"/>]]
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| ==Key parameter for laser materials==
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| The estimate of maximal power achievable at given loss <math>\beta</math>, is very sensitive to <math>\beta</math>. The estimate of the upper bound of <math>\beta</math>, at which the desired output power <math>P_{\rm s}</math> is achievable is robust. This estimate is plotted versus normalized power
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| <math>s=P_{\rm s}/P_{\rm d}</math> in figure 5. Here, <math> P_{\rm s}</math> is the output power of the laser, and
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| <math>P_{\rm d}=R^2/Q</math> is dimensional scale of power; it is related with the key parameter
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| <math>P_{\rm k}=P_{\rm d}/\beta^3</math>.
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| The thick dashed line represents the estimate for the uncovered disk. The thick solid line shows the same for the disk with undoped cap. The thin solid line represents the qualitative estimate <math>\beta=s^{1/3}</math> without coefficients. Circles corresponds to the experimental data for the power achieved and corresponding estimates for the background loss <math>\beta</math>. All future experiments and numerical simulations and estimates are expected to give values of <math>(\beta, s)</math>, that are below the red dashed line in Fig.5 for the uncovered disks, and below the blue curve for the disks with anti-ASE cap. This can be interpreted as a scaling law for disk lasers
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| .<ref name="scaling">{{cite journal
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| |title=Scaling laws of disk lasers
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| |author=D.Kouznetsov
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| |coauthors=J.-F.Bisson, K.Ueda
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| |journal=[[Optical Materials]]
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| |year=2009
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| |volume=31
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| |issue=5
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| |pages=754–759
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| |doi=10.1016/j.optmat.2008.03.017
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| |url=http://www.ils.uec.ac.jp/~dima/PAPERS/2009optmat.pdf
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| }}
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| </ref>
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| In the vicinity of the curves mentioned, the efficiency of the disk laser is low; most of the pumping power goes to ASE, and is absorbed at the edges of the device. In these cases, the distribution of the pump energy available among several disks may significantly improve the performance of the lasers. Indeed, some lasers reported using several elements combined in the same cavity.
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| ==Pulsed operation==
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| Similar scaling laws take place for pulsed operation. In [[quasi continuous wave]] regime, the maximal mean power can be estimated by scaling the saturation intensity with the [[fill factor]] of the pump, and the product of the duration of pump to the repetition rate. At short duration pulses,
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| more detailed analysis is required
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| .<ref name="RLP">{{cite journal
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| |author=D.Kouznetsov.
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| |title=Storage of energy in disk-shaped laser materials
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| |journal=[[Research Letters in Physics]]
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| |volume=2008
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| |pages=717414
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| |year=2008
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| |url=http://www.hindawi.com/journals/rlp/aip.717414.html
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| |doi=10.1155/2008/717414
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| |bibcode = 2008RLPhy2008E..17K
| |
| }}</ref>
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| At moderate values of the repetition rate (say, higher than 1 Hz), the maximal energy of the output pulses is roughly inversely proportional to the cube of the background loss <math>\beta</math>; the undoped cap may provide an additional order of magnitude of mean output power, under the condition that this cap does not contribute to the background loss.
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| At low repetition rate (an in the regime of single pulses) and sufficient pump power, there is no general limit of energy, but the required size of the device grows quickly with increase of the required pulse energy
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| <!-- , even at the optimal design !-->, setting the practical limit of energy; it is estimated that from a few joules to a few thousand joules can be extracted in an optical pulse from a single active element, dependently on the level of the background internal loss of the signal in the disk.
| |
| .<ref name="spie2009*"> | |
| {{cite journal
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| |journal=[[JOSAB]]
| |
| |volume=26
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| |issue=1
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| |year=2009
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| |pages=26–35
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| |title=Scaling of thin-disk lasers--influence of amplified spontaneous emission
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| |author=J.Speiser
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| |url=http://www.opticsinfobase.org/abstract.cfm?URI=josab-26-1-26
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| |doi=10.1364/JOSAB.26.000026
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| |bibcode = 2008JOSAB..26...26S }}
| |
| </ref>
| |
| | |
| ==See also==
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| *[[VCSEL]]
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| *[[VECSEL]]
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| *[[Thermal shock]]
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| *[[round-trip gain]]
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| *[[power scaling]]
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| *[[gain medium]]
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| *[[List of laser articles]]
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| | |
| == References ==
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| <references/>
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| <!--
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| *{{cite journal|author= K. Contag| coauthors=M. Karszewski, C. Stewen, A. Giesen, and H. Hugel| title=Theoretical modelling and experimental investigation of the diode-pumped thin-disk Yb:YAG laser| volume=29| pages=697–703| year=1999| journal=Quantum Electronics| issue=8| url= http://www.turpion.org/php/paper.phtml?journal_id=qe&paper_id=1555&year_id=1999&volume=29&issue_id=8&fpage=697&lpage=703| doi=10.1070/QE1999v029n08ABEH001555|bibcode = 1999QuEle..29..697C }}
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| **{{cite journal|title=''Erratum:''| year=1999| journal=Quantum Electronics| volume=29| issue=11| pages=1025| url=http://www.turpion.org/php/paper.phtml?journal_id=qe&paper_id=1686&year_id=1999&volume=29&issue_id=11&fpage=1025&lpage=1025| doi=10.1070/QE1999v029n11ABEH001686|author=Contag, K.|last2=Karszewski|first2=M|last3=Stewen|first3=C|last4=Giesen|first4=A|last5=Hugel|first5=H|bibcode = 1999QuEle..29.1025C }}
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| !-->
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| {{DEFAULTSORT:Disk Laser}}
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| [[Category:Solid-state lasers]]
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