Saturated absorption spectroscopy: Difference between revisions

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In [[atomic physics]], '''Raman cooling''' is a sub-recoil cooling technique that allows the cooling of [[atoms]] using optical methods below the limitations of [[Doppler cooling]], limited by the recoil energy of a photon given to an atom. This scheme can be performed in simple [[optical molasses]] or in molasses where an [[optical lattice]] has been superimposed, which are called respectively free space Raman cooling <ref>[http://link.aps.org/doi/10.1103/PhysRevLett.69.1741 ''Laser cooling below photon recoil with three-level atoms''], Mark Kasevich, [[Steven Chu]], Phys. Rev. Lett. '''69''', 1741 (1992)</ref> and Raman side-band cooling.<ref>[http://link.aps.org/doi/10.1103/PhysRevLett.84.439 ''Beyond Optical Molasses: 3D Raman Sideband Cooling of Atomic Cesium to High Phase-Space Density''], Andrew J. Kerman, Vladan Vuletic, Cheng Chin, and Steven Chu, Phys. Rev. Lett. '''84''', 439 (2000)</ref> Both techniques make use of [[Raman scattering]] of laser light by the atoms.
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==Two photon Raman process==
The transition between two [[Hyperfine structure|hyperfine states]] of the atom can be triggered by two [[laser]] beams: the first beam excites the atom to a virtual excited state (for example because its frequency is lower than the real transition frequency), and the second beam deexcites the atom to the other hyperfine level. The frequency difference of the two beams is exactly equal to the transition frequency between the two hyperfine levels.
 
[[Image:RamanProcess.png|center]]
 
The illustration of this process is shown in the schematic illustration of a two-photon Raman process. It enables the transition between the two levels <math>|g_1\rangle</math> and <math>|g_2\rangle</math>. The intermediate, virtual level is represented by the dashed line, and is red-detuned with respect to the real excited level, <math>|e\rangle</math>. The frequency difference <math>f_2-f_1</math> here matches exactly the energy difference between <math>|g_1\rangle</math> and <math>|g_2\rangle</math>.
 
== Free space Raman cooling==
 
In this scheme, a pre-cooled cloud of atoms (whose temperature is of a few tens of microkelvins) undergoes a series of pulses of Raman-like processes. The beams are counterpropagating, and their frequencies are just as what has been described above, except that the frequency <math>f_2</math> is now slightly [[Laser detuning|red-detuned]] (detuning <math>\Delta</math>) with respect to its normal value. Thus, atoms moving towards the source of the laser 2 with a sufficient velocity will be resonant with the Raman pulses, thanks to the [[Doppler effect]]. They will be excited to the <math>|g_2\rangle</math> state, and get a momentum kick decreasing the modulus of their velocity.  
 
If the propagation directions of the two lasers are interchanged, then the atoms moving in the opposite direction will be excited and get the momentum kick that will decrease the modulus of their velocities. By regularly exchanging the lasers propagating directions and varying the detuning <math>\Delta</math>, one can manage to have all atoms for which the initial velocity satisfies <math>|v|>v_{max}</math> in the state <math>|g_2\rangle</math>, while the atoms such that <math>|v|<v_{max}</math> are still in the <math>|g_1\rangle</math> state. A new beam is then switched on, whose frequency is exactly the transition frequency between <math>|g_2\rangle</math> and <math>|e\rangle</math>. This will [[optical pumping|optically pump]] the atoms from the <math>|g_2\rangle</math> state to the <math>|g_1\rangle</math> state, and the velocities will be randomized by this process, such that a fraction of the atoms in <math>|g_2\rangle</math> will acquire a velocity <math>|v|<v_{max}</math>.
 
By repeating this process several times (eight in the original paper, see references), the temperature of the cloud can be lowered to less than a microkelvin.
 
== Raman side-band cooling ==
 
This cooling scheme starts from atoms in a [[magneto-optical trap]]. An optical lattice is then ramped up, such that an important fraction of the atoms are trapped. If the lasers of the lattice are powerful enough, each site can be modelled as a harmonic trap. Since the atoms are not in their ground state, they will be trapped in one of the excited levels of the harmonic oscillator. The aim of Raman side-band cooling is to put the atoms into the ground state of the harmonic potential in the lattice site.  
 
We consider a two level atom, the ground state of which has a quantum number of F=1, such that it is three-fold degenerate with m=-1, 0 or 1. A magnetic field is added, which lifts the degeneracy in m due to the [[Zeeman effect]]. Its value is exactly tuned such that the Zeeman splitting between m=-1 and m=0 and between m=0 and m=1 is equal to the spacing of two levels in the harmonic potential created by the lattice.   
 
[[Image:RamanSidebandCooling.png|center]]
 
By means of Raman processes, an atom can be transferred to a state where the magnetic moment has decreased by one and the vibrational state has also decreased by one (red arrows on the picture). After that the atoms which are in the lowest vibrational state of the lattice potential (but with <math>m\neq 1</math>) are [[optical pumping|optically pumped]] to the m=1 state (role of the <math>\sigma_+</math> and <math>\pi</math> light beams). Since the temperature of the atoms is low enough with respect to the pumping beam frequencies, the atom is very likely not to change its vibrational state during the pumping process. Thus it ends up in a lower vibrational state, which is how it is cooled.
In order to reach this efficient transfer to the lower vibrational state at each step, the parameters of the laser, i.e. power and timing, should be carefully tuned. In general, these parameters are different for different vibrational states because the strength of the coupling ([[Rabi frequency]]) depends on the vibrational level. Additional complication to this naive picture arises from the [[Recoil temperature|recoil of photons]], which drive this transition. The last complication can be generally avoided by performing cooling in a so-called [[Lamb Dicke regime]]. In this regime the atom is trapped so strongly in the optical lattice that it effectively does not change its momentum due to the photon recoils. The situation is similar to the [[Mössbauer effect]].
 
 
This cooling scheme allows to obtain a rather high density of atoms at a low temperature, using only optical techniques. It is still not sufficient to attain for example [[Bose-Einstein condensation]], but it can be a starting point for such experiments. For instance, the Bose-Einstein condensation of [[Cesium]] has been achieved for the first time in an experiment that used Raman side-band cooling as its first step.<ref>''Bose-Einstein condensation of Cesium'', Tino Weber, Jens Herbig, Michael Mark, Hanns-Christoph Nägerl, Rudolf Grimm, Science, 299, 232</ref>
 
== References ==
{{Reflist}}
 
[[Category:Atomic physics]]
[[Category:Cooling technology]]

Revision as of 19:43, 11 February 2014



Straight-edged knives, like the Virtorinox Rosewood Straight Edge Steak Knives ($one hundred) may seem like a very good option at initially glance. The Victorinox Rosewood Straight-Edge Steak Knife Set was America's Test Kitchen's major choose in their critique of price range steak knife sets, and it gets four.six stars (of 22 reviews) on Amazon. The blades reduce with so pretty small work on my element.” Like other Victorinox knives, this What Material Tends to make The Best Cutting Board set comes with a lifetime warranty. If your concept of a steak knife is a massive, macho thing like John Candy utilizes in that remarkable Fantastic Outdoors steak scene , the Victorinox set won't fit that fantasy. Obtaining steak knives set.

Blessed the lens - my father had his knife that no a single else was to ever touch and all worthy males I knew had at least a little pen knife that was mentioned to be greater than any other knife of any other man! I, on the other hand, have but one particular knife that I use for all occasions. If there is a knife continuum, you would be on 1 end, I would be on the other end. Just came back by to say that I referred this post to my pal and she tells me she purchased a glove and Chef knife here.

In a long profession of the specialist knife maker in Seki, Master Ichiro Hattori continues to devote all his power and knowledge to every detail of his knives without the need of any compromises. Just about every Hattori produced knife is a masterpiece of the higher-finish high-quality and super fantastic cutting performance. The paring knife is 1 of the most useful of the Japanese chefs' knives that you could have in your kitchen.

They could also demand a lot more upkeep, nonetheless that can be solved with obtaining good knife sharpeners ! The knife is a full tang a single piece, which suggests it couldbetter stability than two piece knives, even so it lacks a bolster. With no a bolster it could lack in balance and stability, but this is what you get or a $40 knife set. This category of knife set can run consumers anywhere from a couple hundred bucks to a couple thousand.

Like in a knife block or in a drawer (but only if they are in a sheath, as the knives could be broken). To steel a blade, hold the knife flat against a surface and slide it along, gradually raising the back of the blade until it just starts to cut into the surface. Knife block sets deliver a choice of tools along with a hassle-free and safe countertop storage solution. Smaller sized knife with a two to 2 1/2" pointed blade.

I have observed this set in a number of retail retailers all over the net with a price tag around $130 to $180. The only point that can be improved is the length of the steak knives, a small larger steak knives with a slightly longer handle and the set could be best. And if the set had integrated a utility knife with a plain blade, that would have been good. First of all, you have to have a fantastic set of pots and pans.

And with silverware you eat from the outside in. If we're doing multiple courses you want to location the subsequent course on the outside of the key course here we have our salad fork and our appetizer-size knife. As for glassware, you will start off with your water glass right at twelve 'clock above your key course knife. In these circumstances, exactly where weight is an challenge, this knife will present no dilemma.

For the knife collectors that wanted a knife that was fierce and worked great in a wide assortment of scenarios they picked the Buck CSAR-T. A modified tanto blade and G-10 handle give this knife remarkable strength when prying andtactical circumstances. With a 7 inch blade the razor sharp Cold Steel Bushman is a good camping knife for the outdoorsmen on a spending budget. When out camping, nothing at all like a Swiss knife.

But like I said, see what feels very good in your hand, and find out how to preserve your blades sharp, and you are going to do just fine in the knife department. Others that are "necessary" (imnsho) are a Santoku and bread knife. If you love tomatoes, go ahead and get a tomato knife but it's not required with a fantastic serrated bread knife. Also, a six 6" utility knife can be valuable, but isn't actually required. If you have any issues about where and how to use Ideal cutting board for meat, you can get hold of us at our website. I would love to attempt much more and that knife set……….

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