Haar measure: Difference between revisions

From formulasearchengine
Jump to navigation Jump to search
← Older editNewer edit →
en>Shreevatsa
m fix blind replacement of "is is" with "is". The right replacement here would be "it is".
Line 1: Line 1:
{{Refimprove|date=September 2007}}
Many folks have also noticed this disadvantage: You can't record a show whilst you watch another program, which causes it to be less than ideal as a DVR. Based in Fremont, California, Sonic CCTV has become one from the leading suppliers of surveillance and home alarm system products within North America. When selecting a DVR choose  samsung sme-2220 review a uncomplicated, simple device  [http://Www.Sunroc.de/?goto=http://cctvdvrreviews.com Best Cctv dvr uk] as this will keep the charge down. It may include certain duplications, however it is better than containing some concealed matters.<br><br>
The '''active laser medium''' (also called '''gain medium''' or '''lasing medium''') is the source of optical [[gain]] within a [[laser]]. The gain results from the [[stimulated emission]] of electronic or molecular transitions to a lower energy state from a higher energy state
previously populated by a [[laser pumping|pump source]].


Examples of active laser media include:
This is perfect in case you are feeling stuck, unfulfilled, or if you just understand that you are capable of achieving more. Electric fences are devised in this particular way that they may provide having a high voltage shock to an attempted intruder for any very short volume of time. A USA Today article examined 168 sexual assault charges against athletes.<br><br>Even remote access of CCTV is achievable but such advanced features can be found at higher price ranges of CCTVs. Many people might think that CCTV systems are equipped for commercial use only. First, the digital video surveillance cameras are getting to be computers boost the local tissue, and connecting with a network of computers instead using a dedicated computer. Today's high definition security cameras have made it possible for entrepreneurs to help keep a watch over their facilities and guide their employees.<br><br>You will have to leave the lights within the bedroom because camera does not have a IR function. Because CCTV deters burglars and intruders, many people choose to utilize CCTV as part of the home's security package. Swann security systems allow one to look at multiple cameras from your own home at a similar time. This can be useful for enhancing security therefore inside a broader way at premises.<br><br>However to your specific difficutly, there could possibly be some particular restricted problems characterizing which you can better come to some decision in case you indeed need a CCTV. Joint logo can improve the standing of certain products as CCTV.<br><br>This further reduces the cost of installation plus makes the means of installation easy. If the crime has recently occurred, the recording recorded by cameras CCTC will be useful for investigators that have committed the crime.<br><br>Some argue that even if CCTV footage is not viewed, the actual fact that it's recorded and archived can be a violation of privacy rights. You may also position it behind your windshield in order that you can record the roads you happen to be taking. It has different types though this function most likely are not available on other versions. I ended up doing my homework and getting some cameras and a DVR recorder off a national company which we fitted ourselves. Weather it's houses, public venues or roads, CCTv's are being utilized to keep a a record of intruders and [http://Learnlsn.org/members/whitekuester/activity/47860/ decrease] the rate of crime. Even if you have some hidden fact in the bed room from the person, they will get you which and that too without leaving any trace and marks.<br><br>This may be the advantage that certain will get from recording images. Attach the digital camera's power source into a wall outlet and to the CCTV camera. Think of time you'll save not out looking for  samsung sme-2220 [http://Wiki.ol261.info/wiki/Benutzer:TokiNethken dvr security] system what you desire, browsing line as well as the cost of fuel. While some of the are ideal to have installed within residential house premises, there  [http://www.000babes.com/external_link/?url=http%3A%2F%2Fcctvdvrreviews.com&domain=cctvdvrreviews.com cctv dvr cage] are those that can be installed only within big warehouses and factory sites.<br><br>If you use cameras that are designed for inside only, you'll end up needing to spend much more money to [http://Www.Pazdzierz.Com.pl/index.php?title=Unknown_Facts_About_Samsung_Sde_3000_Made_Known exchange] them whenever they become damaged by the elements. That didn't begin to cover the several other apps that I realized I had arrived at rely on for my phone. These will all have enormous implications for that city and its particular surrounding state, not least inside  samsung sme 4220 security system crucial field of transport. There are two varieties of burglar security systems - monitored ones and bells-only security systems.<br><br>
*Certain [[crystal]]s, typically doped with [[rare earth element|rare-earth]] [[ion]]s (e.g. [[neodymium]], [[ytterbium]], or [[erbium]]) or [[transition metal]] ions ([[titanium]] or [[chromium]]); most often [[yttrium aluminium garnet]] (YAG), [[yttrium orthovanadate]] (YVO<sub>4</sub>), or [[sapphire]] (Al<sub>2</sub>O<sub>3</sub>);<ref>Hecht, Jeff. ''The Laser Guidebook: Second Edition.'' McGraw-Hill, 1992.  (Chapter 22)</ref>
*[[Glass]]es, e.g. silicate or phosphate glasses, doped with laser-active ions;<ref>Hecht, Chapter 22</ref>
*[[Gas]]es, e.g. mixtures of [[helium]] and [[neon]] (HeNe), [[nitrogen]], [[argon]], [[carbon monoxide]], [[carbon dioxide]], or metal vapors;<ref>Hecht, Chapters 7-15</ref>
*[[Semiconductor]]s, e.g. [[gallium arsenide]] (GaAs), [[indium gallium arsenide]] (InGaAs), or [[gallium nitride]] (GaN).<ref>Hecht, Chapters 18-21</ref>
* Liquids, in the form of dye solutions as used in [[dye lasers]].<ref>[[F. J. Duarte]] and L. W. Hillman (Eds.), ''Dye Laser Principles'' (Academic, New York, 1990).</ref><ref>[[F. P. Schäfer]] (Ed.), ''Dye Lasers'', 2nd Edition (Springer-Verlag, Berlin, 1990).</ref>


In order to lase, the active gain medium must be in a nonthermal energy distribution known as a [[population inversion]].  The preparation of this state requires an external energy source and is known as [[laser pumping]]. Pumping may be achieved with electrical currents (e.g. semiconductors, or gases via [[glow discharge|high-voltage discharges]]) or with light, generated by [[discharge lamp]]s or by other lasers ([[semiconductor laser]]s).  More exotic gain media can be pumped by [[chemical reactions]], [[nuclear fission]], or with high-energy [[electron beam]]s.<ref name="rp">[http://www.rp-photonics.com/gain_media.html Encyclopedia of laser physics and technology]</ref>
Customers will have basically disconnect the regular marketplace of marketing strategies. If you reveal excessive information about yourself it does not take long for somebody to fill within the important gaps using public information for example the electoral roll.<br><br>CCTV, close circuit television, has become the popular choice with the people to watch and secure their houses and business. Unique slide-off feature allows full accessibility to your camera and lens. In various cities, CCTV cameras and security systems have helped in reducing the crime rate inside monitored areas.<br><br>Regular and welcome visitors may have access towards the security code, and may come at their convenience, yet, unwanted or unexpected visitors have to be 'allowed' access. CCTV surveillance systems can prove to be a deterrent to crime and assist in evidence gathering, these cameras aren't always too favored by members in the public. Such cameras are also used to monitor  [http://www.nsva.org/Guestold/go.php?url=http://cctvdvrreviews.com samsung cctv dvr software] babysitters, nannies and housekeepers in your own home or helpers and servants at office.
 
==Example of a model of gain medium==
[[Image:LaserLevels1.png|thumb|right|200px|Fig.1. Simplified scheme of levels a gain medium.]]
A universal model valid for all laser types does not exist.<ref name="siegman">
{{cite book
|url=http://www.uscibooks.com/siegman.htm
|author=A.E.Siegman
|title=Lasers
|year=1986
|publisher=University Science Books
|isbn= 0-935702-11-3
}}
</ref>
The simplest model includes two systems of sub-levels: upper and lower.  Within each sub-level system, the fast transitions ensure that thermal equilibrium is reached quickly, leading to the [[Maxwell–Boltzmann statistics]] of excitations among sub-levels in each system ''(fig.1)''.  The upper level is assumed to be [[metastable]].
Also, gain and refractive index are assumed independent of a particular way of excitation. 
 
For good performance of the gain medium, the separation between sub-levels should be larger than working temperature; then, at pump frequency <math>~\omega_{\rm p}~</math>, the absorption dominates.
 
In the case of [[Amplifier|amplification]] of optical signals, the lasing frequency is called ''signal frequency.'' However, the same term is used even in the laser [[oscillators]], when amplified radiation is used to transfer energy rather than information.  The model below seems to work well for most optically-pumped [[solid-state laser]]s.
 
===Cross-sections===
The simple medium can be characterized with [[cross section (physics)|effective cross-sections]] of [[Absorption (electromagnetic radiation)|absorption]] and [[Emission (electromagnetic radiation)|emission]] at frequencies <math>~\omega_{\rm p}~</math> and <math>~\omega_{\rm s}~</math>.
*Let <math>~N~</math> be concentration of active centers in the solid-state lasers.
*Let <math>~N_1~</math> be concentration of active centers in the ground state.
*Let <math>~N_2~</math> be concentration of excited centers.
*Let <math>~N_1+N_2=N~</math>.
 
The relative concentrations can be defined as <math>~n_1=N_1/N~</math> and <math>~n_2=N_2/N~</math>.
 
The rate of transitions of an active center from ground state to the excited state can be expressed with <math>~ W_{\rm u}=
\frac{I_{\rm p}\sigma_{\rm ap}}{ \hbar \omega_{\rm p} }+\frac{I_{\rm s}\sigma_{\rm as}}{ \hbar \omega_{\rm s} } ~</math> and
The rate of transitions back to the ground state can be expressed with <math>~W_{\rm d}=\frac{ I_{\rm p} \sigma_{\rm ep}}{ \hbar \omega_{\rm p} }+\frac{I_{\rm s}\sigma_{\rm es}}{ \hbar \omega_{\rm s} } +\frac{1}{\tau}~</math>,
where <math>~\sigma_{\rm as} ~</math> and <math>~\sigma_{\rm ap} ~</math> are [[Absorption cross section|effective cross-sections]] of absorption at the frequencies of the signal and the pump.  
 
<math>~\sigma_{\rm es} ~</math> and <math>~\sigma_{\rm ep} ~</math> are the same for stimulated emission;
 
<math>~\frac{1}{\tau}~</math> is rate of the spontaneous decay of the upper level.
 
Then, the kinetic equation for relative populations can be written as follows:
<math>~
\frac
{{\rm d}n_2}
{{\rm d}t}
=
W_{\rm u} n_1 -
W_{\rm d} n_2
~</math>,
 
<math>~
\frac{{\rm d}n_1}{{\rm d}t}=-W_{\rm u} n_1 + W_{\rm d} n_2
~</math>
However, these equations keep <math>~ n_1+n_2=1 ~</math>.
 
The absorption <math>~  A ~</math> at the pump frequency and the gain <math>~  G ~</math> at the signal frequency can be written
as follows:
<math>~  A = N_1\sigma_{\rm pa} -N_2\sigma_{\rm pe} ~</math>,
<math>~  G = N_2\sigma_{\rm se} -N_1\sigma_{\rm sa} ~</math>.
 
===Steady-state solution===
In many cases the gain medium works in a continuous-wave or [[quasi-continuous function|quasi-continuous]] regime, causing the time [[derivative]]s of populations to be negligible.  
 
The steady-state solution can be written: 
<math>~ n_2=\frac{W_{\rm u}}{W_{\rm u}+W_{\rm d}} ~</math>,
<math>~ n_1=\frac{W_{\rm d}}{W_{\rm u}+W_{\rm d}}.</math>
 
The dynamic saturation intensities can be defined:
<math>~ I_{\rm po}=\frac{\hbar \omega_{\rm p}}{(\sigma_{\rm ap}+\sigma_{\rm ep})\tau} ~</math>,
<math>~ I_{\rm so}=\frac{\hbar \omega_{\rm s}}{(\sigma_{\rm as}+\sigma_{\rm es})\tau} ~</math>.
 
The absorption at strong signal:
<math>~ A_0=\frac{ND}{\sigma_{\rm as}+\sigma_{\rm es}}~</math>.
 
The gain at strong pump:
<math>~ G_0=\frac{ND}{\sigma_{\rm ap}+\sigma_{\rm ep}}~</math>,
where <math>~ D=
\sigma_{\rm pa}
\sigma_{\rm se}
-
\sigma_{\rm pe}
\sigma_{\rm sa}
~</math>
is determinant of cross-section. 
 
Gain never exceeds value <math>~G_0~</math>, and absorption never exceeds value <math>~A_0  U~</math>.
 
At given intensities <math>~I_{\rm p}~</math>,  <math>~I_{\rm s}~</math> of pump and signal, the gain and absorption
can be expressed as follows:
<math>~A=A_0\frac{U+s}{1+p+s}~</math>,
<math>~G=G_0\frac{p-V}{1+p+s}~</math>,
 
where
<math>~p=I_{\rm p}/I_{\rm po}~</math>,
<math>~s=I_{\rm s}/I_{\rm so}~</math>,
<math>~U=\frac{(\sigma_{\rm as}+\sigma_{\rm es})\sigma_{\rm ap}}{D}~</math>,
<math>~V=\frac{(\sigma_{\rm ap}+\sigma_{\rm ep})\sigma_{\rm as}}{D}~</math> .
 
===Identities===
The following identities<ref name="uns">{{cite journal
| author=D.Kouznetsov
| coauthors=J.F.Bisson, K.Takaichi, K.Ueda
| 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
| year=2005
| doi=10.1364/JOSAB.22.001605
| bibcode=2005JOSAB..22.1605K
}}</ref> take place:
<math>U-V=1 ~ </math>, <math>~ A/A_0 +G/G_0=1~.\ </math>
 
The state of gain medium can be characterized with a single parameter, such as population of the upper level, gain or absorption.
 
===Efficiency of the gain medium===
The efficiency of a '''gain medium''' can be defined as
<math>~ E =\frac{I_{\rm s} G}{I_{\rm p}A}~</math>.
 
Within the same model, the efficiency can be expressed as follows:
<math>~E =\frac{\omega_{\rm s}}{\omega_{\rm p}} \frac{1-V/p}{1+U/s}~</math>.
 
For the efficient operation both intensities, pump and signal should exceed their saturation intensities;
<math>~\frac{p}{V}\gg 1~</math>, and <math>~\frac{s}{U}\gg 1~</math>.
 
The estimates above are valid for a medium uniformly filled with pump and signal light.  The [[spatial hole burning]] may slightly reduce the efficiency because some regions are pumped well, but the pump is not efficiently withdrawn by the signal in the nodes of
the interference of counter-propagating waves.
 
==See also==
*[[Population inversion]]
*[[Laser construction]]
*[[Laser science]]
*[[List of laser articles]]
*[[List of laser types]]
 
==References and notes==
<references/>
 
==External links==
*[http://www.rp-photonics.com/gain_media.html Gain media] Encyclopedia of Laser Physics and Technology
 
{{DEFAULTSORT:Active Laser Medium}}
[[Category:Laser gain media| ]]
[[Category:Laser science]]

Revision as of 06:45, 20 February 2014

Many folks have also noticed this disadvantage: You can't record a show whilst you watch another program, which causes it to be less than ideal as a DVR. Based in Fremont, California, Sonic CCTV has become one from the leading suppliers of surveillance and home alarm system products within North America. When selecting a DVR choose samsung sme-2220 review a uncomplicated, simple device Best Cctv dvr uk as this will keep the charge down. It may include certain duplications, however it is better than containing some concealed matters.

This is perfect in case you are feeling stuck, unfulfilled, or if you just understand that you are capable of achieving more. Electric fences are devised in this particular way that they may provide having a high voltage shock to an attempted intruder for any very short volume of time. A USA Today article examined 168 sexual assault charges against athletes.

Even remote access of CCTV is achievable but such advanced features can be found at higher price ranges of CCTVs. Many people might think that CCTV systems are equipped for commercial use only. First, the digital video surveillance cameras are getting to be computers boost the local tissue, and connecting with a network of computers instead using a dedicated computer. Today's high definition security cameras have made it possible for entrepreneurs to help keep a watch over their facilities and guide their employees.

You will have to leave the lights within the bedroom because camera does not have a IR function. Because CCTV deters burglars and intruders, many people choose to utilize CCTV as part of the home's security package. Swann security systems allow one to look at multiple cameras from your own home at a similar time. This can be useful for enhancing security therefore inside a broader way at premises.

However to your specific difficutly, there could possibly be some particular restricted problems characterizing which you can better come to some decision in case you indeed need a CCTV. Joint logo can improve the standing of certain products as CCTV.

This further reduces the cost of installation plus makes the means of installation easy. If the crime has recently occurred, the recording recorded by cameras CCTC will be useful for investigators that have committed the crime.

Some argue that even if CCTV footage is not viewed, the actual fact that it's recorded and archived can be a violation of privacy rights. You may also position it behind your windshield in order that you can record the roads you happen to be taking. It has different types though this function most likely are not available on other versions. I ended up doing my homework and getting some cameras and a DVR recorder off a national company which we fitted ourselves. Weather it's houses, public venues or roads, CCTv's are being utilized to keep a a record of intruders and decrease the rate of crime. Even if you have some hidden fact in the bed room from the person, they will get you which and that too without leaving any trace and marks.

This may be the advantage that certain will get from recording images. Attach the digital camera's power source into a wall outlet and to the CCTV camera. Think of time you'll save not out looking for samsung sme-2220 dvr security system what you desire, browsing line as well as the cost of fuel. While some of the are ideal to have installed within residential house premises, there cctv dvr cage are those that can be installed only within big warehouses and factory sites.

If you use cameras that are designed for inside only, you'll end up needing to spend much more money to exchange them whenever they become damaged by the elements. That didn't begin to cover the several other apps that I realized I had arrived at rely on for my phone. These will all have enormous implications for that city and its particular surrounding state, not least inside samsung sme 4220 security system crucial field of transport. There are two varieties of burglar security systems - monitored ones and bells-only security systems.

Customers will have basically disconnect the regular marketplace of marketing strategies. If you reveal excessive information about yourself it does not take long for somebody to fill within the important gaps using public information for example the electoral roll.

CCTV, close circuit television, has become the popular choice with the people to watch and secure their houses and business. Unique slide-off feature allows full accessibility to your camera and lens. In various cities, CCTV cameras and security systems have helped in reducing the crime rate inside monitored areas.

Regular and welcome visitors may have access towards the security code, and may come at their convenience, yet, unwanted or unexpected visitors have to be 'allowed' access. CCTV surveillance systems can prove to be a deterrent to crime and assist in evidence gathering, these cameras aren't always too favored by members in the public. Such cameras are also used to monitor samsung cctv dvr software babysitters, nannies and housekeepers in your own home or helpers and servants at office.

Retrieved from "https://en.formulasearchengine.com/index.php?title=Haar_measure&oldid=221718"